1. Field of the Invention
The present invention generally relates to a production method for a metal matrix composite material. More specifically, the present invention relates to a production method for a metal matrix composite material excellent in properties, such as plastic workability, thermal conductivity, room-temperature or high-temperature strength, high stiffness, neutron absorption performance, wear resistance and low thermal expansibility.
2. Description of the Related Art
Heretofore, there has been known a method of producing a composite material having an aluminum matrix through a powder metallurgy process, comprising the steps of:
(1) mixing a powder of a ceramic material serving as a reinforcing material, such as Al2O3, SiC, B4C, BN, aluminum nitride or silicon nitride, with an aluminum powder serving as a matrix;
(2) subjecting the mixed powder to canning or cold compaction to form a compact;
(3) subjecting the compact to degassing, sintering, etc.; and
(4) forming the sintered compact into a desired shape.
The sintering process in the step (3) includes: a technique (A) of simply heating the compact; a technique (B) of pressing the compact at high temperatures, such as hot pressing; a technique (C) of sintering the compact through hot plastic working, such as hot extruding, hot forging or hot rolling; a technique (D) of pressing the compact while applying a pulse current thereto, i.e., subjecting the compact to so-called “pulse-current pressure sintering” (as disclosed, for example, in JP 2001-329302A); and a technique (E) based on a combination of two or more of the techniques (A) to (D). There has also been known a technique of performing the sintering process in conjunction with the degassing process.
In recent years, aluminum matrix composite materials have been increasingly developed for use in new applications requiring not only strength but also a high Young's modulus, wear resistance, low thermal expansibility and nuclear-radiation absorption capability. Although each of the functions can be enhanced by increasing an amount of ceramic additives having the respective functions, an approach of simply increasing the amount of ceramic additives will cause significant deterioration in sinterability and plastic workability, such as, extrudability, rollability or forgeability.
From this standpoint, there has been proposed a technique of preparing a ceramic preform, and impregnating the ceramic preform with molten aluminum alloy to allow ceramic particles to be uniformly dispersed over an aluminum alloy matrix in a high density. In reality, this technique is likely to involve problems about insufficiency of the impregnation with the molten aluminum alloy, and occurrence of defects, such as shrinkage during solidification of the molten aluminum alloy.
International Publication No. WO 2006/070879 relates to a method of producing an aluminum matrix composite material, which comprises the steps of: (a) mixing an aluminum powder and a ceramic powder to prepare a mixed powder; (b) subjecting the mixed powder to pulse-current pressure sintering together with a metal sheet to form a cladded material where a sintered compact is cladded with the metal sheet; and (c) subjecting the cladded material to plastic working to obtain an aluminum matrix composite material.
In WO 2006/070879, before a mixed powder prepared by mixing an aluminum powder and a ceramic powder is subjected to a rolling process, it is necessary to subject the mixed powder to pulse-current pressure sintering while sandwiching the mixed powder between metal sheets, so as to preform a cladded material in such a manner as to be maintained in a predetermined shape. The reason is that it is difficult or substantially impossible to roll the cladded material unless it is performed by sintering in such a manner as to be maintained in a predetermined shape.
As described above, it is essential for WO 2006/070879 to preform the cladded material in such a manner as to be maintained in a predetermined shape, i.e., to subject the mixed powder to pulse-current pressure sintering, which leads to deterioration in process efficiency and difficulty in achieving an intended cost reduction. Thus, there remains a strong need for solving these problems.