Effects of Artificial Aging and Precipitation on Tensile Mechanical Properties and Failure Mechanism of the Friction Stir Processed Dual-phase Mg-Li Alloy

The present study is to clarify the artificial aging and texture effects on tensile mechanical properties and failure behaviors of the a/B dual- phase Mg-8.5Li-2.8Al-1.1Zn (LAZ931) alloy through the friction stir process (FSP). It is noted that the Mg-rich a-phase was dissolved in the Li-rich B-phase matrix after the FSP modification. The increasing microhardness within the stir zone (SZ) was resulted from the grain refinement of the B-phase. After performing an artificial aging at 150 °C, needle-like ultra-fine grains of the a-phase precipitated from the B-phase matrix, especially occurred at the SZ. The crystallographic orientation and the texture of LAZ931-FSP were determined by X-ray diffraction and pole figure analysis. The tensile strength was increased, but the elongation was decreased for the LAZ931-FSP specimens. However, the elongation of LAZ931-FSP was increased after the artificial aging treatment. The inter-granular failure resulted from the decohesion at a/B-interface and cracks propagation along the B-phase grain boundaries.