Microstructural dynamics during high-strain-rate superplastic flow in PM 7475 alloy

A 7475 aluminum alloy processed by powder metallurgically (P/M7475) has shown superplastic elongation more than 1000 % at a temperature of 788 K. The maximum elongation of P/M 7475 was recorded near a strain rate of 1x10(-1) s(-1), which is 3 orders magnitude faster than that of ingot metallurgically processed 7475 (I/M7475). This excellent superplastic performance at a higher strain rate is owing to a fine grain size of about 1 mu m developed by dynamic recrystallization at an early stage of superplastic flow. Morphology of grain boundary sliding with straining was inspected by the scanning electronmicroscopy. The contribution of grain boundary sliding was found to be low at an early stage of deformation, but was increasing with deformation. It was found that this trend was corresponding to an increase of misorientation angle by dynamic recrystallization with straining.