Simultaneously Improved Bendability and Strength of Al–Mg–Si–Cu–Zn Alloys by Controlling the Formation and Evolution of Primary Fe-Rich Phase

In present work, the formation, evolution, and distribution of the primary Fe-rich phase in an Al–Mg–Si–Cu–Zn–Fe–Mn alloy are coupling controlled by ultrasonic melt treatment (USMT) and thermomechanical processing (TMP). It is shown in the results that the size of grains and Fe-rich phase in the as-cast state can be greatly reduced by the applied optimum USMT at 680 °C. Additionally, the transformation rate of β-Fe-rich phase to α-Fe-rich phase can be also enhanced. After the coupling control of USMT and TMP, the number density and distribution uniformity of multiscale Fe-rich particles can be greatly increased or improved, which contributes to the fine-grained recrystallization microstructure and weakened texture. Finally, compared with the 6xxx series Al alloys (such as AA6016 and AA6111), the alloy sheet in the pre-aging state exhibits substantially improved bendability and strength (the plastic strain ratio and tensile strength are 0.67 and 304 MPa, respectively). The effect of USMT on the formation and transformation of primary Fe-rich phase and the mechanisms of improved bendability and strength are deeply discussed.