Tensile properties of short fiber-reinforced SiC/Ai composites: Part I. effects of matrix precipitates

Abstract

The tensile behavior of aluminum matrix composites reinforced with 8 and 20 pet SiC whiskers or paniculate was characterized. Two matrix alloys were employed, a solution-hardened Al-Mg alloy (5456) and a precipitation-hardened Al-Cu-Mg alloy (2124). The precipitation-hardened alloy was aged to develop a variety of precipitate microstructures. It was found that additions of SiC caused monotonie increases in the elastic modulus, 0.2 pct offset yield stress, work-hardening rate, and ultimate tensile stress. The proportional limit, however, was found to first decrease and then increase with SiC content. Whiskers caused a greater increase in the longitudinal elastic modulus than particles. For the 2124 alloy, it was found that the proportional limit could be varied between 60 and 650 MPa by changing the precipitate microstructure, while changes in the SiC content had much smaller effects. These observations are discussed in relation to current theories of the strengthening of short fiber composites, with primary emphasis being placed on the effects of SiC additions on the elastic modulus and the work-hardening rate.