Microstructure and high strain rate superplasticity of in situ composite synthesised from aluminium and nano-Zro₂ particles by powder metallurgy

Pure aluminium matrix composites reinforced mainly with a fine needle-like Al₃Zr phase were synthesised by the reaction between nanocrystalline ZrO₂ particles and pure aluminium using powder metallurgy followed by hot extrusion and hot rolling. After extrusion, the composite fabricated with 5 vol.-%ZrO₂ had a strain rate sensitivity (m value) of 0·31 and a total elongation of 156% at 650°C and 1·3 × 10^-1 s^-1. The high strain rate superplasticity was improved by hot rolling. After hot rolling, the m value of the composite fabricated with 10%ZrO₂ particles was 0·40 and the total elongation was 204% at 640°C and 1·3 × 10^-1 s^-1. The superplastic deformation mechanism for the present composites involves grain boundary sliding and interfacial sliding. From this mechanism, the following experimental results can be easily understood: the total elongation increased with temperature, and the strain rate at which maximum total elongation was attained increased with increasing deformation temperature.