Establishing a correlation between interfacial microstructures and corrosion initiation sites in Al/Cu joints by SEM–EDS and AFM–SKPFM

• Interfaces of FS welded Al/Cu joint was characterized by OM, SEM, AFM and SKPFM.
• A eutectic phase mainly consisting of CuAl2 IMC and an Al-rich phase was detected.
• Severe mechanical deformation caused a concurrent depletion/enrichment mechanism.
• A correlation between phases and their Volta potential distribution is found.
• Corrosion initiated from sites with relatively higher absolute Volta potentials.

A lap joint of AA3003 and pure copper was produced by friction stir welding and the induced interfaces were investigated. Interfacial regions were characterized by SEM–EDS, AFM, SKPFM, OM and Vickers micro-hardness. Multimodal Gaussian distribution (for characterization of surface potential patterns) showed the formation of multiple compounds. A quantitative correlation between microstructure constituents and Volta potential distribution was recognized and confirmed by corrosion attacked sites observations. It was observed that the Al-rich regions proximate the dispersed Cu particles and Cu–Al intermetallics were most susceptible to corrosion attack initiation due to a galvanic driving force between these surface constituents.

Interfacial microstructure characterization of an aluminum/copper friction stir weld: (a–d) SEM, OM, SKPFM and AFM images of Al/Cu interface around the tool pin, (e) Volta potential line-profile record on the SKPFM result, and (f) histogram plot and simulated multinomial Gaussian distribution corresponding to image (e). It is notable that all images demonstrate the same area from different points of view.Figure optionsDownload as PowerPoint slide