Aluminum alloy, bar-like material, forge-formed article, machine-formed article, wear-resistant aluminum alloy with excellent anodized coat using the same and production methods thereof

Abstract

An aluminum alloy containing 5 to 12% (mass %; similarly applicable hereinafter) of Si, 0.1 to 1% of Fe, less than 1% of Cu and 0.3 to 1.5% of Mg and having the valance formed of Al and impurities is cast by a continuous casting process. When the cast mass consequently obtained is homogenized, then extruded and/or forged and/or machined and subjected to an anodizing treatment, the resultant formed article is endowed with excellent wear resistance because the anodized coat formed thereon in a thickness of 30 .mu.m or more with hardness Hv of 400 or more allows the presence therein of eutectic Si particles having particle diameters in the range of 0.4 to 5.5 .mu.m.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is an application filed under 35 U.S.C. .sctn.111(a) claiming the benefit pursuant to 35 U.S.C. .sctn.119(E)(1) of the filing date of Provisional Application No. 60/535,501 filed Jan. 12, 2004 pursuant to 35 U.S.C. .sctn. 111(b).

TECHNICAL FIELD

[0002] This invention relates to aluminum alloys, bar materials, forged parts and machined parts which are capable of providing sleeve parts for use in automobiles, require the hardness and thickness of an anodized coat, shun sustaining a crack and demand wear resistance; wear-resistant aluminum alloys using the aluminum alloys mentioned above and excelling in anodized coat hardness; sleeve parts; and methods for the production thereof.

BACKGROUND ART

[0003] Among other automobile parts, the casts of the ADC12, AC4C, A390 and Al--Si types and the alloys for the Al--Si type expanded materials of A4032 alloy have been hitherto formed by subjecting extruded materials and forged materials to the T6 treatment, the machining treatment and the anodizing treatment, and the parts consequently obtained have been put to use.

[0004] The casts of the Al--Si type and the alloys for the Al--Si type expanded materials have their Cu and Mg contents adjusted with the object of exalting the wear resistance and strength thereof.

[0005] Though the alloy materials mentioned above contain Cu in large amounts with a view to exalting their wear resistance and strength, they are supposed to encounter difficulty in acquiring the thickness and the hardness of an anodized coat.

[0006] The concept of limiting the Ni content as an impurity to less than 0.05% has been proposed (Patent Document 1 (JP-A HEI 10-204566), for example).

[0007] The material of Patent Document 1 is characterized by containing 6 to 12% (weight %, that is applied hereinafter) of Si, 0.1 to 1.0% of Fe, 1.0 to 5.0% of Cu, 0.1 ro 1.0% of Mn, 0.4 to 2.0% of Mg, 0.01 to 0.3% of Ti and 0.005 to 0.2% of Sr, limiting the content of Ni as an impurity to less than 0.05% and having the balance formed of Al and impurities, having dispersed in the matrix thereof eutectic Si particles of an average particle diameter of 1.5 to 5.0 .mu.m and allowing the presence therein of 5000 or more and less than 10000 eutectic Si particles of this average particle diameter per mm.sup.2.

[0008] However, the material disclosed in Patent Document 1, on being anodized, has formed a film having an unduly low hardness, specifically hardness Hv only in the approximate range of 310 to 370.

[0009] The conventional Al--Si type alloys, therefore, have been mostly such parts as are put to use without undergoing an anodizing treatment. The parts, that need an anodized coat and have an ability to form the coat, have been applied to products (portions) that have no need for the hardness of the coat. Thus, they have proved useful in markedly limited applications and have incurred difficulty in satisfying the demand of the market.

[0010] In the case of the 6000 type alloys and the 5000 type alloys that have a proper ability to succumb to an anodizing treatment, when the coat is applied in a thickness 30 .mu.m or more, the coat sustains a crack and the coated alloy product becomes no longer suitable for the intended use.

[0011] This invention, therefore, aims to provide aluminum alloys, bar materials, forged parts and machined parts which are capable of providing sleeve parts for use in automobiles, require the hardness and thickness of an anodized coat, shun generation of a crack and demand wear resistance; wear-resistant aluminum alloys using the aluminum alloys mentioned above and excelling in anodized coat hardness; sleeve parts; and methods for the production thereof.

[0012] With a view to accomplishing the object mentioned above, the present inventors have made a diligent study regarding the characteristic properties of the Al--Si type aluminum alloys and the anodized coats formed on the surfaces thereof. They have perfected this invention based on the knowledge acquired consequently.

DISCLOSURE OF THE INVENTION

[0013] The aluminum alloy according to this invention forms in consequence of an anodizing treatment an anodized coat having a thickness of 30 .mu.m or more and hardness Hv of 400 or more and allows the presence, in the coat, of eutectic Si particles having particle diameters in the range of 0.4 to 5.5 .mu.m.

[0014] Further, the aluminum alloy according to this invention forms in consequence of an anodizing treatment an anodized coat having a thickness of 40 .mu.m or more and hardness Hv of 400 or more and allows the presence, in the coat, of eutectic Si particles having particle diameters in the range of 0.8 to 5.5 .mu.m.

[0015] The aluminum alloy mentioned above contains 5 to 12% (mass %; similarly applicable hereinafter) of Si, 0.1 to 1% of Fe, less than 1% of Cu and 0.3 to 1.5% of Mg, and has the balance formed of Al and impurities, has dispersed in the matrix thereof eutectic Si particles having particle diameters in the range of 0.4 to 5.5 .mu.m, inclusive of 60% or more of the eutectic Si particles having particle diameters of 0.8 to 2.4 .mu.m, and allows the presence therein of 4000 or more and less than 40000 eutectic Si particles per mm.sup.2.

[0016] The aluminum alloy mentioned above, when containing 9 to 12% of Si, has 80% or more of the eutectic Si particles with particle diameters of 0.8 to 2.4 .mu.m.

[0017] The aluminum alloy mentioned above consists in substantially no Cu.

[0018] The aluminum alloy mentioned above consists in containing at least one component selected from among 0.1 to 1% of Mn, 0.04 to 0.3% of Cr, 0.04 to 0.3% of Zr, and 0.01 to 0.1% of V.

[0019] The aluminum alloy mentioned above consists in containing at least one component selected from among 0.01 to 0.3% of Ti, 0.0001 to 0.05% of B and 0.001 to 0.1% of Sr.

[0020] The aluminum alloy mentioned above consists in being a bar material cast by a continuous casting technique.

[0021] The aluminum alloy mentioned above in 9) the ninth aspect of the present invention consists in being a bar material obtained by subjecting a bar material cast by the continuous casting technique further to an extruding process or an extruding and drawing process.

[0022] The bar material according to this invention consists in being formed of an aluminum alloy.

[0023] The bar material of this invention consists in being used as a sleeve part.

[0024] The bar material of this invention consists in being a forged part formed by subjecting a bar material to a forging process.

[0025] The bar material of this invention consists in being a machined part formed by subjecting a bar material or a forced part to a machining process.

[0026] This invention further consists in being a wear-resistant aluminum alloy allowing the presence, in an anodized coat, of eutectic Si particles of particle diameters in the range of 0.4 to 5.5 .mu.m, forming the coat in a thickness of 30 .mu.m or more and with hardness Hv of 400 or more and consequently excelling in hardness of the anodized coat.

[0027] This invention also consists in being a wear-resistant aluminum alloy allowing the presence, in an anodized coat, of eutectic Si particles of particle diameters in the range of 0.8 to 5.5 .mu.m, forming the coat in a thickness of 40 .mu.m or more and with hardness Hv of 400 or more and consequently excelling in hardness of the anodized coat.

[0028] This invention consists in being a sleeve part resulting from subjecting a machined part to a treatment for forming an anodized coat and consequently excelling in hardness of the anodized coat.

[0029] Further, this invention consists in a method for the production of a wear-resistant aluminum alloy excellent in hardness of an anodized coat, comprising casting the aluminum alloy of the composition mentioned above to a continuous casting process, subjecting the resultant cast mass to a homogenizing treatment, extruding and/or forging and/or machining the homogenized cast mass and anodizing the resultant formed cast, thereby allowing the presence, in the anodized coat, of eutectic Si particles of particle diameters in the range of 0.4 to 5.5 .mu.m and forming the coat in a thickness of 30 .mu.m or more and with hardness Hv of 400 or more.

[0030] This invention also consists in a method for the production of a sleeve part excellent in hardness of an anodized coat and formed of an aluminum alloy, comprising casting an aluminum alloy of the composition mentioned above by a continuous casting process, subjecting the resultant cast mass to a homogenizing treatment, extruding and/or forging and/or machining the homogenized cast mass and anodizing the resultant formed cast, thereby allowing the presence, in the anodized coat, of eutectic Si particles of particle diameters in the range of 0.4 to 5.5 .mu.m and forming the coat in a thickness of 30 .mu.m or more and with hardness Hv of 400 or more.

[0031] The anodized coat produced as described above cannot form a crack. The thickness and hardness of the coat mentioned above do not represent mere target qualities, but indicate the qualities which can be attained by heeding and controlling the limits on the particle diameter distribution of eutectic Si particles in the anodized coat and the content of Cu therein.

[0032] This invention, as described above, concerns an aluminum alloy which allows the presence of eutectic Si particles having particle diameters in the range of 0.4 to 5.5 .mu.m in an anodized coat formed by an anodizing treatment and permits manufacture of sleeve parts furnished with an anodized coat excelling in hardness and possessing resistance to wear and other wear-resistant aluminum alloy products which can be properly utilized for automobile parts and other parts requiring the hardness and thickness of an anodized coat, shunning generation of a crack and demanding wear resistance.

[0033] This aluminum alloy acquires sufficient hardness without requiring any special anodizing treatment and, therefore, can be applied to parts that are put to use without being anodized in advance.

[0034] This invention concerns an aluminum alloy which allows the presence of eutectic Si particles having particle diameters in the range of 0.8 to 5.5 .mu.m in an anodized coat formed by an anodizing treatment and permits manufacture of sleeve parts furnished with an anodized coat excelling further in hardness and possessing wear resistance and other wear-resistant aluminum alloy products.

[0035] The aluminum alloy of this invention is characterized by containing 5 to 12% (mass %; similarly applicable hereinafter) of Si, 0.1 to 1% of Fe, less than 1% of Cu and 0.3 to 1.5% of Mg and having the balance formed of Al and impurities, having dispersed in the matrix thereof eutectic Si particles of particle diameters in the range of 0.4 to 5.5 .mu.m, inclusive of 60% or more of the eutectic Si particles existing with particle diameters of 0.8 to 2.4 .mu.m, and allowing the presence therein of 4000 or more and less than 40000 eutectic Si particles per mm.sup.2, thereby permitting manufacture of sleeve parts furnished with an anodized coat excelling further in hardness and possessing a wear resistance and other wear-resistant aluminum alloy products.

[0036] Further, the aluminum alloy of this invention, when containing 9 to 12% of Si, has 80% or more of the eutectic Si particles with particle diameters of 0.8 to 2.4 .mu.m and therefore permits manufacture of sleeve parts furnished with an anodized coat excelling further in hardness and possessing wear resistance and other wear-resistant aluminum alloy products.

[0037] The aluminum alloy of this invention contains substantially no Cu and therefore acquires a further exalted ability to undergo an anodizing treatment and permits provision of sleeve parts furnished with an anodized coat excelling further in hardness and possessing wear resistance and other wear-resistant aluminum alloy products.

[0038] The aluminum alloy of this invention contains one or two or more components selected from among 0.1 to 1% of Mn, 0.04 to 0.3% of Cr, 0.04 to 0.3% of Zr and 0.01 to 0.1% of V and, owing to the inclusion of Mn, Cr, Zr and V, induces precipitation of the Al--Mn type, Al--Mn--Fe--Si type, Al--Cr type, Al--Cr--Fe--Si type, Al--Zr type or Al--V type particles and thereby effects refinement of recrystallized particles, acquires exalted workability and permits formation of sleeve parts of complicated shapes and other wear-resistant aluminum alloy products. Further, the inclusion of Mn, Cr, Zr and V results in inducing precipitation of the particles of the Al--Mn type, Al--Mn--Fe--Si type, Al--Cr type, Al--Cr--Fe--Si type, Al--Zr type and Al--V type, suppressing recrystallization of the sleeve parts by a heat treatment given after the formation thereof and exalting the ductility and toughness of the sleeve parts.

[0039] The aluminum alloy of this invention contains at least one component selected from among 0.01 to 0.3% of Ti, 0.0001 to 0.05% of B and 0.001 to 0.1% of Sr and, when containing Ti and B, induces refinement of the texture of the cast mass, prevents the alloy mass from sustaining a crack during the course of forging, allows the aluminum alloy of this invention to be cast stably, further imparts exalted workability to the cast mass and permits manufacture of sleeve parts of complicated shapes. The inclusion of Sr results in allowing the eutectic Si particles to be refined and consequently enabling the aluminum alloy of this invention to acquire improvement in ductility and toughness.

