Response of aluminium/graphite composite to deformation in the semi-solid state

Abstract

Semi-solid deformation of Al/graphite (Gr) composites was studied. The effects of deformation temperatures and deformation rates on the macrostructures, morphologies, the deformation force, and the formability of the composites were studied. For Al-10 wt% Gr composites, the semi-solid deformation stress increases as strain increases at lower strain rate. At higher strain rate, the stress first increases to a local maximum, then decreases before it starts to increase again as strain increases. For Al-30 wt% Gr composites, the stress decreases as strain increases. For both the Al-10 wt% Gr composites and Al-30 wt% Gr composites, the higher the deformation strain rate is, the more severe is the degree of cracking. The higher the deformation strain rate, the larger is the deformation stress, not counting the effects of fracturing. The deformation stresses required to semi-solid-deform Al-30 wt% Gr composites are larger than those for Al-10 wt% Gr composites, which is contrary to the normal solid-state deformation behaviours of Al-Gr composites. Composites deformed at 620 °C tend to require a higher deformation stress than at 630 °C for the same deformation strain, due to smaller liquid fraction and lower ductility at 620 °C. The effects of deformation temperatures on the ductility of the compacts are not significant at lower deformation strain rate. However, at the highest deformation strain rate, the ductility is better for higher deformation temperature.