US20080274373A1 - Engine Part - Google Patents

Engine Part Download PDF

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Publication number
US20080274373A1
US20080274373A1 US11/570,172 US57017205A US2008274373A1 US 20080274373 A1 US20080274373 A1 US 20080274373A1 US 57017205 A US57017205 A US 57017205A US 2008274373 A1 US2008274373 A1 US 2008274373A1
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Prior art keywords
plating layer
chromium plating
chromium
less
mass
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US11/570,172
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English (en)
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Naohisa Takahashi
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Yamaha Motor Co Ltd
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Yamaha Motor Co Ltd
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Assigned to YAMAHA HATSUDOKI KABUSHIKI KAISHA reassignment YAMAHA HATSUDOKI KABUSHIKI KAISHA ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: TAKAHASHI, NAOHISA
Publication of US20080274373A1 publication Critical patent/US20080274373A1/en
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/56—Electroplating: Baths therefor from solutions of alloys
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/16—Selection of particular materials
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/04—Electroplating: Baths therefor from solutions of chromium
    • C25D3/06—Electroplating: Baths therefor from solutions of chromium from solutions of trivalent chromium
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2530/00—Selection of materials for tubes, chambers or housings
    • F01N2530/02—Corrosion resistive metals
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12771—Transition metal-base component
    • Y10T428/12806—Refractory [Group IVB, VB, or VIB] metal-base component
    • Y10T428/12826—Group VIB metal-base component
    • Y10T428/12847—Cr-base component

Definitions

  • the present invention relates to an engine part, and more particularly to an engine part which is subjected to a high temperature due to a high-temperature exhaust gas discharged from an engine.
  • 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 along exhaust gas.
  • the V-type engine 201 includes cylinders 203 , cylinder heads 204 , and head covers 205 .
  • the aesthetically excellent V-type engine 201 is likely to be mounted to the motorcycle such that the engine is exposed on the outside, and is highly influential to the exterior appearance of the entire motorcycle.
  • Exhaust pipes extend from the two cylinders 203 of the V-type engine 201 and are united into the single exhaust pipe 202 , which extends toward and above the rear wheel so as to allow exhaust gas to be discharged at the rear portion of the body.
  • the exhaust pipe 202 must have a certain thickness for allowing the exhaust gas generated in the engine 201 to be efficiently discharged.
  • the portion constituting a muffler 202 a has an increased diameter in order to accommodate the structure for muffling.
  • the exhaust pipe accounts for a relatively large part of the exterior appearance of the entire motorcycle, and thus the shape and color of the exhaust pipe are highly influential to the entire motorcycle design.
  • engine components such as the cylinders 203 , the cylinder heads 204 , the head covers 205 , and the exhaust pipe 202 for guiding the exhaust gas from the engine as well as a cover thereof, will be referred to as “engine parts”.
  • engine parts the shape and color of engine parts are important factors in determining the entire motorcycle design.
  • decorative chromium plating provides an excellent metallic luster, and also excels in anticorrosiveness, it is also used in various fields other than engine parts. In order to obtain excellent exterior appearance and anticorrosiveness, it is unnecessary to form the decorative chromium plating so as to be thick. In fact, when formed thick, decorative chromium plating will result in a poor color tone and surface finish. Therefore, in general, decorative chromium plating is preferably used at a thickness in the range from 0.1 ⁇ m to 0.15 ⁇ m.
  • hard chromium plating (industrial chromium plating) is also widely used in industrial products. Since hard chromium plating has a low friction coefficient and an excellent abrasion resistance, it is used for sliding sections of various machine parts, for example. Since abrasion resistance is a requirement, hard chromium plating is usually formed to a thickness of several ⁇ m or more. Moreover, hard chromium plating does not have a decorativeness surface as does decorative chromium plating.
  • decorative chromium plating has a surface roughness (Ra) of 1 ⁇ m or less (typically, 0.2 ⁇ m or less) after the plating, while hard chromium plating has a surface roughness of 1 ⁇ m or more.
  • Decorative chromium plating is usually formed by using a plating solution of chromate, including hexavalent chromium (Cr 6+ ).
  • Hexavalent chromium is inexpensive, and a chromium plating layer formed from a plating solution containing hexavalent chromium (hereinafter referred to as a “hexavalent chromium plating solution”) shows good contact with a base substrate, and has excellent anticorrosiveness and abrasion resistance.
  • a chromium plating layer formed from a hexavalent chromium plating solution has a silver-gray color with a characteristically metallic luster. For these reasons, a hexavalent chromium plating solution is widely used for engine parts for motorcycles.
  • hexavalent chromium is known for its highly biotoxic nature. When performing plating with a hexavalent chromium plating solution, it has become a requirement that safety of the workers is ensured and that environmental pollution is prevented.
  • Patent Document 1 Japanese Laid-Open Patent Publication No. 2003-41933
  • Patent Document 2 Japanese Laid-Open Patent Publication No. 52-065138
  • Patent Document 3 Japanese Laid-Open Patent Publication No. 52-092834
  • Patent Document 4 Japanese Laid-Open Patent Publication No. 9-95793
  • Patent Document 5 Japanese Laid-Open Patent Publication No. 9-228069
  • a plating solution containing trivalent chromium (hereinafter referred to as a “trivalent chromium plating solution”).
  • a chromium plating layer which is formed by using a conventional trivalent chromium plating solution has a problem of being inferior to a plating layer which is formed from a hexavalent chromium plating solution, in terms of stability of growth of the chromium plating layer and the plating film-forming characteristics of the resultant chromium plating layer, e.g., anticorrosiveness and abrasion resistance.
  • an engine part is heated to a high temperature due to heat generation associated with fuel combustion and a high-temperature exhaust gas.
  • a chromium plating layer is formed on an engine part by using a conventional trivalent chromium plating solution, there is a problem in that the chromium plating layer is likely to have cracks responsive to heating. If a crack occurs in a chromium plating layer, rust will occur from that portion, thus severely degrading the exterior appearance.
  • trivalent chromium plating solutions of various compositions have been proposed since twenty or more years ago.
  • trivalent chromium plating solutions have hardly been used for engine parts, in particular.
  • the present invention solves such conventional problems, and intends to provide an engine part having a chromium plating layer which is formed by using a trivalent chromium plating solution; which has as good film-forming characteristics as those of a plating layer that is formed from a hexavalent chromium plating solution; and which has excellent thermal resistance.
  • An engine part according to the present invention is an engine part comprising: a metal substrate; a chromium plating layer covering at least a portion of a surface of the metal substrate, the chromium plating layer being formed from a trivalent chromium plating solution, wherein, the chromium plating layer includes a boron content of no less than 0.05 mass % and no more than 0.3 mass %, and the chromium plating layer has a thickness or 0.7 ⁇ m or less.
  • the boron content in the chromium plating layer is no less than 0.05 mass % and no more than 0.1 mass %.
  • the chromium plating layer includes an iron content of 2 mass % or less.
  • the chromium plating layer covers a region of the metal substrate surface that is heated to a temperature of 350° C. or more.
