Using ECAP to achieve grain refinement, precipitate fragmentation and high strain rate superplasticity in a spray-cast aluminum alloy

An aluminum 7034 alloy, produced by spray casting and with an initial grain size of ~2.1 ?m, was processed by equal-channel angular pressing (ECAP) at 473 K to produce an ultrafine grain size of ~0.3 ?m. It is shown that the rod-like MgZn2 precipitates present in the as-received alloy are broken into very small spherical particles during ECAP and these particles become distributed reasonably uniformly throughout the material. The presence of these fine MgZn2 particles, combined with a distribution of fine Al3Zr precipitates, is very effective in restricting grain growth so that submicrometer grains are retained at elevated temperatures up to at least ~670 K. Tensile testing of the pressed material revealed high elongations to failure, including elongations of >1000% when testing at a temperature of 673 K at initial strain rates at and above 10?2 s?1. These results confirm the occurrence of high strain rate superplasticity in the spray-cast alloy