Abstract
This paper contains the results of an investigation to determine the effectiveness of primers in promoting adhesion and improving the environmental durability of epoxy adhesive bonds on grit-blasted aluminum substrates. The control for this study consisted of phosphoric acid anodization of substrates followed by the application of EC 3924 B primer. The following primers were evaluated on grit-blasted substrates: (1) EC 3924 B; (2) Metlbond 6726; (3) Dow Corning Z-6040; and (4) EA 9203. In addition, grit blasting followed by Alodine application was compared with the other primers. Studies include shear strength evaluations of each primer/adhesive system at 23 and 105°C. In order to assess the relative durability of each system, shear strength testing at 93°C of samples exposed for 2 weeks to a 93°C/condensing humidity environment and wedge crack extension testing of samples exposed for a 2-week period to a 60°C/condensing humidity environment were performed. The peel strengths of the systems were determined by conducting floating roller peel studies at -55, 23, and 105°C. Statistical analysis of the data revealed that the level of performance provided by EC 3924 B, solvent-borne, corrosion inhibiting control primer on phosphoric acid-anodized surfaces exceeded that of all the primers on grit-blasted substrates. However, when comparing the primers applied after only a grit-blast treatment, y-glycidoxypropyltrimethoxysilane primer showed statistically better results than the other primer systems.