JPWO2006043507A1 - Engine parts - Google Patents

Abstract

The engine component of the present invention includes a metal substrate and a chromium plating layer that covers at least part of the surface of the metal substrate and is formed of a trivalent chromium plating solution, and is contained in the chromium plating layer. Is 0.05 mass% or more and 0.3 mass% or less, and the thickness of a chromium plating layer is 0.7 micrometer or less.

Description

  The present invention relates to an engine component, and more particularly to an engine component that is exposed to high temperature by high-temperature exhaust gas discharged from the engine.

  In vehicles such as motorcycles and all-weather four-wheel vehicles, in addition to the performance of the vehicles themselves, having an excellent design is one of the important issues. FIG. 9 is a side view showing an example of a sports type motorcycle. A motorcycle 200 shown in FIG. 9 includes a V-type engine 201 and an exhaust pipe 202 for guiding exhaust gas. The V-type engine 201 includes a cylinder 203, a cylinder head 204, and a head cover 205. Since the V-shaped engine 201 is excellent in shape and appearance, it is often mounted on a motorcycle so as to be exposed to the outside, and has a great influence on the appearance of the entire motorcycle.

  The exhaust pipe 202 is led from each of the two cylinders 203 of the V-type engine 201, is gathered together, and is extended to the rear wheel side so as to eject exhaust gas from the rear part of the vehicle body. The exhaust pipe 202 needs to have a predetermined thickness in order to efficiently exhaust the exhaust gas generated in the engine 201. In addition, the exhaust pipe 202 is configured to mute at a portion constituting the silencer 202a. The diameter increases to accommodate the structure. For this reason, the proportion of the exhaust pipe in the overall appearance of the motorcycle is relatively large, and the influence of the shape and color of the exhaust pipe on the design of the entire motorcycle is great.

  Engine parts such as the cylinder 203, the cylinder head 204, and the head cover 205, and the exhaust pipe 202 and its cover for guiding exhaust gas from the engine are referred to as engine parts in this specification. For the reasons described above, the shape and color of engine parts are important factors in determining the design of the entire motorcycle.

  Conventionally, the engine parts appearing in such an appearance are given a glossy metal color by performing a surface treatment such as plating, and the design of the engine parts is enhanced. Among them, decorative chrome plating has been widely used for engine parts because it can impart a unique silver-white color with luster to the material to be plated (for example, Patent Document 1).

  Decorative chrome plating has an excellent metallic luster and excellent corrosion resistance, and is therefore used in various fields other than engine parts. In order to obtain excellent appearance and corrosion resistance, it is not necessary to form a thick decorative chrome plating. On the contrary, if the decorative chrome plating is formed thick, the color tone and the surface finish are deteriorated. Therefore, generally, the decorative chrome plating is preferably used in a thickness of 0.1 μm to 0.15 μm.

  In addition, as chromium plating, hard chromium plating (industrial chromium plating) is also widely used for industrial products. Since hard chrome plating has a low friction coefficient and excellent wear resistance, it is used for sliding parts of various machine parts. Since wear resistance is required, hard chrome plating is usually formed with a thickness of several μm or more. Further, hard chrome plating does not have a surface with excellent decorative properties like decorative chrome plating. Usually, decorative chrome plating after plating has a surface roughness (Ra) of 1 μm or less, typically 0.2 μm or less, whereas hard chrome plating has a surface roughness of 1 μm or more. ing.

For the formation of the decorative chrome plating, a chromic acid plating solution containing hexavalent chromium (Cr ⁶⁺ ) is usually used. Hexavalent chromium is inexpensive, and the chromium plating layer formed from a plating solution containing hexavalent chromium (hereinafter referred to as a hexavalent chromium plating solution) has good adhesion to the base material, and is resistant to corrosion and resistance. Excellent wear resistance. Furthermore, the chromium plating layer formed from the hexavalent chromium plating solution has a silvery white color with a unique metallic luster. For these reasons, hexavalent chromium plating solutions are widely used for motorcycle engine parts.

  However, hexavalent chromium is known to be highly toxic to living organisms. When plating with hexavalent chromium plating solution, it is required to ensure the safety of workers and prevent environmental pollution. It has become like this.

In order to solve the problem of hexavalent chromium, it is desired to perform decorative chromium plating using trivalent chromium (Cr ³⁺ ), which is less toxic than hexavalent chromium. Plating solutions have been proposed (Patent Documents 2 and 3).
JP 2003-41933 A Japanese Patent Laid-Open No. 52-065138 JP-A-52-092934 JP-A-9-95793 Japanese Patent Laid-Open No. 9-228069

  From the viewpoint of environment and safety, it is preferable to use a plating solution containing trivalent chromium (hereinafter referred to as trivalent chromium plating solution). However, the chromium plating layer formed by using the conventional trivalent chromium plating solution is stable in the growth of the chromium plating layer, plating film characteristics such as corrosion resistance and wear resistance of the formed chromium plating layer, etc. There was a problem that it was inferior to the plating layer formed from the hexavalent chromium plating solution.

  Engine parts are heated to a high temperature by heat generated by combustion of fuel and high-temperature exhaust gas. When a chromium plating layer is formed on an engine part using a conventional trivalent chromium plating solution, there is a problem that cracks are likely to occur in the chromium plating layer by heating. If a crack occurs in the chromium plating layer, rust is generated from that portion, and the appearance is remarkably impaired.

  For this reason, trivalent chromium plating solutions having various compositions have been proposed for more than 20 years, but in particular, trivalent chromium plating solutions are rarely used for engine parts.

  The present invention solves such a conventional problem, is formed using a trivalent chromium plating solution, has the same good film forming characteristics as a plating layer formed from a hexavalent chromium plating solution, and is heat resistant. An object of the present invention is to provide an engine component having a chromium plating layer excellent in the above.

  The engine component of the present invention is an engine component comprising a metal substrate and a chromium plating layer that covers at least a part of the surface of the metal substrate and is formed of a trivalent chromium plating solution. The content of boron contained in the chromium plating layer is 0.05% by mass or more and 0.3% by mass or less, and the thickness of the chromium plating layer is 0.7 μm or less.

  In a preferred embodiment, the content of boron contained in the chromium plating layer is 0.05% by mass or more and 0.1% by mass or less.

  In a preferred embodiment, the content of iron contained in the chromium plating layer is 2% by mass or less.

  In a preferred embodiment, the chromium plating layer covers a region heated to a temperature of 350 ° C. or higher on the surface of the metal substrate.

  In a preferred embodiment, the engine component further includes a base plating layer provided between the metal base surface and the chromium plating layer, and the chromium plating layer is heated to a temperature of 350 ° C. or higher. The region has a thickness of 0.2 μm or more and 0.7 μm or less.

  In a preferred embodiment, the base plating layer includes at least one of C and S.

  In a preferred embodiment, the base plating layer further contains Ni.

  In a preferred embodiment, the base plating layer is made of a metal having a lower hardness than Cr constituting the chromium plating layer.

  In a preferred embodiment, the base plating layer is formed from Ni plating.

  In a preferred embodiment, the color tone of the chrome plating layer has an L * value measured by CIE (Commission Internationale de l'Eclairage) 1976 in the range of 68 to 80.

  In a preferred embodiment, the metal substrate is made of a material mainly composed of Fe, Al, Zn, or Mg.

  In a preferred embodiment, the metal substrate is a metal tube that defines a passage through which exhaust gas from the engine passes.

  The engine of the present invention includes any one of the above engine parts.

  The transportation device of the present invention includes any one of the engine parts or engines described above.

  According to the present invention, the boron content in the chromium plating layer is adjusted to 0.05% by mass or more and 0.3% by mass or less, and the thickness of the chromium plating layer is 0.7 μm or less. Using a chromium plating solution, it is possible to obtain a chromium plating layer having good film forming characteristics comparable to those of a plating layer formed from a hexavalent chromium plating solution and excellent in heat resistance. Therefore, an engine component having a good appearance can be obtained using the trivalent chromium plating solution.

  Further, by setting the boron content in the chromium plating layer to 0.1% by mass or less and the iron content to 2% by mass or less, the same level as the chromium plating layer formed from the hexavalent chromium plating solution A silver-white color tone can be obtained. Furthermore, by setting the thickness of the chromium plating layer in the range of 0.2 μm or more and 0.7 μm or less, an engine component that hardly causes thermal discoloration can be obtained.

It is a figure which shows typically the structure of the components for engines by this invention. (A) is a figure which shows the analysis result by the X ray diffraction method of the chromium plating layer formed using trivalent chromium, (b) is X of the chromium plating layer formed using hexavalent chromium. It is a figure which shows the analysis result by a line diffraction method. It is a figure which shows typically a mode that a "CS concentrated layer" or a "C-S-Ni concentrated layer" produces | generates in the interface vicinity of a chromium plating layer and a base plating layer by heating. (A) is a schematic diagram for demonstrating that discoloration of a chromium plating layer can be prevented by enlarging the thickness of a chromium plating layer, (b) is a part of conventional chromium-nickel plating layer. It is a figure explaining typically. 1 is a side view of a motorcycle in which an engine component of the present invention is used. (A) is a figure which shows typically the part of the exhaust pipe connected directly to an engine, (b) is a figure which shows the cross section of the catalyst accommodating part of an exhaust pipe typically, (c) FIG. 4 is a diagram schematically showing a cross section of a manifold portion. It is a figure which shows the example of the chromium plating apparatus used for this invention. (A) is a figure which shows typically the state arrange | positioned so that the distance of the curved part of a metal base material and an electrode may become the shortest, (b) is a curved part and electrode of a metal base material. It is a figure which shows typically the state arrange | positioned so that distance may become long. 1 is a side view showing the appearance of a motorcycle.

Explanation of symbols

30, 201 Engine 4, 4a, 202 Exhaust pipe 203 Cylinder 204 Cylinder head 205 Head cover 1 Metal substrate 2 Base plating layer 3 Chrome plating layer 5 Metal pipe 6 Passage 7 Silencer part 8 Catalyst 9 Bending part 9a Convex surface part 9b Inside Side surface 10 Plating layer 11 Chromium plating tank 12 Pump 13 Filter 14 Adjustment valve 15 Flow meter 16 Ion exchange device 17 Metal substrate 18 Insoluble anode 19 DC power source 20 Chromium plating device 21 Connection portion 22 Catalyst housing portion 23 Other exhaust pipe 24 Pipeline 100, 200 motorcycle

  As a result of examining the composition of the trivalent chromium plating solution and the composition in the formed chromium plating layer, the present inventor has found that the problem that cracks occur in the chromium plating layer is related to the boron content contained in the chromium plating layer. I found out. The growth stability of the chromium plating layer and the corrosion resistance and wear resistance of the formed chromium plating layer are also related to the boron content contained in the chromium plating layer and the boron concentration in the trivalent chromium plating solution. I found out.

  Moreover, the chromium plating layer formed from the conventional trivalent chromium plating solution has a blackish color tone compared with the chromium plating layer formed from a hexavalent chromium plating solution. This was found to be related to the iron content of the formed chromium plating layer.

  Furthermore, when a chromium plating layer formed from a trivalent chromium plating solution is formed on an engine component, the color tone of the surface may change due to heating, and the chromium plating layer may exhibit a bluish purple color. Such discoloration impairs the appearance of a motorcycle equipped with engine parts. The inventor of the present application has found that discoloration due to heating of the chromium plating layer depends on the thickness of the chromium plating layer.

1. Structure of Engine Parts (1) Basic Structure Hereinafter, the structure of engine parts according to the present invention will be described with reference to FIG. As shown in FIG. 1, the engine component of the present invention includes a metal substrate 1, a chromium plating layer 3 that covers at least a part of the surface of the metal substrate 1, and a metal substrate 1 and a chromium plating layer 3. And an underlying plating layer 2 provided therebetween. Hereinafter, each of these components will be described in detail.

(I) Metal base material The metal base material 1 is provided with the intensity | strength suitable for a use, corrosion resistance as needed, etc., and can be formed with the material normally used as components for engines. A typical example is an Fe-based material. In addition, the metal substrate 1 may be formed from a non-Fe material such as an Al-based material, a Zn-based material, an Mg-based material, or a Ti-based material.

  The Fe-based material is Fe or steel containing Fe as a main component, such as steel for machine structure (for example, carbon steel for machine structure (STKM), alloy steel for machine structure), stainless steel (for example, ferritic stainless steel). Steel, austenitic stainless steel, austenitic / ferritic stainless steel, etc.) and mild steel (eg, SPCC, SPHC, etc.). Examples of the Al-based material include Al, Al-Si alloys, and Al alloys such as Al-Si-Mg alloys. The Zn-based material includes Zn, a Zn-plated steel sheet coated with Zn, or a Zn alloy coated with a Zn alloy plating containing Zn as a main component and containing an alloy element such as Ni, Co, Cr, or Al. A plated steel sheet is mentioned. Examples of the Mg-based material include Mg—Al based alloys and Mg—Zn based alloys. Examples of the Ti-based material include Ti or a Ti alloy mainly containing Ti and containing elements such as Al, V, and Si.

  These materials have different characteristics depending on the type. For example, Al is characterized by being lightweight and bright, and Ti being lightweight and having excellent strength. For this reason, an appropriate material can be selected according to a use, a required characteristic, etc.

(Ii) Base Plating Layer A base plating layer 2 formed on the metal substrate 1 is used as a base plating for the chromium plating layer 3. From the viewpoint of preventing cracks generated in the chromium plating layer and stably growing a chromium plating layer having excellent corrosion resistance and wear resistance, the base plating layer 2 may not be provided. In chrome plating, a base plating layer is usually formed under the chrome plating layer for the purpose of improving the adhesion to the base material. For this reason, it is preferable that the base plating layer 2 is excellent in adhesiveness with various metal base materials and adhesiveness with a chromium plating layer. Furthermore, it is preferable to have other characteristics such as corrosion resistance.

  The metal which comprises the base plating layer 2 used for this invention can be prescribed | regulated by the relationship with the hardness (Vickers hardness) of chromium used for formation of a chromium plating layer. Specifically, the metal constituting the underlying plating layer 2 is preferably formed of a metal having a hardness lower than that of chromium (about 350 to 1200 Hv). By interposing a layer made of a metal with low hardness between the chromium plating layer and the metal substrate, it is possible to reduce the stress on the chromium plating layer due to heat cycle, so the occurrence of cracks is suppressed, and the surface A chromium plating layer having excellent properties can be obtained. Examples of metals having a lower hardness than chromium include nickel (Ni) (hardness: about 150 to 350 Hv), copper (Cu) (hardness: about 40 to 250 Hv), tin (Sn) (hardness: about 20 to 200 Hv), Lead (Pb) (impossible to measure) and the like can be mentioned.

  As the base plating layer containing these metals, for example, a layer made of nickel plating, copper plating, tin plating, lead plating, zinc-nickel plating or the like is used. These plating layers may be formed independently, and two or more kinds may be combined to constitute a plurality of base plating layers. Further, a plurality of plating layers of the same kind, such as different types of additives, such as additives, may be formed. A typical base plating layer used as a base treatment for the chromium plating layer is nickel plating, which further improves the corrosion resistance, glossiness, and the like.

  The base plating layer 2 contains elements constituting various additives. These additives are added to the plating solution for forming the base plating layer 2 for the purpose of improving the gloss of the chromium plating layer. Specifically, primary brighteners (non-butyne brighteners such as saccharin sodium, naphthalene-1,3,6-trisulfonic acid trisodium, benzenesulfonic acid), secondary brighteners (2-butyl-1,4- Diol, sodium allyl sulfonate, etc.) are used. Each of these additives contains C and / or S as a constituent element. C and / or S contained in the base plating layer is approximately 0.001 to 1.0% by mass in total, although it varies depending on the type of the base plating layer and the type of additive. As will be described in detail below, these elements are concentrated to about 0.1 to 10% by mass by heating, resulting in discoloration of the surface of the chromium plating layer. Furthermore, when the base plating layer 2 is a nickel plating layer, Ni contained in the nickel plating layer is also greatly involved in the discoloration of the surface.

