The effects of Al surface treatment, adhesive thickness and microcapsule inclusion on the shear strength of bonded joints

The influences of various Al surface treatments, adhesive thicknesses as well as the incorporation of synthesized microcapsules into epoxy adhesive on the shear strength of adhesive/ Al joints have been investigated using lap-shear tensile tests. First, the influence of adhesive thickness on the shear strength of joints has been presented. Then, the effects of various Al surface treatments on the surface roughness of Al and shear strength of joint have been researched. Atomic force microscopy was used to study the Al surface morphologies and textures. Finally the few micron-sized polymeric microcapsules were synthesized and the shear performances of microcapsule filled epoxy adhesives were inspected. It was observed that the HCl acid based etching increased both micro-roughness and nano-texture of the Al surface and led to the peak shear strength. Moreover, HCl-nitric acid treatment offered the maximum value for the cohesive failure. Capsule inclusions into the adhesive displayed different influences on the joint shear performances depending on the capsule morphology and the surface treatment of Al. [Display omitted] •The HCl acid based etching increased both micro-roughness and nano-texture of the Al surface and led to the peak shear strength.•By following an in-situ polymerization technique very fine urea-formaldehyde microcapsules have been achieved.•The integration of 10 wt% hollow microcapsule enhanced shear performances of adhesive/Al joint.•The integration of filled microcapsules into the adhesive mostly increased the cohesive failure.