JP2013064192A - Abrasion-resistant member made from aluminum alloy, and method for producing same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abrasion-resistant member made from an aluminum alloy.SOLUTION: The abrasion-resistant member made from an aluminum alloy comprises a base that comprises an aluminum alloy and a coating layer that coats at least a portion of the surface of the base, wherein the aluminum alloy has a residual hardness of 120 Hv or more as measured at room temperature after being retained in an air atmosphere at 400°C for 10 hours, and the coating layer is a crystalline Ni-P layer comprising Ni and NiP. The crystalline Ni-P layer is obtained by heating an Ni-P plating layer, which is formed on the surface of the base by electroless Ni-P plating, at a temperature of, for example, 300°C or higher. The crystalline Ni-P layer is imparted with a compressive residual stress. It is preferred that the aluminum alloy includes 1-7% of Fe, because the crystalline Ni-P layer having excellent adhesion properties can be obtained.

Description

  The present invention relates to an aluminum alloy wear-resistant member and a method for producing the same.

In the field of transportation equipment such as automobiles, motorcycles, and aircraft, with the recent heightening of environmental awareness, weight reduction effective for reducing fuel consumption or reducing CO ₂ emissions has been strongly promoted. For this reason, the member conventionally comprised with the steel material and the cast iron material is also being replaced by the aluminum alloy.

  In accelerating the replacement with such an aluminum alloy, not only the heat resistance but also the wear resistance, corrosion resistance, fatigue resistance strength and the like have recently been emphasized. Under such circumstances, for example, a description relating to an aluminum alloy wear-resistant member having a hard film formed on its surface is introduced in the following patent documents.

Japanese Patent No. 3009527 JP 2004-277784 A

Methods for forming a hard film or the like on an aluminum alloy include a dry process and a wet process. The dry process is a method of forming a hard film such as TiN, CrN, DLC, Al ₂ O ₃ or the like on the substrate surface by PVD, CVD, ion nitriding, thermal spraying or the like. The wet process is a method in which an aluminum alloy is immersed in a specific solution to form an anodic oxide film or various platings on the surface thereof.

  The film formed by the dry process has a Vickers hardness of about 1000 to 3000 Hv, and is harder than the film formed by the wet process. However, dry processes are low in mass productivity, and equipment costs and processing costs are high.

  On the other hand, if a wet process is used, it is easy to improve productivity and reduce costs. However, among hard coatings formed by a wet process, Cr plating (800 to 1000 Hv) excellent in wear resistance and the like is not environmentally preferable in terms of using hexavalent chromium. Composite plating (dispersion plating) is difficult to manage because the plating solution is unstable.

  In contrast to these plating methods, electroless Ni—P plating has relatively few environmental problems and is excellent in mass productivity. However, the Ni—P plating layer is not hard compared to a film formed by a dry process or Cr plating, and generally lacks wear resistance. Even a relatively hard Ni-P plating layer having a low P concentration has a Vickers hardness of 500 to 700 Hv. It is known that when the Ni—P plating layer is heated to 300 ° C. or higher, the maximum hardness is 900 to 1000 Hv and hardness comparable to Cr plating can be obtained. ) Was softened and the strength required for the member could not be secured. Further, when a large load is applied to the member, the Ni—P plating layer cannot follow the deformation of the base material, and cracks and peeling may occur in the Ni—P plating layer. Thus, conventionally, it has been difficult to ensure the wear resistance of the aluminum alloy member by the Ni-P plating layer.

  The present invention has been made in view of such circumstances, and provides an aluminum alloy member having improved wear resistance by Ni-P plating in consideration of mass productivity, production cost, environmental performance, and the like. For the purpose. Moreover, it aims at providing the manufacturing method collectively.

  The inventor has intensively studied to solve this problem, and succeeded in hardening the Ni—P plating layer formed on the surface of the substrate made of aluminum alloy without softening the substrate. By developing this result, the present invention described below has been completed.

《Aluminum alloy wear-resistant member》
(1) The aluminum alloy wear-resistant member of the present invention is an aluminum alloy wear-resistant member comprising a base made of an aluminum alloy and a coating layer covering at least a part of the surface of the base, The aluminum alloy has a residual hardness of 120 Hv or more measured at room temperature after being kept in an atmospheric atmosphere at 400 ° C. for 10 hours, and the coating layer is made of nickel (Ni) and phosphorus (P) and is crystalline. It consists of the crystalline Ni-P layer which is.

(2) The aluminum alloy wear-resistant member of the present invention (suitably referred to as “abrasion-resistant member”) is coated with a coating layer comprising a crystalline Ni—P layer, and has excellent wear resistance. Demonstrate sex. In addition, the wear-resistant member of the present invention can also exhibit excellent heat resistance, corrosion resistance, fatigue resistance, durability, and the like. However, the reason why the wear-resistant member of the present invention exhibits excellent characteristics is not necessarily clear. The current situation is considered as follows.

First, the crystalline Ni—P layer is different from an amorphous Ni—P plating layer (this is appropriately referred to as “amorphous Ni—P layer”) formed by electroless Ni—P plating or the like. Very hard. This crystalline Ni—P layer exhibits sufficient hardness according to the degree of crystallinity, not only when the P concentration is low, but also when the P concentration is high. This is presumably because the crystalline Ni—P layer has a composite structure in which a precipitated phase such as Ni ₃ P is dispersed in the crystallized Ni matrix.

  Next, a large compressive residual stress may be generated in the crystalline Ni—P layer. This compressive residual stress is considered to be generated due to the difference in thermal expansion between the coating layer and the substrate, the precipitation of crystalline Ni and Ni-P by heating the amorphous Ni-P layer, and the like. Specifically, when a member composed of a substrate and a coating layer is heated, the coating layer is similarly thermally expanded without being peeled off from the thermally expanding substrate. Crystalline Ni phase and Ni—P phase are precipitated from the amorphous Ni—P layer during the temperature rise or during the subsequent holding, but the coating layer mainly composed of the crystalline Ni phase and Ni—P phase is The coefficient of thermal expansion is different from that of the substrate. For this reason, in the temperature lowering process, a heat shrinkage difference occurs between them. As a result, it is considered that compressive residual stress was generated in the crystalline Ni-P layer having a smaller thermal expansion coefficient than that of the substrate.