  Hereinafter, nickel plating, which is a representative example of the base plating layer, will be described in detail. Nickel plating is roughly classified into matte nickel plating, semi-bright nickel plating, and bright nickel plating depending on the type of brightener added to the plating solution and the presence or absence of addition. These can be combined appropriately and appropriately according to the required properties and applications, thereby obtaining a desired appearance.

  Of these, bright nickel plating is obtained by adding brighteners such as saccharin and benzenesulfonic acid to the plating solution, and is excellent in surface leveling (smoothing) action and adhesion to the chromium plating layer. It is widely used as a base layer formed directly under the chromium plating layer. The brightener used for bright nickel plating usually contains about 0.001 to 1.0% by mass in total of at least one of C and S in the plating layer, and the corrosion resistance tends to decrease as the S content increases. It is in.

  In contrast, matte nickel plating is different from bright nickel plating in that it does not contain a brightener in the plating solution. Matte nickel plating is inferior in gloss compared to bright nickel plating, but is excellent in plating layer adhesion (adhesion), corrosion resistance, and anti-discoloration action.

  Semi-bright nickel plating is obtained by adding a non-coumarin semi-bright agent to the plating solution. Unlike the above-described brighteners, the semi-brightener has a low content of C and / or S. For this reason, although corrosion resistance is favorable compared with bright nickel plating, it is inferior to glossiness.

  In general, when nickel plating layers having different S contents are formed in layers, a potential difference is generated between the plating layers, and a film having a high S content is preferentially corroded. Utilizing such properties, the nickel plating is often composed of two or more layers to improve the corrosion resistance. For example, in the case of two-layer plating in which a semi-bright nickel plating layer and a bright nickel plating layer are sequentially formed on a base metal, the bright plating layer has a lower potential than the semi-bright plating layer and is preferentially corroded. For this reason, the base metal under the semi-gloss plating layer is protected without being corroded. In the above two-layer plating layer, for the purpose of further improving the corrosion resistance, a tri-nickel plating layer (a kind of bright nickel plating layer) with a large S content is formed between the semi-bright nickel plating layer and the bright nickel plating layer, In some cases, three-layer plating is used. In many cases, S contained in the trinickel plating layer is mainly supplied from an additive other than the brightener. In this case, the uppermost bright nickel plating layer is preferentially corroded, and then the intermediate trinickel plating layer is corroded to protect both the semi-bright nickel plating layer and the base metal. become.

  In order to effectively exhibit the action of such nickel plating, the thickness of the nickel plating layer is preferably about 10 to 30 μm in total. More preferably, it is about 15 μm or more and 25 μm or less.

  In addition, when forming foundation | substrate plating layers other than a nickel plating layer, it is preferable to control to the thickness of about 10-30 micrometers.

(Iii) Chromium plating layer On the base plating layer 2, a chromium plating layer 3 is formed. The chromium plating layer 3 is a decorative chromium plating layer formed by electroplating using a trivalent chromium plating solution, as will be described in detail below.

  Whether the chromium plating layer is formed using a trivalent chromium plating solution or a hexavalent chromium plating solution can be determined by measuring the crystal state of the chromium plating layer. Specifically, it can be easily determined by X-ray diffraction of the chromium plating layer. FIGS. 2A and 2B show the results of analysis of the chromium plating layer by the X-ray diffraction method, respectively. Details of the measurement method are as follows.

Analytical instrument: X-ray diffractometer RAD-3C type, manufactured by Rigaku Corporation Measurement conditions: Cu counter-cathode used, energized at 40 kV / 40 mA X-ray diffraction results of a chromium plating layer formed using a hexavalent chromium plating solution As shown in 2 (b). A very large diffraction peak of about 1200 cps is observed near the diffraction angle of about 40θ to 50θ, and a large diffraction peak of about 200 cps is observed near the diffraction angles of about 65θ and about 83θ, respectively. These peaks are derived from (111) -oriented crystals, (200) -oriented crystals, and (211) -oriented crystals in order of increasing diffraction angle.

On the other hand, the X-ray diffraction result of the chromium plating layer formed using the trivalent chromium plating solution is as shown in FIG. Only a small diffraction peak of about 100 cps derived from a crystal with a (111) orientation is observed in the vicinity of a diffraction angle of about 40-50θ. The value obtained by dividing the half width of the peak derived from the (111) oriented crystal by the peak intensity (half width / peak height) is about 0.6 rad / cps, which is observed when hexavalent chromium is used ( Compared to the value of (111) oriented crystals (about 7.9 × 10 ⁻⁴ rad / cps).

  From these figures, the chromium plating layer formed using the trivalent chromium plating solution has a substantially amorphous structure, whereas the chromium plating layer using hexavalent chromium has many It can be seen that it has a crystal structure consisting of crystals. Whether the plating layer has a crystal structure or an amorphous structure is, for example, whether a diffraction peak having a (half-value width / peak height) of about 0.001 rad / cps or less is observed near the diffraction angle of about 40-50θ. It can be determined depending on why.

  The amount of boron contained in the chromium plating layer 3 is 0.05% by mass or more and 0.3% by mass or less. When the boron content is more than 0.3% by mass, the chromium plating layer 3 is cracked by heating at 400 ° C. or higher. On the other hand, when the boron content is less than 0.05%, the corrosion resistance and wear resistance of the chromium plating layer 3 are lowered. Further, the stability of the plating growth when forming the chromium plating layer 3 is lowered. Preferably, the boron content is 0.05 mass% or more and 0.2 mass% or less, and more preferably 0.05 mass% or more and 0.1 mass% or less. The smaller the boron content, the more reliably the cracks can be prevented, and the corrosion resistance and wear resistance are excellent.

  Here, “stability of plating growth” means that the throwing power (adhesiveness) of the chromium plating layer by plating treatment is constant over time. Specifically, when a hull cell test is performed, there is no appearance defect such as insufficient plating thickness, scorching, or striation over a wide current density region, or a portion that is difficult to be plated (for example, an electrode) It means that a plating layer having a predetermined thickness is also formed on the surface to be plated disposed on the opposite side of the surface.

  Further, the “corrosion resistance of plating” means corrosion resistance imparted by the plating process. Specifically, when the plating test of the plating corrosion resistance test method specified in JIS H8502 is performed using the sample after the plating treatment, if the resting number satisfies 7.0 or more, “the plating corrosion resistance is excellent”. That's it.

  “Abrasion resistance of plating” means the wear resistance (hardness) imparted by the plating process. Specifically, when the Vickers hardness specified in JIS Z 2244 is measured using a sample after plating, when the Vickers hardness is in a range of 350 Hv 0.1 (test force 0.9807 N) or more, “plating wear resistance” It is excellent in performance. "

  Thus, when the chromium plating layer 3 contains boron, a chromium plating layer excellent in corrosion resistance and wear resistance is obtained. Moreover, the chromium plating layer can be stably grown. However, boron has a hardening effect on the plating layer, and when the content exceeds the above range, the hardness of the chromium plating layer is increased by heating to a high temperature (particularly 400 ° C. or more), As a result of increased stress on the chromium plating layer due to heat cycle, cracks and the like are likely to occur on the surface. When a crack is generated, rust is likely to be generated starting from the crack. If a large number of cracks are generated, the film may be peeled off and the appearance may be impaired. Moreover, a color tone will fall when content exceeds the above-mentioned range.

  Since boron hardens the chromium plating layer as described above, cracks are likely to occur when the chromium plating layer containing boron is formed thick. For this reason, it is preferable that the thickness of the chromium plating layer 3 is 0.7 μm or less. If the chromium plating layer 3 is thicker than 0.7 μm, it becomes difficult to form a chromium plating layer without cracks even if the boron content is in the above-mentioned range. In order to prevent the occurrence of cracks more reliably, the thickness of the chromium plating layer 3 is preferably 0.5 μm or less.

  From the viewpoint of preventing cracking due to heating, the boron content of the chromium plating layer only needs to be 0.3% by mass or less only in the region where the temperature of the engine component is high. However, it is difficult to change the boron content of a part of the chromium plating layer that continuously covers the surface of the engine component by plating. For this reason, it is preferable that the boron content in a chromium plating layer exists in the above-mentioned range in any area | region of a chromium plating layer.

  However, just because the boron content is within the above-mentioned range in any region of the chromium plating layer, the engine component of the present invention does not need to be used in an environment where the whole is heated to a high temperature. The present invention is preferably used for an engine component in which a part is exposed to a high temperature.

  As long as the chromium plating layer 3 has the boron content described above, a chromium plating layer having good film forming characteristics comparable to those of a plating layer formed from a hexavalent chromium plating solution and excellent in heat resistance can be obtained from trivalent chromium. It can be formed using a plating solution. However, the chromium plating layer formed from the trivalent chromium plating solution has a darker color tone than the chromium plating layer formed from the hexavalent chromium plating solution. The cause of this color tone being blackish is related to the concentration of iron and boron contained in the chromium plating layer, and the color tone becomes darker as the iron content increases. Details are unknown, but the iron in the chromium plating layer contains black iron, such as when iron is combined with various elements in the plating solution when growing the chromium plating layer from the trivalent chromium plating solution This is considered to generate precipitates.

  For this reason, in order to obtain a silver-white color tone similar to that of the chromium plating layer formed from the hexavalent chromium plating solution, the content of boron in the chromium plating layer 3 is 0.1% by mass or less. The content is preferably 2% by mass or less. The lower the iron content, the better, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less.

  However, in the case where the engine component of the present invention is not used in such a manner as to be compared with the chromium plating layer formed from the hexavalent chromium plating solution, the boron content should be 0.3% by mass or less, By setting the content to 7% by mass or less, although the color tone is somewhat dull, a chrome plating layer having a color tone comparable to that of chrome plating can be obtained.

  The boron and iron contents of the chromium plating layer are all represented by the maximum values when the contents of each element contained in the depth direction of the chromium plating layer are analyzed by the GDS analysis method.

  When the content of boron in the chromium plating layer 3 is 0.1% by mass or less and the content of iron is 2% by mass or less, the color tone of the chromium plating layer is CIE (Commission Internationale de l'Eclairage) 1976. The measured L * value satisfies the range of 68-80. The L value is measured using a spectroscopic color difference meter (for example, TC-1800MK-II manufactured by Tokyo Denshoku Color Analyzer). This value is about the same as that of a chromium plating layer formed from a hexavalent chromium plating solution. For this reason, even if the chromium plating layer 3 in which the iron content is limited to the above-described range and the chromium plating layer formed from the hexavalent chromium plating solution are arranged side by side, the difference in color tone is hardly noticeable.

  By having such a structure for engine parts, using trivalent chromium plating solution, it has good film forming characteristics comparable to the plating layer formed from hexavalent chromium plating solution, and has excellent heat resistance. A chromium plating layer can be obtained. Further, by setting the boron content in the chromium plating layer to 0.1% by mass or less and the iron content to 2% by mass or less, the same level as the chromium plating layer formed from the hexavalent chromium plating solution A silver-white color tone can be obtained.

(Iv) Mechanism for preventing discoloration The engine component of the present invention can be suitably used for engine parts such as a cylinder, a cylinder head, and a head cover, and an exhaust pipe for leading exhaust gas from the engine. However, when the engine component of the present invention is used in a place exposed to heat of 350 ° C. or higher, the color tone of the surface may change due to heating, and the chromium plating layer may exhibit a bluish purple color. When the engine component of the present invention is used in such a place, it is preferable that the chromium plating layer has a thickness of 0.2 μm or more. Hereinafter, the reason why the chromium plating layer can be prevented from being discolored by heating by controlling the thickness of the chromium plating layer will be described with reference to FIGS.

  FIG. 3 may be referred to as a “CS enriched layer” or “CS—Ni enriched layer” (hereinafter simply referred to as “enriched layer”), which is thought to cause discoloration of the surface of the chromium plating layer. .) Is a diagram for explaining a mechanism in which C and / or S gathers in the vicinity of the interface between the chromium plating layer and the base plating layer by heating. FIG. 3 shows a typical configuration of the present invention in which a nickel plating layer is formed between an Fe substrate and a chromium plating layer. The nickel plating layer is semi-gloss in order from the Fe substrate side. It consists of three layers: a nickel plating layer, a trinickel plating layer, and a bright nickel plating layer.

  In addition, various elements which comprise the additive contained in a chromium plating layer or a nickel plating layer gather by heating in the vicinity of the interface of a chromium plating layer and a nickel plating layer. FIG. 3 shows elements that are considered to be involved in the discoloration of the chromium plating layer, that is, the elements (at least one of C, S, and Ni) constituting the above-described concentrated layer, and bonds to these elements. Only elements that are easily processed (Fe, Cr, etc.) are shown, and other elements (for example, O that gathers in the vicinity of the interface by heating) are omitted.

  As shown in FIG. 3, C or S mainly moves from the nickel plating layer side to the chromium plating layer side and gathers in the vicinity of the interface. As described above, C or S is an element mainly constituting a non-butyne-based brightener (such as benzenesulfonic acid) added to the nickel plating solution, and particularly in the bright nickel plating layer and the trinickel plating layer. Contains a large amount of S. Therefore, a “CS enriched layer” in which a large amount of C or S gathers is formed in the vicinity of the interface. Here, the “C—S concentrated layer” means a layer in which at least one of C and S is gathered. In addition, although C or S may diffusely move from the chromium plating layer side, since the ratio is very small compared with the case where it diffuses and moves from the nickel plating layer side, it is not illustrated.

  When the base plating layer is a nickel plating layer, a “CS—Ni concentrated layer” containing Ni is formed. Ni, like C or S, is also considered to be involved in discoloration. Here, the “concentrated layer of C—S—Ni” means a layer in which at least one of C, S, or Ni is gathered.

  The reason why discoloration of the surface of the chromium plating layer is caused by the formation of such a concentrated layer is unknown in detail. For example, Cr constituting the chromium plated layer is an element constituting the above concentrated layer. It is considered that discoloration is caused because it is combined with (C or S or Ni) and the refractive index of the chromium plating layer is changed. Iron is also considered a causative substance that causes discoloration. When the metal substrate is made of an Fe-based material, heating may cause Fe to diffuse from the Fe-based material and concentrate in the vicinity of the interface (not shown).

  Such discoloration of the surface of the chromium plating layer based on the concentrated layer can be prevented by setting the thickness of the chromium plating layer to 0.2 μm or more. Hereinafter, the reason will be described with reference to FIGS. 4 (a) and 4 (b).

  FIG. 4B is a diagram schematically illustrating a part of a conventional Cr-nickel plating layer. As shown in FIG. 4B, since the thickness of the conventional chromium plating layer is as small as about 0.1 μm or less, incident light is transmitted to the vicinity of the interface between the chromium plating layer and the nickel plating layer. . As a result, a part of incident light is absorbed by the concentrated layer generated in the vicinity of the interface, and the degree of discoloration due to heating becomes more prominent.

  On the other hand, when the thickness of the chromium plating layer is 0.2 μm or more, as shown in FIG. 4A, most of the incident light is reflected near the surface of the chromium plating layer. It does not penetrate to the vicinity of the interface between the nickel plating layer. Therefore, only the interference color due to the oxide film formed on the outermost surface of the normal chromium plating layer is provided, and the influence of the concentrated layer can be suppressed.

  In order to effectively exhibit such an action, the thickness of the chromium plating layer is set to 0.2 μm or more. From the viewpoint of preventing thermal discoloration due to heating, the chrome plating layer should be thick. Preferably, the thickness of the chromium plating layer is 0.3 μm or more, more preferably 0.4 μm or more.

  From the above, in order to prevent generation of cracks and discoloration due to heating, the thickness of the chromium plating layer is preferably 0.2 μm or more and 0.7 μm or less, and is 0.3 μm or more and 0.5 μm. The following is more preferable. If the thickness of the chromium plating layer is 0.4 μm or more and 0.5 μm or less, the generation of cracks can be prevented almost certainly and discoloration due to heating can also be reliably prevented.

