Locus of failure of T-peel joints formed between aluminium and various adhesives

Joints were made by bonding pretreated aluminium alloy L61 either a one-part epoxide, a two-part epoxide or a two-part polyurethane. The joints were then immersed in water at 60 degrees C for periods up to 119 days before being broken in a T-peel test. After a phosphoric acid anodisation treatment the one-part epoxide and the polyurethane clearly failed cohesively within the adhesive. When viewed with a magnifying glass or a low powered microscope, the other systems (chromic acid etch/one-part epoxide, chromic acid etch/two part polyurethane, phosphoric acid anodisation/two-part epoxide) gave apparent interfacial failure. Auger electron spectroscopy was used to determine the true locus of failure. Three distinct failure modes were found, namely interfacial failure, cohesive failure within the adhesive and failure within the oxide. (C) 1997 Elsevier Science Limited.