Effect of homogenization on microstructures and mechanical properties of hot compressed Mg–9Al–1Zn alloy

Abstract

The effect of homogenization before hot compression on the microstructures and mechanical properties of the compressed specimens of a Mg–9%Al–1%Zn–0.2%Mn (AZ91) alloy is investigated. Homogenizations were carried out at 415°C for 24 and 100h. The as-cast and homogenized alloy samples were hot compresses at 350°C with a strain rate of 0.2s−1. Eutectic Mg17Al12 (β) phase observed along grain boundaries in the as-cast sample disappears by homogenization at 415°C for 24h; however, the solute atoms were concentrated near the grain boundaries. In the 100-h-homogenized sample, solute atoms were distributed uniformly in the grains. During heating and holding process before compression, a large amount of Mg17Al12 phase precipitated in the region of high Al concentration. With increasing homogenization time, more uniform precipitation of Mg17Al12 phase occurs during holding before compression. The precipitation is very uniform in the 100-h-homogenized sample. During hot compression, dynamic recrystallization (DRX) mainly occurs in the Mg17Al12-precipitating region. These DRXed grains have high Schmid factors for (0 0 0 1)1 1 2¯ 0 basal slip. Thus, the DRX ratios and the basal slip Schmid factors of the compressed specimens increase with increasing homogenization time. The compressed specimens of 100h homogenized samples show a much higher ultimate tensile strength (UTS) of 329±3MPa and over tenfold increase in the elongation to failure (23.8±2.5%) than that of the compressed specimen of as-cast sample (UTS 256±5MPa and elongation 2.2±0.8%).