  The thickness of the chromium plating layer 3 is measured by observation with an optical microscope (magnification: 400 times). Specifically, the thickness direction cross section of the plating layer is mirror-polished and etched. Thereby, a chromium plating layer and a base plating layer are separated clearly. Since the surface roughness Ra of the chromium plating layer is at most about 0.01 μm, it is considered that the influence of the surface roughness Ra on the thickness of the chromium plating layer is almost negligible. In addition, since the thickness of the chromium plating layer varies slightly depending on the measurement site, a total of three locations are measured in any observation region by changing the measurement location, and the average value is defined as “thickness of the chromium plating layer”. .

  As another discoloration prevention means by forming a thickened layer, for example, a method of reducing the content of C or S is conceivable, but this method is not practical. For example, in order to reduce the content of C or S, the amount of brightener contained in the underlying plating layer has to be reduced, but as a result, the gloss is lowered and the design of engine parts is reduced. Will be significantly impaired. When it is listed as one of the important issues that an excellent design is provided as in the present invention, the design must be prevented from being damaged as the brightener is reduced.

  In order to prevent discoloration due to heating, it is sufficient that the portion of the chromium plating layer 3 heated to a temperature of 350 ° C. or higher satisfies the thickness in the above range, and the chromium plating formed on the metal substrate 1 is sufficient. It is not necessary for all parts of the layer 3 to satisfy the thickness in the above range. Further, in the region where the temperature is only 350 ° C. or less, the thickness of the chromium plating layer 3 may be 0.2 μm or less. In general, the chrome plating layer is colored from white to yellow and golden by heating, and further changes from golden to purple at a high temperature of about 350 to 500 ° C. Such a change in color tone does not appear uniformly over the entire portion where the chromium plating layer is formed, but occurs remarkably in a portion that is easily exposed to high-temperature exhaust gas. Therefore, in order to prevent discoloration from golden to purple, the thickness of the chromium plating layer that is exposed to a temperature that is most likely to undergo discoloration by heating, that is, a temperature of 350 ° C. or higher, is controlled within the above range. good.

  Examples of the “part heated to a temperature of 350 ° C. or higher” include, for example, a part of engine parts constituting the engine such as a cylinder, a cylinder head, and a head cover, and a flow path for guiding exhaust gas discharged from the engine. A part of the exhaust pipe or a cover of the exhaust pipe may be mentioned. The exhaust pipe referred to here may be an exhaust pipe that directly guides the exhaust gas, or may be an exhaust pipe (double pipe) that is indirectly heated by the exhaust gas. The exhaust pipe includes a manifold unit that guides exhaust gas from each cylinder, a catalyst device storage unit that covers the catalyst device, a silencer (muffler), and the like.

(2) Specific structure and application to a motorcycle A specific structure of an engine component according to the present invention will be described with reference to FIG. FIG. 5 shows a motorcycle 100 using an exhaust pipe which is an engine component of the present invention. As shown in FIG. 5, the motorcycle 100 includes an engine 30 composed of a four-cycle internal combustion engine, and an exhaust pipe 4 that guides the exhaust gas in order to exhaust the exhaust gas generated by the engine 30 from the rear of the vehicle body. ing. The exhaust pipe 4 is connected to the engine 30 and includes an exhaust pipe assembly portion 4a that constitutes an exhaust path that is largely bent so as to guide exhaust gas exhausted from the front of the engine 30 to the rear, and a silencer 4b. . The exhaust pipe collecting portion 4a may be integrally constituted by one part, or may be constituted by joining a plurality of parts. In the present embodiment, the exhaust pipe 4 is exposed as a whole so as to appear on the exterior of the motorcycle 100, and constitutes a part of the design of the entire motorcycle 100. As will be described in detail below, when the entire exhaust pipe 4 is exposed, the chromium plating layer of the exhaust pipe 4 is not cracked and rusted or discolored due to heat for a long time. The effect of the present invention for maintaining the appearance appears remarkably in the appearance. However, as long as at least a part of the exhaust pipe 4 appears on the exterior, a part of the exhaust pipe 4 may be covered with a cowl or a protector depending on the design of the motorcycle. Further, the shape of the motorcycle using the exhaust pipe is not limited to that shown in FIG. 5. For example, the exhaust pipe of the present invention may be adopted for a motorcycle having a structure as shown in FIG.

  Next, referring to FIGS. 6 (a), (b) and (c), it is preferable to set the thickness of the chromium plating layer to 0.2 μm or more. The “region” will be specifically described. These drawings are sectional views showing a part of the exhaust pipe 4.

  FIG. 6A shows an exhaust pipe assembly portion 4a of the exhaust pipe 4 that is directly connected to the engine. As shown in FIG. 6A, an exhaust pipe assembly 4a connected to an engine (not shown) includes a metal pipe 5 that defines a passage 6 through which exhaust gas passes, and an outer surface of the metal pipe 5. Covering plating layer 10. The metal tube 5 has a bent portion 9. The bent portion 9 is a portion where the passage 6 is bent or the direction in which the passage 6 extends is changed.

  As described above, the plating layer 10 is composed of a base plating layer and a chromium plating layer. The metal tube 5 only needs to define the passage 6, and may have a double tube structure including an inner tube defining the passage 6 and an outer tube held so as to surround the outside of the inner tube. Good.

  Exhaust gas entering from the exhaust pipe assembly 4a directly connected to the engine (not shown) moves through the passage 6 at a high speed, and therefore collides with the metal pipe 5 at the bent portion 9, and is formed by bending. It collides violently with the inner surface 9b of the metal tube 5 located on the convex surface portion 9a. For this reason, the outer portion 9a is heated to a temperature of about 350 ° C. or higher (for example, about 400 to 500 ° C.) by the high temperature exhaust gas.

  Further, when the metal pipe 5 has a double pipe structure, a single pipe structure is often adopted in the connecting portion 21 that connects the other exhaust pipe member 23. When the double pipe structure is employed for the connecting portion 21, the metal pipe 5 may be deformed or damaged due to a difference in thermal expansion between the outer pipe and the inner pipe during welding with the other exhaust pipe member 23. Because. When the metal pipe 5 adopts such a structure, the inner surface of the connecting portion 21 is in direct contact with the high-temperature exhaust gas, so that the connecting portion 21 has a temperature of about 350 ° C. or higher (for example, about 400 to 500 ° C.).

  FIG. 6B schematically shows a cross-section of the catalyst storage portion 22 that stores the catalyst device 8 of the exhaust pipe 4. The catalyst device 8 is provided in the catalyst storage unit 22 and decomposes at least one component contained in the exhaust gas when the exhaust gas passes therethrough. Since the catalyst device 8 generates heat during decomposition, the catalyst storage unit 22 is heated to a temperature of about 350 ° C. or higher (for example, about 400 to 500 ° C.).

  Further, when the engine 30 (FIG. 5) includes a plurality of cylinders, the exhaust pipe 4 may include a manifold portion for guiding exhaust gas generated in each cylinder together to the rear of the motorcycle 100. is there. FIG. 6C shows the exhaust pipe 4 in which the branch pipes 4d and 4e connected to the cylinder are gathered by the manifold portion 15 and discharged by the integrated exhaust pipe member 4f. In the manifold portion 15 of the exhaust pipe collecting portion 4a, the exhaust gas is collected from the plurality of branch pipes 4d and 4e, thereby increasing the flow rate of the exhaust gas and bending the flow path. 15 collides with the inner surface. For this reason, the manifold portion 15 is heated to a temperature of about 350 ° C. or higher (for example, about 400 to 500 ° C.) by the exhaust gas.

  The motorcycle of the present embodiment has a chromium plating layer of 0.2 μm or more so as to cover the outside of the portions heated to high temperatures of these exhaust pipes exemplified with reference to FIGS. 6 (a), (b) and (c). Is formed. For this reason, even if it exposes to high temperature exhaust gas, discoloration of the chromium plating layer by heating can be prevented.

  In addition, the chromium plating layer formed using trivalent chromium has the same excellent color tone as when hexavalent chromium is used because the Fe content in the chromium plating layer is reduced. Can do.

  The present invention also includes a transportation device including the above-described engine component. Examples of the transportation equipment include vehicles such as motorcycles equipped with engines and all-weather four-wheeled vehicles, ships equipped with engines, transportation equipment such as airplanes, and the like.

2. Next, a method for manufacturing the engine component of the present invention will be described. The engine component according to the present invention is manufactured by sequentially forming a base plating layer and a chromium plating layer on a metal substrate having a predetermined shape. Hereinafter, the manufacturing method will be described in detail.

  First, in order to degrease and clean the surface of the metal substrate, the metal substrate is immersed in a tank such as a water washing tank, an ultrasonic alkaline degreasing tank, an electric field degreasing tank, or an acid treatment activation tank for a predetermined time. Thereby, since the surface of a metal base material is fully degreased, it becomes easy to form a base plating layer and a chromium plating layer on the metal surface.

  Next, using the metal substrate washed as described above, an underplating layer and a chromium plating layer are sequentially formed on at least the outer surface of the metal substrate by electroplating. Since both the base plating layer and the chromium plating layer are formed by electroplating and the principle is the same, in the following description, the plating apparatus shown in FIG. 7 is used for the process of forming the chromium plating layer. The process of forming the base plating layer will be described without referring to the drawings.

  The base plating layer is formed by immersing the metal base in a plating tank containing a metal solution for which a plating layer is to be formed, and energizing until a desired thickness is obtained. For example, when forming a nickel plating layer consisting of three layers of a semi-bright nickel plating layer, a tri-nickel plating layer, and a bright nickel plating layer as the base plating layer, the metal substrate washed as described above, It is immersed in a semi-bright nickel plating solution, a trinickel plating solution, and a bright nickel plating solution, respectively, and energized until a desired plating layer is formed. The specific plating conditions differ depending on the metal substrate used, the composition of the plating solution, the application, etc., and the conditions usually used for Ni-chrome plating may be selected as appropriate. For example, when a 5-15 μm semi-bright nickel plating layer, a 1-2 μm trinickel plating layer, and a 5-15 μm bright nickel plating layer are sequentially formed on an Fe substrate, the temperature of the plating solution is about 40. It is preferable that the plating solution has a pH of about 2 to 5 at about 65 ° C. The plating time is preferably about 10 to 20 minutes for semi-bright nickel plating and bright nickel plating, and about 1 to 5 minutes for trinickel plating. A strike nickel layer may be further provided between the base plating layer and the metal substrate.

  Next, a chromium plating layer is formed on the metal substrate on which the base plating layer is formed. As shown in FIG. 7, the chrome plating apparatus 20 removes impurities floating in the plating solution, a chrome plating bath 11 for performing chrome plating, a pump 12 that pumps up the plating solution added to the chrome plating vessel 11, and the like. For this purpose, a filter 13, an adjustment valve 14 for adjusting the flow rate of the plating solution, and a flow meter 15 for monitoring the flow rate of the plating solution are included. An ion exchange device 16 for removing metal ions such as Fe contained in the plating solution is installed on the downstream side of the chromium plating device 20. The chromium plating apparatus 20 and the ion exchange apparatus 16 are connected by a metal tube (not shown).

  The chromium plating tank 11 is filled with a trivalent chromium plating solution. The plating solution contains 30 to 40 g / l of basic chromium sulfate as a trivalent chromium ion source in terms of chromium content.

  In order for the amount of boron and iron contained in the chromium plating layer to be in the above-described range, the concentration of boron and iron in the plating solution to be used needs to be within a predetermined range. Specifically, the trivalent chromium plating solution has a boric acid content in the range of 1 to 5 g / l in terms of boron content, and an Fe content of 0.5 mg / l or less.

  The content of boric acid is reduced to about 1/15 to 5/6 as compared with the amount of boron (about 6 to 15 g / l) added to a typical conventional trivalent chromium plating solution. In recent years, the amount of boron discharged into the environment has been regulated, and the use of a plating solution having a low boron concentration is also suitable for compliance with such environmental regulations.

  In addition, a conventional typical trivalent chromium plating solution contains about 0.0001 to 0.0003 mass% of ferrous sulfate as an additive in order to improve the covering of the plating layer. For this reason, when using the conventional trivalent chromium plating solution, about 2-20 mass% Fe is contained in a chromium plating layer. However, the trivalent chromium plating solution used in the present invention preferably does not contain such an additive, and the Fe content is limited to 0.5 mg / l or less.

  Boric acid is used to adjust the pH and ensure that the chromium plating layer has a silver-white color tone. For this reason, in order to reduce the amount of boric acid and maintain an appropriate pH, the trivalent chromium plating solution used in the present invention is 5 to 30 g / l by converting citric acid or a citric acid compound into the amount of citric acid. Included in the range. As the citrate compound, a citrate such as potassium citrate or a metal citrate compound such as nickel citrate can be used. In order to obtain a chromium plating layer with excellent color tone, it is more preferable to use citric acid. The amount of citric acid added is preferably 10 g / l or more and 25 g / l or less, more preferably 20 g / l or more and 25 g / l or less.

  Chrome plating is performed by electroplating. The chromium base 11 is filled with the above-described trivalent chromium plating solution, and the metal substrate 17 to which chromium plating is applied is used as a cathode. Since chromium plating is performed by supplying chromium ions from a plating solution, an insoluble anode 18 that does not dissolve in the chromium plating solution is used for the anode.

  Next, a DC power source 19 is connected between the two poles and energized. Chromium ions contained in the chromium plating solution move toward the metal substrate 17 on the cathode side, and are reduced to metal Cr and deposited.

  When it is desired to form a chromium plating layer of 0.2 μm or more in a region heated to a temperature of 350 ° C. or higher, a metal substrate is arranged and plated so that a chromium plating layer having a desired thickness is formed. Is preferred. In particular, when plating a metal substrate such as an exhaust pipe having a curved shape, it is preferable to dispose the metal substrate so that the distance between the electrode and the material to be plated (metal substrate) is as short as possible.

  For example, as shown to Fig.8 (a), when arrange | positioned so that the distance of the convex part 9a of the bending part of the metal base material 17 and the electrode 18 may become the shortest, the convex shape heated to high temperature The Cr layer can be efficiently formed on the portion 9a.

  On the other hand, as shown in FIG. 8 (b), when the distance between the convex portion 9a of the metal substrate 17 and the electrode 18 is increased, a concave shape opposite to the convex portion 9a. Since the chromium plating layer is easily formed on the portion and the chromium plating layer is hardly formed on the convex portion 9a, the plating efficiency is deteriorated.

  In addition, for example, the thickness of the chromium plating layer can be controlled within a predetermined range by controlling the amount of electricity passing through the electrode surface (current × time), the current density, and the like. In particular, the current density is controlled by devising the arrangement of electrodes and attaching auxiliary electrodes so that a predetermined chromium plating layer is easily formed in a region heated to a temperature of 350 ° C. or higher. be able to. The specific control method should just select appropriate conditions suitably according to the kind and shape of the metal base material to be used, the structure of a plating solution, the thickness of a chromium plating layer, etc. In particular, when ferrous sulfate is not included in the plating solution, since the plating layer generally has poor contact, it is necessary to consider that the current density is uniform by devising the arrangement of the electrodes.

  The boron content of the chromium plating layer to be formed depends not only on the boron concentration in the plating solution, but also on the temperature of the plating solution, the plating time, the stirring speed of the plating solution, etc., and in particular on the temperature of the plating solution. Generally, when the temperature of the plating solution increases, the boron content in the chromium plating layer increases. For this reason, in order to suppress the amount of boron in the chromium plating layer to the above-described range, it is preferable to control the temperature of the plating solution in the range of 25 ° C to 30 ° C.

  In order to bring the iron content in the chromium plating layer into the above range, it is necessary to pay attention to the iron that dissolves into the plating solution from the metal substrate. Even if the metal substrate does not contain iron as a main component, Fe may inevitably gather on the chromium plating layer side. As a result, even if ferrous sulfate is not added to the plating solution, the concentration of iron in the plating solution increases, and iron may be contained in the chromium plating layer.

  In order to eliminate such a possibility, it is necessary to regularly monitor the iron concentration in the plating solution during plating, and to remove iron when the iron concentration exceeds a predetermined value. Iron ions mixed in the plating solution are removed using an ion exchange device 16 provided with a cation exchange resin. The cation exchange resin used in the present invention is not particularly limited as long as it can be easily exchanged with a divalent metal cation such as Fe.