[0040] The aluminum alloy of this invention is a bar material cast by a continuous casting process. This aluminum alloy, therefore, permits manufacture of sleeve parts excelling in hardness and possessing wear resistance and other wear-resistant aluminum alloy products.

[0041] The aluminum alloy of this invention is a bar material resulting from subjecting a bar material cast by a continuous casting process to an extruding process or an extruding and drawing process. Even when the subsequent process omits a forging step or comprises a forging step of a small processing ratio, it enjoys a sufficient processing ratio and acquires exalted ductility and toughness. It also permits easy manufacture of a bar material having a diameter of 20 mm or less which is not easily obtained by the continuous casting technique.

[0042] The formed article which uses the bar material of the aluminum alloy of this invention mentioned above constitutes a product excellent in hardness and possessing wear resistance.

[0043] The bar material of the aluminum alloy of this invention mentioned above permits manufacture of a sleeve part possessing an anodized coat of excellent hardness and excelling in wear resistance.

[0044] The bar material of the aluminum alloy of this invention mentioned above undergoes a forging treatment. The forged part consequently obtained permits manufacture of sleeve parts furnished with an anodized coat excelling in hardness and possessing wear resistance and other wear-resistant aluminum alloy products.

[0045] The bar material or forged part of the aluminum alloy of this invention mentioned above undergoes a machining treatment. The machined part consequently obtained permits manufacture of sleeve parts furnished with an anodized coat excelling in hardness and possessing wear resistance and other wear-resistant aluminum alloy products.

[0046] The aluminum alloy of this invention allows the presence, in an anodized coat, of eutectic Si particles of particle diameters in the range of 0.4 to 5.5 .mu.m and forms the coat in a thickness of 30 .mu.m or more and with hardness Hv of 400 or more. The aluminum alloy product consequently obtained, therefore, excels in hardness of the anodized coat and possesses wear resistance.

[0047] The aluminum alloy of this invention allows the presence, in an anodized coat, of eutectic Si particles of particle diameters in the range of 0.8 to 5.5 .mu.m and forms the coat in a thickness of 40 .mu.m or more and with hardness Hv of 400 or more. The aluminum alloy product consequently obtained, therefore, excels in hardness of the anodized coat and possesses wear resistance.

[0048] The machined part of the aluminum alloy of this invention has undergone a treatment for the formation of an anodized coat. It, therefore, constitutes a sleeve part that is furnished with an anodized coat excelling in hardness and possessing wear resistance.

[0049] Then, the method for the production of an aluminum alloy according to this invention comprises casting an aluminum alloy of the composition mentioned above in accordance with a continuous casting process, subjecting the resultant cast mass to a homogenizing treatment, extruding and/or forging and/or machining the homogenized cast mass and anodizing the resultant formed cast, thereby allowing the presence, in an anodized coat, of eutectic Si particles of particle diameters in the range of 0.4 to 5.5 .mu.m and forming the coat in a thickness of 30 .mu.m or more and with hardness Hv of 400 or more. The method, therefore, permits easy manufacture of wear-resistant aluminum alloy products excelling in hardness of an anodized coat.

[0050] Then, the method for the production of an aluminum alloy according to this invention comprises casting an aluminum alloy of the composition mentioned above in accordance with a continuous casting process, subjecting the resultant cast mass to a homogenizing treatment, extruding and/or forging and/or machining the homogenized cast mass and anodizing the resultant formed cast, thereby allowing the presence, in an anodized coat, of eutectic Si particles of particle diameters in the range of 0.4 to 5.5 .mu.m and forming the coat in a thickness of 30 .mu.m or more and with hardness Hv of 400 or more. The method, therefore, permits easy manufacture of sleeve parts excelling in hardness of an anodized coat.

BEST MODE FOR CARRYING OUT THE INVENTION

[0051] The aluminum alloy according to this invention is characterized by inducing in consequence of an anodizing treatment the formation of an anodized coat having a thickness of 30 .mu.m or more, preferably 40 .mu.m or more, and hardness Hv of 400 or more and the presence of eutectic Si particles of particle diameters in the range of 0.4 to 5.5 .mu.m, preferably 0.8 to 5.5 .mu.m, in the coat.

[0052] The aluminum alloy mentioned above, in one preferred example of the composition thereof, contains 5 to 12% (mass %; similarly applicable hereinafter, preferably 5 to 11%) of Si, 0.1 to 1% of Fe, less than 1% (preferably less than 0.5% and more preferably substantially no content) of Cu and 0.3 to 1.5% (preferably 0.4 to 1%) of Mg, and has the balance formed of Al and impurities.

[0053] The aluminum alloy mentioned above preferably contains at least one component selected from among 0.1 to 1% of Mn, 0.04 to 0.3% of Cr; 0.04 to 0.3% of Zr and 0.01 to 0.1% of V.

[0054] Preferably it further contains one or two or more components selected from among 0.01 to 0.3% of Ti, 0.0001 to 0.05% of B and 0.001 to 0.1% of Sr.

[0055] The aluminum alloy of this composition excels in workability and ability to yield to an anodizing treatment and acquires an ability to retain the hardness (Hv: 400 or more) of the anodized coat mentioned above.

[0056] It proves advantageous in respect that this aluminum alloy acquires sufficient hardness without undergoing any special anodizing treatment and therefore fits application to parts that are put to use without requiring an anodizing treatment.

[0057] Particularly, Si while coexisting with Mg induces precipitation of Mg.sub.2Si particles and exalts the strength of the aluminum alloy and, owing to the distribution of eutectic Si, adds to strength and wear-resistance. The Si content is in the range of 5 to 12%, preferably 5 to 11%. If the Si content falls short of 5%, the shortage will prevent this effect of Si from being manifested fully satisfactorily. If it exceeds 12%, the excess will result in inducing precipitation of a primary crystal of Si and exerting an adverse effect to bear on the ability to undergo an anodizing treatment.

[0058] The Fe content is preferred to fall in the range of 0.1 to 1% (preferably 0.1 to 0.5% and more preferably 0.21 to 0.3%). The reason for this range is that the Fe content is capable of inducing precipitation of the particles of the A--Fe type or A--Fe--Si type and, during the heat treatment after the formation of a sleeve part, repressing recrystallization and exalting the ductility and the toughness of the sleeve part. Then, in the extruded material, the Fe content is capable of refining recrystallized particles during the course of extrusion, exalting the forgeability of the material in the subsequent step and consequently permitting manufacture of sleeve parts of complicated shapes. If the Fe content falls short of 0.1%, the shortage will prevent the effect of Fe from being manifested satisfactorily. If it exceeds 1%, the excess will result in increasing the precipitation of coarse crystals of the A--Fe type or A--Fe--Si type, exerting an adverse effect to bear on the ability of the aluminum ally to succumb to an anodizing treatment and impairing the ductility and the toughness of the aluminum alloy.

[0059] The Cu content is less than 1% (preferably 0.9% or less and more preferably less than 0.5%) or substantially absent.

[0060] The inclusion of Cu results in inducing precipitation of CuAl.sub.2 particles and consequently contributing to the strength and hardness of the aluminum alloy. If the Cu content is 1% or more, the excess will result in decreasing the hardness of the anodized coat. For the purpose of further increasing the hardness of the coat, the Cu content is preferred to be less than 0.5% and more preferably to be substantially nil.

[0061] Cu is dissolved during the course of an anodizing treatment. Since the Cu ions formed by this dissolution are precious metal ions, Cu is precipitated again on the surface of the aluminum alloy matrix and is suffered to render the formation of an anodized coat difficult and degrade the denseness of the coat. By controlling the Cu content, it is made possible to exalt the formability and the denseness of the anodized coat and increase the hardness of the coat.

[0062] The coexistence of Mg and Si is effective in inducing precipitation of Mg.sub.2Si particles and contributing to the strength of the aluminum alloy. The Mg content falls preferably in the range of 0.3 to 1.5% and more preferably in the range of 0.4 to 1%. If the Mg content falls short of 0.3%, the shortage will result in decreasing the effect. If it exceeds 1.5%, the excess will results in lowering the workability of the aluminum alloy.

[0063] The inclusion of at least one component selected from among 0.1 to 1% (preferably 0.2 to 0.4%) of Mn, 0.04 to 0.3% (preferably 0.15 to 0.25%) of Cr, 0.04 to 0.3% (preferably 0.1 to 0.2%) of Zr and 0.01 to 0.1% (preferably 0.05 to 0.1%) of V in the composition of the aluminum alloy mentioned above is effective in inducing precipitation of the particles of the Al--Mn type, Al--Mn--Fe--Si type, Al--Cr type, Al--Cr--Fe--Si type, Al--Zr type or Al--V type, suppressing recrystallization during the heat treatment after the formation of a sleeve part and exalting the ductility and toughness of the sleeve part. Then, in the case of the extruded material, the inclusion is effective in refining the recrystallized particles during the course of the extrusion, exalting the forgeability of the extruded material in the subsequent step and consequently enabling the sleeve part to be formed in a complicated shape. If the Mn content falls short of 0.1%, the Cr content falls short of 0.04%, the Zr content falls short of 0.04% and the V content falls short of 0.01%, these shortages will result in preventing the effects of these elements from being manifested satisfactorily. If the Mn content exceeds 1%, the Cr content exceeds 0.3%, the Zr content exceeds 0.3% and the V content exceeds 0.1%, their excesses will result in adding to the precipitation of coarse crystals, exerting an adverse effect to bear on the ability of the aluminum alloy to succumb to an anodizing treatment and impairing the ductility and toughness of the aluminum alloy.

[0064] The inclusion of at least one component selected from among 0.01 to 0.3% (preferably 0.01 to 0.2% and more preferably 0.002 to 0.1%) of Ti, 0.0001 to 0.05% (preferably 0.005 to 0.1%) of B and 0.001 to 0.2% (preferably 0.005 to 0.1% and more preferably 0.005 to 0.05%) of Sr is favorable for the following reason. To be specific, the inclusion of Ti and B is effective in refining the texture of a cast mass, preventing the cast mass from being fractured during the course of casting and exalting the workability of the cast mass and consequently permitting sleeve parts to be formed in complicated shapes. If the Ti content falls short of 0.01%, the shortage will result in preventing the effects of its inclusion from being manifested sufficiently. If its content exceeds 0.3%, the excess will result in inducing crystallization of giant intermetallic compound particles and exerting an adverse effect to bear on the aluminum alloy's workability and ability to succumb to an anodizing treatment. Then, the inclusion of Sr is effective in refining the eutectic Si and exalting the aluminum alloy's workability and ability to succumb to an anodizing treatment. If the Sr content falls short of 0.001%, the shortage will prevent the effect of the inclusion from being manifested satisfactorily. If it exceeds 0.2%, the excess will result in degrading the effect.

[0065] The Ni content is preferred to be 0.1% or less.

[0066] In this invention, it has been found that the state of distribution of eutectic Si particles in an anodized coat is extremely important and further that the control thereof enables the coat to acquire a thickness of 30 .mu.m or more and hardness Hv of 400 or more and prevents the coat from generating a crack.

[0067] For this purpose, it is important to uniformly specify the state of dispersion of eutectic Si in an alloy matrix. The aluminum alloy can be precluded from sustaining a crack by allowing the presence of eutectic Si particles in the anodized coat and enabling the aluminum alloy to excel in hardness of the coat and acquire an increased thickness.

[0068] To be specific, the eutectic Si particles dispersed in the alloy matrix have particle diameters of 0.4 to 5.5 .mu.m (preferably 0.8 to 5.5 .mu.m). It is proper and necessary that 60% or more (preferably 80% or more) of the eutectic Si particles have particle diameters of 0.8 to 2.4 .mu.m and that the matrix allow the presence therein of 4000 or more and less than 40000 (preferably 10000 or more and less than 38000) eutectic Si particles per mm.sup.2.

[0069] Incidentally, the expression "the eutectic Si particles have particle diameters of 0.4 to 5.5 .mu.m" means that the substantial particle diameter distribution is in the range of 0.4 to 5.5 .mu.m. For example, it means that 95% or more, preferably 98% or more, of the eutectic Si particles have particle diameters falling in the range of 0.4 to 5.5 .mu.M.

[0070] The eutectic Si particles in the anodized coat have particle diameters of 0.4 to 5.5 .mu.m as described above. If the particle diameters fall short of 0.4 .mu.m, particularly 0.3 .mu.m, the shortage will result in heightening the voltage of the bath used for the anodizing treatment, increasing the resistance to the anodization, rendering the flow of electric current difficult and permitting no easy formation of the coat. If the particle diameters exceed 5.6 .mu.m, particularly 6.0 .mu.m, the excess will result in forming a cause for degrading the ability of the aluminum alloy to succumb to an anodizing treatment and aggravating the surface coarseness of the formed coat.

[0071] Of the eutectic Si particles, those that have particle diameters of 0.8 to 2.4 .mu.m account for a proportion of 60% or more as described above. If this proportion falls short of 60%, particularly within 50% inclusive, the shortage will result in increasing the difference between the portion allowing easy flow of electric current and the portion not allowing easy flow of electric current during the course of the anodizing treatment, disrupting the uniformity of flow of the electric current and consequently preventing the formed coat from acquiring a uniform thickness.

