Effect of a homogeneous recrystallized microstructure and a bimodal microstructure on mechanical properties in Mg-5Zn-0.6Zr alloys

For typical Mg-Zn-Zr alloys, exhilaratingly high strength of a yield strength (YS) higher than 300 MPa can hardly be attained by traditional rolling. In this paper, we compare the mechanical properties and strengthening mechanisms of the Mg-5Zn-0.6Zr alloys having a homogeneous dynamical recrystallized microstructure and a bimodal microstructure with high-density nano substructures. The Mg-5Zn-0.6Zr alloy with the bimodal microstructure (rolled at 150 °C with a thickness reduction of 60%) exhibits a YS of 332 MPa, an ultimate tensile strength (UTS) of 360 MPa, and an elongation of 5%. The high strength is attributed to the microstructure with high-density nano substructures, high-density nano (Mg, Zr)Zn₂ precipitates, ultrafine recrystallized grains, and strong basal texture. In comparison, the Mg-5Zn-0.6Zr alloy with homogeneous microstructure (rolled at 200 °C with a thickness reduction of 70%) exhibits a YS of 209 MPa, an UTS of 317 MPa, and an elongation of 17%, which contains coarser recrystallized grains, coarser precipitates, weaker texture, and lower density of dislocations, further resulting in low strength. The difference between the strengthening mechanism in two kinds of microstructure is discussed in detail. The results facilitate the preparation of wrought Magnesium alloy with high strength by reasonable microstructure construction.