Grain refinement of magnesium alloys by in-situ formed Al2RE particles: a comprehensive review
Amirali Iranpour Mobarakeh, Fatemeh Asghari, Shaghayegh Khoshdel, Hamed Mirzadeh, Mehdi Malekan, M. Emamy
Abstract
Grain refinement in Mg–Al-based alloys remains a major challenge, as conventional refiners such as zirconium are ineffective due to the strong affinity between Al and Zr. However, the addition of rare earth (RE) elements enables the in-situ formation of Al 2 RE intermetallic compounds, which serve as efficient heterogeneous nucleation sites during solidification. Their grain refining ability becomes more pronounced when multiple RE elements are simultaneously added, leading to synergistic effects . Moreover, Al 2 RE particles with suitable morphology are thermally stable and promote particle-stimulated nucleation (PSN) during subsequent thermomechanical processing , promoting dynamic recrystallization (DRX) and grain refinement in the solid state. This review presents a comprehensive overview of grain refinement mechanisms in Mg–Al-RE alloys, focusing on the in-situ formation of Al 2 RE phases and impact on their microstructures and mechanical performance. Firstly, the grain refinement strategies in both the liquid and solid states are outlines, followed by a mechanistic discussion of the nucleation behavior of Al 2 RE phases and their crystallographic compatibility with the α-Mg matrix. Then, the influence of various individual and combined RE elements on the grain refinement efficiency and mechanical properties is summarized, including their effects during thermomechanical processing and hot deformation. Finally, the research gaps are identified and distinct future directions are proposed, including the evaluation of underexplored RE elements, the synergistic effects of combined RE additions , and the behavior of Al 2 RE phases under advanced manufacturing processes including additive manufacturing .