Ultra-high tensile strength induced by multiple precipitates in extruded ZK60 alloy via co-alloying Ca and Er

Obtaining ultra-high strength in commercial ZK60 wrought alloys is rather difficult by conventional processes due to their limited precipitation hardening. In this work, we proposed a novel strategy to enhance the strength of ZK60 alloy by constructing a high density of multi-scale particles in the matrix. As expected, the ultra-high tensile strength, such as ultimate tensile strength of 436 MPa and yield strength of 400 MPa, is achieved in the co-addition of minor Ca and Er in ZK60 extrusion alloys, outperforming most of Mg-Zn-based alloys reported previously. The co-addition of Ca and Er induces more multi-scale particles, including submicron-broken particles and fine dynamic precipitates formed in the matrix during extrusion. Note that fine precipitates at sub-grain boundaries stabilize their misorientations due to the pinning role and thus retard the dynamic recrystallization process, which intensifies the deformation texture of the bimodal structures. Solute segregation of Ca and Zn to grain boundaries was also observed, which favors refining recrystallized grains by solute drag effect. Compared to ZK60 alloy, the enhanced tensile strength in co-modified ZK60 alloy with Ca and Er is mainly attributed to the Orowan strengthening of multiscale particles. These results are expected to provide an important reference for fabricating high-strength Mg-Zn-based alloys.