Friction stir welding of as-cast and pre-aged Al–Si–Zn–Mg–Fe alloy: Microstructure, mechanical and corrosion properties

Abstract

Al–Si–Zn–Mg–Fe alloy in as-cast and artificially aged (T6) conditions was friction stir-welded with a traveling speed of 200 mm/min and a rotation speed of 800 rpm. Their microstructure, mechanical and corrosion properties were investigated. α-Al, Si, Mg2Si, MgZn2 and Fe-rich phase were detected in the as-cast and pre-aged Al–Si–Zn–Mg–Fe before and after FSW. The secondary phases in pre-aged Al–Si–Zn–Mg–Fe after FSW are slightly more than those in the as-cast Al–Si–Zn–Mg–Fe after FSW. For the pre-aged Al–Si–Zn–Mg–Fe after FSW, the grains are refined and the dislocation density decreases. Hardness of the pre-aged Al–Si–Zn–Mg–Fe is higher than that of the as-cast one, whereas the hardness of weld nugget zones (NZs) of the both FSWed Al–Si–Zn–Mg–Fe joints is lower than their base materials, and the strength coefficients of both FSWed joints of the as-cast and pre-aged Al–Si–Zn–Mg–Fe are 0.82 and 0.9 respectively. The ultimate tensile strength (UTS) and yield strength (YS) of the pre-aged Al–Si–Zn–Mg–Fe after FSW (UTS = 208.86 MPa and YS = 156.72 MPa) is about 35% higher than that of as-cast Al–Si–Zn–Mg–Fe after FSW (UTS = 159.4 MPa and YS = 112.06 MPa) mainly due to the smaller grain size and more precipitates in the former. The corrosion resistance (CR) of the FSWed joint of the pre-aged Al–Si–Zn–Mg–Fe is the highest, owing to the most refined grain size, highest HAGBs, lowest KAM, increase in the close-packed {111} (α-Al) texture, dispersed particles of secondary phases, followed by the pre-aged Al–Si–Zn–Mg–Fe and then the FSWed joint of the as-cast Al–Si–Zn–Mg–Fe, and the as-cast one is the lowest.