Achieving superior thermal stability in an Al-Mg-Mn-Sc alloy by suppressing Al3(Sc, Zr) phase aggregation subjected to cryogenic homogeneous deformation

Abstract

Nanometer precipitates are essential for enhancing high specific strength in aluminum alloys, yet their coarsening at elevated temperatures causes severe property degradation. Recently, second-phase engineering for tailoring precipitate size and spatial distribution in the matrix has become a recent research hotspot. Here, we report that cryorolling (CR) refines and homogenizes Al₃(Sc,Zr) precipitates in an Al-Mg alloy containing scandium and zirconium, yielding exceptional thermal stability and mechanical performance. Crystal plasticity simulations were carried out for cryogenic and room-temperature deformation behaviors, which reveal that CR promotes a more coordinated strain distribution, accumulation of high-density dislocations under high stress and stress gradient, activation of hard-oriented slip systems, and coordinated operation of multiple slip systems, resulting in a more uniform deformation path than room-temperature rolling (RTR). The resulting precipitate refinement and uniform deformation minimize spatial clustering of Al₃(Sc,Zr), suppressing short-range diffusion of Sc and Zr and retarding the coarsening kinetics of Al₃(Sc,Zr). After annealing at 480 °C for 1 h, the average particle size of the Al₃(Sc,Zr) phase in the CR samples remained essentially unchanged. In contrast, the Al₃(Sc,Zr) phase in the RTR samples underwent significant coarsening, exhibiting an average particle size 71 % larger than that in the CR samples. Because Al₃(Sc,Zr) impedes grain-boundary migration and dislocation climb at elevated temperatures, the fine-grained microstructure and high dislocation density in the CR material are retained, leading to superior thermal stability during annealing. This study demonstrates a promising route for enhancing the thermal stability of high-strength aluminum alloys that is readily scalable to industrial production.