Microstructural evolution and plastic stability during superplastic flow in a 7475 aluminium alloy

Superplastic behaviour and microstructural evolution were examined at 788 K for strain rates in the range 2 x 10(-4)-2 x 10(-3) s(-1) in a 7475 aluminium alloy of nominal composition Al-(1.2-1.9)Cu-(5.2-6.2)Zn-(1.9-2.6)Mg (wt-%). In addition, the variation of the strain hardening and plastic stability parameters with strain was investigated based on experimental grain growth and cavitation data. The strain hardening parameter at 2 x 10(-4) s(-1) was high over a wide range of strain because of the high grain growth rate. Decrease in the strain hardening parameter due to cavitation was negligible. The highest plastic stability parameter was attained at 2 x 10(-4) s(-1), although the strain rate sensitivity was the lowest for the strain rate range investigated. This demonstrates the influence of spain growth on high plastic stability during superplastic deformation. MST/3839.