Alloys or metallic compositions – Aluminum base
Patent
1980-04-11
1983-05-17
Dean, R.
Alloys or metallic compositions
Aluminum base
420529, 420538, 420548, 420550, 420551, 420552, 420553, 420554, C22C 102
Patent
active
043839703
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for preparation of graphite-containing aluminum alloys which comprises throwing and dispersing graphite particles, especially graphite particles not coated with a metal, into a melt of aluminum or an aluminum alloy.
For many slip-contact structural elements in internal combustion engines, such as bearings, gears, pistons, cylinders, sliders and the like, metallic alloys containing a solid lubricant are ordinarily used. This method is employed to compensate for a lost in lubrication by providing a self-lubricating action of the solid lubricant when a film of a lubricating oil film is destroyed. It is known that graphite is very suitable as such a solid lubricant. Therefore, various alloys containing graphite particles have heretofore been proposed and manufactured. However, most of metallic alloys containing graphite particles are prepared according to powder metallurgy, so that resulting sintering products do not have sufficient mechanical properties.
In a case of large-size products, the manufacturing cost becomes much higher than in case of cast or forged products. Thus, there has been an earnest effort in the art to develop a casting technique capable of dispersing graphite particles uniformly into metallic alloys without using or floating graphite particles.
More specifically, the following methods have been recently proposed as the technique of dispersing the graphite particles into aluminum (Al) alloy melt (having a graphite solubility lower than 0.01% by weight) with which graphite is metallurgically incompatible, without the floating of graphite particles.
There have been proposed a method in which a mixed powder of graphite particles coated with nickel and halogenide is incorporated into a melt of a hyper-eutectic Al-Si (silicon) alloy melt and swirls are formed in the melt by an agitator to disperse the graphite particles uniformly into the melt and a method in which metal-coated graphite particles suspended in a carrier gas are blown into a melt of an aluminum alloy, as shown in Japanese patent publication Ser. No. 45-13224.
These methods, however, involve problems or defects described below. In each of these methods, it is an indispensable requirement that the surfaces of graphite particles to be dispersed should be metal-coated.
A metal coating may be formed on the surfaces of graphite particles by chemical plating or the like. However, the process includes complicated steps, problems are included in sewage treatment equipments and the like and therefore, the costs of products are disadvantageously increased.
Furthermore, since the surfaces of metal-coated graphite particles are in the oxidized state, even if they are thrown and dispersed into a melt, they are likely to rise to the surface of the melt because of a poor wettability with the melt and it is impossible to disperse the graphite particles uniformly into the melt. It is proposed that the wettability may be improved by treating the graphite particles in an atmosphere of hydrogen.
In this case, however, many blowholes are formed by discharge of hydrogen from the interior of the graphite particles and practically valuable products cannot be obtained.
It is necessary to incorporate graphite in aluminum or its alloy in an amount of 4 to 30% by weight in order to attain a sufficient lubricating effect of the graphite under dry friction. The use of metal-coated graphite particles is not suitable for throwing and dispersing such a large amount of graphite particles into a melt in a short time at a high efficiency.
Further, when it is intended to throw and disperse a large amount of metal-coated graphite particles into the melt at a time, heat necessary for melting the metal is taken from the melt as the matrix, and the temperature of the matrix is rapidly lowered to reduce the fluidity of the melt, and the added metal-coated graphite particles are apt to float to the surface of the melt. The metal-coated graphite particles which are once floated to the surface of the melt are not dispersed into the melt ag
REFERENCES:
patent: 3600163 (1971-08-01), Badia et al.
Komuro Katsuhiro
Ohsawa Masato
Soeno Koh
Suwa Masateru
Dean R.
Hitachi , Ltd.
Hitachi Chemical Company Ltd.
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