Effects of processing parameters on microstructure and mechanical properties of friction stir additive manufactured Al-Zn-Mg-Cu alloy

Abstract A multilayered build was fabricated by friction stir additive manufacturing (FSAM) with different parameters, using 4-mm thick 7A04-T6 aluminum alloy sheets in this study. The parameters effect on the microstructure and mechanical properties of the builds were investigated combined scanning electron microscopy (SEM), transmission electron microscopy (TEM), vickers hardness and tensile tests. Macro-softening phenomenon was observed in the builds. The precipitation and growth of the Mg (Zn, Cu, Al) 2 or MgZn 2 phase with the effect of the effective thermal cycles during the FSAM process mainly attributed to the formation of the macro-softening. The more effective thermal cycles experienced during the FSAM process, the more Mg (Zn, Cu, Al) 2 or MgZn 2 phase precipitated and coarsened, resulting in a more pronounced decrease in the mechanical properties of the build. Heat input affected the macro-softening behavior of the build by influencing the degree of dissolution, re-precipitation and coarsening of the precipitates during the FSAM process. Too low or too high heat input resulted in the incomplete dissolution or further precipitation and growth of the precipitates, aggravating the macro-softening phenomenon, and reducing the precipitation strengthening ability of the build. The mechanical properties of the build fabricated at the rotation speed of 700 rpm and travelling speed of 160 mm/min were the best in this study.