Combined effect of surface pretreatment and nanomaterial reinforcement on the adhesion strength of aluminium joints

Nowadays, it is known that adhesive and cohesive forces should be developed in order to improve the mechanical performance of adhesive joints. In this context, while the adhesive forces are improved with surface pre -treatments applied to the adherends, the adhesive and cohesive forces are improved with the nanomaterial reinforcement to the adhesive. For this purpose, in this study, AA7075-T6 aluminium alloy adherends were combined with epoxy adhesive as a single lap joint. As a preliminary study, abrading and FPL-etching (Forest Products Laboratory) surface pretreatments were applied to aluminium alloy adherends and after two different surface pretreatments, the changing surface morphology (with optical microscope, contact angle, profilometer measurements) and shear strength were compared. With abrading and FPL-etching surface pretreatments, an increase of 40.83% and 69.63%, respectively, was determined in the shear strength compared to untreated adhesive joints. After the preliminary study, in order to increase the mechanical performance of the adhesive joints, nano sized ANP (alumina nanopowder), MWCNT (multiwalled carbon nanotubes) and SNP (silica nanopowder) were added to the adhesive. Thus, it was investigated how the combined effect of different surface pretreatments and nanomaterial types at various reinforcement ratios changed the shear strength of the adhesive joints. After shear tests, significant increase in shear strength was observed in FPL-etched adhesive joints compared to abraded adhesive joints in all reinforcement nanomaterial types and reinforcement ratios. And also, significant improvements in the shear strength of adhesive joints were determined in all types of nanomaterial reinforcements. The highest shear strength was obtained at 10.0 wt % SNP reinforcement with 104.32% improvement in FPL-etched adhesive joints compared to nonreinforced FPL-etched adhesive joints. The evalu-ation of shear strength was supported by the failure images taken from the fracture surfaces after shear tests, and it was determined that the failure type was changed from adhesive to cohesive with nanomaterial reinforcement compared to nonreinforced adhesive joints.