Analysis of effects of process factors on corrosion resistance of adhesive bonded joints for aluminum alloys

In the adhesive bonding process, the hydrolytic stability or corrosion resistance is of significant importance in achieving acceptable joint durability. The aim of this study is to identify the process factors affecting corrosion durability of adhesive bonded joints for aluminum alloys. For this purpose, experiments were carried out to investigate the influence of varying the surface treatment-primer-adhesive combination. The tests used for the evaluation of corrosion resistance included neutral salt spray and floating roller peel testing. In addition, the residual peel strengths after 300 days of exposure to salt spray were statistically analyzed using analysis of variance (ANOVA) and Tukey test (alpha = 0.05) in order to understand the interaction effects between the process factors. The surface morphology, chemical composition and oxide thickness played a major role in the control of adhesion performance and joint durability. In particular, a hybrid sol-gel coating consisting of TPOZ (zirconium n-propaxine) and gamma-GPS (gamma-glycidoxypropyltrimethoxysilane) produced a microscopically rough surface with an increased surface energy compared with the standard phosphoric oxide. Furthermore, a non-chromate primer exhibited adequate corrosion protection efficiency when used with a sol-gel coating. The incorporation of zirconium oxide (ZrO2) in the sol-gel coating increased surface densification through pore-filling and planarization, finally resulting in high corrosion durability.