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.