Strengthening And Toughening Mechanism Of Mg-Al-Y Alloy Containing Long Period Stacking Ordered Phase

Mg-1Al-12Y alloy was prepared by melting and casting.The as-cast alloy was treated by solution treatment at different times and temperatures.The effects of solution treatment time and temperature on the microstructure and mechanical properties of the alloy were investigated.The results show that the significant improvement of the mechanical properties of the alloy after solution treatment is mainly attributed to the precipitation of the long-period stacking ordered phase（LPSO）.After solution treatment at 540℃for 4h,the mechanical properties of the alloy are optimal.Compared with the as-cast alloy,the ultimate tensile strength and elongation are increased by 23%and 179%,respectively.The microstructure of the alloy after uniaxial tensile deformation was analyzed by electron backscatter diffraction（EBSD）and transmission electron microscope（TEM）.The results show that LPSO strengthened the alloy by inhibiting twin activation and hindering non-basal slip movement.The microstructure evolution and deformation behavior of three Mg-1Al-12Y alloys with different LPSO content during in-situ tensile were studied by scanning electron microscope（SEM）and EBSD technology.The results show that the deformation of the three alloys is dominated by slip and supplemented by twinning.During the tensile,a single slip system dominates the deformation in each grain,and the activation frequency of basal slip is the highest.The intersection between twins in T4-8h alloy is not conducive to the coordination of deformation,resulting in stress concentration and reducing the plasticity of the alloy.The high content of LPSO in T4-4h alloy inhibits the activation of deformation twins and is conducive to plasticity.In addition,more non-basal slip activation and cross slip in T4-4h alloy are also instrumental in plastic deformation.The effects of temperatures and strain rates on the hot compression properties of Mg-1Al-12Y alloy were studied by Gleeble-3500.The results show that the peak stress decreases with the decrease of strain rate or the increase of compression temperature.The mechanical properties and microstructure evolution of T4 Mg-1Al-12Y alloy with different LPSO content during ex-situ compression were compared.It was found that LPSO could play a strengthening role at 300℃and 350℃,and the strengthening effect of LPSO failed when the temperature increased to 400℃.At 350℃and a strain rate of 0.01s^-1strain rate,the high content of LPSO always exhibits a significant inhibitory effect on the activation of the twin,which is one of the main reasons for the higher mechanical properties of the alloy.