Effect of Strain Rate and Temperature on Fracture and Microstructure Evolution of AZ91D Magnesium Alloy Processed by Laser Surface Melting

In this study, microstructure evolution and fracture of the AZ91D magnesium alloy processed by laser surface melting (LSM) were investigated in the temperature range of room temperature (RT) ~ 350 °C and the strain rate range of 10⁻⁴ to 10⁻¹ s⁻¹. Macro fracture morphology of the LSM-treated sample was tortuous, and this was responsible for the improved strength compared to that of the as-received sample at different temperatures and strain rates. Micro fracture morphology of the laser-melted zone was always the ductile mode at different temperatures and strain rates, whereas micro fracture morphologies of the untreated zone were brittle fracture at RT and the ductile mode at high temperatures. Dynamic recrystallization was not observed in the laser-melted zone at different temperatures and strain rates, and this can contribute to the improved strength of the LSM-treated sample. In addition, the improved strength of the LSM-treated sample was also attributed to better thermal stability compared to that of the as-received sample.