  A specific removal method is as follows. First, during plating, the plating solution is periodically pumped from the plating tank 11 by the pump 12, and the suspended matter is removed using the filter 13. Next, the plating solution from which the suspended matter has been removed is introduced into the ion exchange device 16 while adjusting the flow rate by the adjustment valve 14, and metal cations such as Fe ions are removed by the cation exchange resin. The flow rate of the plating solution is monitored by the flow meter 15. The plating solution processed by the ion exchange device 16 is periodically collected to check the Fe concentration. In order to reduce the Fe concentration of the chromium plating layer to 2% by mass or less as in the present invention, it is necessary to control the Fe concentration in the plating solution to about 0.0001% by mass or less. Until the ion exchanger 16 is removed.

  The plating solution from which the Fe ions have been removed in this way (regenerated plating solution) is circulated from the outlet of the ion exchange device 16 through the conduit 24 to the plating tank 11. For example, the regenerated plating solution may be stored in a suitable storage container (not shown).

  In addition, the method of removing the metal cation in a plating solution using the ion exchange apparatus 16 is demonstrated in detail by patent document 4 etc., for example, and can be applied to the method of this invention. Various modifications have been proposed (for example, Patent Document 5), and these modifications can also be applied to the method of the present invention.

  The chromium plating layer after plating has a surface roughness (Ra) of about 1 μm or less, and preferably has a surface roughness of 0.2 μm or less. For this reason, after plating, the chromium plating layer has a sufficient luster without particularly finishing the surface.

3. Experimental example (Experimental example 1)
In this experimental example, the following experiment was conducted for the purpose of clarifying that the stability of plating growth is ensured by setting the lower limit of the boron content of the chromium plating layer to 0.05 mass%.

  First, a metal tube made of STKM material was prepared, and a Ni plating layer composed of a semi-gloss Ni plating layer, a tri-Ni plating layer, and a bright Ni plating layer was formed by the following method. Table 1 shows the composition of the plating solution used to form these plating layers. Note that C and / or S contained in the tri-Ni plating solution is supplied from an additive other than the brightener.

Semi-bright Ni plating layer (thickness of about 5 to 15 μm)
Plating condition: energized at 10-12V (volt), 1800-2800A (ampere).
Tri Ni plating layer (thickness about 1-5μm)
Plating conditions: 3 to 3.5V, 20 to 40A energized.
Glossy Ni plating layer (thickness about 5-15μm)
Plating conditions: 10-12V, 1800-2800A energized.

Next, using the chromium plating apparatus provided with the ion exchange apparatus shown in FIG. 6, the chromium plating layer was formed on the base plating layer (the thickness of the chromium plating layer is 0.3 μm). As the chromium plating solution, four types of trivalent chromium plating solutions (Nos. 1 to 4) shown in Table 2 were used. The constituent components of the trivalent chromium plating solutions of Sample 1 to Sample 4 are the same except that the contents of ferrous sulfate and boric acid are different. Specifically, each of these trivalent chromium plating solutions contains citric acid, and the addition amounts of ferrous sulfate are 0 (sample 1) and 2.5 mg / l (sample 2), respectively. 5 mg / l (sample 3) and 10 mg / l (sample 4). In terms of the amount of Fe, they are 0 (sample 1), 0.05 mg / l (sample 2), 0.1 mg / l (sample 3), and 0.3 mg / l (sample 4), respectively. The addition amount of boric acid is 5 g / l (sample 1), 5 g / l (sample 2), 30 g / l (sample 2), and 60 g / l (sample 3).

In order to adjust the boron content contained in the plating layer to various ranges, the temperature of the plating solution is changed in the range of about 25 to 60 ° C., the current density is changed in the range of about 10 to 30 A / dm ² , and the plating solution The degree of air agitation was adjusted.

  When the trivalent chromium plating solution of Sample 1 of the present invention was used, Fe ions mixed during plating were removed using an ion exchange apparatus equipped with a cation exchange resin. Specifically, the plating solution was periodically sent to an ion exchange device, and the Fe concentration contained in the plating solution was controlled to be in the range of 0 to 0.0001% by mass. As a result, when the trivalent chromium plating solution of the present invention example of Sample 1 was used, the Fe content contained in the chromium plating layer was 0.2 mass% at the maximum when measured in the thickness direction of the plating layer. became. On the other hand, when the trivalent chromium plating solutions of Sample 2 to Sample 4 were used, Fe ions were not removed by the ion exchange device, so the Fe content (maximum value) contained in the chromium plating layer was They were 2.0 mass%, 7.0 mass%, and 15.0 mass%.

  For each sample, the stability of plating growth was measured according to the above-described method, and the following criteria were evaluated based on the thickness of the chromium plating layer at each measurement site.

<Stability of plating growth>
Evaluation criteria (◎ to Δ are examples of the present invention)
A: The thickness of the chromium plating layer is in the range of 0.25 mm or more and less than 0.5 mm. A: The thickness of the chromium plating layer is in the range of 0.20 mm or more and less than 0.25.
Δ: The thickness of the chromium plating layer is in the range of 0.05 mm or more and less than 0.20 mm.
X: The thickness of the chromium plating layer is less than 0.05 mm.

The obtained results are shown in Table 3.

  From Table 3, even when any trivalent chromium plating solution of Sample 1 to Sample 4 is used, if the chromium plating layer does not contain any boron (the content is zero), the growth of plating is Although it becomes extremely unstable, it can be seen that the plating grows stably by setting the plating conditions so that the chromium plating layer contains at least 0.05 mass% or more of boron. As far as the purpose of stably growing the plating is concerned, the higher the boron content in the chromium plating layer, the better.

  Thus, it is clear that boron is an indispensable component to ensure the stability of plating growth, and simply adding citric acid instead of boric acid does not provide excellent plating characteristics. became. Although the plating grew stably with the addition of boron, this effect was similarly seen regardless of the Fe content in the plating layer.

  Next, for the purpose of investigating the above-described effects of boron in more detail, after forming a chromium plating layer in the same manner as described above using the trivalent chromium plating solution of Sample 1, the plating corrosion resistance and plating wear resistance are Measurements were made according to the methods described above, and each was evaluated according to the following criteria.

<Plating corrosion resistance>
Evaluation criteria (◎ to Δ are examples of the present invention)
A: Rating number is 9.0 or more.
A: Rating number is 8.0 or more and less than 9.0.
Δ: Rating number is 7.0 or more and less than 8.0.
X: The rating number is less than 7.0.

<Plating wear resistance>
Evaluation criteria (◎ to Δ are examples of the present invention)
A: Vickers hardness is 500 Hv or more.
○: Vickers hardness is 450 Hv or more and less than 500 Hv.
Δ: Vickers hardness is 350 Hv or more and less than 450 Hv.
X: Vickers hardness is less than 350 Hv.

  Table 4 shows the obtained results. Table 4 also shows the results of plating growth stability.

  From Table 4, when the chromium plating layer does not contain boron at all (the content is zero), the plating corrosion resistance and the plating wear resistance are remarkably lowered, but at least 0.05 mass% of boron is contained in the chromium plating layer. It can be seen that these characteristics are improved by setting the plating conditions to include the above. This result is the same as the result of the plating growth stability described above. Therefore, it can be seen that boron is an indispensable component not only for improving the stability of plating growth but also for improving plating corrosion resistance and plating wear resistance.

  However, as shown in Table 4, when the boron content in the chromium plating layer exceeds 0.1 mass%, the plating corrosion resistance and the plating wear resistance gradually decrease. This result is different from the above-described stability of plating growth.

  From the above results, in order to improve the plating film forming characteristics comprehensively evaluated from the three characteristics of plating growth stability, plating corrosion resistance, and plating wear resistance, the boron content in the chromium plating layer is set to 0. It is preferable to control within the range of 0.05 to 0.3% by mass.

(Experimental example 2)
In this experimental example, the following experiment was conducted for the purpose of clarifying that the color tone of the chromium plating layer immediately after plating is improved by controlling the boron content and the Fe content in the chromium plating layer.

  Specifically, using the four types of trivalent chromium plating solutions of Sample 1 to Sample 4 of Experimental Example 1, a chromium plating layer was formed in the same manner as Experimental Example 1 described above.

  About each sample obtained in this way, the color tone immediately after plating was measured by the following method and evaluated according to the following criteria.

<Color tone immediately after plating>
The L * value was measured based on the method described in CIE 1976 using a spectroscopic color difference meter (TC-1800MK-II manufactured by Tokyo Denshoku Color Analyzer). The color tone of the chromium plating layer obtained using the hexavalent chromium plating solution is in the range of 70 to 80 in terms of L * value. In this experimental example, when the L * value was 68 or more, it was considered that the same color tone as that of the chromium plating layer obtained from the hexavalent chromium plating solution was obtained.

Evaluation criteria A: Excellent color tone comparable to hexavalent chromium is obtained.
(L * value = 70 or more, 80 or less)
○: The metallic luster is slightly lowered, but the same color tone as hexavalent chromium is obtained.
(L * value = 68 or more, less than 70)
Δ: Slightly blackish tone (L * value = 65 or more and less than 68).
X: The color tone becomes blackish (L * value = less than 65).

  These results are shown in Table 5.

  As is apparent from Table 5, when the trivalent chromium plating solution of Sample 4 was used and the Fe content in the chromium plating layer was controlled to 15.0% by mass, regardless of the boron content in the chromium plating layer, A blackish chrome plating layer was obtained.

  When the trivalent chromium plating solution of Sample 3 is used and the Fe content in the chromium plating layer is controlled to 7.0% by mass, the tint is slightly blackish by controlling the boron content to 0.3% by mass or less. A chromium plating layer was obtained.

  On the other hand, when the trivalent chromium plating solution of Sample 2 was used and the Fe content in the chromium plating layer was reduced to 2.0 mass%, the boron content was controlled to 0.3 mass% or less, so that it was slightly blackish When the boron content was controlled to 0.1% by mass or less, a chromium plating layer having almost the same color tone as the chromium plating layer obtained from the hexavalent chromium plating solution was obtained. . Similar results were obtained when the trivalent chromium plating solution of Sample 1 was used, the Fe content in the chromium plating layer was reduced to 0.2% by mass, and the boron content was controlled to 0.3% by mass or less. It was. When the Fe content in the chromium plating layer is reduced to 0.2% by mass and the boron content is controlled to 0.1% by mass or less, the color tone is almost indistinguishable from the chromium plating layer obtained from the hexavalent chromium plating solution. The chromium plating layer which has was obtained.

  Therefore, in order to obtain a trivalent chromium plating layer having the same color tone as when hexavalent chromium is used, the amount of Fe in the trivalent chromium plating layer is suppressed to 2.0% by mass or less and boron is added. It can be seen that the amount may be reduced to 0.1% by mass or less. As far as the color tone is concerned, the smaller the Fe content and the boron content in the chromium plating layer, the better the characteristics.

(Experimental example 3)
In this experimental example, it was investigated how the cracking state before and after heating and the color tone of the chromium plating layer change depending on the thickness of the chromium plating layer.

  Specifically, using the trivalent chromium plating solution of Sample 1 of Experimental Example 1, a chromium plating layer was formed in the same manner as in Experimental Example 1 described above. The thickness of the chromium plating layer can be adjusted by appropriately controlling the plating time according to the size of the plating material used. In this experimental example, the thickness of the chromium plating layer was changed to 0.1 to 1.5 μm by changing the plating time in the range of 0.3 to 5 minutes.

  About each sample obtained in this way, the generation | occurrence | production condition of the crack observed immediately after plating (before heating) was measured with the following method, and the following reference | standard evaluated. Furthermore, according to the method mentioned above, the color tone of the chromium plating layer immediately after plating was measured and evaluated.

  Next, after each sample was placed in an atmospheric furnace and heated under the conditions of 400 ° C. × 8 hours, the occurrence of cracks after heating was examined when the occurrence of cracks observed immediately after plating was examined. The same measurement method and evaluation criteria were used.

<The occurrence of cracks>
Measurement method: Using an optical microscope (magnification 400 times), a crack generated on the surface of the chromium plating layer (about 10 mm × 10 mm) is observed.

Evaluation criteria (◎ to Δ are examples of the present invention)
A: No cracks are generated.
○: Discontinuous cracks are slightly observed.
Δ: Slightly continuous cracks occur.
X: Many continuous cracks are generated.

  Table 6 summarizes the occurrence of cracks. Table 7 shows the color tone of the chromium plating layer immediately after plating.

  As shown in Table 6, when the thickness of the chromium plating layer is increased and the boron content in the chromium plating layer is increased, it is understood that cracks are likely to occur.

  For example, looking at the experimental results before heating (immediately after plating), the boron content in the chromium plating layer is increased to 1.5% by mass when the thickness of the chromium plating layer is in the range of 0.1 to 0.3 μm. However, almost no cracks occurred. Cracks are likely to occur as the thickness of the chromium plating layer increases to 0.5 μm or more. When the thickness of the chromium plating layer is 1.5 μm, cracks occurred regardless of the boron content of the chromium plating layer. .

  On the other hand, when the heat treatment was performed at 400 ° C. for 8 hours, there was a tendency that cracks were more likely to occur than before the heating. Specifically, even if the thickness of the chromium plating layer is in the range of 0.1 to 0.7 μm, if the boron content in the chromium plating layer is not controlled to 0.05 to 0.3% by mass, it is cracked. It was not possible to effectively prevent the occurrence of. A more preferable boron content is 0.05 to 0.2% by mass. In addition, when the thickness of the chromium plating layer exceeds 0.7 μm, cracks are likely to occur. When the thickness of the chromium plating layer is 1.5 μm, cracks occurred regardless of the boron content in the chromium plating layer. .

  Considering these experimental results, in order to effectively prevent the occurrence of cracks before and after heating, the thickness of the chromium plating layer is set to 0.7 μm or less, and the boron content in the chromium plating layer is set to 0.05 μm. It can be seen that it should be controlled in the range of ~ 0.3% by mass.

  Next, for samples having a boron content of 0.05% by mass and 0.1% by mass in the chromium plating layer, the thickness of the chromium plating layer was changed in the range of 0.05 μm to 0.7 μm, and the discoloration caused by heating was changed. The degree of evaluation was performed.

<Degree of thermal discoloration>
Measuring method: Using a spectroscopic color difference meter (TC-1800MK-II manufactured by Tokyo Denshoku Color Analyzer), based on the method described in CIE 1976, L * value, a * value, and b * value before and after heating were ,taking measurement. The values before heating are L ₀ * values, a ₀ * values, and b ₀ * values, respectively, and the values after heating are L ₁ * values, a ₁ * values, and b ₁ * values, respectively. The color difference ΔE * value after heating is measured as follows.

Evaluation criteria (◎ to Δ are examples of the present invention)
A: ΔE * value <1
○: 1 ≦ ΔE * value <3
Δ: 3 ≦ ΔE * value <4
×: 4 ≦ ΔE * value

  As is clear from Table 7, when the thickness (μm) of the chromium plating layer is 0.2 μm or more, the change in color tone before and after heating is small, and when it is 0.3 μm or more, the color tone hardly changes. I understood.

  INDUSTRIAL APPLICABILITY The present invention can be widely used in vehicles such as motorcycles equipped with engines and all-weather four-wheeled vehicles, ships equipped with engines, and transportation equipment such as airplanes.

  The present invention relates to an engine component, and more particularly to an engine component that is exposed to high temperature by high-temperature exhaust gas discharged from the engine.

  In vehicles such as motorcycles and all-weather four-wheel vehicles, in addition to the performance of the vehicles themselves, having an excellent design is one of the important issues. FIG. 9 is a side view showing an example of a sports type motorcycle. A motorcycle 200 shown in FIG. 9 includes a V-type engine 201 and an exhaust pipe 202 for guiding exhaust gas. The V-type engine 201 includes a cylinder 203, a cylinder head 204, and a head cover 205. Since the V-shaped engine 201 is excellent in shape and appearance, it is often mounted on a motorcycle so as to be exposed to the outside, and has a great influence on the appearance of the entire motorcycle.

