Ultrafine-grained AZ61 alloy produced by high-pressure torsion: Advent of superplasticity and effect of anisotropy

In this study, an AZ61 Mg alloy was processed by high-pressure torsion (HPT) for grain refinement. The HPT process was carried out using the facility with an upscaled capacity of 500 ton so that 30 mm diameter disks were processed under 6 GPa. Tensile tests were carried out at elevated temperatures and microstructures were observed by transmission electron microscopy (TEM). The grain size was well reduced to similar to 320 nm after HPT processing at 423 K for 10 turns. This reduction in the grain size led to superplastic elongation more than 400% at 473 K with an initial strain rate of 1.0 x 10(-3) s(-1). The results were then compared with those obtained using conventional 10 mm diameter disks. The total elongation is invariably higher for the 30 mm disks than the 10 mm disks. This difference is discussed based on the anisotropy due to material flow.

Automated summary

In this study, an AZ61 Mg alloy was processed by high-pressure torsion (HPT) to refine the grain size. Using a facility with an upscaled capacity of 500 ton, 30 mm diameter disks were processed under 6 GPa. Tensile tests at elevated temperatures showed that the grain size was reduced to around 320 nm after HPT processing at 423 K for 10 turns. This grain size reduction led to a superplastic elongation of more than 400% at 473 K with an initial strain rate of 1.0 x 10(-3) s(-1). Comparing the results with conventional 10 mm diameter disks, it was found that the total elongation was invariably higher for the 30 mm disks, and this difference was attributed to the anisotropy due to material flow.