The effect of B and Sb on the corrosion behavior of T6-treated Al–Si–Mg alloys

The influence of B and Sb on the microstructure and corrosion behavior of T6-treated Al-Si-Mg alloys has been specifically studied. It is found that the addition of 0.03 wt.% B to Al-Si-Mg alloys results in the lowest corrosion rate (0.02451 mm/y) when immersed in 3.5 wt.% NaCl solution for 3 days. This improvement can be attributed to the transformation of coarse dendritic α-Al grains into refined equiaxed grains, which is beneficial for the formation of uniform and compact passive film. In contrast, the Al-Si-Mg alloy with addition of 0.2 wt.% Sb shows the highest corrosion rate (0.05795 mm/y), which can be attributed to two reasons. First, the addition of Sb contributes to the transformation of rod-like eutectic Si particles into a spherical morphology, increasing the number of micro-galvanic corrosion sites and thus accelerating the corrosion process. Second, the generated Mg3Sb2 phase, being more noble than the eutectic Si phase, strengthens the micro-galvanic corrosion.