Effect of friction stir processing on microstructure and tensile properties of as-cast Mg–8Li–3Al–2Sn (wt.%) alloy

Abstract

A new Mg–8Li–3Al–2Sn (LAT832, wt.%) alloy was cast by vacuum induction melting and processed by friction stir processing (FSP). Microstructure and tensile properties of as-cast and FSP LAT832 samples were studied comparatively. It is found that, as-cast LAT832 sample consists of α-Mg+β-Li duplex-phase matrix and MgLiAl2 and Li2MgSn intermetallic phases. After FSP, an inverted-trapezoidal stir zone (SZ) is formed and onion-ring structure occurs at the center of SZ. Complete dynamic recrystallization (DRX) occurs in SZ of FSP LAT832 sample and α-Mg grains are significantly refined, but the microstructure is inhomogeneous. Li2MgSn phase is crushed into coarse particles while MgLiAl2 phase is decomposed into fine AlLi particles. Tensile properties of as-cast LAT832 sample are significantly enhanced by FSP, which benefits from strengthening effect of grain refinement of α-Mg phase and broken Li2MgSn particles.