Potential of strain-integrated gas infusion (SIGI) casting on post-heat treatment kinetics of AZ91 magnesium alloy

Abstract

Heat treatments play a crucial role in enhancing the mechanical properties of AZ91 Mg alloy by dissolving coarse phases during solution treatment and promoting precipitation during aging. However, non-uniform microstructures and coarse secondary phases in conventional casting methods hinder the effectiveness of these treatments, leading to reduced ductility, inconsistent properties, and prolonged durations. To overcome these challenges, this study introduces the Strain Integrated Gas-Infusion (SIGI) casting process that integrates strain and gas infusion in the semi-solid state. The impact of the SIGI process on the solution treatment and aging kinetics of AZ91 Mg alloy is explored. The SIGI process refines α-Mg and β-Mg₁₇Al₁₂ phases, significantly enhancing mechanical properties. Experimental and quantitative analyses reveal that the SIGI process accelerates solute atom dissolution, reducing solution treatment times by half, and promotes faster nucleation and growth of precipitates during aging, shortening aging times by one-third. These improvements result in substantial gains in ultimate tensile strength (∼40–50%) and ductility (∼20–30%) after age hardening compared to conventional casting. The mechanisms driving these changes, including enhanced nucleation rates, reduced diffusion distances, and microstructural refinement, are discussed. These findings demonstrate the potential of the SIGI casting process to advance magnesium alloy performance for engineering applications.