  In the crystalline Ni-P layer on which such compressive residual stress is acting, cracks and the like are hardly generated. This not only contributes to the improvement of the wear resistance, but also contributes to the improvement of the corrosion resistance and the fatigue strength when a repeated load acts (improvement of fatigue resistance).

  By the way, even if the amorphous Ni—P layer is crystallized or subjected to high temperature heating that causes compressive residual stress in the crystalline Ni—P layer, the substrate exhibits sufficient residual hardness, and crystalline Ni—P The function of the P-layer holding and the wear-resistant member is ensured. Therefore, according to the wear-resistant member of the present invention, the substrate having excellent softening resistance and the crystalline Ni-P layer (coating layer) having excellent wear resistance act synergistically to provide excellent wear resistance. It is thought that will come out stably.

  In addition, since the wear-resistant member of the present invention is composed of a substrate and a coating layer excellent in high-temperature characteristics, it can exhibit sufficient wear resistance and strength even in a high-temperature environment.

<< Method for Producing Aluminum Alloy Wear Resistant >>
(1) The present invention can be grasped not only as the wear-resistant member described above but also as a manufacturing method thereof. That is, the present invention is a method for producing the above-described aluminum alloy wear-resistant member, wherein a plating step of forming an Ni-P plating layer on the substrate surface by bringing an electroless Ni-P plating solution into contact with the substrate surface; And a crystallization step of crystallizing the Ni-P plating layer by heating the Ni-P plating layer, and can be grasped as a method for producing an aluminum alloy wear-resistant member.

(2) According to the production method of the present invention, the amorphous Ni—P plating layer formed by electroless Ni—P plating on the surface of the substrate is heated at a predetermined temperature, whereby the above-described crystalline Ni—P is obtained. Layers can be easily formed. Therefore, according to this manufacturing method, there are few environmental problems, and the above-described wear-resistant member can be mass-produced efficiently and at low cost.

<Others>
(1) “Residual hardness” as used herein means the hardness of an object that has been subjected to a predetermined heating process, measured at room temperature with a Vickers hardness tester. More specific measurement conditions are an average value of hardness measured five times with respect to the cross section of the object using a micro Vickers hardness tester under the conditions of test load: 0.245 N and holding time: 20 seconds.

  In the case of the aluminum alloy according to the present invention, it is preferable that the residual hardness after being held in an atmospheric pressure atmosphere at 400 ° C. for 10 hours is 120 Hv or more, 130 Hv or more, 140 Hv, or 145 Hv or more. When measuring the residual hardness, the thermal history (usage history) of the aluminum alloy is basically not questioned. The residual hardness measured after applying the above heat treatment to the aluminum alloy with which the crystalline Ni—P layer is in close contact may be 120 Hv or more.

(2) “Residual stress” as used herein is defined based on the X-ray stress measurement method standard (X-ray Material Strength Division Committee of the Society of Materials Science (1997)). More specifically, the surface of the object is irradiated with characteristic X-ray Cu—Kα, and is determined by the sin ² ψ method from the obtained Ni (311) diffraction peak. The stress constant required for determining this residual stress was determined by the Young's modulus and Poisson's ratio of nickel.

  As described above, compressive residual stress acts on the crystalline Ni-P layer. Although the value of this compressive residual stress is not ask | required, it is preferable in it being 200 Mpa or more, 300 Mpa or more, and 900 Mpa or more. The residual stress acting on the crystalline Ni—P layer can be proportionally increased as the applied heating temperature is higher.

(3) The form, metal structure, processing stage, etc. of the aluminum alloy according to the present invention do not matter. For example, ingots, rapidly solidified powders, ribbons and crushed powders, compacts and billets, sintered materials and wrought materials (extruded materials, etc.), raw materials, and intermediate products It may be the final product.

(4) Unless otherwise specified, “x to y” in this specification includes the lower limit value x and the upper limit value y. Any numerical value included in the various numerical values or numerical ranges described in the present specification can be newly established as a new lower limit value or upper limit value such as “ab”.

It is a graph which shows the relationship between heating temperature and the hardness of a base | substrate. It is a graph which shows the relationship between heating temperature and the hardness of a coating layer. It is a graph which shows the relationship between heating temperature and the residual stress of a coating layer. It is an X-ray diffraction image of each coating layer. Base No. It is an external appearance photograph which shows a mode that electroless Ni-P plating was given to 11 aluminum alloy. Base No. It is an external appearance photograph which shows a mode that electroless Ni-P plating was given to the aluminum alloy of C3. Specimen No. after ball-on-disk test It is a figure which shows the cross-sectional shape of 1 wear scar. Specimen No. after ball-on-disk test It is a figure which shows the cross-sectional shape of 2 friction marks. Specimen No. after ball-on-disk test It is a figure which shows the cross-sectional shape of 3 friction marks.

  The contents described in this specification can be applied not only to the wear-resistant member of the present invention but also to the manufacturing method thereof. A component related to a manufacturing method can be a component related to an object if understood as a product-by-process. One or two or more components arbitrarily selected from the present specification can be added to the above-described components of the present invention. Which embodiment is the best depends on the target, required performance, and the like.

<Coating layer>
(1) Although the coating layer according to the present invention is composed of a crystalline Ni-P layer, this "crystalline" does not have to be a complete crystal of the entire coating layer. It suffices if there is a crystal part that can be detected by X-rays. Further, the component composition and metal structure of the crystalline Ni—P layer are not limited in the present invention. The metal structure of the crystalline Ni—P layer cannot be specified in general, but is considered to be composed of, for example, a crystal phase of Ni and a precipitated phase such as Ni ₃ P. This metal structure differs depending on the component composition, crystallinity, thermal history, etc. of the crystalline Ni-P layer.

