Corrosion of coated aluminium alloy 7075-T6 galvanic test assemblies, part I: unscribed panels

Galvanic corrosion of samples consisting of coated aluminium alloy 7075-T6 panels connected to stainless steel 316 fasteners was examined. Two coating systems were evaluated, one containing chromate pretreatment and primer along with a topcoat, and the other a chromate free system. No intentional defects such as scribes were imparted to investigate the attack associated with intrinsic defects in the coatings. The galvanic current between the fasteners and panel was greater for the assembly with chromate-free coatings than for the one with chromated coatings, and for the exposure to a salt spray chamber than for immersion. The attack was much deeper for the chromated system and more localised. The galvanic current increased with time and then was equal to that measured for a sample with an intentional scribe.