Biaxial Deformation Behavior of AZ31 Magnesium Alloy at High Temperatures

Abstract

The evaluation of plastic deformation processing of materials has been based mainly on uniaxial tensile tests. However, for the analysis of multiaxial stress conditions in sheet-metal plastic forming, more complex tests, such as the controlled biaxial test with cruciform specimens, are required. In this report, we examine the relationship between the biaxial deformation behavior and microstructure of AZ31 magnesium alloy for initial strain rates of 3.0 x 10^-3 s⁻¹ and 2.8 x 10⁻⁴ s⁻¹ at 573 K and 623 K using cruciform specimens. The results show that the flow stress increases with decreasing sheet thickness, and the occurrence of tensile twins is confirmed during biaxial tensile deformation at an elongation of 30 % in a cross-section of a specimen under 623 K for a strain rate of 2.8 x 10⁻⁴ s⁻¹. This deformation behavior and evolution of the micro structure is unique in biaxial tensile tests, and is not recognized in uniaxial tensile tests with the same elongation. Since this controls the width direction of the specimen during deformation, we can only guess that the plate thickness direction can be deformed freely and without restraint. In other words, for biaxial tensile test conditions, the transition point of the microstructure under the influence of the constraint of grain boundary sliding is at 623 K for a strain rate of 2.8 x 10⁻⁴ s⁻¹.