Microstructure and mechanical properties of magnesium-lithium alloy prepared by friction stir processing

In this study, the fine-grained Mg-Li alloy was prepared by friction stir processing (FSP). The microstructure and mechanical properties of the friction-stir-processed (FSPed) Mg-Li alloy were investigated. The result showed that FSP resulted in the grain refinement, and the average grain size of the beta-Li phase was about 7.5 mu m. Besides the alpha-Mg and beta-Li phases, a small amount of Li3Mg7, Li2MgAl and AlLi phases were obtained. Compared with the base metal (BM), the weakening of the crystallographic texture occurred in the FSPed material, and the c-axis of the alpha-phase and the crystallographic orientation of the beta-phase were tilted about 45 degrees with respect to the transverse direction (TD). The average microhardness (HV 67.8) of the stir zone was higher than that of the BM (HV 61.5). The yield strength (YS) and the ultimate tensile strength (UTS) of the FSPed material were higher than those of the BM, while the elongation slightly reduced. Grain refinement had more significant effect on strength improvement compared with the texture variation for the FSPed material. The fracture surfaces of the BM and FSPed materials showed dimple characteristics.