Improving mechanical properties of an AZ91 alloy by properly combining aging treatment and torsion deformation

Abstract

In this work, peak-aging and torsion deformation were applied on an extruded AZ91 alloy to tailor its microstructure and mechanical properties. Comprehensive microstructure analyses were performed on the samples subjected to different deformation and peak-aging routes. The experimental results show that reversing the sequence of the applied deformation and peak-aging treatment on the AZ91 sample significantly influences its mechanical properties. The sample subjected to peak-aging and subsequent torsion deformation has higher yield strength compared to the sample subjected to pre-torsion deformation and subsequent aging treatment. Some precipitates exhibit irregular shapes due to the interaction with twin boundaries. The precipitates found in twins have the OR of (0001)t ∼ 6°//(1¯ 1 2¯)β and [2 1¯1¯ 0]t//[1¯ 11]β with the α-Mg lattice. The precipitates in the matrix generally have the Burgers OR, but this OR was slightly deviated by the presence of plenty of dislocations. The present comparative study suggests that it is more effective to strengthen age-hardenable Mg–Al alloys by applying peak-aging prior to torsion deformation.