Influence of the curing temperature of a cataphoretic coating on the development of filiform corrosion of aluminium

Abstract

Aluminium alloys are known to be particularly sensitive to filiform corrosion. The initiation of this particular type of corrosion is related to different parameters such as the presence of defects, the permeability of the coating to water and oxygen, the adherence of the paint system and the presence of salts. In this work, the filiform corrosion resistance of Al 6016 substrates coated with a cataphoretic paint was studied. The curing of the coating was performed at different temperatures (185, 175, 165, 155 and 135 °C) in order to modify its mechanical properties and its permeability to oxygen. The paint properties were studied by different techniques allowing the estimation of the degradation of the metal–primer system and giving some information about intrinsic paint properties. The corrosion protection of the coating was evaluated by a normalized filiform corrosion test and by electrochemical impedance spectroscopy on scratched samples. The glass transition value and the internal stresses of the cataphoretic coatings obtained for different curing temperatures were determined by a stressmeter equipment. This study enabled us to underline the influence of the curing temperature on the intrinsic properties of the coatings such as the glass transition temperature, the internal stresses, the adherence, the permeability and the corrosion protection properties.