Copper-aluminium joining by novel locked projection welding process

Leveraged by the transition to carbon neutrality, manufacturing industry shifts towards multi-material structures, combining material properties, optimising costs and enabling lightweight design. In automotive production, lightweight hybrid design reduces fuel consumption, hence the emission of greenhouse gasses. Amongst other measures, this is achieved by combining steel and aluminium alloys in body-in-white manufacturing, as well as using both copper and aluminium alloys for optimised weight, cost and performance of battery packs for electric vehicles. Albeit joining sheet-like components is often performed by cost-efficient resistance welding processes, robust dissimilar joining by these processes has proven to be a challenge due to discrepancies in physical and metallurgical properties. Multiple researchers have proposed improvements to resistance (spot) welding processes for highly dissimilar metal joining. These influence the growth rate, morphology and/or composition of the formed intermetallic compounds at the dissimilar metal interface, hereby aiming to improve the mechanical joint strength and altering the failure mode. However, the presented improvements still suffer from limited cross tension strength and/or brittle joint failure, especially for small-scale joints. In this work, a novel resistance welding process variant is presented, developed for joining material combinations with a highly dissimilar melting temperature. By complementing the metallurgic joint with a mechanical connection, the presented locked projection welding technique is designed to yield ductile joint failure opposed to the brittle failure that characterises such dissimilar resistance spot welds. The novel welding process is validated on a copper-aluminium material combination and compared to resistance spot welds based on joint morphology and mechanical properties.

Automated summary

Leveraging the transition to carbon neutrality, the manufacturing industry is shifting towards multi-material structures to optimize costs and enable lightweight design, especially in automotive production. Joining dissimilar materials, such as steel and aluminum alloys, and copper and aluminum alloys, has proven to be a challenge due to discrepancies in physical and metallurgical properties. This study presents a novel resistance welding process, called locked projection welding, which combines metallurgical and mechanical connections to achieve a ductile joint failure, as opposed to the brittle failure exhibited by traditional resistance spot welds.