Effect of large thickness-reduction on microstructure evolution and tensile properties of Mg-9Al-1Zn alloy processed by hard-plate rolling

The effect of large thickness-reduction on microstructure evolution and tensile properties of Mg-9 Al-1 Zn alloy(AZ91) processed by hard-plate rolling(HPR) was investigated.Increasing rolling reduction from55 % to 85 % increases the volume fraction and refines average size of fine grains(<3 μm,FGs),leading to an optimized bimodal-grained structure consisting of coarse grains(CGs) uniformly embedded in FG regions.The sample with 85 % reduction exhibits the highest yield strength of～314 MPa,ultimate tensile strength of～381 MPa and elongation of～11 %.The high strength is primarily due to the contribution of grain boundaries(GBs) strengthening by FGs(accounting for～65 % of strength),meanwhile the improved ductility originates from the optimized bimodal-grained structure and weakened basal texture that favor a higher ductility.The present findings successfully overcome the trade-off dilemma that the largereduction rolling processing on Mg alloys usually enhances strength at expense of ductility.In addition,the intensified heterogeneous deformation and favorable formation of a bimodal-grained microstructure during large-reduct ion HPR was addressed by tracing micro structure evolution details in grains of intere st via quasi-in-situ electron back scattering diffraction(EBSD).The present study can be instructive for further designing novel Mg alloys by tailoring bimodal-grained structures for superior combination of mechanical properties.