The effect of pre-bond moisture on epoxy-bonded sulphuric acid anodised aluminium

The adhesive bonding of sulphuric acid anodised aluminium has been investigated in wet and dry environments. Crack growth resistance was investigated using the wedge test at 40°C/96% r.h. DC-SAA joints bonded at 85% r.h. showed a significant decrease in crack growth resistance, compared with joints bonded at lower r.h. The differences were smaller between AC-SAA joints, but bonding at 85% and 11% r.h. reduced the crack growth resistance compared with 33% and 52% r.h. Significant blister formation was observed in the adhesive bondline after bonding at 85% r.h. TEM cross-sections showed that bonding at 85% r.h. also resulted in a ∼200 nm wide region in the adhesive close to the oxide surface with very little thixotropic agent. This was explained by desorption of water from the oxide during curing of the adhesive.