Use of impressed current for accelerated corrosion testing of aluminium alloy panels

Abstract

Previous studies have shown how galvanic coupling between stainless steel 316 fasteners and a coated aluminium alloy 7075-T6 test panel could accelerate the coating degradation during exposure to corrosive environments. In this work, impressed current between the fastener and panel was evaluated for use instead of simple galvanic coupling. Two coating systems, including a chromate-containing and a non-chromated coating system, were exposed to ASTM B117 and cyclic salt spray exposure environments. The coatings were scribed prior to exposure to further accelerate the corrosion rate. The nature of attack depended on the magnitude of the applied impressed current and the exposure environment for the chromate-free adhesion promoting surface pre-treatment. However, the nature of the attack did not depend upon the magnitude of applied current for the chromated pre-treatment system. The response of the current during drying and rewetting also varied depending on the coating system.