High Strain Rate and/or Low Temperature Superplasticity in AZ31 Mg Alloys Processed by Simple High-Ratio Extrusion Methods

There have been numerous efforts in processing metallic alloys into fine-grained materials, so as to exhibit high strain rate superplasticity (HSRSP) and/or low temperature superplasticity (LTSP). The current study applied the most simple and feasible one-step extrusion method on the commercial AZ31 magnesium ingot to result in HSR&LTSP. The one-step extrusion was undertaken using a high extrusion ratio at 250-350° C, and the grain size after one-step extrusion became ∼ 1-4 μm. The processed AZ31 plate exhibited satisfactory room temperature tensile elongation of 30-50%; 200°C elongations of 600% at 1 × 10^-4 S^-1 and 425% at 1 × 10^-3 s^-1; and 300°C elongations of 900% at 1 × 10^-4 s^-1, 520% at 8 × 10^-3 s^-1 300% at 2 × 10^-2 s^-1, and 210% at 1 × 10^-1 s^-1. This suggests that the current AZ31 Mg alloy has possessed HSRSP at relatively low temperatures of 280-300°C, as well as LTSP at 200°C. The low flow stress of 15-30 MPa and the true strain rate sensitivity of 0.3-0.4 both suggest that grain boundary sliding and solute drag creep have operated under these loading conditions. The current results imply that the simple high-ratio extrusion method might be a feasible processing mean for industry applications.