Microstructural evolution of silicon carbide/aluminum oxide composites processed by melt oxidation

Abstract

The nucleation and growth mechanisms during high temperature oxidation of liquid Al-3 wt% Mg and Al-3 wt% Mg-7 wt% Si alloys were studied to provide a better understanding of the composite fabrication process, especially in the presence of SiC reinforcement. Al2O3-matrix composites with and without SiC particulates have been produced by directed oxidation of aluminum alloys. The microstructure consists of three interpenetrating phases: the SiC preform, a continuous α-Al2MO3 matrix, and a network of unoxidized metal. The volume fraction of metal within the oxidation product decreases with increasing processing temperature. The preform does not show any evidence of degradation by the molten alloy, but the growth front tends to climb up the particles, increasing the oxidation area and therefore enhancing the rate of composite growth. The amount of porosity was found to increase with the Mg content in the alloy, from 2.0 vol% for 0.5 wt% Mg to 5.8 vol% for 3 wt% Mg. The role of magnesium and silicon in the growth process are discussed.