[0072] Particularly in the case of the Si content of 9 to 12% (especially 10.5.+-.0.5%) that finds a wide application for uses on the commercial scale, the proportion mentioned above is preferred to be 80% or more.

[0073] When the alloy matrix contains 4000 or more and less than 40000 eutectic Si particles of particle diameters of 0.8 to 2.4 .mu.m per mm.sup.2, the flow of the electric current during the course of the anodizing treatment is fixed and the produced coat is allowed to have a uniform thickness. Though the eutectic Si particles dispersed in the aluminum alloy matrix allow more difficult flow of electric current than the matrix, since the difficulty can be suppressed, the anodized coat can be formed in a uniform thickness. The degradation of the hardness of the coat can be suppressed further because the possibility of the eutectic Si surviving dissolution during the course of the anodizing treatment and persisting in the coat can be diminished and the possibility of the residual eutectic Si particles in the coat degrading the denseness of the coat surrounding the eutectic Si particles can be suppressed.

[0074] To be more specific, the aluminum alloy of the composition mentioned above is cast by the continuous casting process, such as the gas pressure hot top continuous casting process, the resultant cast mass is subjected to the homogenizing treatment, and the homogenized alloy mass is either directly machined or subjected to a proper processing selected from among extruding, forging and machining operations. By further subjecting the resultant formed aluminum alloy to the anodizing treatment, it is made possible to obtain an aluminum alloy product which excels in hardness of the anodized coat and allows the coat to acquire an increased thickness without sustaining a crack.

[0075] The state of the generation of the eutectic Si in the alloy is affected by the temperature of the melt of the alloy and the speed of casting while the melt of the alloy of the given composition is solidified by the continuous casting process.

[0076] The aluminum alloy contemplated by this invention, therefore, can be obtained by controlling the temperature of the melt and the speed of casting, thereby enabling the eutectic Si particles to acquire particle diameters in the range of 0.4 to 5.5 .mu.m. Further, by controlling the temperature of the melt and the speed of casting, thereby enabling 60% or more of the eutectic Si particles to possess particle diameters of 0.8 to 2.4 .mu.m, it is made possible to obtain the aluminum alloy aimed at by this invention.

[0077] It is provided, however, that the speed of solidification must be controlled to a rather higher level than ever because the aluminum alloy of this invention has a small Cu content, forms a small region of solid-liquid coexistence during solidification, and becomes liable to solidify. In the case of a forging diameter of 72 mm, for example, the speed of solidification is preferred to be in the range of 200 to 350 mm/min.

[0078] The gas pressure hot top continuous casting process presses the gap between the melt and the mold with a gas and therefore permits the speed of casting to be increased. It is, therefore, at an advantage in permitting easy production of the aluminum alloy of this invention having the particle diameters of the eutectic Si controlled in a given state.

[0079] The state of generation of the eutectic Si in the alloy succumbs to the influences of the temperature of homogenization and the time of homogenization during the course of the homogenizing treatment and controls the particle diameter of the eutectic Si and controls the shape of the eutectic Si particles as well.

[0080] By controlling the temperature of homogenization and the time of homogenization, thereby enabling the eutectic Si particles to assume particle diameters in the range of 0.4 to 5.5 .mu.m, therefore, it is made possible to obtain the aluminum alloy of this invention. Further, by controlling the temperature of homogenization and the time of homogenization, thereby enabling 60% or more of the eutectic Si particles to assume particle diameters of 0.8 to 2.4 .mu.m, it is made possible to obtain the aluminum alloy of this invention.

[0081] Owing to the assumption of a granular form by the eutectic Si particles, the cast mass is enabled to have the workability thereof exalted as compared with the acerate form prior to the anodizing treatment. Further, the ability of the aluminum alloy to succumb to an anodizing treatment is exalted.

[0082] The homogenizing treatment does not need to be particularly restricted but is only required to satisfy the conditions mentioned above. It may be properly carried out at a temperature of 450.degree. C. or more and lower than 500.degree. C. (preferably 480.degree. C. or more) for a period of four hours or more.

[0083] The primary crystal Si is preferred to be in the following state (position of distribution of particles, average particle diameter, and ratio of occupation of area) or to be substantially absent from the outer peripheral part of the cast mass which is destined to form a sleeve part in consequence of an anodizing treatment. If the primary crystal Si is present in the part subjected to the anodizing treatment, it will prevent the flow of electric current from being fixed during the course of the anodizing treatment, render the thickness of the coat uneven, decrease the denseness of the coat and lower the hardness of the coat.

[0084] Position of distribution of particles of primary crystal Si: Absent of the primary crystal Si from the outer periphery of the cast mass through the position of 20% or less of the radius of the cast mass (0.2% or less of the ratio of occupation of area).

[0085] Average particle diameter of primary crystal Si: 30 .mu.m or less.

[0086] Ratio of occupation of area by primary crystal Si: 0.8% or less.

[0087] For example, the procedure of setting the Si content at 12% or less and controlling the conditions of the amount of gas pressure, the speed of casting and the temperature of the melt during the course of a gas pressure hot top continuous casting operation is at an advantage in enabling the primary crystal Si to assume the state mentioned above.

[0088] The aluminum alloy mentioned above may be cast through the continuous casting process to form cast billets and the cast billets may be subjected to a homogenizing treatment and then machined directly without being modified. Otherwise, the cast billets may be subjected to properly selected processes, such as extruding, forging and machining operations. Alternatively, the aluminum alloy may be cast to manufacture bar materials and the bar materials may be manufactured into formed articles having given shapes.

[0089] The manufacture of bar materials into formed articles may be accomplished by properly combining various processes, such as machining and forging operations. The bar materials are preferred to undergo an extruding or drawing process prior to the forging or machining process. The bar materials which have undergone the extruding or drawing process are at an advantage in enjoying exalted ductility and excelling in workability and imparting ductility to end products. While round bars measuring 20 mm or less in diameter are not easily obtained by the continuous casting method, they can be easily obtained through the extruding or drawing process.

[0090] The extruding process does not need to be particularly restricted but may be properly attained by using an extruding device of 2500 tons, for example, and extruding a given bar material at the highest extruding rate of 8 m/min.

[0091] The anodizing treatment that is performed on a formed article does not need to be particularly restricted but may be properly accomplished by using an aqueous 15-wt % sulfuric acid solution as the electrolytic bath.

[0092] The coat may be obtained in a given thickness by adjusting the temperature of the bath, the electric voltage and the time of the treatment.

[0093] The aluminum alloy of this invention and the sleeve parts manufactured therefrom can be effectively used in sleeve portions of more exacting requirements because their matrix parts excel in hardness and their coats enjoy an exalted ability to resist wear. They are suitable for the following uses, for example.

[0094] (a) Compressor parts, such as scrolls and pistons, for use in air conditioning devices.

[0095] (b) Compressor pistons for use in automobile air suspensions.

[0096] (c) Automobile engines, transmissions and ABS grade hydraulic parts, such as spools and sleeves.

[0097] (d) Brake master cylinder pistons/caliper pistons for automobiles

[0098] (e) Clutch cylinder pistons for automobiles

[0099] (f) Brake caliper bodies for automobiles

[0100] The wear-resistant aluminum alloy that is consequently obtained does not restrict the uses to be found therefor. Among other automobile parts, it is particularly suitable for brake caliper pistons, air suspension quality compressor pistons and other parts that require a coat excelling in hardness and defying infliction of a crack.

[0101] Examples of this invention will be explained below in contrast with Comparative Examples.

[0102] Test 1

EXAMPLE 1

[0103] The aluminum alloys having the compositions shown in Table 1 were manufactured by the gas pressure hot top continuous casting method into cast billets (8 inches in diameter). These cast billets were subjected to a homogenizing treatment at 490.degree. C. for 12 hours and extruded by an indirect extruding device to form extruded bars 44 mm in diameter. The extruded bars were subjected to a T6 treatment performed by an ordinary method. The extruded bars resulting from this treatment were used as test materials and were tested for ability to succumb an anodizing treatment, hardness of coat, presence or absence of the occurrence of a crack in the coat, wear resistance and mechanical properties based on the standards shown below. The results of the test were rated. The test materials were further tested for determining the cross section, eutectic Si particles in an anodized coat and state of distribution of particle diameters by the use of an image analysis system under the following conditions.

[0104] The determination was performed by cutting a given sample in an arbitrary size, embedding the cut sample in an abrading resin, micro-abrading the resin till eutectic Si particles became detectable and visually examining the abraded surface.

[0105] Conditions of determination: LUZEX joined to an optical microscope, magnifications on a picture plane: 1240, and calculated from the results of a continuous determination of 20 fields of view.

[0106] Thickness of coat: 44 to 47 .mu.m

[0107] In the data shown in Table 1, those that deviated from the conditions conforming to this invention are indicated with an underline.

[0108] Rating of Test 1

[0109] "Ability to Succumb to an Anodizing Treatment"

[0110] A cross section of a given extruded bar perpendicular to the direction of extrusion was cut till it formed a smooth surface having a fixed surface roughness. The cross section was used as a sample for rating the ability.

[0111] For the anodizing treatment, an aqueous 15-wt % sulfuric acid solution was used as the electrolytic bath and the anodizing treatment was performed, with the bath temperature, voltage and time so set as to form an anodized coat of a target thickness of 40 .mu.m on the sample surface.

[0112] The cross section of the sample consequently obtained was visually observed and measured for coat thickness with arbitrary 10 mm lengths. The ability of the sample to succumb to the anodizing treatment was rated by the average thickness of the actually formed coat. The thickness of the coat formed under the same conditions served as the index for the ability to succumb to the anodizing treatment. The results are shown in Table 3.

[0113] .smallcircle.: Average coat thickness of 40 .mu.m or more

[0114] x: Average coat thickness of 33 .mu.m or less

[0115] .DELTA.: Intermediate between .smallcircle. and x.

[0116] "Coat Hardness"

[0117] The determination was performed by cutting a given sample which had undergone an anodizing treatment in an arbitrary size, embedding the cut sample in a resin, micro-abrading the resin till the coat thickness became detectable, and determining and rating the hardness of the coat. The results are shown in Table 3.

[0118] .smallcircle.: Average coat hardness Hv of 400 or more

[0119] x: Average coat hardness Hv of 330 or less

[0120] .DELTA.: Intermediate between .smallcircle. and x.

[0121] "Wear Resistance"

[0122] A given sample was tested for wear resistance by the use of an Ogoshi abrasion tester under the conditions of 1 m/s in speed of abrasion, 200 m in distance of abrasion, 3.2 kg in load and S50C (Hv 750) in opposite material. The results were compared in terms of the relative amount of wear. The results are shown in Table 2.

[0123] .smallcircle.: Less than 6.0.times.10.sup.-7 mm.sup.2/kg

[0124] x: More than 9.0.times.10.sup.-7 mm.sup.2/kg

[0125] .DELTA.: 6.0 to 9.0.times.10.sup.-7 mm.sup.2/kg

[0126] "Crack in Coat"

[0127] A given sample that had undergone an anodizing treatment had the surface condition thereof observed under an optical microscope to determine and rate the presence or absence of a crack in the coat. The results are shown in Table 3.

[0128] .smallcircle.: Absence of a crack in the coat.

[0129] x: Presence of a crack in the coat.

[0130] "Mechanical Properties"

[0131] A JIS No. 4 test piece was taken from the central part of an extruded material in parallel to the direction of extrusion and tested for tensile strength. The passage of the commendable tensile strength: 310 (N/mm.sup.2) and proof strength: 230 (N/mm.sup.2) was taken as the standard. The results are shown in Table 2.

EXAMPLES 2 TO 13 AND COMPARATIVE EXAMPLES 1 TO 10

[0132] The same procedure as in Example 1 was repeated, with the compositions changed as shown in Table 1. The conditions of forming an anodized coat were the same as in Example 1.

[0133] It is clear from Table 2 and Table 3 that Examples 1 to 13 of this invention invariably excelled in ability to succumb to an anodizing treatment, hardness of coat, freedom from infliction of a crack in the coat and wear resistance, and were possessed of tensile strengths exceeding 310 N/mm.sup.2 and proof strengths exceeding 230 N/mm.sup.2 as respect mechanical properties.

[0134] Comparative Example 1 was deficient in the ability to succumb to an anodizing treatment because it had a small Si content. Further, Comparative Examples 1, 2, 4, 5 and 8 were deficient in the ability to succumb to an anodizing treatment and in hardness of the coat because they had large Cu contents.

