Comparative study on contribution of bimodal microstructure and heterogeneous microstructure to mechanical properties of ZK60 alloy

In this work, we compared the effects of bimodal microstructure and heterogeneous microstructure on the mechanical properties and strengthening mechanisms of ZK60 alloy. The bimodal microstructure is composed of coarse un-dynamically recrystallized (un-DRXed) grains with strong basal texture and fine dynamically recrystallized (DRXed) grains with weak texture, while the heterogeneous microstructure is composed of coarse DRXed grains and fine DRXed grains. The result suggests that high-density dislocations and high-density precipitates have significant contribution to the strength. The high-density dislocations in un-DRXed grains cause the formation of an uneven distribution of precipitates in the ZK60 alloy which results in the high yield strength of 305 MPa, ultimate tensile strength of 344 MPa and elongation of 12% in the bimodal-structured ZK60 alloy. In comparison, the heterogeneous-structured ZK60 alloy lacks the strengthening effect from high-density dislocations and precipitates, and a lower YS of 226 MPa, and UTS of 305 MPa are achieved. The result also indicates the weak texture, low density of dislocations, low density of precipitates, and stronger ability of storing dislocations in coarse grains for heterogeneous microstructure are helpful to the ductility. Thus, HE sample exhibits higher elongation of 23% than BI sample. The finding shed light on the microstructure designing of high-performance Mg alloys.