Corrosion behavior and mechanism of the weld zone in laser-welded dissimilar high-strength aluminum alloy joints: effect of filler powder composition

Abstract Driven by the increasing demand for lightweight and high-strength structures in marine engineering, laser welding has emerged as a pivotal technology for joining dissimilar high-strength aluminum alloys. However, the microstructural heterogeneity and variations in the electrochemical potential of second phases render the weld zone (WZ) highly susceptible to localized corrosion, thereby underscoring the critical role of filler material selection in mitigating corrosion degradation. Addressing the limitations of previous studies that are restricted to single filler material systems, this work evaluates three representative atomized powders (AlCu5, AlSi12, and AlMg5). By integrating microstructural characterization with multiscale electrochemical analysis, this study elucidates the mechanisms governing the variations in corrosion resistance within the WZs of AA2195/AA7075 joints. The results demonstrate that both base metals exhibit corrosion resistance superior to that of the WZs. The corrosion resistance of WZs produced using different filler powders decreases in the order of AlCu5 > AlSi12 > AlMg5. In chloride-containing environments, variations in corrosion resistance among the WZs are primarily attributed to the synergistic interplay of second-phase characteristics, local potential distributions, and microstructural features. Crucially, the distribution of second phases and their potential difference relative to the matrix exert the dominant influence. In the AlCu5 WZ, the cathodic θ phase exhibits a minimal potential difference (110.7 mV) relative to the matrix, thereby conferring the highest corrosion resistance. In the AlSi12 WZ, the cathodic Si phase and anodic Q phase form a local galvanic couple with a significant potential difference of 356.0 mV, yielding intermediate corrosion resistance. In the AlMg5 WZ, the anodic T phase exhibits the maximum potential difference (375.3 mV) relative to the matrix. This substantial driving force accelerates severe anodic dissolution, ultimately resulting in the lowest corrosion resistance.