  • the engine part further comprises an underlying plating layer provided between the metal substrate surface and the chromium plating layer, wherein, the chromium plating layer has a thickness of no less than 0.2 m and no more than 0.7 ⁇ m in the region that is heated to a temperature of 350° C. or more.
  • the underlying plating layer includes at least one of C and S.
  • the underlying plating layer further includes Ni.
  • the underlying plating layer is formed of a metal having a hardness lower than that of the Cr composing the chromium plating layer.
  • the underlying plating layer is formed from Ni plating.
  • the chromium plating layer has a color tone such that an L* value measured according to CIE (Commission Internationale de l'Eclairage) 1976 is in a range of no less than 68 and no more than 80.
  • CIE Commission Internationale de l'Eclairage
  • the metal substrate is composed of a material containing Fe, Al, Zn, or Mg as a main component.
  • the metal substrate is a metal tube defining a passage through which an exhaust gas from an engine travels.
  • An engine according to the present invention comprises any of the aforementioned engine parts.
  • a transportation apparatus comprises any of the aforementioned engine parts or engine.
  • a boron content in the chromium plating layer is adjusted to no less than 0.05 mass % and no more than 0.3 mass %, and the chromium plating layer has a thickness or 0.7 ⁇ m or less. Therefore, by using a trivalent chromium plating solution, a chromium plating layer which has as good film-forming characteristics as those of a plating layer that is formed from a hexavalent chromium plating solution and which has good thermal resistance can be obtained. Thus, an engine part having good exterior appearance can be obtained by using a trivalent chromium plating solution.
  • a boron content in the chromium plating layer to be 0.1 mass % or less and an iron content to be 2 mass % or less, a silver-gray color tone similar to that of a chromium plating layer which is formed from a hexavalent chromium plating solution can be obtained.
  • the thickness of the chromium plating layer in a range of no less than 0.2 m and no more than 0.7 ⁇ m, an engine part which is not likely to experience thermal discoloration can be obtained.
  • FIG. 1 is a diagram schematically showing the structure of an engine part according to the present invention.
  • FIG. 2( a ) is a graph showing X-ray diffraction analysis results of a chromium plating layer formed by using trivalent chromium; and (b) is a graph showing X-ray diffraction analysis results of a chromium plating layer formed by using hexavalent chromium.
  • FIG. 3 is a diagram schematically showing the generation of a “C—S thickened layer” or a “C—S—Ni thickened layer”, obtained by heating, near an interface between a chromium plating layer and an underlying plating layer.
  • FIG. 4( a ) is a schematic diagram for explaining prevention of discoloration of a chromium plating layer by increasing the thickness of the chromium plating layer; and (b) is a diagram schematically showing a portion of a conventional chromium-nickel plating layer.
  • FIG. 5 is a side view showing a motorcycle in which an engine part according to the present invention is used.
  • FIG. 6( a ) is a diagram schematically showing a portion of an exhaust pipe which is directly connected to an engine; (b) is a diagram schematically showing a cross section of a catalyst accommodating section of an exhaust pipe; and (c) is a diagram schematically showing a cross section of a manifold section.
  • FIG. 7 is a diagram showing an example of a chromium plating apparatus used in the present invention.
  • FIG. 8( a ) is a diagram schematically showing an arrangement in which a minimum distance exists between a curved portion of a metal substrate and an electrode; and (b) is a diagram schematically showing an arrangement in which a long distance exists between a curved portion of a metal substrate and an electrode.
  • FIG. 9 is a side view showing the exterior appearance of a motorcycle.
  • the inventor has found that the problem of cracks occurring in a chromium plating layer is related to the boron content within the chromium plating layer.
  • the inventor has also found that the stability of growth of a chromium plating layer and the anticorrosiveness and abrasion resistance of the resultant chromium plating layer are also related to the boron content within the chromium plating layer and the boron concentration within the trivalent chromium plating solution.
  • a chromium plating layer which is formed from a conventional trivalent chromium plating solution has a blackish color tone as compared to a chromium plating layer which is formed from a hexavalent chromium plating solution. This has been found to be related to the iron content in the resultant chromium plating layer.
  • the surface color tone may change due to heating, so that the chromium plating layer may appear blue-violet.
  • Such discoloration will degrade the exterior appearance of a motorcycle or the like in which the engine part is mounted.
  • the inventor has found that the discoloration of a chromium plating layer due to heating depends on the thickness of the chromium plating layer.
  • the engine part according to the present invention includes a metal substrate 1 , a chromium plating layer 3 covering at least a portion of the surface of the metal substrate 1 , and an underlying plating layer 2 provided between the metal substrate 1 and the chromium plating layer 3 .
  • these constituent elements will be specifically described.
  • the metal substrate 1 which has a mechanical strength suitable to its purpose and a necessary level of anticorrosiveness and the like, can be formed from a material which is usually used for an engine part.
  • a typical example would be an Fe-type material.
  • the metal substrate 1 may be formed from any non-Fe material, such as an Al-type material, a Zn-type material, an Mg-type material, or a Ti-type material.
  • Fe-type materials include Fe or steels whose main component is Fe, such as: steel tubes for machine structural purposes (e.g., carbon steel tubes for machine structural purposes (STKM) or alloy steels for machine structural purposes); stainless steel (e.g., ferrite-type stainless steel, austenite-type stainless steel, or austenite/ferrite-type stainless steel); and mild steel (e.g., SPCC or SPHC).
  • steel tubes for machine structural purposes e.g., carbon steel tubes for machine structural purposes (STKM) or alloy steels for machine structural purposes
  • stainless steel e.g., ferrite-type stainless steel, austenite-type stainless steel, or austenite/ferrite-type stainless steel
  • mild steel e.g., SPCC or SPHC
  • Al-type materials include: Al; and Al alloys such as Al—Si alloys or Al—Si—Mg—type alloys.
  • Zn-type materials include: Zn; Zn-plated steel plates, on which Zn plating is provided; and Zn alloy-plated steel plates, on which Zn alloy plating whose main component is Zn and which includes alloying elements such as Ni, Co, Cr, or Al is provided.
  • Mg-type materials include Mg—Al type alloys and Mg—Zn type alloys.
  • Ti-type materials include: Ti; and Ti alloys whose main component is Ti and which includes elements such as Al, V, or Si.
  • Al is light-weight and shiny
  • Ti is light-weight and has excellent mechanical strength. Therefore, any appropriate material may be selected depending on the purpose, required characteristics, and the like.
  • the underlying plating layer 2 formed on the metal substrate 1 defines an underlying plating for the chromium plating layer 3 . From the standpoint of preventing cracks from occurring in the chromium plating layer and allowing a chromium plating layer having good anticorrosiveness and abrasion resistance to stably grow, the underlying plating layer 2 does not need to be provided.
  • an underlying plating layer is usually formed under the chromium plating layer with the purpose of providing enhanced contact with the base substrate, for example. Therefore, it is preferable that the underlying plating layer 2 exhibits good contact with various metal substrates, as well as good contact with the chromium plating layer. There might be other preferable characteristics, e.g., anticorrosiveness.
