Effects of microstructure modification and pressurized solidification on mechanical property of AZ91 alloy

• Grain size of AZ91 alloy reduced from 500 μm to 124 μm by SiC inoculants.
• Solution route is 400 °C + 16 h for spheroidization without notable grain growth.
• Pressurized solidification favors the flow and feeding capacity of residual liquid.
• Relative density increases continuously with the increase of holding pressure.
• Tensile strength reaches 167 MPa for modified alloy with applied pressure.

Microstructure modification and pressurized solidification were conducted to improve the mechanical property of AZ91 alloy. The addition of SiC inoculants causes remarkable grain refinement and formation of Mg2Si phase with script-like morphology. After solution treatment, the spheroidization process of Mg2Si phase is elucidated and its morphology transforms into particulate-shaped with smooth boundary. Moreover, pressurized solidification is beneficial for enhancing the feeding behavior of residual liquid and the relative density increases continuously with increasing the applied pressure. Due to the combined effect of grain size strengthening, solution strengthening and reduction of stress concentration of brittle phase, maximum tensile strength reaches 167 MPa as for refined AZ91 alloy coupled with exerting pressure during solidification and solution treatment.