High-Productivity and High-Strength Fe/Al and Al/Al Dissimilar Joining by Spot Forge-Welding

To realize high-speed and high-strength joining of dissimilar materials that can be used in an automobile manufacturing line, two types of dissimilar lap-joining were examined using spot forge-welding. The material combinations were high-tensile steel SPFC980 × aluminum (Al) alloy AA5083 and Al alloy AA2024 × Al alloy AA6061. The processing time was less than 0.1 second via diffusion bonding with plastic flow. Joint strength depended on the reduction ratio ( R ), which indicates the degree of plastic flow, and the joints fractured in base metal (BM) at R > 1.8 in the SPFC980 × AA5083 and at R > 1.4 in the AA2024 × AA6061. In each case, the maximum tensile-shear load reached approximately 4 kN. Cross-sections showed metallurgical joining in the forged area. Electron probe microanalysis for elemental oxygen in cross-sections of SPFC980 × AA5083 joints revealed that the contamination layer at the bonded interface decreased with increasing R ; formation of new surface by plastic flow occurred better at the forged center than at the edge. Under the R condition for BM fracture, both combinations had suitable solid-state bonding interfaces for dissimilar joining. The reaction layer (RL) at the bonded interface of the SPF980 × AA5083 joint was suppressed to a thickness of several nanometers. No distinct RL formed at the bonded interface of the AA2024 × AA6061 joint; the boundary showed high crystallinity similar to that of the BM grain boundary. These results may facilitate the development of next-generation solid-state spot-welding systems capable of multimaterial manufacturing for transportation vehicles.