Effects of dynamic recrystallisation during deep rolling of semisolid slab and heat treatment on microstructure and properties of AZ31 alloy

A novel process of manufacturing high performance AZ31 alloy strip was put forward by combining semisolid rolling, deep rolling and heat treatment, and the effects of dynamic recrystallisation during deep rolling of semisolid slab and heat treatment on microstructure and properties of AZ31 alloy were investigated. When the casting temperature was set from 650 to 690 degrees C and the vibration frequency was controlled at 80 Hz, AZ31 alloy strip with the cross-section size of 46160 mm and fine near round and rosette grains was manufactured by semisolid rolling. Dynamic recrystallisation happened during deep rolling process. Dynamic recrystallisation grain size decreases with the increase in deep rolling temperature in a certain scope. With the increase in deep rolling deformation amount, the microstructure evolved gradually from coarse primary grains and twins to fine dynamic recrystallisation grains and twist primary grains as well as small regular equiaxed grains. AZ31 alloy strip with very fine equiaxed grain in size of 6 mu m was obtained by deep rolling. After solution treatment at 415 degrees C for 20 h, the saturated solid solution of AZ31 alloy strip has been formed. After solution treatment at 415 degrees C for 20 h and aging at 230 degrees C for 16 h, the deep rolled AZ31 alloy strips exhibit excellent mechanical properties; the ultimate tensile strength, yield strength, elongation to failure and hardness could reach 330 MPa, 204 MPa, 11% and 71 HV respectively.