Developing grain refinement and superplasticity in a magnesium alloy processed by high-pressure torsion

Experiments were conducted on a Mg-9% Al alloy to evaluate the microstructural characteristics and the tensile properties at elevated temperatures after processing by high-pressure torsion (HPT) at room temperature and at 423 K. Ultrafine grain sizes were achieved by processing samples in both an extruded and a cast condition. The results demonstrate the viability of using HPT as a processing technique for achieving significant grain refinement in magnesium alloys which are not processed easily by equal-channel angular pressing (ECAP). Superplastic ductilities were achieved in tensile testing at a temperature of 473 K with a maximum measured elongation of 810%. In general, higher superplastic elongations were achieved after processing by HPT at 423 K because of the development of some limited internal cracking when processing at room temperature.