  The exhaust pipe 202 is led from each of the two cylinders 203 of the V-type engine 201, is gathered together, and is extended to the rear wheel side so as to eject exhaust gas from the rear part of the vehicle body. The exhaust pipe 202 needs to have a predetermined thickness in order to efficiently exhaust the exhaust gas generated in the engine 201. In addition, the exhaust pipe 202 is configured to mute at a portion constituting the silencer 202a. The diameter increases to accommodate the structure. For this reason, the proportion of the exhaust pipe in the overall appearance of the motorcycle is relatively large, and the influence of the shape and color of the exhaust pipe on the design of the entire motorcycle is great.

  Engine parts such as the cylinder 203, the cylinder head 204, and the head cover 205, and the exhaust pipe 202 and its cover for guiding exhaust gas from the engine are referred to as engine parts in this specification. For the reasons described above, the shape and color of engine parts are important factors in determining the design of the entire motorcycle.

  Conventionally, the engine parts appearing in such an appearance are given a glossy metal color by performing a surface treatment such as plating, and the design of the engine parts is enhanced. Among them, decorative chrome plating has been widely used for engine parts because it can impart a unique silver-white color with luster to the material to be plated (for example, Patent Document 1).

  Decorative chrome plating has an excellent metallic luster and excellent corrosion resistance, and is therefore used in various fields other than engine parts. In order to obtain excellent appearance and corrosion resistance, it is not necessary to form a thick decorative chrome plating. On the contrary, if the decorative chrome plating is formed thick, the color tone and the surface finish are deteriorated. Therefore, generally, the decorative chrome plating is preferably used in a thickness of 0.1 μm to 0.15 μm.

  In addition, as chromium plating, hard chromium plating (industrial chromium plating) is also widely used for industrial products. Since hard chrome plating has a low friction coefficient and excellent wear resistance, it is used for sliding parts of various machine parts. Since wear resistance is required, hard chrome plating is usually formed with a thickness of several μm or more. Further, hard chrome plating does not have a surface with excellent decorative properties like decorative chrome plating. Usually, decorative chrome plating after plating has a surface roughness (Ra) of 1 μm or less, typically 0.2 μm or less, whereas hard chrome plating has a surface roughness of 1 μm or more. ing.

For the formation of the decorative chrome plating, a chromic acid plating solution containing hexavalent chromium (Cr ⁶⁺ ) is usually used. Hexavalent chromium is inexpensive, and the chromium plating layer formed from a plating solution containing hexavalent chromium (hereinafter referred to as a hexavalent chromium plating solution) has good adhesion to the base material, and is resistant to corrosion and resistance. Excellent wear resistance. Furthermore, the chromium plating layer formed from the hexavalent chromium plating solution has a silvery white color with a unique metallic luster. For these reasons, hexavalent chromium plating solutions are widely used for motorcycle engine parts.

  However, hexavalent chromium is known to be highly toxic to living organisms. When plating with hexavalent chromium plating solution, it is required to ensure the safety of workers and prevent environmental pollution. It has become like this.

In order to solve the problem of hexavalent chromium, it is desired to perform decorative chromium plating using trivalent chromium (Cr ³⁺ ), which is less toxic than hexavalent chromium. Plating solutions have been proposed (Patent Documents 2 and 3).
JP 2003-41933 A Japanese Patent Laid-Open No. 52-065138 JP-A-52-092934 JP-A-9-95793 Japanese Patent Laid-Open No. 9-228069

  From the viewpoint of environment and safety, it is preferable to use a plating solution containing trivalent chromium (hereinafter referred to as trivalent chromium plating solution). However, the chromium plating layer formed by using the conventional trivalent chromium plating solution is stable in the growth of the chromium plating layer, plating film characteristics such as corrosion resistance and wear resistance of the formed chromium plating layer, etc. There was a problem that it was inferior to the plating layer formed from the hexavalent chromium plating solution.

  Engine parts are heated to a high temperature by heat generated by combustion of fuel and high-temperature exhaust gas. When a chromium plating layer is formed on an engine part using a conventional trivalent chromium plating solution, there is a problem that cracks are likely to occur in the chromium plating layer by heating. If a crack occurs in the chromium plating layer, rust is generated from that portion, and the appearance is remarkably impaired.

  For this reason, trivalent chromium plating solutions having various compositions have been proposed for more than 20 years, but in particular, trivalent chromium plating solutions are rarely used for engine parts.

  The present invention solves such a conventional problem, is formed using a trivalent chromium plating solution, has the same good film forming characteristics as a plating layer formed from a hexavalent chromium plating solution, and is heat resistant. An object of the present invention is to provide an engine component having a chromium plating layer excellent in the above.

  The engine component of the present invention is an engine component comprising a metal substrate and a chromium plating layer that covers at least a part of the surface of the metal substrate and is formed of a trivalent chromium plating solution. The content of boron contained in the chromium plating layer is 0.05% by mass or more and 0.3% by mass or less, and the thickness of the chromium plating layer is 0.7 μm or less.

  In a preferred embodiment, the content of boron contained in the chromium plating layer is 0.05% by mass or more and 0.1% by mass or less.

  In a preferred embodiment, the content of iron contained in the chromium plating layer is 2% by mass or less.

  In a preferred embodiment, the chromium plating layer covers a region heated to a temperature of 350 ° C. or higher on the surface of the metal substrate.

  In a preferred embodiment, the engine component further includes a base plating layer provided between the metal base surface and the chromium plating layer, and the chromium plating layer is heated to a temperature of 350 ° C. or higher. The region has a thickness of 0.2 μm or more and 0.7 μm or less.

  In a preferred embodiment, the base plating layer includes at least one of C and S.

  In a preferred embodiment, the base plating layer further contains Ni.

  In a preferred embodiment, the base plating layer is made of a metal having a lower hardness than Cr constituting the chromium plating layer.

  In a preferred embodiment, the base plating layer is formed from Ni plating.

  In a preferred embodiment, the color tone of the chrome plating layer has an L * value measured by CIE (Commission Internationale de l'Eclairage) 1976 in a range of 68 to 80.

  In a preferred embodiment, the metal substrate is made of a material mainly composed of Fe, Al, Zn, or Mg.

  In a preferred embodiment, the metal substrate is a metal tube that defines a passage through which exhaust gas from the engine passes.

  The engine of the present invention includes any one of the above engine parts.

  The transportation device of the present invention includes any one of the engine parts or engines described above.

  According to the present invention, the boron content in the chromium plating layer is adjusted to 0.05% by mass or more and 0.3% by mass or less, and the thickness of the chromium plating layer is 0.7 μm or less. Using a chromium plating solution, it is possible to obtain a chromium plating layer having good film forming characteristics comparable to those of a plating layer formed from a hexavalent chromium plating solution and excellent in heat resistance. Therefore, an engine component having a good appearance can be obtained using the trivalent chromium plating solution.

  Further, by setting the boron content in the chromium plating layer to 0.1% by mass or less and the iron content to 2% by mass or less, the same level as the chromium plating layer formed from the hexavalent chromium plating solution A silver-white color tone can be obtained. Furthermore, by setting the thickness of the chromium plating layer in the range of 0.2 μm or more and 0.7 μm or less, an engine component that hardly causes thermal discoloration can be obtained.

  As a result of examining the composition of the trivalent chromium plating solution and the composition in the formed chromium plating layer, the present inventor has found that the problem that cracks occur in the chromium plating layer is related to the boron content contained in the chromium plating layer. I found out. The growth stability of the chromium plating layer and the corrosion resistance and wear resistance of the formed chromium plating layer are also related to the boron content contained in the chromium plating layer and the boron concentration in the trivalent chromium plating solution. I found out.

  Moreover, the chromium plating layer formed from the conventional trivalent chromium plating solution has a blackish color tone compared with the chromium plating layer formed from a hexavalent chromium plating solution. This was found to be related to the iron content of the formed chromium plating layer.

  Furthermore, when a chromium plating layer formed from a trivalent chromium plating solution is formed on an engine component, the color tone of the surface may change due to heating, and the chromium plating layer may exhibit a bluish purple color. Such discoloration impairs the appearance of a motorcycle equipped with engine parts. The inventor of the present application has found that discoloration due to heating of the chromium plating layer depends on the thickness of the chromium plating layer.

1. Structure of Engine Parts (1) Basic Structure Hereinafter, the structure of engine parts according to the present invention will be described with reference to FIG. As shown in FIG. 1, the engine component of the present invention includes a metal substrate 1, a chromium plating layer 3 that covers at least a part of the surface of the metal substrate 1, and a metal substrate 1 and a chromium plating layer 3. And an underlying plating layer 2 provided therebetween. Hereinafter, each of these components will be described in detail.

(I) Metal base material The metal base material 1 is provided with the intensity | strength suitable for a use, corrosion resistance as needed, etc., and can be formed with the material normally used as components for engines. A typical example is an Fe-based material. In addition, the metal substrate 1 may be formed from a non-Fe material such as an Al-based material, a Zn-based material, an Mg-based material, or a Ti-based material.

  The Fe-based material is Fe or steel containing Fe as a main component, such as steel for machine structure (for example, carbon steel for machine structure (STKM), alloy steel for machine structure), stainless steel (for example, ferritic stainless steel). Steel, austenitic stainless steel, austenitic / ferritic stainless steel, etc.) and mild steel (eg, SPCC, SPHC, etc.). Examples of the Al-based material include Al, Al-Si alloys, and Al alloys such as Al-Si-Mg alloys. The Zn-based material includes Zn, a Zn-plated steel sheet coated with Zn, or a Zn alloy coated with a Zn alloy plating containing Zn as a main component and containing an alloy element such as Ni, Co, Cr, or Al. A plated steel sheet is mentioned. Examples of the Mg-based material include Mg—Al based alloys and Mg—Zn based alloys. Examples of the Ti-based material include Ti or a Ti alloy mainly containing Ti and containing elements such as Al, V, and Si.

  These materials have different characteristics depending on the type. For example, Al is characterized by being lightweight and bright, and Ti being lightweight and having excellent strength. For this reason, an appropriate material can be selected according to a use, a required characteristic, etc.

(Ii) Base Plating Layer A base plating layer 2 formed on the metal substrate 1 is used as a base plating for the chromium plating layer 3. From the viewpoint of preventing cracks generated in the chromium plating layer and stably growing a chromium plating layer having excellent corrosion resistance and wear resistance, the base plating layer 2 may not be provided. In chrome plating, a base plating layer is usually formed under the chrome plating layer for the purpose of improving the adhesion to the base material. For this reason, it is preferable that the base plating layer 2 is excellent in adhesiveness with various metal base materials and adhesiveness with a chromium plating layer. Furthermore, it is preferable to have other characteristics such as corrosion resistance.

  The metal which comprises the base plating layer 2 used for this invention can be prescribed | regulated by the relationship with the hardness (Vickers hardness) of chromium used for formation of a chromium plating layer. Specifically, the metal constituting the underlying plating layer 2 is preferably formed of a metal having a hardness lower than that of chromium (about 350 to 1200 Hv). By interposing a layer made of a metal with low hardness between the chromium plating layer and the metal substrate, it is possible to reduce the stress on the chromium plating layer due to heat cycle, so the occurrence of cracks is suppressed, and the surface A chromium plating layer having excellent properties can be obtained. Examples of metals having a lower hardness than chromium include nickel (Ni) (hardness: about 150 to 350 Hv), copper (Cu) (hardness: about 40 to 250 Hv), tin (Sn) (hardness: about 20 to 200 Hv), Lead (Pb) (impossible to measure) and the like can be mentioned.

  As the base plating layer containing these metals, for example, a layer made of nickel plating, copper plating, tin plating, lead plating, zinc-nickel plating or the like is used. These plating layers may be formed independently, and two or more kinds may be combined to constitute a plurality of base plating layers. Further, a plurality of plating layers of the same kind, such as different types of additives, such as additives, may be formed. A typical base plating layer used as a base treatment for the chromium plating layer is nickel plating, which further improves the corrosion resistance, glossiness, and the like.

  The base plating layer 2 contains elements constituting various additives. These additives are added to the plating solution for forming the base plating layer 2 for the purpose of improving the gloss of the chromium plating layer. Specifically, primary brighteners (non-butyne brighteners such as saccharin sodium, naphthalene-1,3,6-trisulfonic acid trisodium, benzenesulfonic acid), secondary brighteners (2-butyl-1,4- Diol, sodium allyl sulfonate, etc.) are used. Each of these additives contains C and / or S as a constituent element. C and / or S contained in the base plating layer is approximately 0.001 to 1.0% by mass in total, although it varies depending on the type of the base plating layer and the type of additive. As will be described in detail below, these elements are concentrated to about 0.1 to 10% by mass by heating, resulting in discoloration of the surface of the chromium plating layer. Furthermore, when the base plating layer 2 is a nickel plating layer, Ni contained in the nickel plating layer is also greatly involved in the discoloration of the surface.

  Hereinafter, nickel plating, which is a representative example of the base plating layer, will be described in detail. Nickel plating is roughly classified into matte nickel plating, semi-bright nickel plating, and bright nickel plating depending on the type of brightener added to the plating solution and the presence or absence of addition. These can be combined appropriately and appropriately according to the required properties and applications, thereby obtaining a desired appearance.

  Of these, bright nickel plating is obtained by adding brighteners such as saccharin and benzenesulfonic acid to the plating solution, and is excellent in surface leveling (smoothing) action and adhesion to the chromium plating layer. It is widely used as a base layer formed directly under the chromium plating layer. The brightener used for bright nickel plating usually contains about 0.001 to 1.0% by mass in total of at least one of C and S in the plating layer, and the corrosion resistance tends to decrease as the S content increases. It is in.

  In contrast, matte nickel plating is different from bright nickel plating in that it does not contain a brightener in the plating solution. Matte nickel plating is inferior in gloss compared to bright nickel plating, but is excellent in plating layer adhesion (adhesion), corrosion resistance, and anti-discoloration action.

  Semi-bright nickel plating is obtained by adding a non-coumarin semi-bright agent to the plating solution. Unlike the above-described brighteners, the semi-brightener has a low content of C and / or S. For this reason, although corrosion resistance is favorable compared with bright nickel plating, it is inferior to glossiness.

  In general, when nickel plating layers having different S contents are formed in layers, a potential difference is generated between the plating layers, and a film having a high S content is preferentially corroded. Utilizing such properties, the nickel plating is often composed of two or more layers to improve the corrosion resistance. For example, in the case of two-layer plating in which a semi-bright nickel plating layer and a bright nickel plating layer are sequentially formed on a base metal, the bright plating layer has a lower potential than the semi-bright plating layer and is preferentially corroded. For this reason, the base metal under the semi-gloss plating layer is protected without being corroded. In the above two-layer plating layer, for the purpose of further improving the corrosion resistance, a tri-nickel plating layer (a kind of bright nickel plating layer) with a large S content is formed between the semi-bright nickel plating layer and the bright nickel plating layer, In some cases, three-layer plating is used. In many cases, S contained in the trinickel plating layer is mainly supplied from an additive other than the brightener. In this case, the uppermost bright nickel plating layer is preferentially corroded, and then the intermediate trinickel plating layer is corroded to protect both the semi-bright nickel plating layer and the base metal. become.

  In order to effectively exhibit the action of such nickel plating, the thickness of the nickel plating layer is preferably about 10 to 30 μm in total. More preferably, it is about 15 μm or more and 25 μm or less.

  In addition, when forming foundation | substrate plating layers other than a nickel plating layer, it is preferable to control to the thickness of about 10-30 micrometers.

(Iii) Chromium plating layer On the base plating layer 2, a chromium plating layer 3 is formed. The chromium plating layer 3 is a decorative chromium plating layer formed by electroplating using a trivalent chromium plating solution, as will be described in detail below.

  Whether the chromium plating layer is formed using a trivalent chromium plating solution or a hexavalent chromium plating solution can be determined by measuring the crystal state of the chromium plating layer. Specifically, it can be easily determined by X-ray diffraction of the chromium plating layer. FIGS. 2A and 2B show the results of analysis of the chromium plating layer by the X-ray diffraction method, respectively. Details of the measurement method are as follows.