1 TABLE 1 Composition (mass %) Test material Si Fe Cu Mn Mg Cr Ti Sr Al Ex. 1 5.0 0.2 0.3 0.2 0.4 0.1 0.01 0.01 Balance Ex. 2 5.0 0.2 0.4 0.2 0.4 0.1 0.01 0.01 Balance Ex. 3 5.0 0.2 0.9 0.2 0.4 0.1 0.01 0.01 Balance Ex. 4 5.0 0.2 0.9 0.2 0.8 0.1 0.01 0.01 Balance Ex. 5 7.5 0.2 0.4 0.2 0.4 0.1 0.01 0.01 Balance Ex. 6 7.5 0.2 0.9 0.2 0.4 0.1 0.01 0.01 Balance Ex. 7 7.5 0.2 0.95 0.2 0.8 0.1 0.01 0.01 Balance Ex. 8 8.1 0.2 0.6 0.2 0.4 0.1 0.01 0.01 Balance Ex. 9 10.1 0.2 0.3 0.2 0.4 0.1 0.01 0.01 Balance Ex. 10 10.1 0.2 0.4 0.2 0.4 0.1 0.01 0.01 Balance Ex. 11 10.1 0.2 0.4 0.2 0.8 0.1 0.01 0.01 Balance Ex. 12 10.5 0.2 0.9 0.2 0.4 0.1 0.01 0.01 Balance Ex. 13 10.5 0.2 0.9 0.2 0.8 0.1 0.01 0.01 Balance Comp. Ex. 1 4.5 0.2 2.5 0.2 1.1 0.1 -- -- Balance Comp. Ex. 2 7.0 0.2 3.0 0.2 1.1 0.1 -- -- Balance Comp. Ex. 3 7.5 0.2 1.4 0.2 0.3 0.1 -- -- Balance Comp. Ex. 4 7.5 0.2 2.5 0.2 0.4 0.1 -- -- Balance Comp. Ex. 5 8.2 0.2 2.5 0.2 0.6 0.1 -- -- Balance Comp. Ex 6 10.2 0.2 1.6 0.2 0.1 0.1 -- 0.01 Balance Comp. Ex. 7 10.7 0.2 1.5 0.2 0.4 0.1 -- 0.01 Balance Comp. Ex. 8 10.5 0.2 2.7 0.2 0.4 0.1 -- 0.01 Balance Comp. Ex. 9* 0.7 0.2 0.3 -- 1.0 0.1 -- -- Balance Comp. Ex. 10* 0.8 0.2 0.4 0.2 1.0 0.2 -- -- Balance

[0135]

2TABLE 2 Tensile strength Proof strength Test material Wear resistance .sigma.'B (N/mm.sup.2) .sigma.0.2 (N/mm.sup.2) Ex. 1 .smallcircle. 312.0 234.0 Ex. 2 .smallcircle. 337.3 252.3 Ex. 3 .smallcircle. 343.3 240.6 Ex. 4 .smallcircle. 389.4 272.1 Ex. 5 .smallcircle. 343.5 241.5 Ex. 6 .smallcircle. 350.0 258.7 Ex. 7 .smallcircle. 359.3 271.3 Ex. 8 .smallcircle. 357.1 272.7 Ex. 9 .smallcircle. 342.6 249.2 Ex. 10 .smallcircle. 345.2 251.1 Ex. 11 .smallcircle. 346.2 255.3 Ex. 12 .smallcircle. 368.2 263.3 Ex. 13 .smallcircle. 369.2 273.4 Comp. Ex. 1 x 410.0 340.0 Comp. Ex. 2 .smallcircle. 435.0 330.0 Comp. Ex. 3 .smallcircle. 389.3 271.3 Comp. Ex. 4 .smallcircle. 387.1 272.7 Comp. Ex. 5 .smallcircle. 415.0 307.0 Comp. Ex. 6 .smallcircle. 398.3 302.8 Comp. Ex. 7 .smallcircle. 406.8 304.0 Comp. Ex. 8 .smallcircle. 405.0 307.0 Comp. Ex. 9 x 312.0 284.0 Comp. Ex. 10 x 289.9 252.3

[0136]

3 TABLE 3 Pro- portion of Ability Thick- Diameter of eutectic Number Distribution of diameters of eutectic Si particles (%) 0.8 to Hardness to yield ness Test Si particles (.mu.m) (pieces/ .gtoreq.0.8 .gtoreq.1.6 .gtoreq.2.4 .gtoreq.3.2 .gtoreq.4.0 .gtoreq.4.8 .gtoreq.5.5 5.6.ltoreq. 2.4 .mu.m of coat anodization of coat material Max. Min. Ave. mm.sup.2) (.mu.m) (.mu.m) (.mu.m) (.mu.m) (.mu.m) (.mu.m) (.mu.m) (.mu.m) (%) (Hv) treatment (.mu.m) Crack Ex. 1 4.32 0.80 2.20 9643 -- 16.7 46.6 28.2 7.5 1.0 -- -- 63.3 .smallcircle. 422 .smallcircle. 47.1 .smallcircle. Ex. 2 3.52 0.96 2.17 9740 -- 14.9 46.6 31.6 6.9 -- -- -- 61.5 .smallcircle. 412 .smallcircle. 46.5 .smallcircle. Ex. 3 4.96 0.80 2.18 9690 -- 16.3 44.2 27.9 7.0 2.3 2.3 -- 60.5 .smallcircle. 405 .smallcircle. 46.2 .smallcircle. Ex. 4 4.32 0.96 2.05 9830 -- 16.3 44.9 27.9 8.6 2.3 -- -- 61.2 .smallcircle. 403 .smallcircle. 41.3 .smallcircle. Ex. 5 4.80 0.96 2.12 18737 -- 21.4 45.8 24.2 6.7 1.6 0.3 -- 67.2 .smallcircle. 415 .smallcircle. 47.3 .smallcircle. Ex. 6 4.16 0.80 2.08 19245 -- 22.0 44.0 27.1 6.6 0.3 -- -- 66.0 .smallcircle. 403 .smallcircle. 46.7 .smallcircle. Ex. 7 4.16 0.80 2.06 22312 -- 19.6 46.1 23.5 9.8 1.0 -- -- 65.7 .smallcircle. 409 .smallcircle. 43.3 .smallcircle. Ex. 8 3.84 0.80 1.98 24415 -- 21.6 46.8 22.7 8.9 -- -- -- 68.4 .smallcircle. 401 .smallcircle. 41.1 .smallcircle. Ex. 9 4.16 0.80 1.93 31450 -- 31.7 46.8 18.9 2.5 0.1 -- -- 78.5 .smallcircle. 410 .smallcircle. 45.1 .smallcircle. Ex. 10 3.52 0.80 1.81 35543 -- 33.1 46.2 18.8 1.9 -- -- -- 79.3 .smallcircle. 413 .smallcircle. 44.9 .smallcircle. Ex. 11 3.36 0.80 1.85 33471 -- 34.7 46.4 17.7 1.2 -- -- -- 81.1 .smallcircle. 409 .smallcircle. 44.1 .smallcircle. Ex. 12 3.52 0.80 1.83 34768 -- 34.5 47.6 16.1 1.8 -- -- -- 82.1 .smallcircle. 402 .smallcircle. 44.4 .smallcircle. Ex. 13 3.35 0.80 1.87 32275 -- 34.7 47.7 15.7 1.9 -- -- -- 82.4 .smallcircle. 402 .smallcircle. 44.2 .smallcircle. Comp. 4.78 0.96 2.30 8698 -- 16.7 45.3 27.3 6.5 2.6 1.6 -- 62.0 x 325 .DELTA. 38.5 .smallcircle. Ex. 1 Comp. 4.75 0.92 2.17 18698 -- 19.4 44.6 25.6 7.5 2.9 -- -- 64.0 x 298 x 32.2 .smallcircle. Ex. 2 Comp. 4.58 0.90 2.18 21987 -- 21.4 44.2 25.3 8.3 0.8 -- -- 65.6 .DELTA. 381 .DELTA. 39.5 .smallcircle. Ex. 3 Comp. 4.51 0.96 2.05 22098 -- 21.6 45.6 24.5 7.6 0.7 -- -- 67.2 x 324 .DELTA. 39.1 .smallcircle. Ex. 4 Comp. 4.33 0.80 2.08 25349 -- 21.8 46.4 23.6 7.4 0.8 -- -- 68.2 x 322 .DELTA. 37.8 .smallcircle. Ex. 5 Comp. 3.63 0.80 1.93 32115 -- 33.2 46.6 18.7 1.5 -- -- -- 79.8 .DELTA. 365 .DELTA. 38.3 .smallcircle. Ex. 6 Comp. 3.56 0.80 1.81 35543 -- 32.8 46.8 18.8 1.6 -- -- -- 79.6 .DELTA. 374 .DELTA. 38.6 .smallcircle. Ex. 7 Comp. 3.45 0.80 1.85 33471 32.6 46.4 18.6 2.0 0.4 -- -- 79.0 x 313 .DELTA. 37.8 .smallcircle. Ex. 8 Comp. -- -- -- -- -- -- -- -- -- -- -- -- -- .smallcircle. 475 .smallcircle. 44.1 x Ex. 9 Comp. -- -- -- -- -- -- -- -- -- -- -- -- -- .smallcircle. 477 .smallcircle. 44.3 x Ex. 10

[0137] Comparative Examples 9 and 10 showed no discernible sign of eutectic Si particle.

[0138] The diameter and the distribution of eutectic Si particles are the results of measuring in a cross section.

4TABLE 4 Distribution of diameters of eutectic Si particles in anodized coat Distribution of Diameter of diameters of Proportion eutectic Number eutectic Si particles (%) of 0.8 to Test Si particles (.mu.m) (pieces/ .gtoreq.0.8 .gtoreq.1.6 .gtoreq.2.4 .gtoreq.3.2 .gtoreq.4.0 .gtoreq.4.8 .gtoreq.5.5 5.6.ltoreq. 2.4 .mu.m material Max. Min. Ave. mm.sup.2) (.mu.m) (.mu.m) (.mu.m) (.mu.m) (.mu.m) (.mu.m) (.mu.m) (.mu.m) (%) Ex. 3 4.86 0.80 2.11 9530 -- 16.7 44.4 27.9 6.9 2.0 2.1 -- 61.1 Ex. 6 4.06 0.80 2.02 19143 -- 22.4 43.6 28.1 5.8 0.1 -- -- 66.0 Ex. 12 3.32 0.80 1.80 34595 -- 35.2 48.1 15.7 1.0 -- -- -- 83.3

[0139] Test 2 (Bar Material Formed by Hot Top Continuous Casting, Bar Material Formed by Hot Top Continuous Casting+Forging)

[0140] An aluminum alloy having the composition shown in Table 5 was manufactured by the gas pressure hot top continuous casting method disclosed in JP-B SHO 54-42827 into bar materials of a diameter of 72 mm. The bar materials were then subjected to a homogenizing treatment at 490.degree. C. for four hours and subjected to a T6 treatment according to an ordinary method under the conditions shown in Table 6 (a solution treatment at 500 to 510.degree. C. for two to three hours, followed by water cooling and further by an aging treatment at 180 to 190.degree. C. for five to six hours) to obtain test materials. Otherwise, the continuous casting (continuously cast) bar materials were similarly subjected to a homogenizing treatment, then to a shaving treatment to remove the cast skin, cut to given lengths, and the cut lengths were subjected to an annealing treatment and a bonde treatment, and forged into double wall cups measuring 68 mm in outside diameter of the outer cup, 52 mm in inside diameter of the outer cup, 32 mm in outside diameter of the inner cup, 15 mm in inside diameter of the inner cup, 40 mm in height and 10 mm in bottom thickness. These double wall cups were subjected to a T6 treatment according to the ordinary method under the conditions shown in Table 8 (a solution treatment at 500 to 510.degree. C. for two to three hours, following by water cooling and further by an aging treatment at 180 to 190.degree. C. for five to six hours) to obtain forged parts as test materials. The test materials were further machined and thereafter tested for ability to succumb to an anodizing treatment, hardness of coat, the presence or absence of a crack in the coat, wear resistance and mechanical properties under the following standards. They were also tested for the cross section of test material, eutectic Si particles in the anodized coat and distribution of particle diameters by the use of an image analysis system under the conditions shown below.

[0141] The determination was performed through cutting a given sample in an arbitrary size, embedding the cut sample in a resin and micro-abrading the resin till eutectic Si particles became detectable.

[0142] Conditions of determination: Magnifications on a picture plane: 1240, and calculated from the results of a continuous determination of 20 fields of view.

[0143] Thickness of coat: 25 to 47 .mu.m

[0144] In the data shown in Table 5, those that deviated from the conditions conforming to this invention are indicated with an underline.

