Plastic deformation behavior of Mg-8Li dual phase alloy during multi-directional compression

The Mg-8Li dual phase alloy was deformed by multi-directional compression with different passes. Microstructure evolution of deformed Mg-8Li alloy was analyzed by electron backscatter diffraction. X-ray diffraction profile was used to calculate the dislocation density in alpha-Mg and beta-Li phase to reveal the quantitively change trend under different compression passes. The mechanical properties were assessed through tensile and compressive tests. The Mg-8Li alloy exhibited optimal mechanical properties when compressed with 12 passes (sample 12MDC), with a compression yield strength of 183.1 MPa and a tensile yield strength of 124.2 MPa. The improved mechanical properties in sample 12MDC were attributed to an increase in {10 1 2} twin and {101 3}{101 2} double twin boundaries, along with the presence of sub-grain boundaries and a reduced grain size in the alpha-Mg phase. Additionally, the inconsistent results between microhardness and dislocation density calculation manifests the uneven distribution of dislocations in beta-Li phase. Broken alpha-Mg phase brings more phase interface to relieve the strain in beta-Li phase, which results to a decreased dislocation density in sample 12MDC (1.19 x 1011/ m2). Results show that weaken tension-compression yield asymmetry and more even distribution of dislocation in both phases could be achieved when the compression passes increases to 12.