  The amount of P in the crystalline Ni—P layer is appropriately adjusted according to the use, function, required specifications, etc. of the wear-resistant member. However, the crystalline Ni—P layer (especially when it passes through electroless Ni—P plating) is uniform when P is 1 to 13% when the whole is 100 mass% (hereinafter simply referred to as “%”). A stable plating layer is stably formed. That is, when P is too small, sodium hypophosphite or the like, which is a reducing agent, is small, reducing power is reduced, and plating is hardly deposited. If P is excessive, the plating solution becomes unstable, and plating can be difficult in practice. However, unlike the amorphous Ni—P plating layer, the crystalline Ni—P layer according to the present invention can exhibit sufficient hardness even if P is large.

(2) The crystalline Ni—P layer according to the present invention is a Ni—P plating layer formed on the surface of the substrate by electroless Ni—P plating, for example, 300 ° C. to 500 ° C., more preferably 350 to 450. Obtained by heating at ° C. The Ni—P plating layer as it is subjected to electroless Ni—P plating is amorphous, and the state can be maintained up to about 200 ° C. However, when the amorphous Ni—P plating layer is heated to 200 ° C. or higher, crystallization gradually proceeds. In accordance with this crystallization, the hardness of the crystalline Ni—P layer and the compressive residual stress acting on the crystalline Ni—P layer can also increase.

  Of course, the crystalline Ni—P layer can be obtained not only by electroless Ni—P plating but also by electrolytic Ni—P plating. Electroless Ni-P plating eutects P using sodium hypophosphite or the like as a reducing agent, while electrolytic Ni-P plating eutects P using sodium phosphite or the like. In electrolytic Ni-P plating, the current density tends to vary depending on the shape of the substrate, and it is not easy to control the amount of P to be eutectoid, the thickness of the plating, and the like. Therefore, the crystalline Ni—P layer according to the present invention is preferably formed from electroless Ni—P plating.

<< Formation of coating layer (production method of wear-resistant member) >>
The coating layer according to the present invention may be formed by any method, for example, by the following electroless Ni-P plating method.

(1) Cleaning process The cleaning process removes oil stains and the like adhering to the substrate surface by an oxide film formed on the substrate surface, machining or the like. By this cleaning step, the pretreatment of the next step can be performed efficiently, and the adhesion of the Ni—P plating layer can be improved.

  The cleaning process includes, for example, an etching process for removing the oxide film by bringing the substrate into contact with an alkaline solution, and a desmutting process for removing smut generated after the etching process with an acidic solution. The kind of alkaline solution or acidic solution, their concentration, etc. are adjusted as appropriate. If the cleaning process is performed by chemical polishing or electrolytic polishing instead of these processes, the substrate surface can be smoothed.

(2) Pretreatment process (zincate treatment process, activation process)
An aluminum alloy is a difficult-to-plat material, and even when the cleaning process is performed, when it comes into contact with the atmosphere, a dense and strong oxide film is immediately formed and becomes inactive, and the formation of the Ni-P plating layer is likely to be hindered.

  Therefore, when plating is performed on an aluminum alloy, a zincate treatment is often performed as a pretreatment step. The zincate treatment is a treatment in which a substrate is brought into contact with a zincate solution (for example, a sodium hydroxide aqueous solution in which zinc oxide is dissolved) to form zinc replacement plating serving as an intermediate film on the surface of the substrate. By performing this zincate treatment, a Ni—P plating layer having excellent adhesion can be easily formed on the substrate surface. In particular, when the zincate treatment is performed twice or more, a Ni—P plating layer with high adhesion is easily obtained. Accordingly, the zincate treatment is also effective in the present invention as one of the pretreatments for plating.

  However, when electroless Ni-P plating is performed after the zincate treatment, most of the zinc forming the intermediate film is eluted in the plating solution. For this reason, the plating solution is contaminated, and the life of the expensive plating solution is shortened, which is uneconomical.

  Therefore, it is preferable to perform an activation process that can directly plate the substrate surface without performing a zincate treatment. This activation step is a step of activating the substrate surface by bringing a treatment liquid having a pH of 3 to 12 into contact with the substrate surface. The treatment liquid (activation treatment liquid) includes an acid activation treatment liquid or an alkaline activation treatment liquid. Examples of the acid activation treatment liquid include aqueous solutions of hydrochloric acid, hydrofluoric acid, acidic ammonium fluoride, and the like. Examples of the alkaline treatment liquid include aqueous solutions of sodium hydroxide, sodium carbonate, ammonium hydroxide, various amines, and the like. Of course, this activation step is preferably performed after the cleaning step. However, when an acidic activation treatment solution is used, the activation step may also serve as the above-described cleaning step.

  Incidentally, the significance of the activation process is as follows. When electroless plating is performed on an aluminum-based substrate, aluminum as an element does not have a catalytic activity for initiating a reaction of a reducing agent, and thus the electroless plating reaction is not automatically started. However, a practical aluminum-based base material contains elements such as iron and nickel having catalytic activity as impurities or additive elements. If these elements can be exposed on the surface of the aluminum-based substrate, the electroless plating reaction can be automatically started. However, in an aluminum-based base material that has undergone a cleaning process such as degreasing, etching, and acid dipping, the surface is covered with a passive film (aluminum oxide), and the above-mentioned active sites composed of precipitates such as iron and nickel are present. Not fully exposed. Even if the aluminum-based substrate at this stage is added to the electroless plating solution, the plating reaction is not started. Therefore, as the passive film disappears due to the activation process after the cleaning process, the exposure of the active sites proceeds. When the immersion potential is shifted from -1.4 to -1.35 V (vsAg / AgCl), the exposure (activation) of the active sites becomes sufficient, and the electroless plating is automatically performed even on the aluminum-based substrate. To be started.

