Microstructure and Mechanical Properties of a Two-Phase Mg-Li Alloy Processed By Constrained Groove Pressing

Constrained groove pressing (CGP), as a novel severe plastic deformation method, is applied to a two-phase Mg-Li alloy at room temperature, 373 K, 423 K, and 473 K. The microstructural evolution and mechanical properties of Mg-Li alloy sheets during CGP are investigated. The optimum mechanical properties are achieved at 373 K after two passes. The tensile strength and yield strength are 157 MPa and 145 MPa, respectively, with a moderate elongation to failure of 12.4%, and the average micro-hardness is about 63 HV. At 373 K, high-density dislocations induced by CGP are preserved to enhance the strength and microhardness. The cross-orientation procedure improves the deformation homogeneity and results in strength increase and ductility recovery at later stages. Increasing temperature weakens the homogeneity improvement and grain refinement with strain accumulation. The beta-Li phase is refined faster than alpha-Mg phase, and grain sizes about 1 mu m are observed in beta-Li phase. Dynamic recrystallization (DRX) first occurs in the soft and ductile beta-Li phase at 423 K. The grain refinement induced by DRX in beta-Li phase is counteracted by grain coarsening in alpha-Mg phase, which causes no obvious enhancement of mechanical properties at higher temperatures of 423 K and 473 K.