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

An aluminum 7034 alloy, produced by spray casting and with an initial grain size of similar to2.1 mum, was processed by equal-channel angular pressing (ECAP) at 473 K to produce an ultrafine grain size of similar to0.3 mum. 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 similar to670 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. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.