[0145] Test 3 (Bar Material Obtained by Horizontal Continuous Casting, Bar Material Obtained by Horizontal Continuous Casting+Forging)

[0146] An aluminum alloy having the composition shown in Table 5 was manufactured by the horizontal continuous casting method disclosed in JP-A SHO 61-33735 into bar materials of a diameter of 30 mm. The bar materials were then subjected to a homogenizing treatment at 490.degree. C. for four hours and to a T6 treatment according to an ordinary method under the conditions shown in Table 20 (a solution treatment at 500 to 510.degree. C. for two to three hours, followed by water cooling and further by an aging treatment at 180 to 190.degree. C. for five to six hours) to obtain test materials. Otherwise, the continuously cast bar materials were similarly subjected to a homogenizing treatment and then to a shaving treatment to remove the cast skin, and cut to given lengths, and the cut lengths were subjected to an annealing treatment and a bonde treatment, and forged into cups measuring 32 mm in outside diameter, 15 mm in inside diameter, 27 mm in height and 8 mm in bottom thickness. These cups were subjected to a T6 treatment according to the ordinary method under the conditions shown in Table 8 (a solution treatment at 500 to 510.degree. C. for two to three hours, following by water cooling and further by an aging treatment at 180 to 190.degree. C. for five to six hours) to obtain forged parts as test materials. The test materials were further machined and thereafter tested for ability to succumb to an anodizing treatment, hardness of coat, presence or absence of a crack in the coat, wear resistance and mechanical properties under the following standards. They were also tested for the cross section of test material, eutectic Si particles in the anodized coat and distribution of particle diameters by the use of an image analysis system under the conditions shown below.

[0147] The determination was performed by cutting a given sample in an arbitrary size, embedding the cut sample in a resin, micro-abrading the resin till eutectic Si particles became detectable.

[0148] Conditions of determination: magnifications on a picture plane of the image analysis system: 1240, and calculated from the results of a continuous determination of 20 fields of view.

[0149] Thickness of coat: 25 to 47 .mu.m

[0150] In the data shown in Table 5, those (Comparative Examples) that deviated from the conditions conforming to this invention are indicated with an underline.

[0151] Test 4 (Extruded Material/Drawn Material, Extruded Material/Drawn Material+Forging)

[0152] An aluminum alloy having the composition shown in Table 5 was manufactured using the gas-pressure hot top continuous casting method disclosed in JP-B SHO 54-42827 into billets (8 inches in diameter). Then, the cast billets were subjected to a homogenizing treatment at 490.degree. C. for four hours. Subsequently, the cast mass was heated to 350.degree. C. and then extruded by the use of an indirect extruding device to manufacture extruded bars 32 mm in diameter and subjected to a T6 treatment according to an ordinary method under the conditions shown in Table 20 (a solution treatment at 500 to 510.degree. C. for two to three hours, followed by water cooling, and further by an aging treatment at 180 to 190.degree. C. for five to six hours) to obtain extruded bars as test materials. Otherwise, the indirectly extruded bars were drawn into bars 39.2 mm in diameter, subjected to a T6 treatment by an ordinary method under the conditions shown in Table 6 (a solution treatment at 500 to 510.degree. C. for two to three hours, followed by water cooling and further by an aging treatment at 180 to 190.degree. C. for five to six hours) to obtain drawn bars as test materials. Alternatively, the drawn bars 39.2 mm in diameter manufactured from the extruded bars were cut into given lengths, subjected to an annealing treatment and a bonde treatment, and forged into cups measuring 32 mm in outside diameter, 15 mm in inside diameter, 27 mm in height and 8 mm in bottom thickness. These cups were subjected to a T6 treatment by the ordinary method under the conditions shown in Table 8 (a solution treatment at 500 to 510.degree. C. for two to three hours, followed by water cooling and further by an aging treatment at 180 to 190.degree. C. for five to six hours) to obtain forged parts as test materials, machined and subsequently tested for ability to succumb to an anodizing treatment, hardness of a coat, presence or absence of a crack in the coat, wear resistance and mechanical properties by the standard shown below. They were also tested for the cross section of test material, eutectic Si particles in the anodized coat and distribution of particle diameters by the use of an image analysis system under the conditions shown below.

[0153] The determination was performed by cutting a given sample in an arbitrary size, embedding the cut sample in a resin, micro-abrading the resin till eutectic Si particles became detectable.

[0154] Conditions of determination: Magnifications on a picture plane of the image analysis system: 1240, and calculated from the results of a continuous determination of 20 fields of view.

[0155] Thickness of coat: 25 to 47 .mu.m

[0156] In the data shown in Table 5, those that deviated from the conditions conforming to this invention are indicated with an underline.

[0157] Evaluation of Tests 2 to 4

[0158] "Ability to Succumb to Anodizing Treatment"

[0159] A cross section of a given extruded bar perpendicular to the direction of extrusion was cut till it formed a smooth surface having a fixed surface roughness. The cross section was used as a sample for rating the ability.

[0160] For the anodizing treatment, an aqueous 15-wt % sulfuric acid solution was used as the electrolytic bath and the anodizing treatment was performed with the bath temperature, electric voltage and time so set as to form an anodized coat of a target thickness of 30 .mu.m on the sample surface.

[0161] The cross section of the sample consequently obtained was visually observed and measured for coat thickness with arbitrary 10 mm lengths. The ability of the sample to succumb to the anodizing treatment was rated by the average thickness of the actually formed coat. The thickness of the coat formed under the same conditions served as the index for the ability to succumb to the anodizing treatment. The larger the thickness, the better the ability is. The results obtained of samples having undergone no forging treatment are shown in Table 7 and those obtained of samples having undergone a forging treatment are shown in Table 9.

[0162] .smallcircle.: Average coat thickness of 30 .mu.m or more

[0163] x: Average coat thickness of less than 30 .mu.m

[0164] While the preceding test 1 used a target thickness of 40 .mu.m, the present tests 2 to 4 used a target thickness of 30 .mu.m on account of the large total number of samples. Therefore, the standard for the rating was as shown above.

[0165] "Hardness of Coat"

[0166] The determination was performed through cutting a given sample in an arbitrary size, embedding the cut sample in a resin and micro-abrading the resin till eutectic Si particles became detectable. The hardness of the coat was measured and rated. The results of the samples that had not undergone a forging treatment are shown in Table 6 and those of the samples that had undergone the forging treatment are shown in Table 8.

[0167] "Wear Resistance"

[0168] A given sample was tested for relative wear resistance by the use of an Ogoshi abrasion tester under the conditions of 1 m/s in speed of abrasion, 200 m in distance of abrasion, 3.2 kg in load and S50C (Hv: 750) in opposite material. The results obtained of the sample that had not undergone any forging treatment are shown in Table 6 and those of the samples that had undergone the forging treatment are shown in Table 8.

[0169] .smallcircle.: Less than 6.0.times.10.sup.-7 mm.sup.2/kg

[0170] x: More than 9.0.times.10.sup.-7 mm.sup.2/kg

[0171] .DELTA.: 6.0 to 9.0.times.10.sup.-7 mm.sup.2/kg

[0172] "Crack in Coat"

[0173] A given sample that had undergone an anodizing treatment was visually observed through a magnifying mirror having 10 or more magnifications to confirm and rate the presence or absence of a crack. The results of the samples that had not undergone a forging treatment are shown in Table 7 and those of the samples that had undergone the forging treatment are shown in Table 9.

[0174] The results are shown in Table 3.

[0175] .smallcircle.: No crack in the coat

[0176] x: A crack found in the coat

[0177] "Mechanical Properties"

[0178] A JIS No. 4 test piece was taken from the central part of an extruded material in parallel to the direction of extrusion and tested for tensile strength. The passage of the commendable tensile strength of 310 N/mm.sup.2 and proof strength of 230 N/mm.sup.2 was taken as the standard. The results are shown in Table 6.

[0179] "Product Test, Brake Caliper Piston"

[0180] The continuously cast materials, extruded materials and drawn materials of Examples 101 to 104, 121 to 125, 141 to 144 and 150 to 153 having the compositions shown in Table 1 and the forced products thereof (Example 201 to 204, 221 to 225, 241 to 244 and 250 to 253) were manufactured by machining into brake caliper pistons. These brake caliper pistons were subjected to a T6 treatment by following the ordinary method to form anodized coats of 38 .mu.m or more on their surfaces. These brake caliper pistons were incorporated into brake master cylinders of four wheelers and were made to repeat braking operations to determine the conditions of seizure and locking. For the purpose of comparison, the aluminum alloys of Comparative Examples 101, 104, 108, 109, 111, 114, 115, 118 to 120 and 124 to 126 having the compositions shown in Table 1 were similarly manufactured to form brake caliper pistons and tested.

[0181] With 500,000 braking motions as the common standard, the brake caliper pistons of Example 101 to 153 and Examples 201 to 253 and those of the Comparative Examples produced no sign of problem. When the test was further continued with the braking motions increased up to 1,000,000 times, the brake caliber pistons of Examples 11 to 153 and Examples 201 to 253 sustained absolutely no scar, whereas those of the Comparative Examples sustained streaky scratches. The brake caliper pistons using the aluminum alloys of Comparative Examples 125 and 126 and having the compositions shown in Table 1 could not be put to the test because they sustained cracks on their surfaces.

5TABLE 5 Material Composition (wt %) Method of production Si Fe Cu Mn Mg Cr Ti Sr Ex. 101 Hot top continuous forging 5.0 0.25 -- -- 0.4 -- -- -- Ex. 102 Horizontal continuous " " " " " " " " forging Ex. 103 Extruding " " " " " " " " Ex. 104 Extruding/drawing " " " " " " " " Ex. 105 Hot top continuous forging 5.0 0.25 -- -- 0.8 -- -- -- Ex. 106 Hot top continuous forging 5.0 0.25 0.4 -- 0.4 -- -- -- Ex. 107 Hot top continuous forging 5.0 0.25 0.9 -- 0.4 -- -- -- Ex. 108 Horizontal continuous " " " " " " " " forging Ex. 109 Extruding " " " " " " " " Ex. 110 Extruding/drawing " " " " " " " " Ex. 111 Hot top continuous forging 5.0 0.25 0.9 -- 0.8 -- -- -- Ex. 112 Hot top continuous forging 5.0 0.25 0.9 0.2 0.4 -- -- -- Ex. 113 Hot top continuous forging 5.0 0.25 0.9 0.2 0.8 0.1 -- -- Ex. 114 Hot top continuous forging 5.0 0.25 0.9 0.2 0.5 0.1 -- 0.015 Ex. 115 Hot top continuous forging 5.0 0.25 0.9 0.2 0.5 0.1 0.015 -- Ex. 116 Hot top continuous forging 7.0 0.25 -- -- 0.4 -- -- -- Ex. 117 Horizontal continuous " " " " " " " " forging Ex. 118 Extruding " " " " " " " " Ex. 119 Extruding/drawing " " " " " " " " Ex. 120 Hot top continuous forging 7.0 0.25 -- -- 0.8 -- -- -- Ex. 121 Hot top continuous forging 7.0 0.25 0.4 -- 0.4 -- -- -- Ex. 122 Hot top continuous forging 7.0 0.25 0.9 -- 0.8 -- -- -- Ex. 123 Horizontal continuous " " " " " " " " forging Ex. 124 Extruding " " " " " " " " Ex. 125 Extruding/drawing " " " " " " " " Ex. 126 Hot top continuous forging 7.0 0.25 0.9 0.2 0.4 -- -- -- Ex. 127 Hot top continuous forging 7.0 0.25 0.9 0.2 0.8 0.1 -- -- Ex. 128 Hot top continuous forging 7.0 0.25 0.4 0.2 0.5 0.1 -- 0.015 Ex. 129 Hot top continuous forging 7.0 0.25 0.4 0.2 0.5 0.1 0.015 Ex. 130 Hot top continuous forging 8.2 0.25 0.6 -- 0.4 -- -- -- Ex. 131 Hot top continuous forging 10.0 0.25 -- -- 0.4 -- -- -- Ex. 132 Horizontal continuous " " " " " " " " forging Ex. 133 Extruding " " " " " " " " Ex. 134 Extruding/drawing " " " " " " " " Ex. 135 Hot top continuous forging 10.0 0.25 -- -- 0.8 -- -- -- Ex. 136 Hot top continuous forging 10.0 0.25 -- -- 0.4 -- -- 0.015 Ex. 137 Hot top continuous forging 10.0 0.25 0.4 -- 0.4 -- -- -- Ex. 138 Horizontal continuous " " " " " " " " forging Ex. 139 Extruding " " " " " " " " Ex. 140 Extruding/drawing " " " " " " " " Ex. 141 Hot top continuous forging 10.0 0.25 0.9 -- 0.4 -- -- -- Ex. 142 Horizontal continuous " " " " " " " " forging Ex. 143 Extruding " " " " " " " " Ex. 144 Extruding/drawing " " " " " " " " Ex. 145 Hot top continuous forging 10.0 0.25 0.9 -- 0.8 -- -- -- Ex. 146 Hot top continuous forging 10.0 0.25 0.9 0.2 0.4 -- -- -- Ex. 147 Hot top continuous forging 10.0 0.25 0.9 0.2 0.8 0.1 -- -- Ex. 148 Hot top continuous forging 10.5 0.25 0.95 -- 0.8 -- -- -- Ex. 149 Hot top continuous forging 10.5 0.25 0.4 0.2 0.4 0.1 -- 0.015 Ex. 150 Hot top continuous forging 10.5 0.25 0.9 -- 0.4 -- -- 0.015 Ex. 151 Extruding " " " " " " " " Ex. 152 Extruding/drawing " " " " " " " " Ex. 153 Hot top continuous forging 10.5 0.25 0.9 0.2 0.8 0.1 0.015 -- Comp. Ex. Hot top continuous forging 4.5 0.25 2.5 -- 1.1 -- -- -- 101 Comp. Ex. Horizontal continuous " " " " " " " " 102 forging Comp. Ex. Extruding " " " " " " " " 103 Comp. Ex. Extruding/drawing " " " " " " " " 104 Comp. Ex. Hot top continuous forging 7.0 0.25 3.0 -- 1.1 -- -- -- 105 Comp. Ex. Hot top continuous forging 7.0 0.25 3.0 0.2 1.1 0.1 -- -- 106 Comp. Ex. Hot top continuous forging 7.5 0.25 1.4 -- 0.3 -- -- -- 107 Comp. Ex. Hot top continuous forging 7.5 0.25 2.5 0.2 0.4 -- -- -- 108 Comp. Ex. Horizontal continuous " " " " " " " " 109 forging Comp. Ex. Extruding " " " " " " " " 110 Comp. Ex. Extruding/drawing " " " " " " " " 111 Comp. Ex. Hot top continuous forging 8.5 0.25 2.5 0.2 0.6 0.1 -- -- 112 Comp. Ex. Hot top continuous forging 10.3 0.25 1.6 -- 0.1 -- -- -- 113 Comp. Ex. Hot top continuous forging 10.6 0.25 1.5 -- 0.4 -- -- -- 114 Comp. Ex. Horizontal continuous " " " " " " " " 115 forging Comp. Ex. Extruding " " " " " " " " 117 Comp. Ex. Extruding/drawing " " " " " " " " 118 Comp. Ex. Hot top continuous forging 10.5 0.25 1.6 -- 0.5 -- 0.015 -- 119 Comp. Ex. Hot top continuous forging 10.7 0.25 1.5 -- 0.5 -- -- 0.015 120 Comp. Ex. Hot top continuous forging 10.5 0.25 2.7 0.2 0.4 -- -- 0.015 121 Comp. Ex. Extruding " " " " " " " " 122 Comp. Ex. Extruding/drawing " " " " " " " " 123 Comp. Ex. Hot top continuous forging 10.6 0.25 2.5 0.2 0.4 0.1 -- 0.015 124 Comp. Ex. Extruding/drawing 0.7 0.25 0.3 -- 1.0 0.2 0.015 -- 125 Comp. Ex. Extruding/drawing 1.0 0.25 -- 0.8 0.8 -- 0.015 -- 126