  It is sufficient that the activation process itself is performed for several minutes, but it may be performed twice or more as necessary. In any case, it is important that the substrate surface is sufficiently activated by this activation step. This determination can be made based on the natural (standard) electrode potential of the activated substrate. The natural electrode potential is measured by, for example, immersing the activated substrate and the Ag / AgCl electrode in an alkaline aqueous solution (measurement solution) adjusted to pH 11.5, and immediately measuring the natural electrode potential of the substrate with a potentiometer. To do. When the natural electrode potential shifts from -1.4 to -1.35 V, the substrate surface is determined to be in an active state suitable for plating. In short, an activation step of bringing the activation treatment solution into contact with the substrate surface may be performed until the natural electrode potential of the substrate reaches a desired value.

  In addition, if the activation conditions under which the natural electrode potential becomes a desired value can be determined, it is not necessary to measure the natural electrode potential every time, and the activation process may be repeated under the conditions. Incidentally, when measuring the natural electrode potential, the measurement liquid to be used can be used together with the activation treatment liquid. In addition, the activation process is described in detail in Japanese Patent No. 2648716.

(3) Plating step A Ni-P plating layer is formed on the pretreated substrate surface by the plating step. This Ni-P plating layer is efficiently formed by using an electroless Ni-P plating solution. The composition of the electroless plating solution, the temperature of the plating solution, the plating time, and the like are adjusted as appropriate.

  Note that the Ni—P plating layer immediately after plating is amorphous and does not necessarily have high adhesion. In order to enhance this adhesion, the substrate after the plating step may be heated at 200 ° C. for about 1 hour, separately from the next crystallization step.

(4) Crystallization process The amorphous Ni-P plating layer formed on the substrate surface by the crystallization process becomes a crystallized hard crystalline Ni-P layer. In this crystallization step, it is preferable to heat the Ni—P plating layer basically at 300 to 500 ° C., preferably 350 to 450 ° C. The heating time at this time may be about 0.5 to 10 hours.

<Substrate>
The substrate is made of an aluminum alloy that does not soften even when heated in the crystallization process. The aluminum alloy may have any softening resistance such that the residual hardness measured at room temperature after being held at 400 ° C. for 10 hours is 120 Hv or more, and the composition and manufacturing method thereof are not limited. For example, an aluminum alloy as described below is suitable.

<Composition of aluminum alloy>
(1) Fe
Fe is an element that increases the strength and hardness of the aluminum alloy. Specifically, an appropriate amount of Fe forms Al and an intermetallic compound (Al—Fe-based intermetallic compound: first compound phase) in the parent phase (α-Al phase). This first compound phase increases the strength and hardness of the aluminum alloy.

  When the entire aluminum alloy is 100% by mass (this description is omitted below), Fe is 1 to 7%, 3 to 6%, 4 to 6%, and further 4.5 to 5.5%. And preferred. If Fe is insufficient, sufficient strength and hardness cannot be obtained. If Fe is excessive, ductility is lowered, and if it is too high, moldability and workability become difficult.

  Note that Fe is not only effective for the strength of the aluminum alloy, but can also function as a catalyst element (activation element) in performing the above-described electroless Ni—P plating. That is, if Fe is partially exposed from the surface of the substrate after the activation process described above, the Ni—P plating layer starts to be formed starting from that portion. Therefore, by using an aluminum alloy containing Fe for the substrate, a Ni-P plating layer having excellent adhesion and uniformity can be formed. This tendency increases as the Fe content in the aluminum alloy increases in the range of 1% or more.

(2) Zr and Ti
Zr and Ti are important elements that form a second compound phase that enhances the heat resistance of the aluminum alloy in cooperation with Al. The aforementioned first compound phase is not necessarily thermally stable, and may undergo phase transformation, shape change (coarse), etc. when exposed to a high temperature atmosphere for a long time.

An appropriate amount of Zr and Ti form a Al- the L1 ₂ -type structure between Al (Zr, Ti) intermetallic compound (the second compound phase or precipitated phase). This second compound phase is consistent with the parent phase, appears near the boundary (interface) between the Al—Fe-based intermetallic compound and the parent phase, and is stable up to a high temperature range. More specifically, the second compound phase hardly undergoes phase transformation or coarsening at least at or below the temperature at which the precipitation started. The second compound phase precipitated in the vicinity where the first compound phase and the parent phase are in contact with each other stably causes the phase transformation and shape change of the first compound phase responsible for the strength and hardness of the aluminum alloy at high temperatures. Deterrence (so to pin). Thus, it is considered that an aluminum alloy exhibiting excellent softening resistance and heat resistance was obtained by the synergistic action of the first compound phase and the second compound phase.

  In this specification, “matching” means that the basic crystal structure of the second compound phase is the same as that of the parent phase, and the atomic plane or atomic row is connected without excess or deficiency at the boundary (interface) with the parent phase. If you are. However, although dislocations introduced in processing or the like can cause disorder of atomic sequences or point defects, these are excluded.

By the way, the second compound phase is in the form of nanoparticles, and it is also known that the Zr concentration is high in the central part and the Ti concentration is high in the outer part. That is, it is also known that the concentration of Zr and Ti in Al ₃ (Zr, Ti) is inclined from the center to the outer shell. For the formation of such a second compound phase, it is preferable that more Zr is present than Ti and the mass ratio of Zr to Ti (Zr / Ti) is within a predetermined range.

  Therefore, Zr is preferably 0.5 to 3%, 0.66 to 1.5%, 0.7 to 1.3%, and further 0.8 to 1.2%. Ti is preferably 0.5 to 3%, 0.6 to 1%, and more preferably 0.7 to 0.9%. When Zr or Ti is too small, the effect is reduced, and when Zr or Ti is excessive, the melting temperature becomes extremely high and the production cost is increased, and coarse crystallized products or precipitates are formed with Al. Or the workability and formability of the aluminum alloy tend to be reduced.

  And when both mass ratio (Zr / Ti) is 1.1-1.5 and also 1.15-1.4, a stable aluminum alloy is easily obtained to a high temperature range by formation of a 2nd compound phase. Become.