  • the metal composing the underlying plating layer 2 used for the present invention can be defined in terms of a relationship with the hardness (Vickers hardness) of chromium, which is used for forming the chromium plating layer. Specifically, it is preferable that the metal composing the underlying plating layer 2 is formed of a metal having a hardness lower than the hardness of chromium (about 350 to 1200 Hv).
  • the presence of a layer composed of a low-hardness metal interposed between the chromium plating layer and the metal substrate reduces the stress applied to the chromium plating layer due to heat cycles. As a result, the generation of cracks and the like is prevented, and a chromium plating layer having good surface characteristics can be obtained.
  • metals having a lower hardness than that of 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), and lead (Pb) (whose hardness is immeasurable).
  • an underlying plating layer including such metals for example, a layer composed of nickel plating, copper plating, tin plating, lead plating, zinc-nickel plating, or the like is used.
  • a single such plating layer may be formed, or two or more kinds may be combined to result in there being a plurality of underlying plating layers.
  • a plurality of underlying plating layers of the same kind but containing different types of additives, etc. may be formed.
  • a typical underlying plating layer to be used as the underlying treatment for a chromium plating layer is nickel plating, which further enhances anticorrosiveness, luster, and the like.
  • the underlying plating layer 2 includes elements which compose various additives. With the purpose of enhancing the luster of the chromium plating layer, such additives are added in a plating solution for forming the underlying plating layer 2 .
  • a primary brightener a non-butyne-type brightener, e.g., saccharin sodium, naphthalene-1,3,6-trisodium trisulfonate, or benzene sulfonic acid
  • a secondary brightener e.g., 2-butyl-1,4-diol, sodium allylsulfonate
  • Any such additive includes C and/or S as its component elements.
  • a total of about 0.001 to 1.0 mass % of C and/or S is included in the underlying plating layer. As will be specifically described later, these elements will thicken to about 0.1 to 10 mass % responsive to heating, thus causing surface discoloration of the chromium plating layer. Furthermore, in the case where the underlying plating layer 2 is a nickel plating layer, the Ni contained in the nickel plating layer also substantially affects surface discoloration.
  • Nickel plating will be specifically described as a typical example of an underlying plating layer.
  • Nickel plating is generally classified into lusterless nickel plating, semigloss nickel plating, and gloss nickel plating, mainly depending on the type of brightener added in the plating solution, whether such an addition is made or not, etc. These types of plating can be appropriately combined in accordance with the required characteristics, purpose, and the like, whereby the desired exterior appearance can be obtained.
  • gloss nickel plating is obtained by adding a brightener such as saccharin or benzene sulfonic acid to the plating solution.
  • Gloss nickel plating provides an excellent surface leveling (planarize) action and exhibits good contact with the chromium plating layer, and therefore is widely used as an underlying layer to be formed directly under a chromium plating layer.
  • a brightener for gloss nickel plating is usually used in an amount such that a total of about 0.001 to 1.0 mass % of at least one of C and S is included in the plating layer. Anticorrosiveness tends to decrease as the S content increases.
  • Lusterless nickel plating differs from gloss nickel plating in that no brightener is contained in the plating solution. Although providing less luster than gloss nickel plating, lusterless nickel plating is excellent in terms of throwing power (adhesion), anticorrosiveness, discoloration prevention, etc., of the plating layer.
  • Semigloss nickel plating is obtained by adding a non-coumarin-type semi-brightener to the plating solution. Unlike the aforementioned brighteners, semi-brighteners have little C and/or S content. Therefore, it provides better anticorrosiveness but poorer luster than those provided by gloss nickel plating.
  • a tri-nickel plating layer (which is a type of gloss nickel plating layer) having a large S content may be formed between the semigloss nickel plating layer and the gloss nickel plating layer, thus obtaining a three-layer plating structure.
  • the S contained in the tri-nickel plating layer is most often supplied from an additive other than a brightener.
  • the uppermost gloss nickel plating layer is corroded first, and then the intermediate tri-nickel plating layer is corroded, whereby both the semigloss nickel plating layer and the base metal are protected.
  • the nickel plating layer(s) preferably has a total thickness of about 10 to 30 ⁇ m, and more preferably about no less than 15 ⁇ m and no more than 25 ⁇ m.
  • the underlying plating layer is preferably controlled to a thickness of about 10 to 30 ⁇ m.
  • the chromium plating layer 3 is formed on the underlying plating layer 2 .
  • the chromium plating layer 3 is a decorative chromium plating layer which is formed by electroplating using a trivalent chromium plating solution.
  • Whether a chromium plating layer has been formed by using a trivalent chromium plating solution or by using a hexavalent chromium plating solution can be determined by measuring the crystal state of the chromium plating layer. Specifically, the determination can be easily made by subjecting the chromium plating layer to an X-ray diffraction analysis.
  • FIGS. 2( a ) and ( b ) each show X-ray diffraction analysis results of a chromium plating layer. The detailed measurement method was as follows.
  • Measurement conditions A Cu anticathode was used, and power was supplied at 40 kV/40 mA.
  • FIG. 2( b ) X-ray diffraction results of a chromium plating layer which has been formed by using a hexavalent chromium plating solution are shown in FIG. 2( b ).
  • Near diffraction angles of about 40 ⁇ to 50 ⁇ a very large diffraction peak of about 1200 cps is observed, and large diffraction peaks of about 200 cps are observed near diffraction angles of about 65 ⁇ and about 83 ⁇ . In the ascending order of diffraction angles, these peaks correspond to (111) orientation crystal, (200) orientation crystal, and (211) orientation crystal, respectively.
  • FIG. 2( a ) X-ray diffraction results of a chromium plating layer which has been formed by using a trivalent chromium plating solution are shown in FIG. 2( a ). Only a small diffraction peak of about 100 cps is observed near diffraction angles of about 40 to 50 ⁇ , this corresponding to (111) orientation crystal. A value obtained by dividing the half-width of the peak corresponding to (111) orientation crystal by the peak intensity (half-width/peak height) is about 0.6 rad/cps, which is much broader than the value of (111) orientation crystal (about 7.9 ⁇ 10 ⁇ 4 rad/cps) which is observed when using hexavalent chromium.
  • the chromium plating layer obtained by using hexavalent chromium has a crystal structure composed of polycrystals
  • the chromium plating layer obtained by using trivalent chromium plating solution has a substantially amorphous structure.
  • the determination as to whether a plating layer has a crystalline structure or an amorphous structure can be made based on, for example, whether a diffraction peak associated with a (half-width/peak height) value of about 0.001 rad/cps or less is observed or not near diffraction angles of about 40 to 500.
  • the amount of boron contained in the chromium plating layer 3 is no less than 0.05 mass % and no more than 0.3 mass %. If the boron content is more than 0.3 mass %, cracks may occur in the chromium plating layer 3 responsive to heating to 400° C. or above. On the other hand, if the boron content is less than 0.05%, the anticorrosiveness and abrasion resistance of the chromium plating layer 3 become lowered. Moreover, stability of plating growth when forming the chromium plating layer 3 becomes lower.
