IMPACT OF TRIVALENT CHROMIUM CONVERSION LAYERSAND HYBRID SILICATE COATINGS ON CORROSION RESISTANCE OF ALUMINUM ALLOYS

摘要

Trivalent chromium conversion coatings have been deposited onto aluminum 2024-T3 alloyby immersion into or by spraying on a solution of chromic sulfate and hexafluorozirconate for periodsof time varying from 3 minutes to 5 days. This treatment was followed by the deposition of hybridsilicate materials containing different organic modifiers [vinyl, methacrylate, epoxide functionalitiesand poly(2-ethyl-2-oxazoline)] to produce composite coatings. Aluminum alloys coated with thecomposite films, as well as single-layer coated aluminum alloys, i.e. coated with the conversioncoating or the silicate film, were tested by a 168-hour salt spray technique. Significantly bettercorrosion resistance was observed for composite films, which exhibit significantly less localized pitsand corrosion areas, as compared to the single-layer coated aluminum alloys. The effect oftrivalentchromium treatment and its duration, as well as the silicate composition and synthesis conditions oncorrosion resistance of the resultant coatings are discussed.