Effect of Mn/Cr ratio on precipitation behaviors of α-Al(FeMnCr)Si dispersoids and mechanical properties of Al–Mg–Si–Cu alloys

The submicron α-Al(FeMnCr)Si dispersoids in 6XXX aluminum alloys can retain subgrains in the deformed microstructure and improve the mechanical properties of the alloys at elevated temperature. In this study, the precipitation behavior of dispersoids in 6XXX alloys containing various Mn/Cr ratios (0.5–8) during different homogenization heat treatments (soaking at 500, 530, and 560 °C for 0–24 h) was investigated. The effects of the Mn/Cr ratios on the elevated-temperature mechanical properties, dynamic and static recrystallization behaviors of the alloys were evaluated. A suitable Mn/Cr ratio (3.5) contributes to the precipitation of a large number of fine dispersoids, enhancing the dispersion strengthening and Zener drag P Z . Excess Cr incorporation decreased the nucleation rate of the dispersoids which could not be precipitated completely during the homogenization heat treatment, thereby weakening the pinning effect and decreasing the dispersion strengthening effect. During hot deformation and subsequent solution treatment, the M7 alloy achieved the highest percentage of substructures. The M7 alloy exhibited excellent mechanical properties at room and elevated temperatures, and good thermal stability during long-term annealing (300 °C for 100 h).