Creep and superplasticity in a spray-cast aluminum alloy processed by ECA pressing

A commercial spray-cast aluminum 7034 alloy, having a composition of Al-11.5% Zn-2.5% Mg-0.9% Cu-0.2% Zr, was processed by equal-channel angular pressing (ECAP) at a temperature of 473 K to reduce the grain size from ∼2.1 to ∼0.3 μm. Microstructural observations revealed a breaking of the rod-like MgZn2 precipitates during ECAP. Static annealing showed the ultrafine grain size was reasonably stable up to a temperature of 673 K. Tensile and creep tests were conducted using specimens cut from the unpressed bars and from billets processed by ECAP. In tensile testing at 673 K, the results on the as-pressed alloy show a potential for achieving high superplastic elongations to failure of >1000% at stain rates at and above 10−2 s−1. In creep testing at 473 K, the creep rates recorded for the as-pressed samples were significantly faster, by about two orders of magnitude, than for the unpressed alloy.