Analytical instrument: X-ray diffractometer RAD-3C manufactured by Rigaku Corporation Measurement conditions: Use Cu counter cathode, energize at 40 kV / 40 mA

  The X-ray diffraction result of the chromium plating layer formed using the hexavalent chromium plating solution is as shown in FIG. A very large diffraction peak of about 1200 cps is observed near the diffraction angle of about 40θ to 50θ, and a large diffraction peak of about 200 cps is observed near the diffraction angles of about 65θ and about 83θ, respectively. These peaks are derived from (111) -oriented crystals, (200) -oriented crystals, and (211) -oriented crystals in order of increasing diffraction angle.

On the other hand, the X-ray diffraction result of the chromium plating layer formed using the trivalent chromium plating solution is as shown in FIG. Only a small diffraction peak of about 100 cps derived from a crystal with a (111) orientation is observed in the vicinity of a diffraction angle of about 40-50θ. The value obtained by dividing the half width of the peak derived from the (111) oriented crystal by the peak intensity (half width / peak height) is about 0.6 rad / cps, which is observed when hexavalent chromium is used ( Compared to the value of (111) oriented crystals (about 7.9 × 10 ⁻⁴ rad / cps).

  From these figures, the chromium plating layer formed using the trivalent chromium plating solution has a substantially amorphous structure, whereas the chromium plating layer using hexavalent chromium has many It can be seen that it has a crystal structure consisting of crystals. Whether the plating layer has a crystal structure or an amorphous structure is, for example, whether a diffraction peak having a (half-value width / peak height) of about 0.001 rad / cps or less is observed near the diffraction angle of about 40-50θ. It can be determined depending on why.

  The amount of boron contained in the chromium plating layer 3 is 0.05% by mass or more and 0.3% by mass or less. When the boron content is more than 0.3% by mass, the chromium plating layer 3 is cracked by heating at 400 ° C. or higher. On the other hand, when the boron content is less than 0.05%, the corrosion resistance and wear resistance of the chromium plating layer 3 are lowered. Further, the stability of the plating growth when forming the chromium plating layer 3 is lowered. Preferably, the boron content is 0.05 mass% or more and 0.2 mass% or less, and more preferably 0.05 mass% or more and 0.1 mass% or less. The smaller the boron content, the more reliably the cracks can be prevented, and the corrosion resistance and wear resistance are excellent.

  Here, “stability of plating growth” means that the throwing power (adhesiveness) of the chromium plating layer by plating treatment is constant over time. Specifically, when a hull cell test is performed, there is no appearance defect such as insufficient plating thickness, scorching, or striation over a wide current density region, or a portion that is difficult to be plated (for example, an electrode) It means that a plating layer having a predetermined thickness is also formed on the surface to be plated disposed on the opposite side of the surface.

  Further, the “corrosion resistance of plating” means corrosion resistance imparted by the plating process. Specifically, when a casting test of the plating corrosion resistance test method specified in JIS H8502 is performed using a sample after the plating treatment, if the rating number satisfies 7.0 or more, it is said that “the plating corrosion resistance is excellent”. .

  “Abrasion resistance of plating” means the wear resistance (hardness) imparted by the plating process. Specifically, when the Vickers hardness specified in JIS Z 2244 is measured using a sample after plating, when the Vickers hardness is in a range of 350 Hv 0.1 (test force 0.9807 N) or more, “plating wear resistance” It is excellent in performance. "

  Thus, when the chromium plating layer 3 contains boron, a chromium plating layer excellent in corrosion resistance and wear resistance is obtained. Moreover, the chromium plating layer can be stably grown. However, boron has a hardening effect on the plating layer, and when the content exceeds the above range, the hardness of the chromium plating layer is increased by heating to a high temperature (particularly 400 ° C. or more), As a result of increased stress on the chromium plating layer due to heat cycle, cracks and the like are likely to occur on the surface. When a crack is generated, rust is likely to be generated starting from the crack. If a large number of cracks are generated, the film may be peeled off and the appearance may be impaired. Moreover, a color tone will fall when content exceeds the above-mentioned range.

  Since boron hardens the chromium plating layer as described above, cracks are likely to occur when the chromium plating layer containing boron is formed thick. For this reason, it is preferable that the thickness of the chromium plating layer 3 is 0.7 μm or less. If the chromium plating layer 3 is thicker than 0.7 μm, it becomes difficult to form a chromium plating layer without cracks even if the boron content is in the above-mentioned range. In order to prevent the occurrence of cracks more reliably, the thickness of the chromium plating layer 3 is preferably 0.5 μm or less.

  From the viewpoint of preventing cracking due to heating, the boron content of the chromium plating layer only needs to be 0.3% by mass or less only in the region where the temperature of the engine component is high. However, it is difficult to change the boron content of a part of the chromium plating layer that continuously covers the surface of the engine component by plating. For this reason, it is preferable that the boron content in a chromium plating layer exists in the above-mentioned range in any area | region of a chromium plating layer.

  However, just because the boron content is within the above-mentioned range in any region of the chromium plating layer, the engine component of the present invention does not need to be used in an environment where the whole is heated to a high temperature. The present invention is preferably used for an engine component in which a part is exposed to a high temperature.

  As long as the chromium plating layer 3 has the boron content described above, a chromium plating layer having good film forming characteristics comparable to those of a plating layer formed from a hexavalent chromium plating solution and excellent in heat resistance can be obtained from trivalent chromium. It can be formed using a plating solution. However, the chromium plating layer formed from the trivalent chromium plating solution has a darker color tone than the chromium plating layer formed from the hexavalent chromium plating solution. The cause of this color tone being blackish is related to the concentration of iron and boron contained in the chromium plating layer, and the color tone becomes darker as the iron content increases. Details are unknown, but the iron in the chromium plating layer contains black iron, such as when iron is combined with various elements in the plating solution when growing the chromium plating layer from the trivalent chromium plating solution This is considered to generate precipitates.

  For this reason, in order to obtain a silver-white color tone similar to that of the chromium plating layer formed from the hexavalent chromium plating solution, the content of boron in the chromium plating layer 3 is 0.1% by mass or less. The content is preferably 2% by mass or less. The lower the iron content, the better, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less.

  However, in the case where the engine component of the present invention is not used in such a manner as to be compared with the chromium plating layer formed from the hexavalent chromium plating solution, the boron content should be 0.3% by mass or less, By setting the content to 7% by mass or less, although the color tone is somewhat dull, a chrome plating layer having a color tone comparable to that of chrome plating can be obtained.

  The boron and iron contents of the chromium plating layer are all represented by the maximum values when the contents of each element contained in the depth direction of the chromium plating layer are analyzed by the GDS analysis method.

  When the content of boron in the chromium plating layer 3 is 0.1% by mass or less and the content of iron is 2% by mass or less, the color tone of the chromium plating layer is CIE (Commission Internationale de l'Eclairage) 1976. The measured L * value satisfies the range of 68-80. The L value is measured using a spectroscopic color difference meter (for example, TC-1800MK-II manufactured by Tokyo Denshoku Color Analyzer). This value is about the same as that of a chromium plating layer formed from a hexavalent chromium plating solution. For this reason, even if the chromium plating layer 3 in which the iron content is limited to the above-described range and the chromium plating layer formed from the hexavalent chromium plating solution are arranged side by side, the difference in color tone is hardly noticeable.

  By having such a structure for engine parts, using trivalent chromium plating solution, it has good film forming characteristics comparable to the plating layer formed from hexavalent chromium plating solution, and has excellent heat resistance. A chromium plating layer can be obtained. Further, by setting the boron content in the chromium plating layer to 0.1% by mass or less and the iron content to 2% by mass or less, the same level as the chromium plating layer formed from the hexavalent chromium plating solution A silver-white color tone can be obtained.

(Iv) Mechanism for preventing discoloration The engine component of the present invention can be suitably used for engine parts such as a cylinder, a cylinder head, and a head cover, and an exhaust pipe for leading exhaust gas from the engine. However, when the engine component of the present invention is used in a place exposed to heat of 350 ° C. or higher, the color tone of the surface may change due to heating, and the chromium plating layer may exhibit a bluish purple color. When the engine component of the present invention is used in such a place, it is preferable that the chromium plating layer has a thickness of 0.2 μm or more. Hereinafter, the reason why the chromium plating layer can be prevented from being discolored by heating by controlling the thickness of the chromium plating layer will be described with reference to FIGS.

  FIG. 3 may be referred to as a “CS enriched layer” or “CS—Ni enriched layer” (hereinafter simply referred to as “enriched layer”), which is thought to cause discoloration of the surface of the chromium plating layer. .) Is a diagram for explaining a mechanism in which C and / or S gathers in the vicinity of the interface between the chromium plating layer and the base plating layer by heating. FIG. 3 shows a typical configuration of the present invention in which a nickel plating layer is formed between an Fe substrate and a chromium plating layer. The nickel plating layer is semi-gloss in order from the Fe substrate side. It consists of three layers: a nickel plating layer, a trinickel plating layer, and a bright nickel plating layer.

  In addition, various elements which comprise the additive contained in a chromium plating layer or a nickel plating layer gather by heating in the vicinity of the interface of a chromium plating layer and a nickel plating layer. FIG. 3 shows elements that are considered to be involved in the discoloration of the chromium plating layer, that is, the elements (at least one of C, S, and Ni) constituting the above-described concentrated layer, and bonds to these elements. Only elements that are easily processed (Fe, Cr, etc.) are shown, and other elements (for example, O that gathers in the vicinity of the interface by heating) are omitted.

  As shown in FIG. 3, C or S mainly moves from the nickel plating layer side to the chromium plating layer side and gathers in the vicinity of the interface. As described above, C or S is an element mainly constituting a non-butyne-based brightener (such as benzenesulfonic acid) added to the nickel plating solution, and particularly in the bright nickel plating layer and the trinickel plating layer. Contains a large amount of S. Therefore, a “CS enriched layer” in which a large amount of C or S gathers is formed in the vicinity of the interface. Here, the “C—S concentrated layer” means a layer in which at least one of C and S is gathered. In addition, although C or S may diffusely move from the chromium plating layer side, since the ratio is very small compared with the case where it diffuses and moves from the nickel plating layer side, it is not illustrated.

  When the base plating layer is a nickel plating layer, a “CS—Ni concentrated layer” containing Ni is formed. Ni, like C or S, is also considered to be involved in discoloration. Here, the “concentrated layer of C—S—Ni” means a layer in which at least one of C, S, or Ni is gathered.

  The reason why discoloration of the surface of the chromium plating layer is caused by the formation of such a concentrated layer is unknown in detail. For example, Cr constituting the chromium plated layer is an element constituting the above concentrated layer. It is considered that discoloration is caused because it is combined with (C or S or Ni) and the refractive index of the chromium plating layer is changed. Iron is also considered a causative substance that causes discoloration. When the metal substrate is made of an Fe-based material, heating may cause Fe to diffuse from the Fe-based material and concentrate in the vicinity of the interface (not shown).

  Such discoloration of the surface of the chromium plating layer based on the concentrated layer can be prevented by setting the thickness of the chromium plating layer to 0.2 μm or more. Hereinafter, the reason will be described with reference to FIGS. 4 (a) and 4 (b).

  FIG. 4B is a diagram schematically illustrating a part of a conventional Cr-nickel plating layer. As shown in FIG. 4B, since the thickness of the conventional chromium plating layer is as small as about 0.1 μm or less, incident light is transmitted to the vicinity of the interface between the chromium plating layer and the nickel plating layer. . As a result, a part of incident light is absorbed by the concentrated layer generated in the vicinity of the interface, and the degree of discoloration due to heating becomes more prominent.

  On the other hand, when the thickness of the chromium plating layer is 0.2 μm or more, as shown in FIG. 4A, most of the incident light is reflected near the surface of the chromium plating layer. It does not penetrate to the vicinity of the interface between the nickel plating layer. Therefore, only the interference color due to the oxide film formed on the outermost surface of the normal chromium plating layer is provided, and the influence of the concentrated layer can be suppressed.

  In order to effectively exhibit such an action, the thickness of the chromium plating layer is set to 0.2 μm or more. From the viewpoint of preventing thermal discoloration due to heating, the chrome plating layer should be thick. Preferably, the thickness of the chromium plating layer is 0.3 μm or more, more preferably 0.4 μm or more.

  From the above, in order to prevent generation of cracks and discoloration due to heating, the thickness of the chromium plating layer is preferably 0.2 μm or more and 0.7 μm or less, and is 0.3 μm or more and 0.5 μm. The following is more preferable. If the thickness of the chromium plating layer is 0.4 μm or more and 0.5 μm or less, the generation of cracks can be prevented almost certainly and discoloration due to heating can also be reliably prevented.

  The thickness of the chromium plating layer 3 is measured by observation with an optical microscope (magnification: 400 times). Specifically, the thickness direction cross section of the plating layer is mirror-polished and etched. Thereby, a chromium plating layer and a base plating layer are separated clearly. Since the surface roughness Ra of the chromium plating layer is at most about 0.01 μm, it is considered that the influence of the surface roughness Ra on the thickness of the chromium plating layer is almost negligible. In addition, since the thickness of the chromium plating layer varies slightly depending on the measurement site, a total of three locations are measured in any observation region by changing the measurement location, and the average value is defined as “thickness of the chromium plating layer”. .

  As another discoloration prevention means by forming a thickened layer, for example, a method of reducing the content of C or S is conceivable, but this method is not practical. For example, in order to reduce the content of C or S, the amount of brightener contained in the underlying plating layer has to be reduced, but as a result, the gloss is lowered and the design of engine parts is reduced. Will be significantly impaired. When it is listed as one of the important issues that an excellent design is provided as in the present invention, the design must be prevented from being damaged as the brightener is reduced.

  In order to prevent discoloration due to heating, it is sufficient that the portion of the chromium plating layer 3 heated to a temperature of 350 ° C. or higher satisfies the thickness in the above range, and the chromium plating formed on the metal substrate 1 is sufficient. It is not necessary for all parts of the layer 3 to satisfy the thickness in the above range. Further, in the region where the temperature is only 350 ° C. or less, the thickness of the chromium plating layer 3 may be 0.2 μm or less. In general, the chrome plating layer is colored from white to yellow and golden by heating, and further changes from golden to purple at a high temperature of about 350 to 500 ° C. Such a change in color tone does not appear uniformly over the entire portion where the chromium plating layer is formed, but occurs remarkably in a portion that is easily exposed to high-temperature exhaust gas. Therefore, in order to prevent discoloration from golden to purple, the thickness of the chromium plating layer that is exposed to a temperature that is most likely to undergo discoloration by heating, that is, a temperature of 350 ° C. or higher, is controlled within the above range. good.

  Examples of the “part heated to a temperature of 350 ° C. or higher” include, for example, a part of engine parts constituting the engine such as a cylinder, a cylinder head, and a head cover, and a flow path for guiding exhaust gas discharged from the engine. A part of the exhaust pipe or a cover of the exhaust pipe may be mentioned. The exhaust pipe referred to here may be an exhaust pipe that directly guides the exhaust gas, or may be an exhaust pipe (double pipe) that is indirectly heated by the exhaust gas. The exhaust pipe includes a manifold unit that guides exhaust gas from each cylinder, a catalyst device storage unit that covers the catalyst device, a silencer (muffler), and the like.