  In order to finely disperse the second compound phase in the parent phase in the vicinity of the boundary of the first compound phase, Zr and Ti are sufficiently dissolved in the matrix (supersaturated solid solution) and precipitated later. Just do it. Specifically, after a suitable amount of Zr and Ti are dissolved in supersaturation by rapid solidification, energy serving as a driving force for promoting the precipitation may be applied. Examples of such energy include thermal energy applied by heat treatment and hot working, strain energy applied by plastic working, and the like. Thermal energy may be applied alone by heat treatment, or thermal energy and strain energy may be applied simultaneously by hot working or the like. Furthermore, heat energy may be applied after introducing strain energy, such as performing heat treatment after cold working or warm working. By adding strain energy to thermal energy, precipitation of the second compound phase is accelerated, and a heat-resistant and high-strength aluminum alloy can be efficiently obtained within a short time.

(3) Mg
Mg is an element effective for improving the strength (particularly the room temperature strength) of the aluminum alloy. Mg is preferably 0.5 to 5%, 0.6 to 2.2%, 1 to 2%, and further 1.2 to 1.8%. If Mg is too small, the effect is not obtained, and if it is excessive, workability and formability of the aluminum alloy material are lowered.

(4) Based on the above-described contents, the aluminum alloy according to the present invention has, for example, Fe: 3 to 6%, Zr: 0.66 to 1.5%, Ti: 0 when the whole is 100%. It is preferable to have an alloy composition that is 6 to 1%, a mass ratio of Zr to Ti (Zr / Ti): 1.1 to 1.5, and the balance: Al and inevitable impurities and / or modifying elements.

  The “reforming element” here is an element other than Al, Fe, Zr, Ti, and Mg, and is an element effective for improving the characteristics of the aluminum alloy. The properties to be improved are not limited by type, but include strength, hardness, toughness, ductility, dimensional stability, etc. at high temperatures or room temperatures. Specific examples of such modifying elements include Cr, Co, manganese (Mn), nickel (Ni), scandium (Sc), yttrium (Y), lanthanum (La), vanadium (V), hafnium (Hf), There is niobium (Nb). The composition of each element is arbitrary, but the content is usually very small.

  “Inevitable impurities” are impurities contained in the melted raw material, impurities mixed in at each step, etc., and are elements that are difficult to remove due to cost or technical reasons. Examples of the aluminum alloy according to the present invention include silicon (Si).

<Metal structure of aluminum alloy>
The above-described aluminum alloy includes an Al matrix (α phase), an Al—Fe intermetallic compound phase (first compound phase), and an Al— (Zr, Ti) intermetallic compound (second compound phase). It consists of at least a complex tissue.

  The average size of the second compound phase is preferably 1 to 30, 2 to 20 nm, and more preferably 3 to 15 nm. Whether the size is too small or too large, the effect of improving the heat resistance of the aluminum alloy by the second compound phase can be lowered. The average size was obtained by observing a sample randomly extracted from the aluminum alloy with a transmission electron microscope (TEM) and analyzing the average diameter of 30 or more dispersed second compound phases by an image processing method. Value.

<Method for producing aluminum alloy>
(1) Various methods for producing the aluminum alloy as described above are conceivable. For example, it may be a method for producing an aluminum alloy comprising a solidification step for obtaining a solidified body obtained by rapidly solidifying a molten alloy at a cooling rate of 100 ° C./second or more and a heat treatment step for heating the solidified body at, for example, 300 to 500 ° C. . This heat treatment step is a hot working step in which the solidified body is subjected to plastic working in a hot manner, and it is possible to obtain a metal structure in which the above-mentioned second compound phase is dispersed in an ultrafine and uniform manner in the matrix. It is.

  The rapidly solidified solidified body is in a state where Zr and Ti are supersaturated in the matrix. When this raw material is subjected to hot plastic working, not only a processed material created in a desired shape is obtained, but also heat energy and strain energy are applied to the solidified body sequentially or simultaneously, so that precipitation of the second compound phase occurs. Promoted. Thus, an aluminum alloy having excellent heat resistance in which not only the first compound phase but also a large number of second compound phases are precipitated in the matrix phase can be easily obtained. And it is not necessary to perform the aging treatment etc. which require a long time for precipitation of a 2nd compound phase, and it becomes possible to obtain an aluminum alloy efficiently at low cost. Of course, the second compound phase may be precipitated by heat treatment (for example, aging treatment).

(2) The cooling rate of the solidified body is preferably as high as possible. For example, it is preferably 100 ° C./second, 300 ° C./second or more, 1000 ° C./second or more, 5000 ° C./second or more, further 10,000 ° C./second or more. Thereby, a solidified body (raw material) in which Zr and Ti necessary for the generation of the second compound phase are supersaturated can be easily obtained.

  Such rapid solidification can be performed by, for example, an atomizing method, a spray forming method, a strip casting method (roll casting method, or the like). According to the atomization method, a powdery solidified body (atomized powder in which atomized particles are aggregated) is obtained. According to the spray forming method, a massive solidified body is obtained. According to the continuous casting method, a solidified body made of a ribbon is obtained.

  The size of the solidified body is not limited, but if it is atomized particles, for example, the average particle size is about 50 to 300 μm, and if it is a thin piece, for example, the thickness is about 0.05 to 1.5 mm and about 5 to 8 mm square. preferable.

  The raw material may be such a solidified body itself. However, when using atomized powder (water atomized powder, gas atomized powder, water / gas atomized powder) or crushed powder consisting of thin pieces obtained by crushing or pulverizing thin strips as a raw material, productivity, etc. This is preferable.

(3) Hot plastic working includes extrusion, forging, rolling, and sintering forging. For example, in the case of extrusion processing in which a billet is extruded by hot forming to obtain an extruded material (processed material), it is preferable that the extrusion temperature of the billet is 350 to 500 ° C, further 400 to 480 ° C. If the extrusion temperature is too low, the precipitation of the second compound phase and the heat resistant temperature of the aluminum alloy will be insufficient. Further, the processing force increases, which is not preferable. On the other hand, when the extrusion temperature is excessive, the metal structure is coarsened, and the heat resistance of the aluminum alloy can be lowered.

