Synergistic effect of surface treatment and adhesive type on bonding performance of thin Al6061 joints for automotive applications

The effects of different surface treatments (grinding, plasma surface treatment, and grinding followed by the plasma (GrPl) process) and various adhesives (cyanoacrylate, Bisphenol A (BPA)-based, and Bisphenol A and Bisphenol F (BPA/F)-based adhesive) on the bonding performance of single-lap joints manufactured from thin Al6061-T4 aluminium alloy sheets were investigated in this study. Contact angle measurement was carried out to evaluate the influence of surface treatments on the wettability of the surface of the aluminium alloy adherends. The contact angle on the surface of the untreated sheet was measured to be 71.8 degrees. However, after applying the GrPl process on the ground surface, the contact angle could be reduced to 47 degrees and 25.9 degrees in the parallel and perpendicular directions to the grinding direction, respectively. Shear testing was performed to evaluate the mechanical behaviour of the single-lap joints of aluminium alloy sheets. The shear strengths of BPA/F-based, cyanoacrylate, and BPA-based adhesive-bonded joints produced from ground adherends improved by 47 %, 54 %, and 72 %, respectively. The synergistic impact of GrPl treatment resulted in 126 %, 123 %, and 174 % enhancement in shear strength of BPA/F-based, cyanoacrylate, and BPA-based adhesive-bonded joints, respectively. When the temperature was raised from room temperature to 60 degrees C, the bonding performances of all single-lap joints deteriorated due to the decrease in the strength of the adhesive. However, the joints treated with plasma had the highest shear strength at 60 degrees C. While the BPA-based adhesive had the most beneficial impact on improving the shear strength of single-lap joints at room temperature, the opposite result was obtained at 60 degrees C. All the findings have indicated that the influence of adhesive on the bonding performance of aluminium alloy joints varied significantly depending on the surface treatment and temperature.