(2) Specific structure and application to a motorcycle A specific structure of an engine component according to the present invention will be described with reference to FIG. FIG. 5 shows a motorcycle 100 using an exhaust pipe which is an engine component of the present invention. As shown in FIG. 5, the motorcycle 100 includes an engine 30 composed of a four-cycle internal combustion engine, and an exhaust pipe 4 that guides the exhaust gas in order to exhaust the exhaust gas generated by the engine 30 from the rear of the vehicle body. ing. The exhaust pipe 4 is connected to the engine 30 and includes an exhaust pipe assembly portion 4a that constitutes an exhaust path that is largely bent so as to guide exhaust gas exhausted from the front of the engine 30 to the rear, and a silencer 4b. . The exhaust pipe collecting portion 4a may be integrally constituted by one part, or may be constituted by joining a plurality of parts. In the present embodiment, the exhaust pipe 4 is exposed as a whole so as to appear on the exterior of the motorcycle 100, and constitutes a part of the design of the entire motorcycle 100. As will be described in detail below, when the entire exhaust pipe 4 is exposed, the chromium plating layer of the exhaust pipe 4 is not cracked and rusted or discolored due to heat for a long time. The effect of the present invention for maintaining the appearance appears remarkably in the appearance. However, as long as at least a part of the exhaust pipe 4 appears on the exterior, a part of the exhaust pipe 4 may be covered with a cowl or a protector depending on the design of the motorcycle. Further, the shape of the motorcycle using the exhaust pipe is not limited to that shown in FIG. 5. For example, the exhaust pipe of the present invention may be adopted for a motorcycle having a structure as shown in FIG.

  Next, referring to FIGS. 6 (a), (b) and (c), it is preferable to set the thickness of the chromium plating layer to 0.2 μm or more. The “region” will be specifically described. These drawings are sectional views showing a part of the exhaust pipe 4.

  FIG. 6A shows an exhaust pipe assembly portion 4a of the exhaust pipe 4 that is directly connected to the engine. As shown in FIG. 6A, an exhaust pipe assembly 4a connected to an engine (not shown) includes a metal pipe 5 that defines a passage 6 through which exhaust gas passes, and an outer surface of the metal pipe 5. Covering plating layer 10. The metal tube 5 has a bent portion 9. The bent portion 9 is a portion where the passage 6 is bent or the direction in which the passage 6 extends is changed.

  As described above, the plating layer 10 is composed of a base plating layer and a chromium plating layer. The metal tube 5 only needs to define the passage 6, and may have a double tube structure including an inner tube defining the passage 6 and an outer tube held so as to surround the outside of the inner tube. Good.

  Exhaust gas entering from the exhaust pipe assembly 4a directly connected to the engine (not shown) moves through the passage 6 at a high speed, and therefore collides with the metal pipe 5 at the bent portion 9, and is formed by bending. It collides violently with the inner surface 9b of the metal tube 5 located on the convex surface portion 9a. For this reason, the outer portion 9a is heated to a temperature of about 350 ° C. or higher (for example, about 400 to 500 ° C.) by the high temperature exhaust gas.

  Further, when the metal pipe 5 has a double pipe structure, a single pipe structure is often adopted in the connecting portion 21 that connects the other exhaust pipe member 23. When the double pipe structure is employed for the connecting portion 21, the metal pipe 5 may be deformed or damaged due to a difference in thermal expansion between the outer pipe and the inner pipe during welding with the other exhaust pipe member 23. Because. When the metal pipe 5 adopts such a structure, the inner surface of the connecting portion 21 is in direct contact with the high-temperature exhaust gas, so that the connecting portion 21 has a temperature of about 350 ° C. or higher (for example, about 400 to 500 ° C.).

  FIG. 6B schematically shows a cross-section of the catalyst storage portion 22 that stores the catalyst device 8 of the exhaust pipe 4. The catalyst device 8 is provided in the catalyst storage unit 22 and decomposes at least one component contained in the exhaust gas when the exhaust gas passes therethrough. Since the catalyst device 8 generates heat during decomposition, the catalyst storage unit 22 is heated to a temperature of about 350 ° C. or higher (for example, about 400 to 500 ° C.).

  Further, when the engine 30 (FIG. 5) includes a plurality of cylinders, the exhaust pipe 4 may include a manifold portion for guiding exhaust gas generated in each cylinder together to the rear of the motorcycle 100. is there. FIG. 6C shows the exhaust pipe 4 in which the branch pipes 4d and 4e connected to the cylinder are gathered by the manifold portion 15 and discharged by the integrated exhaust pipe member 4f. In the manifold portion 15 of the exhaust pipe collecting portion 4a, the exhaust gas is collected from the plurality of branch pipes 4d and 4e, thereby increasing the flow rate of the exhaust gas and bending the flow path. 15 collides with the inner surface. For this reason, the manifold portion 15 is heated to a temperature of about 350 ° C. or higher (for example, about 400 to 500 ° C.) by the exhaust gas.

  The motorcycle of the present embodiment has a chromium plating layer of 0.2 μm or more so as to cover the outside of the portions heated to high temperatures of these exhaust pipes exemplified with reference to FIGS. 6 (a), (b) and (c). Is formed. For this reason, even if it exposes to high temperature exhaust gas, discoloration of the chromium plating layer by heating can be prevented.

  In addition, the chromium plating layer formed using trivalent chromium has the same excellent color tone as when hexavalent chromium is used because the Fe content in the chromium plating layer is reduced. Can do.

  The present invention also includes a transportation device including the above-described engine component. Examples of the transportation equipment include vehicles such as motorcycles equipped with engines and all-weather four-wheeled vehicles, ships equipped with engines, transportation equipment such as airplanes, and the like.

2. Next, a method for manufacturing the engine component of the present invention will be described. The engine component according to the present invention is manufactured by sequentially forming a base plating layer and a chromium plating layer on a metal substrate having a predetermined shape. Hereinafter, the manufacturing method will be described in detail.

  First, in order to degrease and clean the surface of the metal substrate, the metal substrate is immersed in a tank such as a water washing tank, an ultrasonic alkaline degreasing tank, an electric field degreasing tank, or an acid treatment activation tank for a predetermined time. Thereby, since the surface of a metal base material is fully degreased, it becomes easy to form a base plating layer and a chromium plating layer on the metal surface.

  Next, using the metal substrate washed as described above, an underplating layer and a chromium plating layer are sequentially formed on at least the outer surface of the metal substrate by electroplating. Since both the base plating layer and the chromium plating layer are formed by electroplating and the principle is the same, in the following description, the plating apparatus shown in FIG. 7 is used for the process of forming the chromium plating layer. The process of forming the base plating layer will be described without referring to the drawings.

  The base plating layer is formed by immersing the metal base in a plating tank containing a metal solution for which a plating layer is to be formed, and energizing until a desired thickness is obtained. For example, when forming a nickel plating layer consisting of three layers of a semi-bright nickel plating layer, a tri-nickel plating layer, and a bright nickel plating layer as the base plating layer, the metal substrate washed as described above, It is immersed in a semi-bright nickel plating solution, a trinickel plating solution, and a bright nickel plating solution, respectively, and energized until a desired plating layer is formed. The specific plating conditions differ depending on the metal substrate used, the composition of the plating solution, the application, etc., and the conditions usually used for Ni-chrome plating may be selected as appropriate. For example, when a 5-15 μm semi-bright nickel plating layer, a 1-2 μm trinickel plating layer, and a 5-15 μm bright nickel plating layer are sequentially formed on an Fe substrate, the temperature of the plating solution is about 40. It is preferable that the plating solution has a pH of about 2 to 5 at about 65 ° C. The plating time is preferably about 10 to 20 minutes for semi-bright nickel plating and bright nickel plating, and about 1 to 5 minutes for trinickel plating. A strike nickel layer may be further provided between the base plating layer and the metal substrate.

  Next, a chromium plating layer is formed on the metal substrate on which the base plating layer is formed. As shown in FIG. 7, the chrome plating apparatus 20 removes impurities floating in the plating solution, a chrome plating bath 11 for performing chrome plating, a pump 12 that pumps up the plating solution added to the chrome plating vessel 11, and the like. For this purpose, a filter 13, an adjustment valve 14 for adjusting the flow rate of the plating solution, and a flow meter 15 for monitoring the flow rate of the plating solution are included. An ion exchange device 16 for removing metal ions such as Fe contained in the plating solution is installed on the downstream side of the chromium plating device 20. The chromium plating apparatus 20 and the ion exchange apparatus 16 are connected by a metal tube (not shown).

  The chromium plating tank 11 is filled with a trivalent chromium plating solution. The plating solution contains 30 to 40 g / l of basic chromium sulfate as a trivalent chromium ion source in terms of chromium content.

  In order for the amount of boron and iron contained in the chromium plating layer to be in the above-described range, the concentration of boron and iron in the plating solution to be used needs to be within a predetermined range. Specifically, the trivalent chromium plating solution has a boric acid content in the range of 1 to 5 g / l in terms of boron content, and an Fe content of 0.5 mg / l or less.

  The content of boric acid is reduced to about 1/15 to 5/6 as compared with the amount of boron (about 6 to 15 g / l) added to a typical conventional trivalent chromium plating solution. In recent years, the amount of boron discharged into the environment has been regulated, and the use of a plating solution having a low boron concentration is also suitable for compliance with such environmental regulations.

  In addition, a conventional typical trivalent chromium plating solution contains about 0.0001 to 0.0003 mass% of ferrous sulfate as an additive in order to improve the covering of the plating layer. For this reason, when using the conventional trivalent chromium plating solution, about 2-20 mass% Fe is contained in a chromium plating layer. However, the trivalent chromium plating solution used in the present invention preferably does not contain such an additive, and the Fe content is limited to 0.5 mg / l or less.

  Boric acid is used to adjust the pH and ensure that the chromium plating layer has a silver-white color tone. For this reason, in order to reduce the amount of boric acid and maintain an appropriate pH, the trivalent chromium plating solution used in the present invention is 5 to 30 g / l by converting citric acid or a citric acid compound into the amount of citric acid. Included in the range. As the citrate compound, a citrate such as potassium citrate or a metal citrate compound such as nickel citrate can be used. In order to obtain a chromium plating layer with excellent color tone, it is more preferable to use citric acid. The amount of citric acid added is preferably 10 g / l or more and 25 g / l or less, more preferably 20 g / l or more and 25 g / l or less.

  Chrome plating is performed by electroplating. The chromium base 11 is filled with the above-described trivalent chromium plating solution, and the metal substrate 17 to which chromium plating is applied is used as a cathode. Since chromium plating is performed by supplying chromium ions from a plating solution, an insoluble anode 18 that does not dissolve in the chromium plating solution is used for the anode.

  Next, a DC power source 19 is connected between the two poles and energized. Chromium ions contained in the chromium plating solution move toward the metal substrate 17 on the cathode side, and are reduced to metal Cr and deposited.

  When it is desired to form a chromium plating layer of 0.2 μm or more in a region heated to a temperature of 350 ° C. or higher, a metal substrate is arranged and plated so that a chromium plating layer having a desired thickness is formed. Is preferred. In particular, when plating a metal substrate such as an exhaust pipe having a curved shape, it is preferable to dispose the metal substrate so that the distance between the electrode and the material to be plated (metal substrate) is as short as possible.

  For example, as shown to Fig.8 (a), when arrange | positioned so that the distance of the convex part 9a of the bending part of the metal base material 17 and the electrode 18 may become the shortest, the convex shape heated to high temperature The Cr layer can be efficiently formed on the portion 9a.

  On the other hand, as shown in FIG. 8 (b), when the distance between the convex portion 9a of the metal substrate 17 and the electrode 18 is increased, a concave shape opposite to the convex portion 9a. Since the chromium plating layer is easily formed on the portion and the chromium plating layer is hardly formed on the convex portion 9a, the plating efficiency is deteriorated.

  In addition, for example, the thickness of the chromium plating layer can be controlled within a predetermined range by controlling the amount of electricity passing through the electrode surface (current × time), the current density, and the like. In particular, the current density is controlled by devising the arrangement of electrodes and attaching auxiliary electrodes so that a predetermined chromium plating layer is easily formed in a region heated to a temperature of 350 ° C. or higher. be able to. The specific control method should just select appropriate conditions suitably according to the kind and shape of the metal base material to be used, the structure of a plating solution, the thickness of a chromium plating layer, etc. In particular, when ferrous sulfate is not included in the plating solution, since the plating layer generally has poor contact, it is necessary to consider that the current density is uniform by devising the arrangement of the electrodes.

  The boron content of the chromium plating layer to be formed depends not only on the boron concentration in the plating solution, but also on the temperature of the plating solution, the plating time, the stirring speed of the plating solution, etc., and in particular on the temperature of the plating solution. Generally, when the temperature of the plating solution increases, the boron content in the chromium plating layer increases. For this reason, in order to suppress the amount of boron in the chromium plating layer to the above-described range, it is preferable to control the temperature of the plating solution in the range of 25 ° C to 30 ° C.

  In order to bring the iron content in the chromium plating layer into the above range, it is necessary to pay attention to the iron that dissolves into the plating solution from the metal substrate. Even if the metal substrate does not contain iron as a main component, Fe may inevitably gather on the chromium plating layer side. As a result, even if ferrous sulfate is not added to the plating solution, the concentration of iron in the plating solution increases, and iron may be contained in the chromium plating layer.

  In order to eliminate such a possibility, it is necessary to regularly monitor the iron concentration in the plating solution during plating, and to remove iron when the iron concentration exceeds a predetermined value. Iron ions mixed in the plating solution are removed using an ion exchange device 16 provided with a cation exchange resin. The cation exchange resin used in the present invention is not particularly limited as long as it can be easily exchanged with a divalent metal cation such as Fe.

  A specific removal method is as follows. First, during plating, the plating solution is periodically pumped from the plating tank 11 by the pump 12, and the suspended matter is removed using the filter 13. Next, the plating solution from which the suspended matter has been removed is introduced into the ion exchange device 16 while adjusting the flow rate by the adjustment valve 14, and metal cations such as Fe ions are removed by the cation exchange resin. The flow rate of the plating solution is monitored by the flow meter 15. The plating solution processed by the ion exchange device 16 is periodically collected to check the Fe concentration. In order to reduce the Fe concentration of the chromium plating layer to 2% by mass or less as in the present invention, it is necessary to control the Fe concentration in the plating solution to about 0.0001% by mass or less. Until the ion exchanger 16 is removed.

  The plating solution from which the Fe ions have been removed in this way (regenerated plating solution) is circulated from the outlet of the ion exchange device 16 through the conduit 24 to the plating tank 11. For example, the regenerated plating solution may be stored in a suitable storage container (not shown).

  In addition, the method of removing the metal cation in a plating solution using the ion exchange apparatus 16 is demonstrated in detail by patent document 4 etc., for example, and can be applied to the method of this invention. Various modifications have been proposed (for example, Patent Document 5), and these modifications can also be applied to the method of the present invention.

  The chromium plating layer after plating has a surface roughness (Ra) of about 1 μm or less, and preferably has a surface roughness of 0.2 μm or less. For this reason, after plating, the chromium plating layer has a sufficient luster without particularly finishing the surface.

3. Experimental example (Experimental example 1)
In this experimental example, the following experiment was conducted for the purpose of clarifying that the stability of plating growth is ensured by setting the lower limit of the boron content of the chromium plating layer to 0.05 mass%.

  First, a metal tube made of STKM material was prepared, and a Ni plating layer composed of a semi-gloss Ni plating layer, a tri-Ni plating layer, and a bright Ni plating layer was formed by the following method. Table 1 shows the composition of the plating solution used to form these plating layers. Note that C and / or S contained in the tri-Ni plating solution is supplied from an additive other than the brightener.

Semi-bright Ni plating layer (thickness of about 5 to 15 μm)
Plating condition: energized at 10-12V (volt), 1800-2800A (ampere).
Tri Ni plating layer (thickness about 1-5μm)
Plating conditions: 3 to 3.5V, 20 to 40A energized.
Glossy Ni plating layer (thickness about 5-15μm)
Plating conditions: 10-12V, 1800-2800A energized.

  Next, using the chromium plating apparatus provided with the ion exchange apparatus shown in FIG. 6, the chromium plating layer was formed on the base plating layer (the thickness of the chromium plating layer is 0.3 μm). As the chromium plating solution, four types of trivalent chromium plating solutions (Nos. 1 to 4) shown in Table 2 were used. The constituent components of the trivalent chromium plating solutions of Sample 1 to Sample 4 are the same except that the contents of ferrous sulfate and boric acid are different. Specifically, each of these trivalent chromium plating solutions contains citric acid, and the addition amounts of ferrous sulfate are 0 (sample 1) and 2.5 mg / l (sample 2), respectively. 5 mg / l (sample 3) and 10 mg / l (sample 4). In terms of the amount of Fe, they are 0 (sample 1), 0.05 mg / l (sample 2), 0.1 mg / l (sample 3), and 0.3 mg / l (sample 4), respectively. The addition amount of boric acid is 5 g / l (sample 1), 5 g / l (sample 2), 30 g / l (sample 2), and 60 g / l (sample 3).

