Enhanced corrosion resistance of AZ91D magnesium alloy through refined and homogeneous microstructure by rapid solidification and hot extrusion technique

• Rapid solidification and hot extrusion technique significantly modified the microstructure of AZ91D magnesium alloy, leading to a substantial enhancement in corrosion resistance ( P w , AC / P w , RS - HE = 361 %) and mechanical properties (UTS = 392.1 MPa, YS = 289.7 MPa, EL = 14.8 %). • Corrosion tests were conducted using multiple methods, including weight loss, hydrogen evolution, potentiodynamic polarization curve, EIS (electrochemical impedance spectroscopy) response, and surface morphology characterization. The corrosion rates of AZ91D magnesium alloy followed the order: as-cast alloy > heat-treated alloy > heat-treated and hot-extruded alloy > rapidly solidified and hot-extruded alloy. • The structure–property relationship between the microstructure and corrosion behavior of AZ91D magnesium alloy was investigated. Results revealed that fine and uniformly distributed second-phase particles and fine grains, more readily form a dense and continuous corrosion product film, thereby reducing corrosion. • The corrosion mechanisms were studied by analyzing the kinetics of corrosion reactions under different processing conditions via EIS responses. The influence of two electrode surface state variables θ (the fraction of the surface area uncovered by the corrosion film) and C M g + (the activity of intermediate univalent Mg ion)—on the corrosion process was analyzed. Achieving both high corrosion resistance and strength simultaneously has always been a long-standing goal for lightweight structural materials. In this study, we prepared an AZ91D magnesium alloy with a refined and homogeneous microstructure by rapid solidification hot extrusion technique. The corrosion behavior of AZ91D magnesium alloy in as-cast (AC), heat-treated (HT), heat-treated and hot-extruded (HT-HE), and rapidly solidified and hot-extruded (RS-HE) states were investigated through weight loss, hydrogen evolution, and electrochemical experiments. The structure–property relationships between the microstructure and macroscopic corrosion behavior of AZ91D magnesium alloy under various processing conditions were elucidated by combining corrosion kinetics and mechanisms. The results demonstrate that Rapid solidification and hot extrusion technique significantly enhances the corrosion resistance of AZ91D magnesium alloy through grain refinement, uniform second-phase dispersion, and extended solid solubility. Furthermore, this study reveals that Rapid solidification and hot extrusion technique markedly improved the mechanical properties of as-cast AZ91D magnesium alloy (UTS = 392.1 MPa, EL = 14.8 %).