  The billet extrusion ratio is preferably 5-30, more preferably 10-20. If the extrusion ratio is too small, the pressure contact between the powder particles or the crushed pieces becomes insufficient, the desired strength and ductility cannot be obtained, and if the extrusion ratio is too large, the processing force increases and molding becomes difficult.

  In addition, the relative density (bulk density / true density) of the billet used for extrusion molding or the like is not limited, but is preferably 60% or more, 70% or more, 80% or more, 85% or more, and further 90% or more. If the relative density is too small, the shape retention and handling properties of the billet are reduced. The upper limit of the relative density is not limited, but 95% or less is preferable in consideration of productivity.

<Others>
In addition to the above-described aluminum alloy, an aluminum alloy having excellent softening resistance described in, for example, Japanese Patent Application Laid-Open No. 2007-92117 and Japanese Patent Application Laid-Open No. 2011-42861 can be used for the base of the wear-resistant member.

<Application>
The wear-resistant member of the present invention does not ask the use or use environment. However, since the wear-resistant member of the present invention has excellent wear resistance, it is suitable for a sliding member that comes into contact with other members or fluid (liquid, gas). Specifically, a piston, an impeller, an intake valve, a connecting rod, a rotor, and the like. In particular, since the substrate according to the present invention is excellent in heat resistance and softening resistance, it is suitable for a member used in a high temperature environment. Specifically, the wear resistant member of the present invention is suitable for a piston of an internal combustion engine, an impeller of a supercharger, and the like. In addition, it is preferable that the wear-resistant member of the present invention is used for a compressor, a shaft, a roller, a pipe, a brake cylinder, an AT transmission device part, a mold, a screw, and the like.

<< Manufacture of wear-resistant parts >>
<Substrate>
Of the many aluminum alloys shown in Table 1 having excellent softening resistance, the base material No. selected as an example was used. A substrate (test piece) made of 11 aluminum alloy (Al-5% Fe-1% Zr-0.85% Ti-1.5% Mg) was prepared. By the way, this substrate is a material obtained by extruding a material extruded at 430 ° C. to a diameter of 50 mm into a disk shape of φ30 mm × thickness 3 mm. “%” Means mass% unless otherwise specified.

<Coating layer>
(1) Cleaning step The substrate was alkali-etched with an aqueous sodium hydroxide solution (concentration 50 g / L) to remove the oxide film formed on the surface of the substrate (etching step). After this was washed with water, the smut formed on the surface of the substrate was removed with an aqueous nitric acid solution (concentration 30%) and further washed with water (desmutting step). In this way, the substrate surface was cleaned (cleaning step).

(2) Activation process The cleaned base | substrate was further immersed in the sodium carbonate aqueous solution of pH 11.5, and the activation process was carried out. This activation process was continued until the standard (natural) electrode potential of the substrate was shifted to -1.4 to -1.35 V (vsAg / AgCl). The standard electrode potential was measured with a potentiometer after immersing the substrate after activation treatment and the Ag / AgCl electrode in the measurement solution. Thus, a pretreatment was carried out for direct plating without carrying out the zincate treatment.

(3) Plating step The pretreated substrate was immersed in a 90 ° C. plating solution for 60 minutes. A commercially available electroless nickel phosphorus plating solution (Okuno Pharmaceutical Co., Ltd. Top Nicolon BL) was used as the plating solution. Thus, a Ni—P plating layer was formed on the surface of the substrate.

(4) Heating process (crystallization process)
The plated substrate was placed in a heating furnace and heated in an atmospheric pressure atmosphere for 1 hour. The heating temperature was 200 ° C, 300 ° C, 350 ° C, 400 ° C and 450 ° C. Thus, a plurality of test pieces having different heating temperatures were obtained.

(5) Comparative Example Base No. of Table 1 C1 and substrate No. Commercially available aluminum alloys (A2618 and A6061) shown in C2 were also prepared. The above-described treatment was performed in the same manner for the bases made of these aluminum alloys.

<Measurement>
(1) Hardness of substrate and coating layer Test specimens having different heating temperatures were cut, respectively, and the hardness of the substrate portion and the coating layer portion of the cut surface was measured at room temperature using a micro Vickers hardness tester (MVK-E manufactured by Akashi Corporation). It measured using. Under the present circumstances, the average value which measured 5 times was calculated | required by making test load: 0.245N and holding time: 20 second. The results are shown in FIGS. 1 and 2, respectively. In FIG. Only the hardness of the coating layer measured for the test piece consisting of 11 was shown, but similar results were obtained for the test pieces consisting of other substrates.

(2) Residual stress of coating layer The residual stress which appeared on the surface (Ni-P plating layer) of the test piece from which heating temperature differs was measured. This measurement was performed based on the X-ray stress measurement method standard (Japan Society for Materials X-ray Material Strength Division Committee (1997)). Specifically, an X-ray diffraction pattern of a test piece was obtained by a parallel beam method and a parallel tilt method using a sample horizontal strong X-ray diffractometer (RINT-TTR manufactured by Rigaku Corporation) (X-ray source: Cu -Kα, output: 50 kV-300 mA). Based on this X-ray diffraction pattern, the residual stress σ was calculated by the sin ² ψ method.
σ = K · Δ (2θ) / Δ (sin ² ψ)
_{K = {E · cotθ 0/} 2 (1 + ν)} · (π / 180)
E: Young's modulus of Ni (202000 MPa),
ν: Poisson's ratio of Ni (0.306),
θ ₀ : Standard Bragg angle (diffraction angle when ψ = 0 deg.)
The results thus obtained are shown in FIG. In this figure, “+” means tensile stress and “−” means compressive stress.