[0182]

6TABLE 6 Heat-treating conditions/mechanical properties of cast bars and extruded material Mechanical property 0.2% Tensile proof strength stremgth Elongation Hardness Wear T6 condition (N/mm.sup.2) (N/mm.sup.2) (%) (HRB) resistance Ex. 101 510.degree. C. .times. 2.5 hrs .fwdarw. Water cooling .fwdarw. 180.degree. C. .times. 6 hrs 322 244 17.9 59.7 .smallcircle. Ex. 102 " 325 246 18.3 59.8 .smallcircle. Ex. 103 " 318 239 18.5 59.2 .smallcircle. Ex. 104 " 316 238 18.9 58.9 .smallcircle. Ex. 105 " 333 263 17.5 61.6 .smallcircle. Ex. 106 " 338 275 17.4 63.1 .smallcircle. Ex. 107 500.degree. C. .times. 2.5 hrs .fwdarw. Water cooling .fwdarw. 190.degree. C. .times. 6 hrs 358 302 16.5 67.6 .smallcircle. Ex. 108 " 360 305 16.9 67.8 .smallcircle. Ex. 109 " 356 299 17.0 67.2 .smallcircle. Ex. 110 " 354 297 17.4 67.0 .smallcircle. Ex. 111 " 366 310 15.5 68.7 .smallcircle. Ex. 112 " 355 298 16.6 67.7 .smallcircle. Ex. 113 " 363 307 16.1 68.8 .smallcircle. Ex. 114 " 356 300 16.4 67.8 .smallcircle. Ex. 115 " 352 297 16.7 67.7 .smallcircle. Ex. 116 510.degree. C. .times. 2.5 hrs .fwdarw. Water cooling .fwdarw. 180.degree. C. .times. 6 hrs 320 249 16.6 59.9 .smallcircle. Ex. 117 " 322 250 17.0 60.1 .smallcircle. Ex. 118 " 315 244 17.3 59.5 .smallcircle. Ex. 119 " 313 241 17.6 59.1 .smallcircle. Ex. 120 " 330 266 15.8 61.9 .smallcircle. Ex. 121 " 336 276 15.6 63.4 .smallcircle. Ex. 122 500.degree. C. .times. 2.5 hrs .fwdarw. Water cooling .fwdarw. 190.degree. C. .times. 6 hrs 363 311 14.0 69.0 .smallcircle. Ex. 123 " 365 315 14.2 69.2 .smallcircle. Ex. 124 " 360 309 14.5 68.6 .smallcircle. Ex. 125 " 358 306 14.9 68.3 .smallcircle. Ex. 126 " 353 299 15.0 68.1 .smallcircle. Ex. 127 " 361 309 14.4 69.1 .smallcircle. Ex. 128 510.degree. C. .times. 2.5 hrs .fwdarw. Water cooling .fwdarw. 180.degree. C. .times. 6 hrs 337 275 15.7 63.6 .smallcircle. Ex. 129 " 335 274 15.6 63.9 .smallcircle. Ex. 130 500.degree. C. .times. 2.5 hrs .fwdarw. Water cooling .fwdarw. 190.degree. C. .times. 6 hrs 340 278 13.9 65.1 .smallcircle. .smallcircle. Ex. 131 510.degree. C. .times. 2.5 hrs .fwdarw. Water cooling .fwdarw. 180.degree. C. .times. 6 hrs 317 242 13.4 60.4 .smallcircle. .smallcircle. Ex. 132 " 318 244 13.6 60.5 .smallcircle. Ex. 133 " 314 237 13.9 60.1 .smallcircle. Ex. 134 " 311 235 14.1 59.9 .smallcircle. Ex. 135 " 327 268 13.0 62.3 .smallcircle. Ex. 136 " 318 240 13.6 60.3 .smallcircle. Ex. 137 " 333 279 12.6 63.8 .smallcircle. Ex. 138 " 334 280 12.9 63.8 .smallcircle. Ex. 139 " 329 274 13.1 63.4 .smallcircle. Ex. 140 " 327 273 13.4 63.2 .smallcircle. Ex. 141 500.degree. C. .times. 2.5 hrs .fwdarw. Water cooling .fwdarw. 190.degree. C. .times. 6 hrs 349 297 11.6 68.4 .smallcircle. Ex. 142 " 351 299 11.8 68.5 .smallcircle. Ex. 143 " 347 294 12.0 68.1 .smallcircle. Ex. 144 " 345 292 12.2 67.9 .smallcircle. Ex. 145 " 360 312 10.5 69.3 .smallcircle. Ex. 146 " 350 300 11.0 68.6 .smallcircle. Ex. 147 " 358 314 10.4 69.5 .smallcircle. Ex. 148 " 360 313 10.2 70.1 .smallcircle. Ex. 149 510.degree. C. .times. 2.5 hrs .fwdarw. Water cooling .fwdarw. 180.degree. C. .times. 6 hrs 336 281 12.8 64.3 .smallcircle. Ex. 150 500.degree. C. .times. 2.5 hrs .fwdarw. Water cooling .fwdarw. 190.degree. C. .times. 6 hrs 350 301 11.6 68.7 .smallcircle. Ex. 151 " 347 294 12.1 68.3 .smallcircle. Ex. 152 " 346 293 12.3 68.1 .smallcircle. Ex. 153 " 356 312 10.4 70.5 .smallcircle. Comp. Ex. 495.degree. C. .times. 2.5 hrs .fwdarw. Water cooling .fwdarw. 190.degree. C. .times. 6 hrs 415 373 13.9 73.1 .DELTA. 101 Comp. Ex. " 416 372 14.3 73.0 .DELTA. 102 Comp. Ex. " 411 368 14.6 72.6 .DELTA. 103 Comp. Ex. " 409 367 14.7 72.4 .DELTA. 104 Comp. Ex. " 417 378 12.1 73.9 .smallcircle. 105 Comp. Ex. " 410 365 12.0 74.1 .smallcircle. 106 Comp. Ex. " 376 321 13.6 71.4 .smallcircle. 107 Comp. Ex. " 410 363 13.1 74.3 .smallcircle. 108 Comp. Ex. " 412 365 13.2 74.4 .smallcircle. 109 Comp. Ex. " 407 359 13.6 74.0 .smallcircle. 110 Comp. Ex. " 406 357 13.7 73.9 .smallcircle. 111 Comp. Ex. " 411 366 12.7 74.5 .smallcircle. 112 Comp. Ex. " 319 244 11.5 60.7 .smallcircle. 113 Comp. Ex. " 383 328 10.2 72.0 .smallcircle. 114 Comp. Ex. " 386 330 10.4 72.3 .smallcircle. 115 Comp. Ex. " 380 324 10.9 71.7 .smallcircle. 117 Comp. Ex. " 378 321 11.2 71.5 .smallcircle. 118 Comp. Ex. " 387 331 9.7 72.2 .smallcircle. 119 Comp. Ex. " 384 329 10.3 72.1 .smallcircle. 120 Comp. Ex. " 405 358 9.3 74.9 .smallcircle. 121 Comp. Ex. " 401 354 9.7 74.4 .smallcircle. 122 Comp. Ex. " 399 351 10.0 74.2 .smallcircle. 123 Comp. Ex. " 403 357 9.4 74.6 .smallcircle. 124 Comp. Ex. 530.degree. C. .times. 2.5 hrs .fwdarw. Water cooling .fwdarw. 180.degree. C. .times. 6 hrs 334 290 22.9 64.1 x 125 Comp. Ex. " 333 294 20.8 64.7 x 126

[0183]