  • the boron content is preferably no less than 0.05 mass % and no more than 0.2 mass %, and more preferably no less than 0.05 mass % and no more than 0.1 mass %. Crack generation can be prevented with more certainty and better anticorrosiveness and abrasion resistance can be obtained as there is less boron content.
  • “stability of plating growth” means that the throwing power (adhesion) of a chromium plating layer in a plating process is constant over time. Specifically, it means that, when a Hull cell test is conducted, poor exterior appearance, e.g., inadequate plating thickness, scorching, or streaks, is prevented over a large area of current density, or that a plating layer with a predetermined thickness is formed also on portions of the material to be plated that are difficult to be plated (e.g., a surface to be plated that is located opposite from an electrode).
  • plating anticorrosiveness means an anticorrosiveness that is imparted through a plating process. Specifically, if a rating number of 7.0 or more is satisfied when performing a CASS test (which is a plating anticorrosiveness test method defined in JIS H8502) by using a sample that has experienced a plating process, it is said that “there is good plating anticorrosiveness”.
  • Platinum abrasion resistance means an abrasion resistance (hardness) that is imparted through a plating process. Specifically, if the Vickers hardness is in the range of 350Hv0.1 (test power: 0.9807N) or more when a Vickers hardness as defined in JIS Z 2244 is measured by using a sample that has experienced a plating process, it is said that “there is good plating abrasion resistance”.
  • the chromium plating layer 3 contains boron, a chromium plating layer having good anticorrosiveness and abrasion resistance can be obtained. Moreover, the chromium plating layer can be allowed to stably grow.
  • boron acts to harden the plating layer, and, if its content exceeds the aforementioned range, the hardness of the chromium plating layer will increase especially when heated to a high temperature (esp., 400° C. or more), so that the stress on the chromium plating layer due to heat cycles will be increased. As a result, cracks and the like are likely to occur on the surface. If cracks occur, rust is likely to occur from the cracks. If a large number of cracks occur, coating may peel, etc., thus degrading the exterior appearance. Moreover, the color tone will be degraded when the content exceeds the aforementioned range.
  • the thickness of the chromium plating layer 3 is preferably 0.7 ⁇ m or less. If the chromium plating layer 3 is thicker than 0.7 ⁇ m, it becomes difficult to form a chromium plating layer without cracks even if the boron content is within the aforementioned range. In order to more certainly prevent crack generation, it is preferable that the thickness of the chromium plating layer 3 is 0.5 ⁇ m or less.
  • the boron content in the chromium plating layer is kept at 0.3 mass % or less only in regions of the engine part that will rise to a high temperature.
  • the boron content in the chromium plating layer remains within the aforementioned range in any region of the chromium plating layer.
  • the engine part according to the present invention is not necessary for the engine part according to the present invention to be used in an environment where its entirety is heated to a high temperature.
  • the present invention is suitably used for an engine part at least a portion of which is exposed to a high temperature.
  • a chromium plating layer 3 has a boron content as described above, it is possible, by using a trivalent chromium plating solution, to form a chromium plating layer which has as good film-forming characteristics as those of a plating layer formed from a hexavalent chromium plating solution and which has good thermal resistance.
  • a chromium plating layer which is formed from a trivalent chromium plating solution has a blackish color tone as compared to a chromium plating layer which is formed from a hexavalent chromium plating solution.
  • the causes for the blackish color tone are related to the concentrations of iron and boron that are contained in the chromium plating layer.
  • the color tone becomes blackish particularly when the iron content increases.
  • the iron within a chromium plating layer binds with various elements within the plating solution, thus generating a deposit containing black iron.
  • the boron content is preferably 0.1 mass % or less and the iron content is 2 mass % or less in the chromium plating layer 3 .
  • the iron content should be as little as possible, and is more preferably 1 mass % or less, and further more preferably 0.5 mass % or less.
  • the boron content may be prescribed to be 0.3 mass % or less and the iron content to be 7 mass % or less, whereby a chromium plating layer with a color tone that qualifies for chromium plating can be obtained, although its color tone may be somewhat muddier.
  • the boron and iron contents in the chromium plating layer are to be each expressed as a maximum value when the content of each element, contained along the depth direction of the chromium plating layer, is analyzed through GDS analysis.
  • the chromium plating layer has a color tone such that an L* value measured according to CIE (Commission Internationale de l'Eclairage) 1976 is in a range from 68 to 80.
  • the L value is to be measured by using a spectrometric color difference meter (e.g., color analyzer TC-1800MK-II (Tokyo Denshoku)). This value is similar to that of a chromium plating layer which is formed from a hexavalent chromium plating solution.
  • the engine part has such a structure, it is possible, by using a trivalent chromium plating solution, to obtain a chromium plating layer which has as good film-forming characteristics as those of a plating layer which is formed from a hexavalent chromium plating solution and which has good thermal resistance. Moreover, by prescribing the boron content to be 0.1 mass % or less and the iron content to be 2 mass % or less in the chromium plating layer, a silver-gray color tone similar to that of a chromium plating layer which is formed from a hexavalent chromium plating solution can be obtained.
  • the engine part according to the present invention can be suitably used in parts of an engine; e.g., a cylinder, a cylinder head, and a head cover; an exhaust pipe for guiding along exhaust gas from the engine; and the like.
  • an engine e.g., a cylinder, a cylinder head, and a head cover
  • an exhaust pipe for guiding along exhaust gas from the engine
  • the chromium plating layer may appear blue-violet.
  • the chromium plating layer has a thickness of 0.2 ⁇ m or more.
  • FIG. 3 is a diagram schematically showing a manner in which C and/or S gather near the interface between the chromium plating layer and the underlying plating layer responsive to heating, thus showing a generation mechanism of a “C—S thickened layer” or a “C—S—Ni thickened layer” (hereinafter may simply be referred to as a “thickened layer”), which is considered as responsible for the surface discoloration of the chromium plating layer.
  • FIG. 3 illustrates a typical structure according to 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 composed of the following three layers, respectively from the Fe substrate side: a semigloss nickel plating layer, a tri-nickel plating layer, and a gloss nickel plating layer.
  • FIG. 3 only shows those elements which are considered as contributive to the discoloration of the chromium plating layer, i.e., the elements (at least one of C, S, and Ni) composing the aforementioned thickened layer and elements (e.g., Fe or Cr) which are likely to bind to these elements, while omitting any other elements (e.g., O which gathers near the aforementioned interface responsive to heating).
  • the elements at least one of C, S, and Ni
  • elements e.g., Fe or Cr
  • C or S moves from the nickel plating layer side to the chromium plating layer side, thus gathering at the aforementioned interface.
  • C or S is mainly the element which composes a non-butyne-type brightener (e.g., benzene sulfonic acid) which is added to the nickel plating solution.
  • a large amount of S is contained in the gloss nickel plating layer and the tri-nickel plating layer. Therefore, near the aforementioned interface, a “C—S thickened layer” in which a large amount of C or S has gathered is formed.
