The effect of forging on the properties of particulate-SiC-reinforced aluminium-alloy composites

Composites of an aluminium-silicon alloy (Al-5Si-0.2%Mg) containing different volume fractions of particulate silicon carbide reinforcement and unreinforced matrix alloy samples were produced by the permanent die casting technique. The cast ingots were cut into blanks to be forged in two steps to obtain rectangular plate-shaped samples. At each step of closed-die hot forging approximately 50% reduction in thickness was obtained. The microstructures and mechanical properties of the matrix alloy and the composite samples were investigated in the as-cast state and after the forging operation. The forged microstructures had a more uniform distribution of the SiC particles and the eutectic silicon in comparison to the as-cast microstructures. Evaluation of the mechanical properties showed that the forged samples had strength values superior to those of the as-cast counterparts. After forging, the yield strength of the matrix alloy and composite samples was increased by about 80%, and the improvement in tensile strength was about 40%. The addition of increasing amounts of particulate SIC decreased the ductility and increased the yield and tensile strength up to an optimum reinforcement volume fraction over which a decrease in strength and ductility was obtained. (C) 2000 Elsevier Science Ltd. All rights reserved.