Dynamic precipitation, microstructure and mechanical properties of Mg-5Zn-1Mn alloy sheets prepared by high strain-rate rolling

Highlights: • Mg-5Zn-1Mn alloy sheets with high strength and good ductility were fabricated by high strain-rate rolling. • The rolled sheets exhibit optimal mechanical properties with ultimate tensile strength of 359 MPa and elongation of 20.1%. • The enhanced strength and ductility benefit from ultrafine XRD grains and high density of nano-precipitates. • The nano-sized Mg-Zn phases were dynamically precipitated by heterogeneous nucleation on dislocations and α-Mn particles. Mg-5Zn-1Mn (wt%) alloy sheets with good strength-ductility balance were successfully fabricated by high strain-rate rolling (HSRR) in a wide temperature range from 250 °C to 400 °C. The microstructural evolution, dynamic precipitation characteristics and mechanical properties of the as-rolled sheets were investigated. The results show that the dynamic precipitation plays a key role in the as-rolled microstructural evolution and the mechanical properties. The uniform and dispersive precipitates with high spatial distribution density mainly nucleated on the α-Mn particles and along the dislocations during the HSRR. A typical bimodal microstructure can be obtained even at the high rolling temperature (400 °C) by the HSRR process due to the dynamic precipitates strongly pinning the boundaries of the dynamic recrystallization (DRX) grains or subgrains. The sheet fabricated by HSRR at 300 °C exhibits high strength and excellent ductility, with the ultimate tensile strength (UTS), yield tensile strength (YS) and elongation (EL) to failure of 359 MPa, 258 MPa and 20.1%, respectively. The superior mechanical properties can be attributed to the ultrafine DRX grains featured with the bimodal microstructure and the precipitates with high density.