  • a “C—S thickened layer” means a layer in which at least one of C and S has gathered. Note that, although C or S may also diffuse over from the chromium plating layer side, such diffusion will account for a very small proportion as compared to the diffusion from the nickel plating layer side, and therefore is omitted from illustration.
  • a “C—S—Ni thickened layer” containing Ni will be formed. Similarly to C or S, Ni is also considered as contributive to discoloration.
  • a “C—S—Ni thickened layer” means a layer in which at least one of C or S and Ni has gathered.
  • the reason why formation of such a thickened layer causes surface discoloration of the chromium plating layer may be that the Cr composing the chromium plating layer may bind to the element (C or S, or Ni) composing the thickened layer and change the refractive index of the chromium plating layer, thus causing discoloration, for example.
  • Iron is also considered as a substance that contributes to discoloration. In the case where the metal substrate is composed of an Fe-type material, responsive to heating, Fe may diffuse from the Fe-type material and become thickened in the area of the aforementioned interface (not shown).
  • FIG. 4( b ) is a diagram schematically showing a portion of a conventional Cr-nickel plating layer.
  • the thickness of the conventional chromium plating layer is as small as about 0.1 ⁇ m or less. Therefore, incident light will be transmitted to the vicinity of the interface between the chromium plating layer and the nickel plating layer. Consequently, a portion of the incident light will be absorbed by the thickened layer which is generated near the interface, thus making the discoloration due to heating more conspicuous.
  • the incident light will for the most part be reflected near the surface of the chromium plating layer, instead of being transmitted over to the vicinity of the interface between the chromium plating layer and the nickel plating layer. Therefore, only the interference colors caused by the usually-occurring oxide coating on the outermost surface of a chromium plating layer are observed, and the influence due to the thickened layer can be minimized.
  • the thickness of the chromium plating layer is set to be 0.2 ⁇ m or more. From the perspective of prevention of thermal discoloration due to heating, the chromium plating layer should be as thick as possible. Preferably, the thickness of the chromium plating layer is 0.3 ⁇ m or more, and more preferably 0.4 ⁇ m or more.
  • the thickness of the chromium plating layer is preferably no less than 0.2 ⁇ m and no more than 0.7 ⁇ m, and more preferably no less than 0.3 ⁇ m and no more than 0.5 ⁇ m.
  • the thickness of the chromium plating layer is no less than 0.4 ⁇ m and no more than 0.5 ⁇ m, crack generation can be almost surely prevented, and discoloration due to heating can be surely prevented.
  • the thickness of the chromium plating layer 3 may be measured through observation with an optical microscope (magnification: ⁇ 400). Specifically, a cross section along the thickness direction of the plating layer is mirror-polished and etched. As a result, the chromium plating layer becomes clearly distinguishable from the underlying plating layer. Note that the chromium plating layer will have a surface roughness Ra of not more than about 0.01 ⁇ m, and therefore the influence of the surface roughness Ra on the thickness of the chromium plating layer is virtually negligible.
  • the thickness of the chromium plating layer will slightly vary depending on the measurement site, a total of three measurements are to be taken in different measurement sites within a given a field of observation, and an average value thereof is to be defined as the “thickness of the chromium plating layer”.
  • Another means for preventing discoloration due to the formation of a thickened layer might be to reduce the C or S content, although this method would not be practical.
  • the amount of brightener to be contained in the underlying plating layer would mainly have to be reduced.
  • good design is considered as an important factor as in the case of the present invention, any deterioration in design because of not using the brightener must definitely be avoided.
  • a portion of the chromium plating layer 3 which is to be heated to a temperature of 350° C. or above satisfies the aforementioned range of thickness. It is not necessary that the entire area of the chromium plating layer 3 formed on the metal substrate 1 satisfy the aforementioned range of thickness. In regions which will only rise to a temperature of 350° C. or less, the thickness of the chromium plating layer 3 may be 0.2 ⁇ m or less.
  • a chromium plating layer is tinted from silver-gray to yellow to gold responsive to heating, and at a high temperature of about 350 to 500° C., becomes discolored from gold to violet. Such changes in color tone will not be uniformly observed over the entire area in which the chromium plating layer is formed, but will be most noticeable in portions which are likely to be exposed to a high-temperature exhaust gas.
  • the thickness of the portion at which discoloration due to heating is most likely to occur i.e., the region of the chromium plating layer that is exposed to a temperature of 350° C. or above, to be in the aforementioned range.
  • Examples of the “region which is to be heated to a temperature of 350° C. or above” may include a portion of an engine part composing an engine, e.g., a cylinder, a cylinder head, a head cover, as well as a portion of an exhaust pipe defining a channel for guiding the exhaust gas discharged from the engine, or a cover of the exhaust pipe.
  • the exhaust pipe may be an exhaust pipe which directly guides exhaust gas, or an exhaust pipe (a double tube) which is indirectly heated by exhaust gas.
  • An exhaust pipe includes a manifold section for guiding along the exhaust gas from each cylinder, a catalytic apparatus accommodating section covering a catalytic apparatus, a muffler, and the like.
  • FIG. 5 shows a motorcycle 100 incorporating an exhaust pipe which is an engine part according to the present invention.
  • the motorcycle 100 includes an engine 30 which is composed of a 4-cycle internal combustion engine, and an exhaust pipe 4 for guiding the exhaust gas generated in the engine 30 so as to be discharged at the rear portion of the body.
  • the exhaust pipe 4 includes an exhaust pipe congregation section 4 a , which is connected to the engine 30 and constitutes a substantially bent exhaust path for allowing the exhaust gas having been discharged at the front of the engine 30 to be guided toward the rear, and a muffler 4 b .
  • the exhaust pipe congregation section 4 a may be integrally formed of a single part, or composed of a plurality of parts which are connected with one another.
  • the exhaust pipe 4 is entirely exposed so as to appear on the exterior of the motorcycle 100 , thus constituting a part of the design of the motorcycle 100 as a whole.
  • the effect of the present invention i.e., cracks or rust does not occur in the chrome plating layer of the exhaust pipe 4 , discoloration is prevented, and the fresh exterior appearance of a brand-new motorcycle is retained for long periods of time, is more clearly enhanced in the exterior appearance in the case where the entire exhaust pipe 4 is exposed.
  • the exhaust pipe 4 at least partially appears on the exterior, a part of the exhaust pipe 4 may be covered by a cowl or a protector, depending on the design of the motorcycle.
  • the shape of the motorcycle for which the exhaust pipe is used is not limited to that shown in FIG. 5 .
  • the exhaust pipe according to the present invention may be adopted in a motorcycle having a structure as shown in FIG. 9 .
  • FIGS. 6( a ), ( b ), and ( c ) the “region of the metal substrate surface that is to be heated to a temperature of 350° C. or above”, on which the chromium plating layer preferably has a thickness of 0.2 ⁇ m or more, will be described.
  • Each of these figures is a cross-sectional view showing a part of the exhaust pipe 4 .
  • FIG. 6( a ) shows an exhaust pipe congregation section 4 a of the exhaust pipe 4 , which is directly connected to an engine.
