Composite strengthening in 6061 and Al-4 Mg alloys

Abstract

Metal matrix composites using prealloyed 6061 Al (containing 1% Mg) and elemental blend Al-4 Mg alloys with 10 vol% SiC particulate reinforcements were fabricated using powder metallurgy techniques. The consolidation of the powders was effected by the section rolling process recently developed at the Defence Metallurgical Research Laboratory. This process involves the successive steps of cold isostatic pressing, vacuum sintering and special canning followed by section rolling. This resulted in a high-integrity composite product. An interfacial layer containing magnesium-rich precipitates observed in both the composites is suggested to be the major reason for the low (compared to the value predicted by the rule of mixtures) modulus and strength values in these composites. This layer also appeared to promote interfacial failure at the alloy/SiC interface. The Al-4 Mg alloy, which is known to be non-heat treatable, was found to respond to precipitation hardening heat treatment in the composite. The enhanced generation of dislocations due to the presence of SiC, promoting a more homogeneous precipitation of the second phase and the possibility of an inhomogeneous distribution of magnesium (as a result of elemental blending) are suggested to be the major factors responsible for rendering the Al-4 Mg alloy amenable to the precipitation hardening heat treatment.