Novel interlayer-adhesive hybrid joining technique for resistance spot welding of dissimilar aluminum-steel sheet materials

Abstract

The push for lightweighting in automotive manufacturing has necessitated the introduction of dissimilar metal joints in the automobile body, often joints between aluminum and steel. Resistance spot welding (RSW), while a well-established, cost-effective and rapid welding process, experiences problems when welding aluminum-steel joints due to the formation of brittle intermetallic compounds, which degrade joint integrity. However, a previous work has shown that stainless steel interlayers can effectively inhibit excessive growth of brittle Fe-Al intermetallic compounds during RSW. This work explores the feasibility of a novel hybrid joining concept where RSW is combined with adhesive bonding together with a 316L stainless steel interlayer deposited via cold spray. Both 1.8-mm-thick extruded 6063-T6 and 2.2-thick cast aluminum sheet materials were welded to 1.5-mm-thick Al-Si-coated Usibor 1500 AS150 press-hardened steel (PHS). Weld joints were characterized with light optical microscopy and scanning electron microscopy, which revealed the formation of a thinner Fe-Al intermetallic layer between the aluminum substrate and the 316L interlayer compared with welding aluminum directly to PHS. Quasistatic tensile testing was performed in the lap-shear configuration. Both the interlayer-only and hybrid approaches showed improved tensile strength, achieving 2.9 kN and 17 kN maximum tensile force compared with 0.92 kN achieved by the reference extruded aluminum-steel RSW specimens. This work shows that this joining technique is a promising approach for providing a fixture point for automotive components prior to curing of the adhesive.