The significance of cavitation in a superplastic aluminum alloy processed by ECAP

A commercial spray-cast aluminum 7034 alloy was processed by equal-channel angular pressing (ECAP) to produce an ultrafine grain size of similar to 0.3 mu m. Tensile tests were conducted on both as-received and as-pressed specimens at 673 K and the results showed the occurrence of high strain rate superplasticity in the as-pressed material. Micrographs of fractured specimens revealed evidence for the development of extensive cavitation during the tensile testing. Quantitative measurements were conducted to evaluate the significance of internal cavitation in the tensile testing of both the as-received and the as-pressed Al-7034 alloy. Measurements were taken to record information on the sizes and shapes of the cavities and these data were evaluated to determine the dominant cavity growth mechanisms. It is shown that the superplastic diffusion growth mechanism is important in ultrafine-grained materials processed by ECAP.