EFFECTS OF ADHEREND SURFACE TREATMENT ON STRESSED DURABILITY OF ADHESIVE BONDED ALUMINUM ALLOYS.

A comparative evaluation of the durability of adhesive bonded aluminum alloy joints made using the ″optimized″ FPL etch and a 10 volt room temperature phosphoric acid anodize was performed based on stress-rupture and crack extension criteria. Stressed blister lap shear and wedge specimens made with two 250 degree F cure and one 350 degree F cure elastomer modified epoxy adhesives were evaluated. For both 250 degree F cure adhesives, the phosphoric acid anodize was superior to the FPL etch based on both stress-rupture and crack extension criteria. For the 350 degree F cure adhesive, the wedge crack extension data showed the phosphoric acid anodize to be equal or slightly superior to the FPL etch, but the stress-rupture data showed the FPL etch to be highly superior to the phosphoric acid anodize. A hypothesis to explain this apparent anomaly is presented. Extensive experimental data are tabulated.