THE EFFECT OF THE SPATIAL-DISTRIBUTION OF REINFORCEMENT ON THE FABRICATION AND HEAT-TREATMENT OF (AL-4WT-PERCENT-CU)-SIC PARTICLE METAL-MATRIX COMPOSITES

The hot workability of particulate-reinforced metal matrix composites (MMCs) is impaired by the presence of the reinforcement. The paper des cribes the effect of the spatial distribution of SiC particle (SiCp) r einforcement on the ability to subject (Al-4wt.%Cu)-SiCp MMCs to a hot -roll powder metallurgy route, with particular reference to the matrix -to-reinforcement-particle-size ratio. All MMCs exhibited edge cracks on rolling, whilst the unreinforced material did not. As the reinforce ment became more uniformly distributed throughout the matrix, so crack ing at the edges became less severe and a higher reduction in thicknes s could be achieved by rolling before edge cracks began to appear. The latter was achieved when the matrix-to-reinforcement-particle-size ra tio tended towards unity. The time required to reach peak hardness und er artificial aging at 463 K was not altered by the presence of the re inforcement. Differential scanning calorimetry experiments showed a ch ange in precipitation sequence in the MMCs with precipitation of the t heta' phase occurring at lower temperatures, and the rate of precipita tion of the theta'' phase slowed down. There was no direct correlation between the homogeneity of the distribution of the reinforcement with in the matrix and the peak hardness. In MMCs with the same size of rei nforcement a higher level of hardness was achieved when a smaller matr ix mass median particle size was used.