The effect of high Al content on the microstructure and mechanical properties of Mg-xAl alloys processed by equal channel angular pressing

In this work, Mg-xAl alloys with an Al content ranging from 10 to 20 wt.% were subjected to equal channel angular pressing (ECAP). The effects of the high Al content on the microstructure and mechanical properties of the alloy before and after ECAP were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis and tensile testing. The results demonstrated that as the amount of Al in the as-cast Mg-xAl alloys increased, the grain size of the as-cast Mg-xAl alloys decreased, whereas the amount of the Mg17Al12 phase with network structure increased. After ECAP, the network β-Mg17Al12 phase was significantly broken into fine pieces. The fine β-Mg17Al12 granules were precipitated from the α-Mg matrix. The broken β-Mg17Al12 phase in the Mg-15Al alloy exhibited a relatively homogeneous distribution. As the Al content increased, the grain size in the α-Mg-rich area decreased. However, the β-Mg17Al12 size in the α+β two-phase area of the ECAPed Mg-15Al alloy was the smallest among the three alloys. The yield strength of the Mg-xAl alloys increased, whereas the elongation to fracture significantly decreased.