Uneven microstructure in ZK60 alloy as a core of AZ31/ZK60 composite rods

AZ31/ZK60 bimetal rods were fabricated via co-extrusion of hybrid billets with ZK60 core prepared by different styles. Uneven microstructures were revealed in ZK60 core of AZ31/ZK60 composite rods prepared by pouring melt (ZK60-melt) into AZ31 sleeve and casting to be ingots to fit AZ31 sleeve (ZK60-ingot) followed by co-extrusion. Compared with the microstructure composed of equiaxed coarse and fine grains in ZK60-melt after co-extrusion, a mixed grain structure with large elongated grains and fine equiaxed grains was observed in ZK60-ingot core in the composite rod. During aging at 180 °C for 12 h abnormal grain growth (AGG) was revealed in ZK60-melt core, but the uneven structure in ZK60-ingot remained thermally stable. Mechanical properties of AZ31/ZK60 composite rods with both ZK60-melt and ZK60-ingot cores were improved significantly by aging.