Compressive stress-strain response of directionally aligned SiCw/Al composite

Abstract

A SiCw/6061Al composite was fabricated through a squeeze-casting route and hot extruded to obtain a composite with directionally aligned whiskers. Based on observed changes in whisker orientation and length before and after deformation, compressive deformation behaviour of the directionally aligned SiCw/Al composite was investigated. It is found that when the compressive temperature is much lower than the solidus of the matrix alloy, the compressive flow stress of the directionally aligned composite is increased with compressive strain first and then decreased. When the compressive temperature equals the solidus of the matrix, however, the compressive flow stress of the directionally aligned composite is increased monotonously with compression strain. During compression, whisker rotation and breakage occurred, and the higher the compressive temperature, the easier the whisker rotation and hence the smaller the degree of whisker breakage. When the compressive strain was quite high, the degree of whisker breakage was serious even at the temperature as high as the solidus of the matrix. Analyzing changes in whisker orientation and breakage before and after compression indicates that the decreased compressive flow stress with compressive strain is the result of the decreased load carrying ability of whiskers caused by whisker rotation and breakage. Compared with whisker rotation, whisker breakage has a bigger contribution to the decreased compressive flow stress. No strain softening in the composite compressed at 580°C can be thought to be a result of the very low strengthening effect of whiskers at such a high temperature. From the point of view of whisker breakage, to get higher properties of SiCw/Al composite parts made by means of plastic forming, too high plastic strain should not be suffered by SiCw/Al composites during the plastic forming.