Effect of Annealing Treatment on Precipitation Behavior of α-Al(MnCr)Si Phases in Al–Mg–Si–Mn Alloy

Micro-segregation of solute elements is inevitable during the casting process of Al–Mg–Si alloys, significantly influencing the precipitation behavior of dispersed phases during subsequent heat treatment, ultimately influencing alloy performance. Mn and Si are typical positive segregation elements and the principal constituents of the dispersed phases in aluminum alloys, and their diffusion behavior directly affects the precipitation of nano-scale α-Al(MnCr)Si phases within grains during subsequent annealing. This study systematically investigates the effects of different annealing conditions (430 °C × 12 h and 530 °C × 12 h) on the precipitation behavior of α-Al(MnCr)Si phases in the Al–Mg–Si–Mn alloy. After annealing at 430 °C, the relatively low diffusion rate promoted the dispersed precipitation of α-Al(MnCr)Si phases as high-density, nano-scale particles within grains. In contrast, annealing at 530 °C substantially enhanced the elements diffusion, accelerating both nucleation and growth of α-Al(MnCr)Si phases and inducing notable Ostwald ripening, resulting in larger α-Al(MnCr)Si phases with a lower number density within grains. This study indicates that the control of annealing parameters can effectively tailor the size, distribution, and number density of nano-scale α-Al(MnCr)Si phases. The findings provide critical theoretical and practical guidance for optimizing annealing processes in Al-Mg-Si-Mn alloys.