  • the exhaust pipe congregation section 4 a which is connected to an engine (not shown), includes a metal tube 5 defining a passage 6 in which exhaust gas travels through, and a plating layer 10 covering the outer side surface of the metal tube 5 .
  • the metal tube 5 includes a bent portion 9 .
  • the bent portion 9 is a portion at which the passage 6 is bent, or a portion at which the longitudinal direction of the passage 6 changes.
  • the plating layer 10 includes an underlying plating layer and a chromium plating layer.
  • the metal tube 5 simply needs to define the passage 6 , and may have a double-tube structure composed of an inner tube defining the passage 6 and an outer tube covering the inner tube from the outside.
  • the exhaust gas that comes through the exhaust pipe congregation section 4 a which is directly connected to the engine (not shown), rapidly travels through the passage 6 , and therefore collides against the metal tube 5 at the bent portion 9 .
  • the exhaust gas collides especially intensely against an inner side surface 9 b of the metal tube 5 that is located at the convex surface portion 9 a , which in itself is formed as a result of the bending. Therefore, the outer convex surface portion 9 a is heated by the high-temperature exhaust gas to a temperature of about 350° C. or more (e.g., about 400 to 500° C.).
  • the metal tube 5 has a double-tube structure
  • a single-tube structure is often adopted for a link section 21 at which another exhaust pipe member 23 is to be connected.
  • the metal tube 5 might deform or be destroyed due to a difference in thermal expansion between the outer tube and the inner tube during the welding to the other exhaust pipe member 23 .
  • the link section 21 will be heated to a temperature of about 350° C. or more (e.g., about 400 to 500° C.) as the high-temperature exhaust gas comes in direct contact with the inner side surface of the link section 21 .
  • FIG. 6( b ) schematically shows a cross section of a catalyst accommodating section 22 of the exhaust pipe 4 , in which a catalytic apparatus 8 is accommodated.
  • the catalytic apparatus 8 which is provided within the catalyst accommodating section 22 , decomposes at least one component contained in the exhaust gas when the exhaust gas travel therethrough. Since the catalytic apparatus 8 is heated responsive to the aforementioned decomposition, the catalyst accommodating section 22 is heated to a temperature of about 350° C. or more (e.g., about 400 to 500° C.).
  • the exhaust pipe 4 may include a manifold section for combining the exhaust gas generated in the respective cylinders so as to allow such exhaust gas to be guided to the rear portion of the motorcycle 100 .
  • FIG. 6( c ) shows an exhaust pipe 4 having a manifold section 15 at which branch pipes 4 d and 4 e (each of which is connected to a cylinder) come together, such that discharge takes place through a unified exhaust pipe member 4 f .
  • exhaust gas comes together through the plurality of branch pipes 4 d and 4 e , whereby the flow rate of the exhaust gas is increased, and the flow paths are deflected.
  • the exhaust gas collides against the inner side surface of the manifold section 15 . Therefore, the manifold section 15 is heated by the exhaust gas to a temperature of about 350° C. or more (e.g., about 400 to 500° C.).
  • those portions of the exhaust pipe which are exemplified as being heated to a high temperature in FIGS. 6( a ), ( b ), and ( c ) are covered from the outside by a chromium plating layer of 0.2 ⁇ m or more.
  • a chromium plating layer of 0.2 ⁇ m or more.
  • the present invention also encompasses a transportation apparatus incorporating the above-described engine part(s).
  • transportation apparatus include a vehicle having an engine (e.g., a motorcycle or an all-climate four-wheeled vehicle) and a transportation apparatus having an engine (e.g., a marine vessel or an airplane).
  • the engine part according to the present invention is produced by sequentially forming an underlying plating layer and a chromium plating layer on a metal substrate having a predetermined shape.
  • the production method will be specifically described.
  • a metal substrate is immersed in a bath such as a water rinse bath, ultrasonic wave alkaline degreasing bath, electrolytic degreasing bath, or acid treatment activation bath for a predetermined period of time.
  • a bath such as a water rinse bath, ultrasonic wave alkaline degreasing bath, electrolytic degreasing bath, or acid treatment activation bath for a predetermined period of time.
  • an electroplating is conducted to sequentially form an underlying plating layer and a chromium plating layer at least on the outer surface of the metal substrate.
  • Both the underlying plating layer and the chromium plating layer are to be formed through electroplating, based on the same principle. Therefore, in the following description, only the step of forming the chromium plating layer will be specifically described by using the plating apparatus shown in FIG. 7 , whereas the step of forming the underlying plating layer will be described without referring to any figures.
  • the underlying plating layer is formed by immersing the aforementioned metal substrate in a plating trough containing a solution of a metal from which a plating layer is to be formed, and applying power until reaching a desired thickness.
  • a plating trough containing a solution of a metal from which a plating layer is to be formed, and applying power until reaching a desired thickness.
  • the metal substrate which has been washed in the aforementioned manner is immersed in a semigloss nickel plating solution, a tri-nickel plating solution, and a gloss nickel plating solution, and power is applied until the respective desired plating layers are obtained.
  • the specific plating conditions will depend on the metal substrate to be used, plating solution composition, purpose, and the like.
  • the conditions which are usually used for Ni-chromium plating can be selected as appropriate.
  • the temperature of the plating solution to be about 40 to 65° C.
  • the pH of the plating solution to be about 2 to 5.
  • the plating time is preferably about 10 to 20 minutes for semigloss nickel plating as well as gloss nickel plating, and about 1 to 5 minutes for tri-nickel plating.
  • a strike nickel layer may be further provided between the underlying plating layer and the metal substrate.
  • a chromium plating apparatus 20 includes a chromium plating trough 11 in which to perform chromium plating, a pump 12 for pumping up a plating solution which has been introduced to the chromium plating trough 11 , a percolator 13 for removing impurities which are suspended in the plating solution, an adjustment valve 14 for adjusting the flow rate of the plating solution, and a flowmeter 15 for monitoring the flow rate of the plating solution.
  • an ion exchange apparatus 16 for removing the metal ions (such as Fe) contained in the plating solution is provided on the downstream end of the chromium plating apparatus 20 .
  • the chromium plating apparatus 20 and the ion exchange apparatus 16 are connected to each other via a metal tube (not shown).
  • the chromium plating trough 11 is filled with a trivalent chromium plating solution.
  • the plating solution contains basic chromium sulfate which converts to 30 to 40 g/l of chromium.
  • the trivalent chromium plating solution has a boric acid content in a range from 1 to 5 g/l as converted to a boron amount, and an Fe content of 0.5 mg/l or less.
  • the boric acid content is reduced to about 1/15 to 5 ⁇ 6 as compared to the amount of boron that is added to a typical conventional trivalent chromium plating solution (about 6 to 15 g/l).
  • a typical conventional trivalent chromium plating solution about 6 to 15 g/l.
  • a typical conventional trivalent chromium plating solution contains about 0.0001 to 0.0003 mass % of ferrous sulfate as an additive, in order to enhance the throwing power and the like of the plating layer. Therefore, when using a conventional trivalent chromium plating solution, the chromium plating layer contains about 2 to 20 mass % of Fe. However, it is preferable that the trivalent chromium plating solution to be used in the present invention does not contain such an additive, and the Fe content is restricted to 0.5 mg/l or less.
