Comprehensive study on the influence of different pretreatment methods and structural adhesives on the shear strength of hybrid CFRP/aluminum joints

The aim of this study was to investigate the influence of laser treatments with varying energy density and wavelength on the surface structure, shear strength and fracture behavior of hybrid compounds of thermoset carbon fiber-reinforced polymer (CFRP) and aluminum (Al) bonded with three different structural adhesives. The CFRP was pretreated by laser with near-infrared (NIR) and ultraviolet (UV) wavelengths and applying different energy densities. Aluminum surfaces were structured with NIR. Reference CFRP/Al-specimens were prepared by acetone cleaning, low pressure oxygen/argon plasma or sand blasting. The surfaces were investigated microscopically before bonding and after mechanical testing. In addition, the surfaces were examined with white light interferometer and sessile droplet test methods. The bonded compounds were characterized in standardized single lap shear tests to reveal the influence of the pretreatment strategies on the joint strength. Suitable process windows for laser pretreatments were identified, including NIR-pretreatment methods that can compete with an UV-laser source. For every adhesive, a suitable pretreatment method was found.