Influence of Heat Treatment on Microstructures and Impact Toughness of Mg-Al-Zn Alloy
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Microstructures and impact properties of the rolled Mg-8.10Al-0.46Zn-0.18Mn-0.18Ag (wt.%) alloy were investigated under various thermal conditions including as-rolled, solid solution (T4) and solid solution plus aging (T6) states. The results show that the impact toughness of the as-rolled alloy is slightly enhanced after solution treatment but remarkably reduced by the subsequent aging process, exhibiting a similar trend with the elongation of the alloy. Fractography analysis suggests that the impact toughness variations are closely associated with the changes in the deformation mode: the superior impact toughness of the as-rolled and T4 samples are mainly attributed to the occurrence of profuse twins during impact testing, while, in the T6 sample, the twinning activity is significantly suppressed due to the presence of β-Mg17Al12 phases. In addition, the lamellar-shaped β-Mg17Al12 phases are easy to fracture, which accelerates the crack propagation and thus degrades the impact property.
This work was supported by National Basic Research Program of China (Grant No. 2013CB632200), National Natural Science Foundation of China (Grant No. 51574291) and the Fundamental Research Funds of Central South University (Grant No. 502221707).