Effect of Nickel Addition on Corrosion Behavior of Laser–Arc Hybrid Welded Al-Mg-Si-Cu Alloy Joints

The corrosion performance of Al-Mg-Si-Cu laser–arc hybrid welded joints modified by 1.8 wt.% Ni remains poorly clarified. In this study, the corrosion behavior was examined via electrochemical measurements combined with SEM, EDS, and SKPFM. Nickel alloying increased the corrosion potential of the α-Al matrix above that of eutectic Si, thereby suppressing the cathodic role of eutectic Si. Nevertheless, the pronounced potential difference and extensive interfacial area between the Al3Ni phase and the α-Al matrix promoted localized galvanic corrosion, resulting in chain-like pits along the Al3Ni phase. This intense galvanic coupling considerably damaged the compactness of the passive film and reduced its resistance. Consequently, the corrosion current density of the welded joint increased significantly from 0.83 μA/cm2 to 1.85 μA/cm2. These findings suggest that Ni alloying is suitable for welding Al-Mg-Si-Cu alloys in applications where high mechanical performance is essential and corrosion resistance is of secondary importance, such as in body-in-white or chassis load-bearing components.