In order to adjust the boron content contained in the plating layer to various ranges, the temperature of the plating solution is changed in the range of about 25 to 60 ° C., the current density is changed in the range of about 10 to 30 A / dm ² , and the plating solution The degree of air agitation was adjusted.

  When the trivalent chromium plating solution of Sample 1 of the present invention was used, Fe ions mixed during plating were removed using an ion exchange apparatus equipped with a cation exchange resin. Specifically, the plating solution was periodically sent to an ion exchange device, and the Fe concentration contained in the plating solution was controlled to be in the range of 0 to 0.0001% by mass. As a result, when the trivalent chromium plating solution of the present invention example of Sample 1 was used, the Fe content contained in the chromium plating layer was 0.2 mass% at the maximum when measured in the thickness direction of the plating layer. became. On the other hand, when the trivalent chromium plating solutions of Sample 2 to Sample 4 were used, Fe ions were not removed by the ion exchange device, so the Fe content (maximum value) contained in the chromium plating layer was They were 2.0 mass%, 7.0 mass%, and 15.0 mass%.

  For each sample, the stability of plating growth was measured according to the above-described method, and the following criteria were evaluated based on the thickness of the chromium plating layer at each measurement site.

<Stability of plating growth>
Evaluation criteria (◎ to Δ are examples of the present invention)
A: The thickness of the chromium plating layer is in the range of 0.25 mm or more and less than 0.5 mm.
A: The thickness of the chromium plating layer is in the range of 0.20 mm or more and less than 0.25.
Δ: The thickness of the chromium plating layer is in the range of 0.05 mm or more and less than 0.20 mm.
X: The thickness of the chromium plating layer is less than 0.05 mm.

  The obtained results are shown in Table 3.

  From Table 3, even when any trivalent chromium plating solution of Sample 1 to Sample 4 is used, if the chromium plating layer does not contain any boron (the content is zero), the growth of plating is Although it becomes extremely unstable, it can be seen that the plating grows stably by setting the plating conditions so that the chromium plating layer contains at least 0.05 mass% or more of boron. As far as the purpose of stably growing the plating is concerned, the higher the boron content in the chromium plating layer, the better.

  Thus, it is clear that boron is an indispensable component to ensure the stability of plating growth, and simply adding citric acid instead of boric acid does not provide excellent plating characteristics. became. Although the plating grew stably with the addition of boron, this effect was similarly seen regardless of the Fe content in the plating layer.

  Next, for the purpose of investigating the above-described effects of boron in more detail, after forming a chromium plating layer in the same manner as described above using the trivalent chromium plating solution of Sample 1, the plating corrosion resistance and plating wear resistance are Measurements were made according to the methods described above, and each was evaluated according to the following criteria.

<Plating corrosion resistance>
Evaluation criteria (◎ to Δ are examples of the present invention)
A: Rating number is 9.0 or more.
A: Rating number is 8.0 or more and less than 9.0.
Δ: Rating number is 7.0 or more and less than 8.0.
X: The rating number is less than 7.0.

<Plating wear resistance>
Evaluation criteria (◎ to Δ are examples of the present invention)
A: Vickers hardness is 500 Hv or more.
○: Vickers hardness is 450 Hv or more and less than 500 Hv.
Δ: Vickers hardness is 350 Hv or more and less than 450 Hv.
X: Vickers hardness is less than 350 Hv.

  Table 4 shows the obtained results. Table 4 also shows the results of plating growth stability.

  From Table 4, when the chromium plating layer does not contain boron at all (the content is zero), the plating corrosion resistance and the plating wear resistance are remarkably lowered, but at least 0.05 mass% of boron is contained in the chromium plating layer. It can be seen that these characteristics are improved by setting the plating conditions to include the above. This result is the same as the result of the plating growth stability described above. Therefore, it can be seen that boron is an indispensable component not only for improving the stability of plating growth but also for improving plating corrosion resistance and plating wear resistance.

  However, as shown in Table 4, when the boron content in the chromium plating layer exceeds 0.1 mass%, the plating corrosion resistance and the plating wear resistance gradually decrease. This result is different from the above-described stability of plating growth.

  From the above results, in order to improve the plating film forming characteristics comprehensively evaluated from the three characteristics of plating growth stability, plating corrosion resistance, and plating wear resistance, the boron content in the chromium plating layer is set to 0. It is preferable to control within the range of 0.05 to 0.3% by mass.

(Experimental example 2)
In this experimental example, the following experiment was conducted for the purpose of clarifying that the color tone of the chromium plating layer immediately after plating is improved by controlling the boron content and the Fe content in the chromium plating layer.

  Specifically, using the four types of trivalent chromium plating solutions of Sample 1 to Sample 4 of Experimental Example 1, a chromium plating layer was formed in the same manner as Experimental Example 1 described above.

  About each sample obtained in this way, the color tone immediately after plating was measured by the following method and evaluated according to the following criteria.

<Color tone immediately after plating>
The L * value was measured based on the method described in CIE 1976 using a spectroscopic color difference meter (TC-1800MK-II manufactured by Tokyo Denshoku Color Analyzer). The color tone of the chromium plating layer obtained using the hexavalent chromium plating solution is in the range of 70 to 80 in terms of L * value. In this experimental example, when the L * value was 68 or more, it was considered that the same color tone as that of the chromium plating layer obtained from the hexavalent chromium plating solution was obtained.

Evaluation criteria A: Excellent color tone comparable to hexavalent chromium is obtained.
(L * value = 70 or more, 80 or less)
○: The metallic luster is slightly lowered, but the same color tone as hexavalent chromium is obtained.
(L * value = 68 or more, less than 70)
Δ: Slightly blackish tone (L * value = 65 or more and less than 68).
X: The color tone becomes blackish (L * value = less than 65).

  These results are shown in Table 5.

  As is apparent from Table 5, when the trivalent chromium plating solution of Sample 4 was used and the Fe content in the chromium plating layer was controlled to 15.0% by mass, regardless of the boron content in the chromium plating layer, A blackish chrome plating layer was obtained.

  When the trivalent chromium plating solution of Sample 3 is used and the Fe content in the chromium plating layer is controlled to 7.0% by mass, the tint is slightly blackish by controlling the boron content to 0.3% by mass or less. A chromium plating layer was obtained.

  On the other hand, when the trivalent chromium plating solution of Sample 2 was used and the Fe content in the chromium plating layer was reduced to 2.0 mass%, the boron content was controlled to 0.3 mass% or less, so that it was slightly blackish When the boron content was controlled to 0.1% by mass or less, a chromium plating layer having almost the same color tone as the chromium plating layer obtained from the hexavalent chromium plating solution was obtained. . Similar results were obtained when the trivalent chromium plating solution of Sample 1 was used, the Fe content in the chromium plating layer was reduced to 0.2% by mass, and the boron content was controlled to 0.3% by mass or less. It was. When the Fe content in the chromium plating layer is reduced to 0.2% by mass and the boron content is controlled to 0.1% by mass or less, the color tone is almost indistinguishable from the chromium plating layer obtained from the hexavalent chromium plating solution. The chromium plating layer which has was obtained.

  Therefore, in order to obtain a trivalent chromium plating layer having the same color tone as when hexavalent chromium is used, the amount of Fe in the trivalent chromium plating layer is suppressed to 2.0% by mass or less and boron is added. It can be seen that the amount may be reduced to 0.1% by mass or less. As far as the color tone is concerned, the smaller the Fe content and the boron content in the chromium plating layer, the better the characteristics.

(Experimental example 3)
In this experimental example, it was investigated how the cracking state before and after heating and the color tone of the chromium plating layer change depending on the thickness of the chromium plating layer.

  Specifically, using the trivalent chromium plating solution of Sample 1 of Experimental Example 1, a chromium plating layer was formed in the same manner as in Experimental Example 1 described above. The thickness of the chromium plating layer can be adjusted by appropriately controlling the plating time according to the size of the plating material used. In this experimental example, the thickness of the chromium plating layer was changed to 0.1 to 1.5 μm by changing the plating time in the range of 0.3 to 5 minutes.

  About each sample obtained in this way, the generation | occurrence | production condition of the crack observed immediately after plating (before heating) was measured with the following method, and the following reference | standard evaluated. Furthermore, according to the method mentioned above, the color tone of the chromium plating layer immediately after plating was measured and evaluated.

  Next, after each sample was placed in an atmospheric furnace and heated under the conditions of 400 ° C. × 8 hours, the occurrence of cracks after heating was examined when the occurrence of cracks observed immediately after plating was examined. The same measurement method and evaluation criteria were used.

<The occurrence of cracks>
Measurement method: Using an optical microscope (magnification 400 times), a crack generated on the surface of the chromium plating layer (about 10 mm × 10 mm) is observed.

Evaluation criteria (◎ to Δ are examples of the present invention)
A: No cracks are generated.
○: Discontinuous cracks are slightly observed.
Δ: Slightly continuous cracks occur.
X: Many continuous cracks are generated.

  Table 6 summarizes the occurrence of cracks. Table 7 shows the color tone of the chromium plating layer immediately after plating.

  As shown in Table 6, when the thickness of the chromium plating layer is increased and the boron content in the chromium plating layer is increased, it is understood that cracks are likely to occur.

  For example, looking at the experimental results before heating (immediately after plating), the boron content in the chromium plating layer is increased to 1.5% by mass when the thickness of the chromium plating layer is in the range of 0.1 to 0.3 μm. However, almost no cracks occurred. Cracks are likely to occur as the thickness of the chromium plating layer increases to 0.5 μm or more. When the thickness of the chromium plating layer is 1.5 μm, cracks occurred regardless of the boron content of the chromium plating layer. .

  On the other hand, when the heat treatment was performed at 400 ° C. for 8 hours, there was a tendency that cracks were more likely to occur than before the heating. Specifically, even if the thickness of the chromium plating layer is in the range of 0.1 to 0.7 μm, if the boron content in the chromium plating layer is not controlled to 0.05 to 0.3% by mass, it is cracked. It was not possible to effectively prevent the occurrence of. A more preferable boron content is 0.05 to 0.2% by mass. In addition, when the thickness of the chromium plating layer exceeds 0.7 μm, cracks are likely to occur. When the thickness of the chromium plating layer is 1.5 μm, cracks occurred regardless of the boron content in the chromium plating layer. .

  Considering these experimental results, in order to effectively prevent the occurrence of cracks before and after heating, the thickness of the chromium plating layer is set to 0.7 μm or less, and the boron content in the chromium plating layer is set to 0.05 μm. It can be seen that it should be controlled in the range of ~ 0.3% by mass.

  Next, for samples having a boron content of 0.05% by mass and 0.1% by mass in the chromium plating layer, the thickness of the chromium plating layer was changed in the range of 0.05 μm to 0.7 μm, and the discoloration caused by heating was changed. The degree of evaluation was performed.

<Degree of thermal discoloration>
Measuring method: Using a spectroscopic color difference meter (TC-1800MK-II manufactured by Tokyo Denshoku Color Analyzer), based on the method described in CIE 1976, L * value, a * value, and b * value before and after heating were ,taking measurement. The values before heating are L ₀ * values, a ₀ * values, and b ₀ * values, respectively, and the values after heating are L ₁ * values, a ₁ * values, and b ₁ * values, respectively. The color difference ΔE * value after heating is measured as follows.

Evaluation criteria (◎ to Δ are examples of the present invention)
A: ΔE * value <1
○: 1 ≦ ΔE * value <3
Δ: 3 ≦ ΔE * value <4
×: 4 ≦ ΔE * value

  As is clear from Table 7, when the thickness (μm) of the chromium plating layer is 0.2 μm or more, the change in color tone before and after heating is small, and when it is 0.3 μm or more, the color tone hardly changes. I understood.

  INDUSTRIAL APPLICABILITY The present invention can be widely used in vehicles such as motorcycles equipped with engines and all-weather four-wheeled vehicles, ships equipped with engines, and transportation equipment such as airplanes.

It is a figure which shows typically the structure of the components for engines by this invention. (A) is a figure which shows the analysis result by the X ray diffraction method of the chromium plating layer formed using trivalent chromium, (b) is X of the chromium plating layer formed using hexavalent chromium. It is a figure which shows the analysis result by a line diffraction method. It is a figure which shows typically a mode that a "CS concentrated layer" or a "C-S-Ni concentrated layer" produces | generates in the interface vicinity of a chromium plating layer and a base plating layer by heating. (A) is a schematic diagram for demonstrating that discoloration of a chromium plating layer can be prevented by enlarging the thickness of a chromium plating layer, (b) is a part of conventional chromium-nickel plating layer. It is a figure explaining typically. 1 is a side view of a motorcycle in which an engine component of the present invention is used. (A) is a figure which shows typically the part of the exhaust pipe connected directly to an engine, (b) is a figure which shows the cross section of the catalyst accommodating part of an exhaust pipe typically, (c) FIG. 4 is a diagram schematically showing a cross section of a manifold portion. It is a figure which shows the example of the chromium plating apparatus used for this invention. (A) is a figure which shows typically the state arrange | positioned so that the distance of the curved part of a metal base material and an electrode may become the shortest, (b) is a curved part and electrode of a metal base material. It is a figure which shows typically the state arrange | positioned so that distance may become long. 1 is a side view showing the appearance of a motorcycle.

Explanation of symbols

30, 201 Engine 4, 4a, 202 Exhaust pipe 203 Cylinder 204 Cylinder head 205 Head cover 1 Metal substrate 2 Base plating layer 3 Chrome plating layer 5 Metal pipe 6 Passage 7 Silencer part 8 Catalyst 9 Bending part 9a Convex surface part 9b Inside Side surface 10 Plating layer 11 Chromium plating tank 12 Pump 13 Filter 14 Adjustment valve 15 Flow meter 16 Ion exchange device 17 Metal substrate 18 Insoluble anode 19 DC power source 20 Chromium plating device 21 Connection portion 22 Catalyst housing portion 23 Other exhaust pipe 24 Pipeline 100, 200 motorcycle

Claims (15)

An engine component comprising a metal base material and a chromium plating layer that covers at least a part of the surface of the metal base material and is formed of a trivalent chromium plating solution,
Content of the boron contained in the said chromium plating layer is 0.05 mass% or more and 0.3 mass% or less, and the thickness of the said chromium plating layer is 0.7 micrometer or less.   The engine component according to claim 1, wherein a content of boron contained in the chromium plating layer is 0.05% by mass or more and 0.1% by mass or less.   The engine component according to claim 2, wherein the content of iron contained in the chromium plating layer is 2% by mass or less.   The engine component according to claim 3, wherein the chromium plating layer covers a region heated to a temperature of 350 ° C. or higher on the surface of the metal substrate. A base plating layer provided between the metal substrate surface and the chromium plating layer;
The engine component according to claim 4, wherein the chromium plating layer has a thickness of 0.2 μm or more and 0.7 μm or less in the region heated to a temperature of 350 ° C. or more.   The engine component according to claim 5, wherein the base plating layer includes at least one of C and S.   The engine component according to claim 6, wherein the base plating layer further contains Ni.   The engine component according to claim 5, wherein the base plating layer is formed of a metal having a lower hardness than Cr constituting the chromium plating layer.   The engine component according to claim 5, wherein the base plating layer is formed of Ni plating.   The engine component according to any one of claims 3 to 9, wherein the color tone of the chrome plating layer has an L * value measured by CIE (Commission Internationale de l'Eclairage) 1976 in a range of 68 to 80. .   The engine component according to any one of claims 5 to 10, wherein the metal substrate is made of a material mainly composed of Fe, Al, Zn, or Mg.   The engine component according to claim 1, wherein the metal base is a metal pipe that defines a passage through which exhaust gas from the engine passes.   An engine comprising the engine component according to any one of claims 1 to 11.   A transportation device comprising the engine component according to claim 12.   A transportation device comprising the engine according to claim 13.