Fracture Behavior And Elevated Temperature Mechanical Properties Of Cast EV31 Magnesium Alloy

EV31 Magnesium alloy exbhibit excellent mechanical properties with low RE levels,which makes it have broad application prospects in rail transit,aerospace,national defense and other fields.However,the current research on EV31 alloys is mainly focused on gravity casting,and there were few reports on low-pressure casting.In this study,room temperature mechanical properties and fracture behaviour of low-pressure casting Mg-2.60Nd-1.29Gd-0.37Zn-0.27Zr（EV31A）alloy under the load of quasi-static,impact and fatigue were investigated firstly,and then tensile and compressive properties of the alloy at elevated temperature were investigated.The results showed that the yield strength,ultimate strength and elongation of as-cast alloy were 93 MPa,192 MPa and 8%;solution and aging treatment could effectively improve the mechanical properties of the alloy,and the yield strength,ultimate strength and elongation of peak aged alloy were 156MPa,292MPa and 6%.The fracture modes of as-cast alloy under quasi-static load were intergranular quasi-cleavage fracture,and transgranular quasi-cleavage fracture for as-quenched and aged alloy respectively.Room temperature impact toughness of as-cast,as-quenched and aged alloy were4.40,9.02 and 5.25J/cm².The fracture surfaces of three states of alloy under impact load were radiation zone,and the fracture modes were intergranular quasi-cleavage fracture,transgranular quasi-cleavage fracture and transgranular quasi-cleavage fracture respectively.The impact toughness of alloy has a good linear relationship with the elongation,hardness and static toughness.The Fracture toughness values of the as-cast,as-quenched and aged alloy were 13.9,16.7 and 17.0 MPa·m^1/2,which indicates that solution and aging treatment could effectively improve the fracture toughness of the alloy.The fracture mode of as-cast alloy is intergranular quasi-cleavage fracture,and that of the as-quenched and aging alloy is transgranular quasi-cleavage fractur.The tensile strength of aged alloy decreases with temperature increased,fracture mode was a mixed mode of ductile and brittle below 300℃while ductile fracture above 300℃.The true stress-strain curves of as-homogenized alloys all show obvious dynamic recrystallization characteristics under hot compression.The deformation activation engergy of alloy were 219 KJ/mol,and the optimum condition for the hot working of alloy is in the region of 450-500℃,0.01-0.1s^-1.