7TABLE 7 Particle diameters of cast bars and extruded material/anodized coat properties Eutectic Si Anodized coat Ave. Max. Min. Proportion Ability Thickness particle particle particle Number of yield to Hardness of diameter diameter diameter pieces/ 0.8 to 2.4 .mu.m anodization of coat coat (.mu.m) (.mu.m) (.mu.m) mm.sup.2 (%) treatment (Hv) (.mu.m) Crack Ex. 101 2.02 4.81 0.4 10,012 64.1 .smallcircle. 432 .smallcircle. 46.8 .smallcircle. Ex. 102 1.91 4.43 0.4 10,889 66.3 .smallcircle. 433 .smallcircle. 46.9 .smallcircle. Ex. 103 2.24 5.26 0.8 9,222 61.5 .smallcircle. 431 .smallcircle. 46.7 .smallcircle. Ex. 104 2.25 5.21 0.8 9,334 60.8 .smallcircle. 430 .smallcircle. 46.6 .smallcircle. Ex. 105 2.01 4.81 0.4 10,043 64.3 .smallcircle. 431 .smallcircle. 46.2 .smallcircle. Ex. 106 2.00 4.79 0.4 10,057 64.5 .smallcircle. 422 .smallcircle. 43.2 .smallcircle. Ex. 107 1.99 4.78 0.4 10,065 64.4 .smallcircle. 410 .smallcircle. 41.1 .smallcircle. Ex. 108 1.90 4.46 0.4 10,907 66.5 .smallcircle. 411 .smallcircle. 41.0 .smallcircle. Ex. 109 2.23 5.23 0.8 9,235 61.8 .smallcircle. 409 .smallcircle. 41.1 .smallcircle. Ex. 110 2.24 5.28 0.8 9,332 61.6 .smallcircle. 408 .smallcircle. 41.0 .smallcircle. Ex. 111 2.00 4.79 0.4 9,992 64.3 .smallcircle. 407 .smallcircle. 40.8 .smallcircle. Ex. 112 1.99 4.78 0.4 9,983 64.7 .smallcircle. 408 .smallcircle. 41.0 .smallcircle. Ex. 113 1.98 4.77 0.4 10,004 64.2 .smallcircle. 406 .smallcircle. 40.7 .smallcircle. Ex. 114 1.91 4.48 0.4 10,616 67.6 .smallcircle. 409 .smallcircle. 41.0 .smallcircle. Ex. 115 2.01 4.80 0.4 10,032 64.1 .smallcircle. 408 .smallcircle. 40.7 .smallcircle. Ex. 116 1.96 4.70 0.4 20,115 68.7 .smallcircle. 430 .smallcircle. 45.8 .smallcircle. Ex. 117 1.88 4.30 0.4 21,633 70.8 .smallcircle. 429 .smallcircle. 45.7 .smallcircle. Ex. 118 2.20 5.12 0.8 18,573 66.0 .smallcircle. 427 .smallcircle. 45.8 .smallcircle. Ex. 119 2.19 5.15 0.8 18,495 65.7 .smallcircle. 428 .smallcircle. 45.7 .smallcircle. Ex. 120 1.97 4.72 0.4 20,104 69.0 .smallcircle. 427 .smallcircle. 45.4 .smallcircle. Ex. 121 1.96 4.70 0.4 20,135 68.8 .smallcircle. 416 .smallcircle. 42.4 .smallcircle. Ex. 122 1.98 4.67 0.4 20,121 69.1 .smallcircle. 406 .smallcircle. 40.6 .smallcircle. Ex. 123 1.89 4.32 0.4 21,602 71.3 .smallcircle. 405 .smallcircle. 40.4 .smallcircle. Ex. 124 2.21 5.14 0.8 18,532 66.7 .smallcircle. 406 .smallcircle. 40.5 .smallcircle. Ex. 125 2.22 5.16 0.8 18,486 66.5 .smallcircle. 405 .smallcircle. 40.4 .smallcircle. Ex. 126 1.97 4.70 0.4 20,114 68.9 .smallcircle. 407 .smallcircle. 40.3 .smallcircle. Ex. 127 1.98 4.72 0.4 20,103 69.3 .smallcircle. 405 .smallcircle. 40.1 .smallcircle. Ex. 128 1.90 4.34 0.4 21,731 71.7 .smallcircle. 414 .smallcircle. 40.5 .smallcircle. Ex. 129 1.97 4.72 0.4 20,170 68.5 .smallcircle. 411 .smallcircle. 40.3 .smallcircle. Ex. 130 1.95 4.68 0.4 25,334 72.3 .smallcircle. 407 .smallcircle. 40.2 .smallcircle. Ex. 131 1.93 4.64 0.4 34,007 80.6 .smallcircle. 427 .smallcircle. 44.9 .smallcircle. Ex. 132 1.79 4.00 0.4 35,863 83.7 .smallcircle. 428 .smallcircle. 44.8 .smallcircle. Ex. 133 2.16 5.20 0.8 32,142 78.5 .smallcircle. 428 .smallcircle. 44.7 .smallcircle. Ex. 134 2.14 5.23 0.8 32,263 78.1 .smallcircle. 427 .smallcircle. 44.7 .smallcircle. Ex. 135 1.95 4.60 0.8 33,989 80.9 .smallcircle. 426 .smallcircle. 44.4 .smallcircle. Ex. 136 1.79 3.94 0.8 34,060 83.1 .smallcircle. 428 .smallcircle. 44.9 .smallcircle. Ex. 137 1.93 4.54 0.8 34,071 81.1 .smallcircle. 416 .smallcircle. 42.0 .smallcircle. Ex. 138 1.78 3.98 0.4 35,891 84.1 .smallcircle. 417 .smallcircle. 41.9 .smallcircle. Ex. 139 2.07 5.06 0.4 32,154 79.2 .smallcircle. 416 .smallcircle. 41.9 .smallcircle. Ex. 140 2.09 5.08 0.8 32,276 79.0 .smallcircle. 416 .smallcircle. 41.8 .smallcircle. Ex. 141 1.91 4.48 0.4 34,084 82.6 .smallcircle. 405 .smallcircle. 39.9 .smallcircle. Ex. 142 1.83 4.14 0.4 35,908 84.7 .smallcircle. 405 .smallcircle. 39.8 .smallcircle. Ex. 143 2.10 5.00 0.8 32,182 80.3 .smallcircle. 404 .smallcircle. 39.8 .smallcircle. Ex. 144 2.09 5.02 0.8 32,297 80.1 .smallcircle. 404 .smallcircle. 39.8 .smallcircle. Ex. 145 1.91 4.57 0.4 34,170 83.3 .smallcircle. 403 .smallcircle. 39.3 .smallcircle. Ex. 146 1.89 4.52 0.4 34,139 82.9 .smallcircle. 406 .smallcircle. 39.6 .smallcircle. Ex. 147 1.91 4.56 0.4 34,269 83.4 .smallcircle. 404 .smallcircle. 39.2 .smallcircle. Ex. 148 19.2 4.60 0.4 34,286 83.5 .smallcircle. 404 .smallcircle. 39.0 .smallcircle. Ex. 149 1.77 3.92 0.4 35,188 84.9 .smallcircle. 417 .smallcircle. 40.1 .smallcircle. Ex. 150 1.76 3.92 0.4 35,201 85.3 .smallcircle. 407 .smallcircle. 39.7 .smallcircle. Ex. 151 1.98 4.37 0.8 34,163 82.2 .smallcircle. 406 .smallcircle. 39.8 .smallcircle. Ex. 152 1.99 4.39 0.8 34,194 82.1 .smallcircle. 406 .smallcircle. 39.6 .smallcircle. Ex. 153 1.91 4.56 0.4 33,948 83.4 .smallcircle. 404 .smallcircle. 39.0 .smallcircle. Comp. Ex. 101 2.02 4.88 0.4 9,224 63.2 x 324 x 31.7 .smallcircle. Comp. Ex. 102 1.92 4.52 0.4 9,976 65.6 x 325 x 31.5 .smallcircle. Comp. Ex. 103 2.26 5.30 0.8 8,766 61.2 x 324 x 31.6 .smallcircle. Comp. Ex. 104 2.28 5.34 0.8 8,704 61.1 x 324 x 31.6 .smallcircle. Comp. Ex. 105 1.98 4.76 0.4 20,346 70.2 x 297 x 29.6 .smallcircle. Comp. Ex. 106 1.97 4.74 0.4 20,359 70.3 x 296 x 29.4 .smallcircle. Comp. Ex. 107 1.96 4.81 0.4 21,052 69.5 .DELTA. 384 .DELTA. 35.8 .smallcircle. Comp. Ex. 108 1.95 4.78 0.4 21,084 69.9 x 325 x 30.7 .smallcircle. Comp. Ex. 109 1.89 4.76 0.4 22,251 72.2 x 324 x 30.5 .smallcircle. Comp. Ex. 110 2.22 5.20 0.8 18,724 67.9 x 325 x 30.6 .smallcircle. Comp. Ex. 111 2.21 5.18 0.8 18,745 67.8 x 326 x 30.5 .smallcircle. Comp. Ex. 112 1.94 4.67 0.4 26,118 72.8 x 322 x 29.9 .smallcircle. Comp. Ex. 113 1.92 4.63 0.4 34,225 82.1 .DELTA. 389 .DELTA. 34.6 .smallcircle. Comp. Ex. 114 1.91 4.58 0.4 34,286 82.4 .DELTA. 381 .DELTA. 34.1 .smallcircle. Comp. Ex. 115 1.81 4.40 0.4 35,946 85.3 .DELTA. 382 .DELTA. 34.0 .smallcircle. Comp. Ex. 117 2.14 5.06 0.8 32,945 79.8 .DELTA. 380 .DELTA. 34.0 .smallcircle. Comp. Ex. 118 2.16 5.08 0.8 33,017 79.6 .DELTA. 380 .DELTA. 33.9 .smallcircle. Comp. Ex. 119 1.92 4.54 0.4 34,346 82.3 .DELTA. 379 .DELTA. 33.7 .smallcircle. Comp. Ex. 120 1.81 4.10 0.4 35,347 85.4 .DELTA. 381 .DELTA. 34.1 .smallcircle. Comp. Ex. 121 1.82 4.08 0.4 35,459 85.8 x 323 x 29.7 .smallcircle. Comp. Ex. 122 2.07 5.02 0.8 34,428 81.9 x 322 x 29.6 .smallcircle. Comp. Ex. 123 2.08 5.00 0.8 34,481 81.8 x 320 x 29.5 .smallcircle. Comp. Ex. 124 1.80 4.06 0.4 35,878 85.3 x 323 x 29.7 .smallcircle. Comp. Ex. 125 -- -- -- -- -- .smallcircle. 462 .smallcircle. 47.1 x Comp. Ex. 126 -- -- -- -- -- .smallcircle. 469 .smallcircle. 47.3 x

[0184]

8TABLE 8 Heat treatment conditions for forged parts Production method of Forging Hardness Wear material for forging treatment T6 conditions (HRB) resistance Ex. 201 Ex. 101 Hot top Presence 510.degree. C. .times. 2.5 hr .fwdarw. 59.2 .smallcircle. continuous Water cooling .fwdarw. forging 180.degree. C. .times. 6 hrs Ex. 207 Ex. 107 Hot top Presence 500.degree. C. .times. 2.5 hr .fwdarw. Water cooling .fwdarw. 190.degree. C. .times. 6 hrs 67.0 .smallcircle. continuous forging Ex. 208 Ex. 108 Horizontal Presence " 67.3 .smallcircle. continuous forging Ex. 210 Ex. 110 Extruding/ Presence " 66.4 .smallcircle. drawing Ex. 216 Ex. 116 Hot top Presence 510.degree. C. .times. 2.5 hr .fwdarw. Water cooling .fwdarw. 180.degree. C. .times. 6 hrs 59.3 .smallcircle. continuous forging Ex. 217 Ex. 117 Horizontal Presence " 59.4 .smallcircle. continuous forging Ex. 219 Ex. 119 Extruding/ Presence " 58.4 .smallcircle. drawing Ex. 221 Ex. 121 Hot top Presence " 62.8 .smallcircle. continuous forging Ex. 222 Ex. 122 Hot top Presence 500.degree. C. .times. 2.5 hr .fwdarw. Water cooling .fwdarw. 190.degree. C. .times. 6 hrs 68.3 .smallcircle. continuous forging Ex. 223 Ex. 123 Horizontal Presence " 68.6 .smallcircle. continuous forging Ex. 225 Ex. 125 Extruding/ Presence " 67.5 .smallcircle. drawing Ex. 228 Ex. 128 Hot top Presence 510.degree. C. .times. 2.5 hr .fwdarw. 62.8 .smallcircle. continuous Water cooling .fwdarw. forging 180.degree. C. .times. 6 hrs Ex. 231 Ex. 131 Hot top Presence 510.degree. C. .times. 2.5 hr .fwdarw. Water cooling .fwdarw. 180.degree. C. .times. 6 hrs 59.7 .smallcircle. continuous forging Ex. 232 Ex. 132 Horizontal Presence " 59.7 .smallcircle. continuous forging Ex. 234 Ex. 134 Extruding/ Presence " 59.1 .smallcircle. drawing Ex. 237 Ex. 137 Hot top Presence " 63.2 .smallcircle. continuous forging Ex. 238 Ex. 138 Horizontal Presence " 63.1 .smallcircle. continuous forging Ex. 240 Ex. 140 Extruding/ Presence " 62.4 .smallcircle. drawing Ex. 241 Ex. 141 Hot top Presence 500.degree. C. .times. 2.5 hr .fwdarw. Water cooling .fwdarw. 190.degree. C. .times. 6 hrs 67.5 .smallcircle. continuous forging Ex. 242 Ex. 142 Horizontal Presence " 67.7 .smallcircle. continuous forging Ex. 243 Ex. 143 Extruding Presence " 67.4 .smallcircle. Ex. 244 Ex. 144 Extruding/ Presence " 67.3 .smallcircle. drawing Ex. 245 Ex. 145 Hot top Presence " 68.5 .smallcircle. continuous forging Ex. 250 Ex. 150 Hot top Presence 500.degree. C. .times. 2.5 hr .fwdarw. Water cooling .fwdarw. 190.degree. C. .times. 6 hrs 67.9 .smallcircle. continuous forging Ex. 252 Ex. 152 Extruding/ Presence " 67.4 .smallcircle. drawing Ex. 253 Ex. 153 Hot top Presence " 69.9 .smallcircle. continuous forging Comp. Ex. Comp. Ex. Hot top Presence 495.degree. C. .times. 2.5 hr .fwdarw. Water cooling .fwdarw. 190.degree. C. .times. 6 hrs 72.6 .DELTA. 201 101 continuous forging Comp. Ex. Comp. Ex. Hot top Presence " 73.3 .smallcircle. 205 105 continuous forging Comp. Ex. Comp. Ex. Hot top Presence " 73.4 .smallcircle. 206 106 continuous forging Comp. Ex. Comp. Ex. Hot top Presence " 73.7 .smallcircle. 208 108 continuous forging Comp. Ex. Comp. Ex. Horizontal Presence " 73.8 .smallcircle. 209 109 continuous forging Comp. Ex. Comp. Ex. Extruding/ Presence " 73.4 .smallcircle. 211 111 drawing Comp. Ex. Comp. Ex. Hot top Presence " 71.4 .smallcircle. 214 114 continuous forging Comp. Ex. Comp. Ex. Horizontal Presence " 71.8 .smallcircle. 215 115 continuous forging Comp. Ex. Comp. Ex. Extruding/ Presence " 70.9 .smallcircle. 218 118 drawing Comp. Ex. Comp. Ex. Hot top Presence " 71.5 .smallcircle. 219 119 continuous forging Comp. Ex. Comp. Ex. Hot top Presence " 71.5 .smallcircle. 220 120 continuous forging Comp. Ex. Comp. Ex. Hot top Presence " 74.1 .smallcircle. 221 121 continuous forging Comp. Ex. Comp. Ex. Extruding Presence " 73.5 .smallcircle. 222 122 Comp. Ex. Comp. Ex. Extruding/ Presence " 73.5 .smallcircle. 223 123 drawing Comp. Ex. Comp. Ex. Extruding/ Presence 530.degree. C. .times. 2.5 hr .fwdarw. Water cooling .fwdarw. 180.degree. C. .times. 6 hrs 63.5 x 225 125 drawing Comp. Ex. Comp. Ex. Extruding/ Presence " 64.2 x 226 126 drawing

