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  Method of producing aluminum composite materialRelated Patent Categories: Metal Founding, Process, Shaping Liquid Metal Against A Forming Surface, Composite Article Forming, Shaping Metal And Uniting To A PreformThe Patent Description & Claims data below is from USPTO Patent Application 20060169434. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] (1) Field of the Invention [0002] The present invention relates to a method of producing aluminum composite material produced by mixing an aluminum fiber and graphite or activated charcoal to an aluminum alloy. [0003] (2) Description of the Background Art [0004] An aluminum alloy has been optimally used in devices including such as automobiles, electric appliances, electronic parts, and precious measurement equipment because of its lightness and malleability. Nevertheless the application of the aluminum alloy is limited to a sliding portion of structure because of low resistance to abrasion. Further, especially in an automobile, comfortable ride and driving performance are not well achieved due to noise and vibration because an aluminum alloy has lower vibration damping property than a cast iron. Accordingly, various composite materials such as graphite and activated charcoal with superior lubricating property and damping property have been added to promote resistance to abrasion and vibration damping property. [0005] A composition in which activated charcoal and ceramic such as alumina particle and alumina fiber are dispersed in aluminum alloy material was disclosed in Japanese Laid Open Patent Publication No. S58-81948. Further, a method of manufacturing the composite material was disclosed in Japanese Laid Open Patent Publication No. H6-24035 in which a compact which was obtained by dehydration or de-alcoholization after aluminum short fiber and graphite were mixed with water or alcohol, and an aluminum alloy was made into a complex. [0006] In both method of an aluminum composite material by mixing activated charcoal or graphite to hot melting aluminum alloy solution disclosed in S58-81948 above and method of an aluminum composite material by impregnating hot melting aluminum alloy solution to an preform prepared by sintering an alumina fiber with activated charcoal or graphite disclosed in H6-24035 above, the activated charcoal or the graphite are exposed to high temperature because of using such hot solution or sintering of aluminum alloy. In the air activated charcoal and graphite can be characteristically easily oxidized and the oxidation of activated charcoal and graphite vigorously proceeds over approximately 600.degree. C., and are lost as carbon dioxide or carbon monoxide. Even though heating over 600.degree. C. by hot solution or sintering of aluminum alloy are used in the methods above, no means to prevent the oxidation of activated charcoal or graphite was disclosed and accordingly the oxidation-loss of activated charcoal and graphite could not be prevented. Thus it was difficult to obtain an aluminum alloy composite material having excellent abrasion resistant and vibration damping properties. BRIEF DESCRIPTION OF THE DRAWINGS [0007] FIGS. 1(a)-1(c) are figures illustrating a preform forming process of the invention. [0008] FIGS. 2(a)-2(d) are figures illustrating an aluminum impregnating process of the invention. [0009] FIG. 3 is a figure showing the evaluation results of an abrasion resistant property, a vibration damping property and hardness of aluminum composite material 4 according to each embodiment and comparison embodiment of the invention. [0010] FIG. 4 is a figure illustrating a structural photograph of aluminum composite layer 12a according to embodiment 1 of the invention. [0011] FIG. 5 is a figure illustrating a structural photograph of aluminum composite layer 12a according to comparison embodiment 1 of the invention. DETAIL DESCRIPTION OF THE INVENTION [0012] According to the invention, a method of manufacturing an aluminum composite material which has excellent abrasion resistant and vibration damping properties is disclosed. [0013] According to an implementation of the invention, the method of manufacturing the aluminum composite material comprises steps of mixing an alumina fiber, graphite and an inorganic binder in water; dehydrating and forming; preform forming process which forms the preform by sintering the mixture at a designated temperature under vacuum, in an inert gas or in a reducing gas; and then an aluminum impregnating process which impregnates the perform with an aluminum alloy by pressure casting. [0014] Further, according to an implementation of the invention, the method of manufacturing the aluminum composite material comprises steps of mixing an alumina fiber, activated charcoal and an inorganic binder in water; dehydrating and forming; preform forming which forms a preform by sintering the mixture at a designated temperature under vacuum, in an inert gas or in a reducing gas; and then an aluminum impregnating process which impregnates the perform with an aluminum alloy by pressure casting. [0015] According to two manufacturing methods, a formed base material obtained by dehydrating and forming the aqueous mixture solution of the alumina fiber, graphite or activated charcoal, and the inorganic binder has almost an homogeneous structure of the alumina fiber and graphite or activated charcoal because graphite and activated charcoal can be coagulated to the alumina fiber by addition of the inorganic binder. Further an oxidation-loss of graphite or activated charcoal over approximately 600.degree. C. can be prevented by heating and sintering the dehydrated-formed base material at the designated sintering temperature under vacuum, in an inert gas or in a reduced gas, and accordingly a preform appropriately having graphite or activated charcoal can be formed. Further a heat-contraction of the preform can be prevented because graphite or activated charcoal does not either coagulate or react with the alumina fiber when it is heated under vacuum, in an inert gas or in a reducing gas. Accordingly a preform having high strength and high breathability can be formed because the temperature of sintering the alumina fiber can be raised farther. Accordingly the preform formed by processing to form the preform above comprises structure dispersing graphite and activated charcoal almost in homogeneous with an excellent strength and breathability. [0016] The hot solution of aluminum alloy is pressurized and cast to the preform above having high strength and high breathability by an impregnation process. Crush of the preform can be prevented because