Recent research efforts in the automotive industry have been focused on the integration of high-strength steels within lightweight vehicles by using improved joining techniques. The present work falls in this subject area and is focused on the analysis of adhesive bonded dual-phase steel/epoxy joints for the automotive industry. Two quasi-static loadcases were considered, i.e. single-lap and T-peel tests, and various surface preparation strategies were evaluated. In particular, the mating surfaces were pre-treated by using pulsed laser irradiation with a fiber laser (1064 nm) and comparisons were made with degreasing and sand blasting. Moreover, the effects of bondline thickness and adhesive type were also assessed. To this aim, two epoxy adhesives with fairly different mechanical behavior (i.e. strain hardening versus elasto-plastic) were deployed for joints fabrication. Finally, T-peel tests were also carried out after sample cycling under controlled high humidity and temperature (i.e. accelerated aging). The obtained results highlighted the beneficial effect of laser irradiation on the joints’ mechanical behavior under both static and hydrothermal loadings

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Hybrid joints consisting of metals and fiber-reinforced polymer composites exhibit highly desirable properties for many lightweight design applications. This study investigates the potential of additively manufactured surface structures for enhancing the bond strength of such joints in comparison to face milled and laser structured surfaces. Titanium samples with different surface structures (as-built surface, groove-, and pin-shaped structures) were manufactured via electron beam melting and joined to carbon fiber-reinforced polyether-ether-ketone (PEEK) via adhesive bonding and thermal direct joining, respectively. Bond strength was evaluated by tensile shear testing. Samples were exposed to salt spray testing for 1000 h for studying bond stability under harsh environmental conditions. The initial tensile shear strengths of the additively manufactured samples were competitive to or in some cases even exceeded the values achieved with laser surface structuring for both investigated joining methods. The most promising results were found for pin-shaped surface structures. However, the hybrid joints with additively manufactured structures tended to be more susceptible to degradation during salt spray exposure. It is concluded that additively manufactured structures can be a viable alternative to laser surface structuring for both adhesive bonding and thermal direct joining of metal-polymer hybrid joints, thus opening up new potentials in lightweight design.

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