Galvanic Test Panels for Accelerated Corrosion Testing of Coated Al Alloys: Part 2-Measurement of Galvanic Interaction

摘要

A test sample incorporating a painted Al alloy panel, uncoated through-hole fasteners, and scribes has recently been shown to provide an accelerated response during atmospheric corrosion testing in the field and in laboratory chambers. In this paper the galvanic current between Type 316 (UNS S31600) stainless steel (SS316) or Ti-6Al-4V (UNS R56400) fasteners and painted and scribed AA7075-T6 (UNS A97075) panels was examined during exposure in a salt fog chamber using a zero-resistance ammeter. The anodic current of the AA7075-T6 panel and the cathodic current of each of the four fasteners were monitored using different connection schemes. The anodic current of the panel depended on the number of fasteners connected. The total cathodic current of fasteners was approximately equal to the anodic current of the AA7075-T6 panel, which validates the accuracy of the current measurement. Furthermore, galvanic interaction between the fasteners was observed such that the cathodic current of other fasteners was decreased when a new fastener was added. Scribes on a panel can interact with distant fasteners, not just the closest ones. The amount of corrosion as determined by charge and optical prqfilometry were close and indicated SS316 fasteners caused more corrosion attack than Ti-6Al-4V fasteners, which also is explained by differences in the cathodic current of the fasteners.