Dynamic precipitation behavior and mechanical properties of a hot rolled Mg–Zn–Gd alloy

Various Mg-2Zn-2Gd (wt.%) alloys were hot rolled at 400°C to 500°C to study the dynamic precipitation behavior and mechanical response in this work. The results show that hot deformation refines grain size significantly from ∼100 μm in the as-cast alloy to 5.70 μm after rolling, accompanied by the formation of dynamically precipitated sub-micro GdZn second-phase (SP) particles that are rarely reported in Mg-Zn-Gd alloys. The fraction of SP particles varies temperature-dependently due to the crystal defect assisted nucleation and growth. As the Mg alloy is rolled at 450°C (R450), plentiful sub-micro SP particles appear owing to the balance of solute diffusion and crystal defect density, along with a high fraction of low angle grain boundaries (78.4%). Hot deformation enhances the strength-ductility synergy and the best comprehensive properties with ultimate tensile strength of 302 MPa, yield strength of 236 MPa and elongation to failure of 15.2% are achieved for R450, representing enhancements of 141.6%, 198.7% and 334.3% respectively as compared to as-cast alloy. The basal slip propagates through the low angle grain boundaries to improve the deformation coordination between grains, and the work hardening is improved through quadruple interactions between SP particles, dislocations, twins and low angle grain boundaries, accounting for the toughening of R450.