the preform formed in the preform forming process has high strength and the aluminum alloy, the aluminum fiber and graphite or activated charcoal can make a complex almost in homogeneous. The hot solution of aluminum is easily impregnated because the preform has high breathability and occurrence of voids of the composite material after forming can be adequately prevented. Specifically according to the preform forming process and aluminum impregnation process, the aluminum composite material having excellent abrasion resistant and vibration damping properties can be obtained with graphite or activated charcoal which are existing almost in homogenous and dispersedly. [0017] Further the aluminum composite material manufactured according to the method of the invention has a low thermal expansion coefficient because graphite or activated charcoal has a low thermal expansion coefficient and also the thermal expansion coefficient of alumina fiber is low, and accordingly a thermal deformation occurs unlikely and excellent form stability can be achieved. Further the aluminum composite material manufactured by mixing graphite can retain the excellent thermal conductivity coefficient of aluminum alloy because graphite has relatively a high thermal conductivity coefficient. [0018] Further such as alumina sol, silica gel and lithium silicate as an inorganic binder can be applied adequately. When such inorganic binder is used, the mixed alumina fiber and graphite or activated charcoal powder in water can coagulate with sufficient strength by hydration. Further the aluminum composite material is that alumina fiber, graphite or activated charcoal are combined with sufficient adhesion because of excellent adhesion of such inorganic binder, and accordingly father excellent abrasion resistant and vibration damping properties can be obtained. [0019] According to another implementation of the invention disclosed in claim 3, the manufacturing method is using graphite above having particle diameters in the range of 0.1 .mu.m to 100 .mu.m. Also another implementation of the invention disclosed in claim 4, the manufacturing method is using activated charcoal above having particle diameters in the range of 0.1 .mu.m to 100 .mu.m. The preform in which graphite or activated charcoal are dispersedly fixed almost in homogeneous to aluminum fiber by using designated amount of graphite or activated charcoal having such particle diameters can be obtained, and also area of adhesion for graphite or activated charcoal and aluminum alloy can be secured and accordingly the aluminum composite material which can carry out farther adequately an abrasion resistant property and a vibration damping property can be obtained. If a particle diameter of graphite or activated charcoal is larger than 100 .mu.m, it is difficult that graphite or activated charcoal are dispersed homogeneously and an distance between each graphite or activated charcoal in the aluminum composite material becomes longer and each graphite or activated charcoal would be separated, and accordingly it is difficult that the abrasion resistant property and the vibration damping property are carried out sufficiently. Further if the particle diameter is large, graphite or activated charcoal would not be sintered. Therefore parts having relatively weak strength occupy large area and volume of preform becomes large, and accordingly strength of the preform becomes insufficient. Therefore it may take place that preform is easily crushed during the pressurized casting process in aluminum impregnation process and an adequate aluminum composite material could not be formed. Graphite or activated charcoal having particle diameter larger than 0.1 .mu.m which is relatively easily obtainable is used. If the particle diameter is smaller than 0.1 .mu.m, graphite or activated charcoal easily floats and cannot be equally mixed by stirring because graphite or activated charcoal is given larger surface tension from water in comparison with its weight during being mixed with aluminum fiber in water. Further, it is preferable that the particle diameter is larger than 5 .mu.m in order to secure sufficient area for adhesion and to perform an adequate binding property. Further, it is more preferable that graphite or activated charcoal having particle diameter in the range of 5 .mu.m to 50 .mu.m is used in order to form farther adequate aluminum composite material. Even though particle diameters of some graphite or activated charcoal are more or less over than the range, it can be included in the invention because a targeted aluminum composite material can be obtained. [0020] According to another implementation of the invention, the manufacturing method is for activated charcoal above having a porous structure; wherein a binding strength of aluminum alloy and activated charcoal is farther strengthened because the aluminum alloy can be impregnated into pores of activated charcoal in aluminum impregnation process. [0021] According to another implementation of the invention, the manufacturing method is for the alumina fiber having an average diameter in the range of 1 .mu.m to 10 .mu.m and the average length of 10 cc/5 gf to 100 cc/5 gf. The average length of alumina fiber is defined as a volume per weight unit because the alumina fiber is generally complex and intertwined. The preform can be formed with adequate compact density by using such average diameter and average length, and accordingly the preform can be excellently strong and breathable. If an average diameter of the alumina fiber is larger than 10 .mu.m, the preform is easily crushed because the volume is large and the strength of the preform is insufficient. If an average length of the alumina fiber is larger than 100 cc/5 gf, a deformation and breaking easily take place because the compact density of the preform is lower and the strength of the preform is insufficient. Further, if the average diameter is smaller than approximately 1 .mu.m or the average length is smaller than approximately 10 cc/5 gf, an defect can easily take place because breathability of the perform is insufficient and the preform cannot sufficiently impregnate the aluminum alloy. Preferably the average diameter is in the range of 1 .mu.m to 5 .mu.m and the average length is in the range of 20 cc/5 gf to 60 cc/5 gf in order to form the preform which has farther excellent strength and breathability. Further, even if some alumina fiber out of the range more or less is mixed, the targeted aluminum composite material can be obtained and accordingly these are also covered by the invention. Continue reading... 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