Corrosion performance and degradation mechanism of a bi-metallic aluminum structure processed by wire-arc additive manufacturing

An Al-5Mg alloy (AA5083) block, deposited over an AA6061 substrate by wire-arc additive manufacturing, was electrochemically tested along two different cross-sectional planes by cyclic polarization in 3.5 wt.% NaCl. The deposited layers and the interlayer boundaries showed similar polarization behavior regardless of the cross-sectional direction. The corrosion of both the substrate and the deposited layers was mainly attributed to the presence of relatively coarse intermetallic Al(Fe, Mn)Si particles. In the substrate, corrosion was governed by deep crevices along the interfaces of directionally aligned Al(Fe, Mn)Si particles with the Al matrix. The deposited layers and the interlayer boundaries showed pitting around numerous Al(Fe, Mn)Si particles and/or Al(Fe, Mn, Cr, Ti)Si at the interlayer boundaries, which were much finer compared to those of the substrate. The abundance of the fine precipitates and their intergranular location caused surface material removal, which was more extensive along the interlayer boundaries. The perpendicular z-y and z-x planes of the deposited block did not show significant differences in anodic polarization behavior. Differences were more distinct in the case of cathodic polarization. Some anisotropy in polarization behavior was noted through the thickness of the z-y plane that complies with the obtained tensile behavior.