<Evaluation>
(1) Hardness of substrate As apparent from FIG. The substrate consisting of 11 hardly changed in hardness even when heated to 450 ° C. More specifically, the hardness of the substrate was stable within the range of 160 to 170 Hv before and after the heating step, and only changed by about 10 to 15 Hv at most. Furthermore, the base material No. The substrate consisting of 11 showed a tendency to increase in hardness as it was heated at a high temperature.

  Incidentally, the hardness (residual hardness) of the substrate after heating at 400 ° C. after the plating step is 165 Hv. It was almost equivalent to the residual hardness of the 11 aluminum alloy simple substance.

  On the other hand, the base material No. C1 and substrate No. When the substrate made of C2 was heated to 200 ° C. or higher, the hardness decreased rapidly. And the hardness (residual hardness) after heating at 400 degreeC became smaller than 80Hv. In any case, the base No. C1 and substrate No. The substrate composed of C2 had a residual hardness of less than 120 Hv and even less than 100 Hv after heating at 400 ° C.

(2) Hardness of coating layer As is clear from FIG. 2, the hardness of the (electroless) Ni-P plating layer formed on the surface of the substrate in the plating step hardly changes up to 200 ° C., and is about 500 Hv. there were.

  However, when heated above 200 ° C., the Ni-P plating layer suddenly increases in hardness. When heated to 300 ° C., the hardness is 1000 Hv, and when heated to 350 ° C., the hardness is 1180 Hv, 400 ° C. The hardness when heated was 1300 Hv.

  Thus, when the Ni-P plating layer is heated to a certain temperature or more, the hardness is abruptly changed because the structure of the Ni-P plating layer is changed. Specifically, it is considered that the Ni-P plating layer changed from an amorphous state to a crystalline state (crystalline Ni-P layer). This can be understood from the measurement result of the residual stress described below.

(3) Crystallinity and residual stress of the coating layer When the surfaces of the Ni-P plating layer before heating and the Ni-P plating layer after heating at 200 ° C. were measured using X-rays as described above, X-ray diffraction The peak was broad, and it was found that both the Ni-P plating layers were in an amorphous state. An X-ray diffraction image of the Ni—P plating layer showing these is shown in FIG. On the other hand, in the case of the Ni—P plating layer heated at 350 ° C., 400 ° C., and 450 ° C., a clear X-ray diffraction peak appeared, and it was found that both the Ni—P plating layers were in a crystalline state. In particular, when heated at 400 ° C. or higher, strong diffraction peaks of Ni and Ni ₃ P were observed.

  As is apparent from FIG. 3, a compressive residual stress of 900 to 1200 MPa is generated on the surface of these Ni—P plating layers, and it was also found that the compressive residual stress increases in proportion to the heating temperature. For example, when the Ni—P plating layer was heated at 400 ° C., a high compressive residual stress of 1017 (MPa) was generated. The residual stress on the surface of the Ni—P plating layer having a broad X-ray diffraction peak could not be accurately evaluated by the above-described method. Therefore, as a reference, when the residual stress on the surface of the Ni-P plating layer before heating was measured with a Brenner Senderoff Contracto Meter type electrodeposition stress meter, it was found to be a tensile residual stress state (reference value: 12 MPa). (Reference: A. Brenner and S. Senderoff; plating, 36, 810, (1949)).

<< Observation >>
(1) Substrate No. 11 and base No. Electroless nickel phosphorous plating was performed on a 10 × 70 × 1 mm plate-like substrate made of a C3 (A1050) aluminum alloy substrate by the method described above. The appearance photographs of these test pieces are shown in FIGS. 5A and 5B, respectively. None of the test pieces were heated after plating.

(2) As is apparent from FIG. In the case of No. 11 test piece, it was found that a uniform Ni—P plating layer having good adhesion was formed without peeling or swelling on the plating surface.

  On the other hand, as is clear from FIG. In the case of the C3 test piece, swelling or the like occurred on the plating surface, and the Ni-P plating layer had poor adhesion.

  The difference in the adhesion of the Ni-P plating layer is considered to be because the component composition of the base material is different. Base No. 11 contains about 5% of Fe. C3 is industrial pure aluminum and does not substantially contain Fe as an impurity (Fe: 0.40% or less / JIS).

  Base No. In the case of the test piece consisting of 11, it appears that Fe appeared on the surface by the cleaning process and the activation process, and the Ni-P plating layer having excellent adhesion was formed by the surface also serving as a catalyst. On the contrary, the base material No. In the case of the test piece made of C3, Fe did not appear on the surface even after the cleaning step and the activation step, and the base material itself did not perform a catalytic action, so it is considered that the adhesion failure of the Ni—P plating layer occurred. Therefore, when an activation process is performed, if an aluminum alloy containing catalytically active Fe, Ni, Pd, Mn, Co, or the like is used for the substrate, a wear-resistant member having a coating layer with excellent adhesion can be obtained. I can say that.

《Abrasion resistance》
In order to evaluate the wear resistance of the Ni-P plating layer formed on the aluminum alloy substrate, the base material No. 1 shown in Table 1 was used. 11 were used to prepare three types of test pieces shown in Table 2. These test pieces were subjected to a ball-on-disk test. The ball-on-disk test was performed by rotating the test piece while keeping a ball (JIS SUJ2) applied with a constant vertical load of 5 N in contact with the evaluation surface (sliding surface) of the test piece. At this time, the sliding speed of the test piece with respect to the ball was 20 cm / s, and the sliding distance was 600 m. This test was conducted in a room temperature atmosphere without lubrication.

  The wear scar depth obtained by measuring the surface of each test piece after this test with a surface roughness meter is also shown in Table 2. Moreover, the cross-sectional shape of the abrasion trace of each test piece after a test was shown to FIG. 6A-FIG. 6C. The thickness of the Ni—P plating layer before the ball-on-disk test was 10 μm.

