Evaluating the Superplastic Flow of a Magnesium AZ31 Alloy Processed by Equal-Channel Angular Pressing

Experiments show that the magnesium AZ31 (Mg-3 pct Al-1 pct Zn) alloy exhibits excellent superplastic properties at 623 K (350 A degrees C) after processing by equal-channel angular pressing using a die with a channel angle of 135 deg and a range of decreasing processing temperatures from 473 K to 413 K (200 A degrees C to 140 A degrees C). A maximum elongation to failure of similar to 1200 pct was achieved in this alloy at a tensile strain rate of 1.0 x 10(-4) s(-1). Microstructural inspection showed evidence for cavity formation and grain growth during tensile testing with the grain growth leading to significant strain hardening. An examination of the experimental data shows that grain boundary sliding is dominant during superplastic flow. Furthermore, a comprehensive review of the present results and extensive published data for the AZ31 alloy shows the exponent of the inverse grain size is given by p a parts per thousand 2 which is consistent with grain boundary sliding as the rate-controlling flow mechanism. (C) The Minerals, Metals & Materials Society and ASM International 2013