Effect Of Initial Microstructure On Microstructure And Mechanical Properties Of Extruded Mg-6Al-2Ca-2Sm Alloy

Magnesium alloy is the lightest metal structural material among practical metals,which can effectively reduce the weight of the product in actual production.In addition,magnesium alloys have a wide range of applications in the automotive industry,aerospace and other fields due to their characteristics such as high specific strength,specific stiffness and specific elastic modulus,and good electromagnetic shielding properties.Compared with as-cast magnesium alloys,deformed magnesium alloys have relatively good mechanical properties.The initial microstructure of the casting slab has an important influence on the final properties of the deformed magnesium alloy.Based on the widely studied Mg-Al alloys,this paper selects alkaline earth element Ca and rare earth element Sm as alloying elements by adopting the composite alloying method.The influence of heat treatment on the microstructure of as-cast alloy is studied.On this basis,the effects of different initial microstructures on the microstructure and mechanical properties of hot-extruded Mg-6Al-2Ca-2Sm alloys were studied,and the tensile properties of Mg-6Al-2Ca-2Sm alloys at different tensile temperatures and different tensile rates were also studied.Through OM,SEM,EDS and other analytical methods,the effects of different initial microstructure on the grain size of hot-extruded Mg-6Al-2Ca-2Sm alloy and the morphology,size,and distribution of the second phase were analyzed.The room temperature tensile test was performed.Through the room temperature tensile test,the effect of the initial microstructure on the mechanical properties of hot-extruded Mg-6Al-2Ca-2Sm alloy at room temperature was analyzed.The effects of tensile temperature and strain rate on the tensile properties of hot-extruded Mg-6Al-2Ca-2Sm alloy were studied through high-temperature tensile test.The results show that:1. In the as-cast Mg-6Al-2Ca-2Sm alloy,the granular Al₂Sm phase is distributed inside the grains,and the fishbone-like Al₂Ca and lamellar?Mg,Al?₂Ca are distributed at the grain boundaries.After solution treated at 420?for 10 h,?Mg,Al?₂Ca transformed into a spherical Al₂Ca phase,while the Al₂Sm phase and Al₂Ca phase did not change as high-temperature stable phases.2. The initial structure has a significant effect on the microstructure and mechanical properties of the hot-extruded Mg-6Al-2Ca-2Sm alloy.The size and morphology of the granular Al₂Sm phase were basically unchanged after hot extrusion,while the fish bone Al₂Ca phase and lamellar?Mg,Al?₂Ca phase were transformed into granular and short rod shapes after hot extrusion.The precipitated phase of as-cast hot-extrusion alloy has segregation,and the distribution of precipitated phase is more uniform in the hot-extrusion alloy structure after solid solution and solid solution+aging treatment,which promotes partial dynamic recrystallization of the alloy.Therefore,the solid solution+aging hot extrusion alloy has the highest mechanical properties,while the as-cast hot extrusion alloy has the lowest mechanical properties.3. Peak stress and elongation of extruded Mg-6Al-2Ca-2Sm alloy are also different at different tensile temperatures and strain rates.Under the same strain rate,the peak high temperature stress of hot-extruded Mg-6Al-2Ca-2Sm alloy decreased with the increase of tensile temperature,and the elongation increased with the increase of tensile temperature.Under the same tensile temperature,the peak high temperature stress of hot-extruded Mg-6Al-2Ca-2Sm alloy increases with the increase of strain rate,and the elongation decreases with the increase of strain rate.4. Different initial structures have a certain effect on the thermal activation energy of the extruded Mg-6Al-2Ca-2Sm alloy.The as-extruded Mg-6Al-2Ca-2Sm alloy has the lowest thermal activation energy,and the solid solution+aging state extrusion Mg-6Al-2Ca-2Sm alloy has the highest thermal activation energy.