  As is clear from these, test pieces No. 1 having a coating layer made of a Ni-P plating layer that was processed at a high temperature on a substrate having sufficient residual hardness. It was confirmed that No. 1 exhibited high wear resistance with almost no wear. On the other hand, in the other test pieces, the wear progressed deeply to the substrate side. From the above, the wear-resistant member composed of the base body and the coating layer belonging to the present invention has a synergistic effect of the excellent residual hardness of the base body made of an aluminum alloy and the heat-hardening characteristics of the Ni-P plating layer. It was found that excellent wear resistance was exhibited.

<Manufacture of base material>
An aluminum alloy (base material) suitable for the above-described substrate is obtained, for example, as follows. A molten aluminum alloy having the composition shown in Table 1 was prepared (melt preparation step). This molten alloy was sprayed in a vacuum atmosphere to obtain an air atomized powder (solidified body) (solidification step). The obtained air atomized powder particles (atomized particles) were classified to prepare atomized powder having a particle size of 150 μm or less. Incidentally, the relationship between the size of the powder particles obtained by air atomization and the cooling rate is known. Thereby, it can be said that the atomized powder consists of particles rapidly solidified at a cooling rate of 10 ⁴ ° C / second or more.

  The atomized powder was cold isostatically pressed (CIP) to obtain an extruded billet (raw material) having a diameter of 40 mm × 40 mm and a relative density of 85%.

  This extruded billet was loaded into a container (not shown) of the extruder. And the extrusion billet heated at 430 degreeC with the heating apparatus provided in the container was extrusion-molded, and obtained a (solid) bar (working material) of φ12 mm × 400 mm (hot plastic working / working process) . The extrusion ratio (cross-sectional area of the raw material / cross-sectional area of the processed material) at this time was 11.1. The following measurements were performed using samples collected from the aluminum alloy bar thus obtained.

<Measurement>
(1) Strength and ductility A tensile test was performed using a test piece cut out from each sample, and the strength and ductility at room temperature and the strength at 300 ° C. (no preheating) were measured. The results are also shown in Table 1. The tensile test is performed in accordance with JIS Z2241, the strength shown in Table 1 is the breaking strength, and the ductility is the rate of extension of the distance between the gauge points from the start of the test to the time of breaking.

(2) Measurement of residual hardness (softening resistance) The residual hardness of each sample (room temperature hardness after heating each sample at a high temperature) was also measured. Specifically, the Vickers hardness of each sample returned to room temperature after being held in an air atmosphere at 400 ° C. for 10 hours was measured. The measurement of Vickers hardness was performed in a room temperature environment using a Vickers tester with a load of 0.98 N and a holding time of 20 s.

<< Evaluation of substrate >>
As is apparent from Table 1, any aluminum alloy containing an appropriate amount of Fe or the like is excellent not only in initial characteristics at room temperature but also in high temperature characteristics. In particular, the high temperature strength tends to increase as the amount of Fe increases. Further, as the Zr amount or Ti amount was appropriate, the high temperature strength and softening resistance were excellent, and sufficient residual hardness was maintained even after heating to 400 ° C.

Claims (13)

A substrate made of an aluminum alloy;
A coating layer covering at least a part of the surface of the substrate;
An aluminum alloy wear-resistant member comprising:
The aluminum alloy has a residual hardness of 120 Hv or more measured at room temperature after being kept in an atmospheric atmosphere at 400 ° C. for 10 hours,
The coating layer is made of a crystalline Ni-P layer made of nickel (Ni) and nickel phosphide (Ni ₃ P);
An aluminum alloy wear-resistant member characterized by   2. The aluminum alloy wear-resistant member according to claim 1, wherein the crystalline Ni—P layer contains 1 to 13% of P when the whole is 100 mass% (hereinafter simply referred to as “%”).   3. The aluminum alloy product according to claim 1, wherein the crystalline Ni—P layer is formed by heating an amorphous Ni—P plating layer formed on the surface of the substrate by electroless Ni—P plating. 4. Wear-resistant member.   The aluminum alloy wear-resistant member according to any one of claims 1 to 3, wherein compressive residual stress is applied to the crystalline Ni-P layer.   The aluminum alloy wear-resistant member according to claim 1 or 4, wherein the aluminum alloy contains 1 to 7% of iron (Fe) when the whole is 100%. When the aluminum alloy is further 100% as a whole,
Zirconium (Zr) 0.5-3%,
Titanium (Ti) 0.5-3%,
An aluminum alloy wear-resistant member according to claim 5 comprising: When the aluminum alloy is further 100% as a whole,
The aluminum alloy wear-resistant member according to claim 6 containing 0.5 to 5% of magnesium (Mg). A method for producing an aluminum alloy wear-resistant member according to any one of claims 1 to 7,
A plating step in which an electroless Ni—P plating solution is brought into contact with the substrate surface to form a Ni—P plating layer on the substrate surface;
A crystallization step of heating the Ni-P plating layer to crystallize the Ni-P plating layer;
A method for producing an aluminum alloy wear-resistant member, comprising:   9. The pretreatment step according to claim 8, further comprising an activation step of activating the substrate surface by bringing a treatment liquid into contact with the substrate surface or a zincate step of performing a zincate treatment on the substrate surface before the plating step. A method of manufacturing an aluminum alloy wear-resistant member.   The method for manufacturing an aluminum alloy wear-resistant member according to claim 9, further comprising a cleaning step of cleaning the surface of the substrate before the pretreatment step. The cleaning step is an etching step of removing the oxide film by bringing the substrate into contact with an alkaline solution;
The method for producing an aluminum alloy wear-resistant member according to claim 10, comprising: a desmutting step of removing smut generated after the etching step with an acidic solution. The substrate is
A solidification process for obtaining a solidified body obtained by rapidly solidifying a molten alloy;
A heat treatment step for heating the solidified body;
The manufacturing method of the wear-resistant member made from an aluminum alloy in any one of Claims 8-11 which consists of an aluminum alloy obtained through these.   The method of manufacturing an aluminum alloy wear-resistant member according to claim 12, wherein the heat treatment step is a hot working step of performing plastic working on the solidified body hot.