  • the trivalent chromium plating solution to be used in the present invention contains citric acid or a citrate compound, as converted to a citric acid amount in a range from 5 to 30 g/l.
  • citrate compounds citrates such as potassium citrate or metal citrate compounds such as nickel citrate can be used.
  • the amount of citric acid to be added is preferably no less than 10 g/l and no more than 25 g/l, and more preferably no less than 20 g/l and no more than 25 g/l.
  • the chromium plating is to be carried out via electroplating.
  • the chromium plating trough 11 is filled with the aforementioned trivalent chromium plating solution, and a metal substrate 17 which is to receive chromium plating is used as a cathode. Since chromium plating is to be performed while supplying chromium ions from the plating solution, an insoluble anode 18 which does not dissolve in a chromium plating solution is used as an anode.
  • the DC power source 19 is connected between the electrodes, and power is supplied therefrom.
  • the chromium ions contained in the chromium plating solution move toward the cathode side, i.e., the metal substrate 17 , where the ions are reduced to metal Cr and deposit.
  • the plating is preferably performed while placing the metal substrate in a position which will allow a chromium plating layer having a desired thickness to be formed.
  • a metal substrate such as a curved exhaust pipe
  • a Cr layer can be efficiently formed at the convex portion 9 a , which will be heated to a high temperature.
  • the thickness of the chromium plating layer can be controlled to be within a predetermined range.
  • the electrode positioning may be controlled, or an auxiliary electrode may be attached to control the current density or the like, for example, thus making it easier to form a predetermined chromium plating layer in regions which are to be heated to a temperature of 350° C. or above.
  • appropriate conditions may be selected according to the type and shape of the metal substrate which is used, the constitution of the plating solution, the thickness of the chromium plating layer, or the like. Especially in the case where no ferrous sulfate is contained in the plating solution, the throwing power of a plating layer will generally worsen, and therefore it is necessary to ensure a uniform current density by optimizing the electrode location, for example.
  • the boron contents in 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, plating time, stirring rate of the plating solution, etc., and in particular on the temperature of the plating solution.
  • the boron content in the chromium plating layer increases as the temperature of the plating solution increases. Therefore, in order to keep the boron amount in the chromium plating layer within the aforementioned range, it is preferable to control the temperature of the plating solution to be in a range from 25° C. to 30° C.
  • the iron ions which stray into the plating solution are to be removed by using the ion exchange apparatus 16 , which includes a cation exchange resin.
  • the cation exchange resin to be used for the present invention may be any resin that permits easy exchange with divalent metal cations such as Fe, without any particular limitations.
  • the specific removal method may be as follows. First, during the plating, the plating solution is regularly pumped up from the plating trough 11 by using the pump 12 , and suspended matter is removed by using the percolator 13 . Next, the plating solution from which the suspended matter has been removed is introduced into the ion exchange apparatus 16 , while adjusting the flow rate via the adjustment valve 14 , and metal cations such as Fe ions are removed by using the cation exchange resin. The flow rate of the plating solution is monitored with the flowmeter 15 . The plating solution which has been processed by the ion exchange apparatus 16 is regularly collected in order to check for Fe concentration.
  • the Fe concentration in the plating solution In order to reduce the Fe concentration within the chromium plating layer to 2 mass % or less as in the present invention, it is necessary to control the Fe concentration in the plating solution to be about 0.0001 mass % or less. Thus, removal by the ion exchange apparatus 16 is performed until the aforementioned range is satisfied.
  • the plating solution (recovered plating solution) from which Fe ions are thus removed exits the outlet of the ion exchange apparatus 16 , and is led through the tube path 24 , thus to be circulated to the plating trough 11 .
  • the recovered plating solution may be stored in an appropriate storage container (not shown), for example.
  • Patent Document 4 a technique of removing metal cations within a plating solution by using the ion exchange apparatus 16 is specifically described in Patent Document 4, for example, and such a technique is applicable to the method of the present invention.
  • various alterations thereof have also been proposed (e.g., Patent Document 5), which are also applicable to the method of the present invention.
  • the chromium plating layer after the plating has a surface roughness (Ra) of about 1 ⁇ m or less, and preferably a surface roughness of 0.2 ⁇ m or less. Therefore, after the plating, the chromium plating layer has sufficient luster, without the need to particularly finish up the surface.
  • Ni plating layer composed of a semigloss Ni plating layer, a tri-Ni plating layer, and a gloss Ni plating layer was formed by the following method.
  • the compositions of the plating solutions used for forming these plating layers are shown in Table 1. Note that the C and/or S contained in the tri-Ni plating solution was supplied from an additive other than a brightener.
  • plating conditions power was supplied at 10 to 12V (volts), 1800 to 2800 A (amperes).
  • Tri-Ni plating layer (thickness: about 1 to 5 ⁇ m)
  • plating conditions power was supplied at 3 to 3.5V (volts), 20 to 40 A (amperes).
  • plating conditions power was supplied at 10 to 12V (volts), 1800 to 2800 A (amperes).
  • a chromium plating layer was formed on the underlying plating layer (the chromium plating layer had a thickness of 0.3 ⁇ m).
  • the chromium plating solution four types of trivalent chromium plating solutions as described in Table 2 were used (Nos. 1 to 4). The components of the trivalent chromium plating solutions of Sample 1 to Sample 4 were identical except for different ferrous sulfate and boric acid contents.
  • each of these trivalent chromium plating solutions contained citric acid, and ferrous sulfate was added in amounts of 0 (Sample 1), 2.5 mg/l (Sample 2), mg/l (Sample 3), and 10 mg/l (Sample 4); or, as converted to Fe amounts, 0 (Sample 1), 0.05 mg/l (Sample 2), 0.1 mg/l (Sample 3), and 0.3 mg/l (Sample 4).
  • boric acid was added in amounts of 5 g/l (Sample 1), 5 g/l (Sample 2), 30 g/l (Sample 2), and 60 g/l (Sample 3).
  • the temperature of the plating solution was varied in a range from about 25 to 60° C.
  • the current density was varied in a range from about 10 to 30 A/dm 2 , while also adjusting the air agitation amount of the plating solution.
  • the Fe ions which strayed into the plating were removed by using an ion exchange apparatus having a cation exchange resin. Specifically, a plating solution was regularly fed to the ion exchange apparatus, and the Fe concentration within the plating solution was controlled to be within the range from 0 to 0.0001 mass %. As a result, in the case where the trivalent chromium plating solution of Sample 1 (Present Invention) was used, the Fe content in the chromium plating layer was 0.2 mass % at the most, when being measured along the thickness of the plating layer.
  • the respective chromium plating layers had Fe contents (maximum values) of 2.0 mass %, 7.0 mass %, and 15.0 mass % because Fe ion removal with an ion exchange apparatus was not performed.
  • chromium plating layer has a thickness in the range of no less than 0.25 mm but less than 0.5 mm.
