Preparation And Mechanism Of High Strength And Toughness Magnesium Alloy

Magnesium alloys have recently attracted much interest in structural applications due to high specific strength,good cast-ability,and excellent damping capacity.However,the low strength and poor plasticity restrict its wide application.In order to improve the microstructure and mechanical properties of AZ91 magnesium alloy,this study adopted electromagnetic stirring technology and traditional solution treatment and aging treatment,and cryogenic treatment.The effect of hot extrusion on the microstructure and properties of electromagnetic stirred AZ91 magnesium alloy was studied.The mechanical properties of AZ91 alloy were increased after electromagnetic stirring.The tensile strength,elongation and hardness were 168MPa,4.1%and 63.8HB of the AZ91alloy,respectively.After electromagnetic stirring,the?-Mg dendrites were refined and the average grain size was 78.1?m.The coarse?-Mg₁₇Al₁₂2 phases on the grain boundaries were broken and reduced,and the lamellar?-Mg₁₇Al₁₂2 phases were clearly refined.After the hot extrusion,the tensile strength and elongation of the electromagnetic stirred AZ91 alloy were 241MPa and 6.3%,respectively.The grain size was significantly refined of the alloy after extrusion.After the homogeneous annealing treatment of extruded AZ91magnesium alloy,the tensile strength and elongation of the alloy had been significantly improved.The tensile strength and elongation of the alloy were 320MPa and 11.3%after homogeneous annealing treatment for 6h.With the increase of the homogeneous annealing treatment time,the grain size tended to be average,and equiaxed crystals were formed after the homogeneous annealing treatment for 6h.After the solution treatment,the tensile strength,elongation and hardness of electromagnetic stirred AZ91 alloy were 238MPa,10.6%and 67.1HB,respectively.The coarse skeletal?-Mg₁₇Al₁₂2 phases disappeared on the grain boundaries,the?-Mg₁₇Al₁₂2 phases almost completely dissolved,and small amount of?-Mg₁₇Al₁₂2 phases existed in a matrix.After aging treatment,the tensile strength improved of electromagnetic stirred AZ91 alloy after solution treatment for 36h.The tensile strength was 248MPa after aging treatment for10h.However,as the aging time increased,the elongation of the alloy gradually decreased.During the aging treatment,firstly,the precipitation of?-Mg₁₇Al₁₂2 phases was dominated by discontinuous precipitation on grain boundaries.As the aging time increased,the layered?-Mg₁₇Al₁₂2 phases formed inside grains,the precipitation of?-Mg₁₇Al₁₂2 phase was dominated by continuous precipitation.After the cryogenic treatment,the tensile strength,elongation and hardness were 238MPa,10.6%and 67.1HB respectively after the cryogenic treatment for 24h.The grains were refined and the precipitation of the second phase particles yielded in the cryogenic process,and the distribution of second phases was more diffuse.After the aging treatment,the tensile strength and elongation of AZ91 alloy were 261MPa and 11.4%after cryogenic treatment for 1h,the elongation almost not changed.The cryogenic treatment played a pre-aging role.