マグネシウム合金 AZ61 の高温 HPT 法による結晶粒微細化および機械的特性

Abstract

A magnesium alloy AZ61 was subjected to a process of severe plastic deformation through high pressure torsion (HPT) at room and elevated temperatures. For the HPT process, a pressure of 3 GPa was applied to the alloy with a disk-shaped sample having dimensions of 10 mm in diameter and 0.8 mm in thickness while the lower anvil was rotated with respect to the upper anvil with a rotation speed of 1 rpm for up to 7 turns. Microstructures were observed using optical microscopy and transmission electron microscopy. Hardness was measured across the diameter of the sample to examine any variation with respect to positions from the center of the disk under different HPT conditions. Tensile tests were carried out at 473 K with initial strain rates ranging from 3.3×10-4 s-1 to 3.3×10-2 s-1. Microstructure observations revealed that the average grain size was reduced to 0.52, 0.37, 0.23 and 0.22 μm after 1, 3, 5 and 7 turns, respectively, for HPT performed at 423 K, Superplasticity with an elongation to failure of 620% was attained for the sample processed after 5 turns at 423 K when the tensile specimen was deformed at 473 K with an initial strain rate of 3.3×10-3 s-1.