Microstructure and Mechanical Properties of Ultra-Light and High-Strength Mg-xLi-3Al-2Zn-0.2Y Alloy Produced by Warm Rolling Coupled Annealing Processes

The effect of the strengthening mechanism on the tensile properties and microstructural evolution of Mg-xLi-3Al-2Zn-0.2Y (x = 5, 8, 11) alloy sheets during rolling and annealing at different temperatures was studied. The results indicated that, with the increase in temperature, the α-Mg matrix gradually softens, which is beneficial for improving the ductility of the Mg-5Li-3Al-2Zn-0.2Y (LAZW5320) and Mg-8Li-3Al-2Zn-0.2Y (LAZW8320) alloys. Shear bands were discovered in the α-Mg matrix of the as-rolled LAZW5320 and LAZW8320 alloys. The Al₂Y phase demonstrates remarkable heat resistance stability, while the AlLi phase is prone to decomposition and dissolution into the β-Li matrix with increasing annealing temperatures. TEM observations reveal that the black AlLi phase consists of numerous nano-phase clusters, with a small number of residual dislocations around them due to insufficient annealing time. Solution strengthening is identified as the main factor enhancing the strength and microhardness of the LAZW8320 and Mg-11Li-3Al-2Zn-0.2Y (LAZW11320) alloys. As the annealing temperature rises, the dissolved atoms of the AlLi phase in these alloys gradually incre ase, promoting the growth of interaction and deformation energy, which is beneficial for the improvement of strength and hardness. Additionally, the dissolved atoms in the AlLi phase pin the dislocation lines, impeding their smooth movement and increasing the pinning stress, thereby increasing the strength and microhardness.