Electrochemical corrosion behavior of 6061 Al alloy under high rotating speed submerged friction stir processing

In this study, we report the high rotating speed submerged friction stir processing (HRS-SFSP) designed to modify 6061 Al alloy to improve its corrosion resistance in saltwater. The effect of this processing technology on the microstructure and corrosion behavior of aluminum alloy was studied. The results show that the grain size of Al alloy after HRS-SFSP was refined from 50.8 µm is refined to 3.21 µm. In addition, compared with the low rotation speed (1800 r/min), a higher proportion of high-angle grain boundaries (77.1 %) formed when the rotation speed was 3600 r/min, which effectively reduced the defect density. At the same time, recrystallization in a large area lowered the energy storage in the grain, which further alleviates the corrosion. In addition, the second phase dominated by Mg2Si was fine and uniformly distributed, which also reduced the galvanic corrosion tendency. Therefore, high corrosion resistance was obtained using HRS-SFSP. On the other hand, continuously increasing the rotation speed coarsened the grains and the second phase,which decreased the corrosion resistance.