Microstructure, tensile properties and corrosion behavior of friction stir processed Mg-9Li-1Zn alloy

Abstract The microstructure, tensile properties and corrosion behavior of friction stir processed Mg-9Li-1Zn alloy were investigated. The results show that the microstructure changes from the initial elongated grains of the α-Mg and β-Li phases to refined equiaxed grains after friction stir processing. Friction stir processing results in remarkable grain refinement and random distribution of crystallographic orientations. The mean grain size of the α-Mg phases decreases from 5.7 μm to 2.1 μm, and that of the β-Li phases decreases from 11.9 μm to 2.2 μm. Compared to those of the base metal, the tensile strength and elongation of the friction stir processed sample along the transverse direction of the base metal reach 305 MPa and 28%, corresponding to 48% and 55% improvements, respectively. Conversely, the yield strength decreases from ∼149 MPa to ∼140 MPa. The corrosion current changes from 2.734 × 10 −3 A/cm 2 to 1.092 × 10 −3 A/cm 2 , which indicates improved corrosion resistance. The reasons for these changes are the weakening of galvanic corrosion caused by the solution of Mg 2 Zn 11 phase and the change in corrosion pattern resulting from grain refinement.