[0185]

9TABLE 9 Particle diameters of cast bars and extruded material/anodized coat properties Eutectic Si Anodized coat Ave. Max. Min. Proportion Ability to Thickness particle particle particle Number of yield to Hardness of diameter diameter diameter pieces/ 0.8 to 2.4 .mu.m anodization of coat coat (.mu.m) (.mu.m) (.mu.m) mm.sup.2 (%) treatment (Hv) (.mu.m) Crack Ex. 201 2.03 4.82 0.4 10,003 63.9 .smallcircle. 433 .smallcircle. 46.7 .smallcircle. Ex. 207 2.01 4.79 0.4 10,055 64.3 .smallcircle. 411 .smallcircle. 40.9 .smallcircle. Ex. 208 1.91 4.48 0.4 10,896 66.3 .smallcircle. 413 .smallcircle. 41.1 .smallcircle. Ex. 210 2.25 5.31 0.8 9,323 61.3 .smallcircle. 410 .smallcircle. 40.8 .smallcircle. Ex. 216 1.98 4.71 0.4 20,106 68.5 .smallcircle. 431 .smallcircle. 45.6 .smallcircle. Ex. 217 1.89 4.32 0.4 21,623 70.5 .smallcircle. 431 .smallcircle. 45.6 .smallcircle. Ex. 219 2.21 5.18 0.8 18,485 65.5 .smallcircle. 430 .smallcircle. 45.8 .smallcircle. Ex. 221 1.97 4.72 0.4 20,123 68.5 .smallcircle. 417 .smallcircle. 42.5 .smallcircle. Ex. 222 2.00 4.68 0.4 20,108 68.7 .smallcircle. 408 .smallcircle. 40.8 .smallcircle. Ex. 223 1.90 4.34 0.4 21,593 71.0 .smallcircle. 406 .smallcircle. 40.5 .smallcircle. Ex. 225 2.24 5.17 0.8 18,472 66.1 .smallcircle. 407 .smallcircle. 40.2 .smallcircle. Ex. 228 1.91 4.36 0.4 21,716 71.5 .smallcircle. 415 .smallcircle. 40.4 .smallcircle. Ex. 231 1.95 4.65 0.4 33,994 80.2 .smallcircle. 429 .smallcircle. 45.1 .smallcircle. Ex. 232 1.80 4.01 0.4 35,852 83.4 .smallcircle. 429 .smallcircle. 44.9 .smallcircle. Ex. 234 2.15 5.24 0.8 32,248 77.9 .smallcircle. 429 .smallcircle. 44.9 .smallcircle. Ex. 237 1.95 4.56 0.8 34,055 80.8 .smallcircle. 417 .smallcircle. 42.1 .smallcircle. Ex. 238 1.79 3.99 0.4 35,878 83.8 .smallcircle. 419 .smallcircle. 42.0 .smallcircle. Ex. 240 2.11 5.11 0.8 32,264 78.8 .smallcircle. 417 .smallcircle. 42.0 .smallcircle. Ex. 241 1.92 4.50 0.4 34,072 82.2 .smallcircle. 406 .smallcircle. 39.8 .smallcircle. Ex. 242 1.85 4.15 0.4 35,895 84.5 .smallcircle. 407 .smallcircle. 39.9 .smallcircle. Ex. 243 2.13 5.01 0.8 32,169 80.0 .smallcircle. 405 .smallcircle. 39.9 .smallcircle. Ex. 244 2.10 5.04 0.8 32,280 79.7 .smallcircle. 404 .smallcircle. 40.0 .smallcircle. Ex. 245 1.92 4.59 0.4 34,152 83.0 .smallcircle. 404 .smallcircle. 39.2 .smallcircle. Ex. 250 1.78 3.96 0.4 35,180 85.1 .smallcircle. 407 .smallcircle. 39.6 .smallcircle. Ex. 252 2.01 4.42 0.8 34,171 81.8 .smallcircle. 407 .smallcircle. 39.4 .smallcircle. Ex. 253 1.93 4.59 0.4 33,924 83.0 .smallcircle. 406 .smallcircle. 38.9 .smallcircle. Comp. Ex. 201 2.04 4.90 0.4 9,199 63.0 x 326 x 31.9 .smallcircle. Comp. Ex. 205 2.00 4.78 0.4 20,321 69.7 x 298 x 29.7 .smallcircle. Comp. Ex. 206 1.99 4.76 0.4 20,331 70.1 x 296 x 29.5 .smallcircle. Comp. Ex. 208 1.97 4.79 0.4 21,072 69.6 x 327 x 30.9 .smallcircle. Comp. Ex. 209 1.91 4.78 0.4 22,238 71.8 x 324 x 30.6 .smallcircle. Comp. Ex. 211 2.22 5.21 0.8 18,731 67.6 x 328 x 30.6 .smallcircle. Comp. Ex. 214 1.94 4.60 0.4 34,261 82.1 .DELTA. 382 .DELTA. 34.2 .smallcircle. Comp. Ex. 215 1.84 4.42 0.4 35,923 84.9 .DELTA. 384 .DELTA. 33.9 .smallcircle. Comp. Ex. 218 2.18 5.11 0.8 32,991 79.3 .DELTA. 381 .DELTA. 33.8 .smallcircle. Comp. Ex. 219 1.93 4.55 0.4 34,317 82.0 .DELTA. 381 .DELTA. 33.5 .smallcircle. Comp. Ex. 220 1.82 4.12 0.4 35,318 85.0 .DELTA. 382 .DELTA. 33.9 .smallcircle. Comp. Ex. 221 1.84 4.11 0.4 35,433 85.5 x 324 x 29.6 .smallcircle. Comp. Ex. 222 2.08 5.03 0.8 34,402 81.7 x 324 x 29.5 .smallcircle. Comp. Ex. 223 2.11 5.03 0.8 34,457 81.5 x 322 x 29.3 .smallcircle. Comp. Ex. 225 -- -- -- -- -- .smallcircle. 463 .smallcircle. 47 x Comp. Ex. 226 -- -- -- -- -- .smallcircle. 471 .smallcircle. 47.2 x

[0186]

10TABLE 10 Material Eutectic Si in anodized coat Ave. particle Max. particle Min. particle Proportion of diameter diameter diameter Number 0.8 to 2.4 .mu.m (.mu.m) (.mu.m) (.mu.m) (pieses/mm.sup.2) (%) 1.98 4.79 0.4 9,689 63.8 2.20 5.17 0.8 8,961 60.6 1.96 4.65 0.4 19,711 68.4 2.04 5.04 0.8 31,681 78.5 1.87 4.43 0.4 33,463 82 1.78 4.08 0.4 35,282 84 2.03 4.95 0.8 31,455 80.1 2.05 4.99 0.8 31,663 79.8

[0187]

11TABLE 11 Forged parts Eutectic Si in anodized coat Ave. particle Max. particle Min. particle Proportion of diameter diameter diameter Number 0.8 to 2.4 .mu.m (.mu.m) (.mu.m) (.mu.m) (pieses/mm.sup.2) (%) 1.98 4.78 0.4 9,503 63.6 1.91 4.67 0.4 19,582 68.0 1.88 4.44 0.4 33,329 81.6 1.80 4.10 0.4 35,110 83.8 2.06 4.97 0.8 31,400 79.3 2.05 4.99 0.8 31,495 79.1

Industrial Applicability

[0188] The aluminum alloy according to this invention derives from an anodizing treatment that results in the presence of eutectic Si particles in the anodized coat, is endowed with excellent wear resistance and can be used for:

[0189] (a) Air-conditioner grade compressor parts, such as scrolls and pistons

[0190] (b) Compressor pistons for use in air suspensions of automobiles

[0191] (c) Spools and sleeves for automobile engines, and transmission and ABS hydraulic parts

[0192] (d) Brake master cylinder pistons/caliper pistons for automobiles

[0193] (e) Clutch cylinder pistons for automobiles

[0194] (f) Brake caliper bodies for automobiles

[0195] It is particularly suitable for brake caliper pistons and air suspension grade compressor pistons and other parts that require a coat excelling in hardness and defying infliction of a crack.

Claims

1. An aluminum alloy that forms in consequence of an anodizing treatment an anodized coat having a thickness of 30 .mu.m or more and hardness Hv of 4000 or more and allows a presence, in the coat, of eutectic Si particles having particle diameters in the range of 0.4 to 5.5 .mu.m.

2. An aluminum alloy that forms in consequence of an anodizing treatment an anodized coat having a thickness of 40 .mu.m or more and hardness Hv of 4000 or more and allows a presence, in the coat, of eutectic Si particles having particle diameters in a range of 0.8 to 5.5 .mu.m.

3. An aluminum alloy according to claim 1 or claim 2, which contains 5 to 12% (mass %; similarly applicable hereinafter) of Si, 0.1 to 1% of Fe, less than 1% of Cu and 0.3 to 1.5% of Mg, and has the balance formed of Al and impurities, has dispersed in a matrix thereof eutectic Si particles having particle diameters in a range of 0.4 to 5.5 .mu.m, inclusive of 60% or more of the eutectic Si particles having particle diameters of 0.8 to 2.4 .mu.m, and allows a presence of 4000 or more and less than 40000 eutectic Si particles per mm.sup.2.

4. An aluminum alloy according to any one of claims 1 to 3, which when containing 9 to 12% of Si, has 80% or more of the eutectic Si particles with particle diameters of 0.8 to 2.4 .mu.m.

5. An aluminum alloy according to any one of claims 1 to 4, which contains substantially no Cu.

6. An aluminum alloy according to any one of claims 1 to 5, further containing at least one component selected from among 0.1 to 1% of Mn, 0.04 to 0.3% of Cr, 0.04 to 0.3% of Zr and 0.01 to 0.1% of V.

7. An aluminum alloy according to any one of claims 1 to 6, further comprising at least one component selected from among 0.01 to 0.3% of Ti, 0.0001 to 0.05% of B and 0.001 to 0.1% of Sr.

8. An aluminum alloy according to any one of claims 1 to 7, wherein the aluminum alloy is a bar material cast by a continuous casting method.

9. An aluminum alloy according to any one of claims 1 to 7, wherein the aluminum alloy is a bar material manufactured by a continuous casting method and then extruded or extruded and drawn.

10. A bar material comprising the aluminum alloy according to any one of claims 1 to 9.

11. A bar material according to claim 10, wherein the bar material is used as a sleeve part.

12. A forged article resulting from subjecting the bar material according to claim 10 or claim 11 to a forging process.

13. A machined article resulting from subjecting the bar material according to claim 10 or claim 11 or the forged article according to claim 12 to a machining process.

14. A wear-resistant aluminum alloy having an anodized coat having a thickness of 30 .mu.m or more and hardness Hv of 400, which allows a presence, in the anodized coat, of eutectic Si particles of particle diameters in a range of 0.4 to 5.5 .mu.M.

15. A wear-resistant aluminum alloy excelling in hardness of an anodized coat, which allows a presence, in an anodized coat, of eutectic Si particles of particle diameters in a range of 0.8 to 5.5 .mu.m and forms the coat in a thickness of 40 .mu.m or more and with hardness Hv of 400 or more.

16. A sleeve part excelling in hardness of an anodized coat, resulting from subjecting the machined article according to claim 13 to an anodizing treatment.

17. A method for the production of a wear-resistant aluminum alloy excelling in hardness of an anodized coat, comprising casting the aluminum alloy according to any one of claims 3 to 7 by a continuous casting process to form a cast mass, homogenizing the cast mass to form a homogenized cast mass, then extruding and/or forging and/or machining the homogenized cast mass to form a formed cast mass and subjecting the formed cast mass to an anodizing treatment, thereby allowing a presence, in the anodized coat, of eutectic Si particles of particle diameters in a range of 0.4 to 5.5 .mu.m and forming the coat in a thickness of 30 .mu.m or more and with hardness Hv of 400 or more.

18. A method for the production of a sleeve part excelling in hardness of an anodized coat and formed of an aluminum alloy, comprising casting the aluminum alloy according to any one of claims 3 to 7 by a continuous casting process to form a cast mass, homogenizing the cast mass to form a homogenized cast mass, then extruding and/or forging and/or machining the homogenized cast mass to form a formed cast mass and subjecting the formed cast mass to an anodizing treatment, thereby allowing a presence, in the anodized coat, of eutectic Si particles of particle diameters in a range of 0.8 to 5.5 .mu.m and forming the coat in a thickness of 40 .mu.m or more and with hardness Hv of 400 or more.