Influence of secondary extrusion on microstructures and mechanical properties of ZK60 Mg alloy processed by extrusion and ECAP

The microstructures and properties of ZK60 alloy were evaluated under four different conditions: extrusion; extrusion and 4 passes of equal channel angular pressing (ECAP); extrusion, 4 passes of ECAP and secondary extrusion; and extrusion, 4 passes of ECAP, annealing and secondary extrusion. Secondary extrusion at ambient temperature was successfully processed to produce ultrafine-grained ZK60 alloy. The results show that ECAP introduces significant grain refinement and there is additional refinement in secondary extrusion. High yield strength of 342 MPa is achieved after secondary extrusion at room temperature, but the elongation to failure is only 0.8%. However, by applying annealing before secondary extrusion, the ductility of ZK60 could be greatly improved to 4.5%, meanwhile the yield strength almost remains the same, and the ultimate strength of up to 388 MPa is obtained.