Effect of grain size and second phase on the corrosion behavior of MIG-welded Al–Mg–Si–Mn–Cr alloy

The effect of grain size and second-phase distribution on the corrosion performance of metal inert gas-welded Al–MgSi–Mn–Cr alloy in different regions was investigated. Due to the welding heat, the transformation of the strengthening phase β ″ (Mg 5 Si 6 ) to B ′ phase (Al 3 Mg 9 Si 7 ) in heat-affected zone I leads to the reduction in strengthening ability of the joint. In comparison with the equiaxed grain of weld zone, base metal exhibits high grain boundary density of the fibrous grain and a large amount of second phases on the grain boundary, which increases the anodic dissolution site, leading to the highest pitting corrosion susceptibility. Additionally, the continuous distribution of β (Mg 2 Si) precipitate and Al(MnFe)Si dispersoid at grain boundary forms a corrosion channel, which promotes the corrosion propagation along grain boundary. Graphical Abstract