  • chromium plating layer has a thickness in the range of no less than 0.20 mm but less than 0.25.
  • chromium plating layer has a thickness in the range of no less than 0.05 mm but less than 0.20 mm.
  • X: chromium plating layer has a thickness less than 0.05 mm.
  • boron is an indispensable component for ensuring stability of plating growth, and that good plating characteristics cannot be obtained from merely adding citric acid instead of boric acid. This effect, i.e., stable growth of plating which is realized by the addition of boron, was similarly observed irrespective of the Fe content in the plating layer.
  • chromium plating layers were formed in a manner similar to the aforementioned method by using the trivalent chromium plating solution of Sample 1, and their plating anticorrosiveness and plating abrasion resistance were measured according to the aforementioned method, based on the following standards.
  • ⁇ : rating number is no less than 9.0.
  • ⁇ rating number is no less than 8.0 but less than 9.0.
  • ⁇ rating number is no less than 7.0 but less than 8.0.
  • X: rating number is less than 7.0.
  • ⁇ Vickers hardness is 500 Hv or more.
  • ⁇ Vickers hardness is no less than 450 Hv but less than Hv.
  • ⁇ : Vickers hardness is no less than 350 Hv but less than Hv.
  • Table 4 also shows results of plating growth stability.
  • the boron content in the chromium plating layer in the range from 0.05 to 0.3 mass %.
  • the L* value was measured according to the method described in CIE 1976.
  • the color tone of a chromium plating layer which is obtained by using a hexavalent chromium plating solution is in a range from 70 to 80 in L* value.
  • a color tone similar to that of a chromium plating layer which is obtained from a hexavalent chromium plating solution has been obtained so long as the L* value is 68 or more.
  • ⁇ A color tone similar to that which is obtained by using hexavalent chromium is obtained, with a slightly lower metallic luster.
  • a trivalent chromium plating layer having a color tone similar to that obtained by using hexavalent chromium can be obtained by reducing the Fe amount in the trivalent chromium plating layer to 2.0 mass % or less and reducing the boron amount to 0.1 mass % or less. Note that, so far as color tone is concerned, better characteristics are obtained as the Fe content and boron content in the chromium plating layer are smaller.
  • chromium plating layers were formed in a manner similar to Experimental Example 1.
  • the thickness of a chromium plating layer can be adjusted by appropriately controlling the plating time depending on the size of the plating material used, and the like. In this Experimental Example, plating time was varied in a range of 0.3 to 5 minutes, thus changing the thickness of the chromium plating layer from 0.1 to 1.5 ⁇ m.
  • each of the aforementioned samples was placed in an atmospheric furnace, and after being heated under the conditions of 400° C. ⁇ 8 hours, occurrence of cracks after heating was examined by the same measurement method and evaluation standards as those used when examining occurrence of cracks observed immediately after plating.
  • Measurement method By using an optical microscope (magnification: ⁇ 400), cracks occurring in the chromium plating layer surface (about 10 mm ⁇ 10 mm) were observed.
  • the experimental results before heating indicate that hardly any cracks occurred while the chromium plating layer had a thickness in the range from 0.1 to 0.3 ⁇ m, even if the boron content in the chromium plating layer was increased to 1.5 mass %. Cracks were more likely to occur as the thickness of the chromium plating layer increased to 0.5 ⁇ m or above, and when the chromium plating layer had a thickness of 1.5 ⁇ m, cracks occurred irrespective of the boron content in the chromium plating layer.
  • the thickness of the chromium plating layer was varied in a range from 0.05 ⁇ m to 0.7 ⁇ m, and the degree of discoloration due to heating was evaluated.
  • Measurement method By using a spectrometric color difference meter (color analyzer TC-1800MK-II (Tokyo Denshoku)), the L* value, a* value, and b* value were measured, before and after heating, according to the method described in CIE 1976.
  • the values before heating are labeled as “L0* value”, “a0* value”, and “b0* value”, whereas the values after heating are labeled as “L1* value”, “a1* value”, and “b1* value”.
  • a color difference ⁇ E* value after heating was measured as follows.
  • the present invention is broadly applicable to a vehicle having an engine (e.g., a motorcycle or an all-terrain four-wheeled vehicle) and a transportation apparatus having an engine (e.g., a ship or an airplane).
  • a vehicle having an engine e.g., a motorcycle or an all-terrain four-wheeled vehicle
  • a transportation apparatus having an engine (e.g., a ship or an airplane).

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US20130071685A1 (en) * 2011-09-21 2013-03-21 Iwaki Film Processing Co., Ltd. Product and method for manufacturing the product
US20130213813A1 (en) * 2012-02-16 2013-08-22 Stacey Hingley Color Control of Trivalent Chromium Deposits
US20130220819A1 (en) * 2012-02-27 2013-08-29 Faraday Technology, Inc. Electrodeposition of chromium from trivalent chromium using modulated electric fields
US20140373516A1 (en) * 2013-06-19 2014-12-25 Dr. Ing. H.C. F. Porsche Aktiengesellschaft Discoloration protection
US11279112B2 (en) 2017-09-27 2022-03-22 Hitachi, Ltd. Coating laminated body and method for producing the same
US20220389607A1 (en) * 2019-12-18 2022-12-08 Atotech Deutschland GmbH & Co. KG Method for reducing the concentration of iron ions in a trivalent chromium eletroplating bath

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US20150050742A1 (en) * 2013-08-16 2015-02-19 Cdti Analysis of Occurrence of Corrosion Products with ZPGM and PGM Catalysts Coated on Metallic Substrates
JP6433277B2 (ja) * 2014-12-10 2018-12-05 株式会社シマノ チタン製部材
JP2015221944A (ja) * 2015-08-07 2015-12-10 日産自動車株式会社 クロムめっき部品及びその製造方法
CN105177649A (zh) * 2015-10-30 2015-12-23 姜少群 一种带有表面复合镀层的毛巾挂架
CA3058275A1 (fr) * 2017-04-04 2018-10-11 Atotech Deutschland Gmbh Procede commande de depot d'une couche de chrome ou d'alliage de chrome sur au moins un substrat
JP7342253B2 (ja) * 2019-10-31 2023-09-11 コヴェンティア ソチエタ ペル アツィオーニ 硫酸系、アンモニア不含三価クロム装飾めっきプロセス
EP3859053A1 (fr) * 2020-01-31 2021-08-04 COVENTYA S.p.A. Procédé de placage décoratif de chrome trivalent exempt d'ammonium à base de sulfate
JP7409998B2 (ja) * 2020-08-27 2024-01-09 日立Astemo株式会社 緩衝器および緩衝器の製造方法
WO2023095774A1 (fr) * 2021-11-29 2023-06-01 株式会社Jcu Composant plaqué de chrome et procédé pour la fabrication de celui-ci
JP7350965B1 (ja) * 2022-11-11 2023-09-26 株式会社Jcu クロムめっき部品及びその製造方法
JP7330349B1 (ja) 2022-11-11 2023-08-21 株式会社Jcu クロムめっき部品及びその製造方法

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JP4691029B2 (ja) 2011-06-01

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