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

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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 \\micron. 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.