An Internal Variable Approach of Orientation Dependent Deformation Mechanism of Rolled AZ31 Magnesium Alloy

Abstract

Load relaxation behavior of an AZ31 Mg alloy has been studied in relation to temperature and orientation dependence. The rolled plate with 50 mm thickness was first homogenized at 400 degrees C for 4 h before preparing test specimens in the directions of 0 degrees (RD), 45 degrees, and 90 degrees (ND) from the rolling direction. A series of tensile tests was consequently carried out under a strain rate of 10(-2)/s at room temperature (RT), 100 degrees C, and 200 degrees C. The RD specimens were found to deform mainly by dislocation slips without twinning. The 45 degrees and 90 degrees specimens were, on the other hand, found to deform in a combined mode of twinning and dislocation slips. Load relaxation tests were also performed to obtain flow curves in terms of stress and strain rate at the three different temperatures. The flow curves in terms of stress vs. strain rate were also found to consist of a plasticity curve due to dislocation glides in the lower strain rate region and a twin curve in the high strain rate range for the 45 degrees and 90 degrees specimens as prescribed by an internal variable theory. These results were consistent with the tensile test results and were further confirmed by microstructure observations.