Galvanic Corrosion of Al Alloys Coupled to Coated PH13-8Mo Stainless Steel

Abstract

The galvanic corrosion behavior of the Al alloys 7075 and 2024 coupled to SermeTel W or Ti-Cd coated PH13-8Mo stainless steel or to anodized Ti-Al-4V has been studied in aerated 3.5% NaCl by continuous monitoring of the galvanic current and by weight loss data. Dissolution rates of Al alloys are lower when these alloys are coupled to coated instead of bare PH13-8Mo steel. When coupled to Al 7075 or Al 2024, the SermeTel coating acts as a sacrificial anode, thereby protecting the Al alloy. The coating in this case suffers from localized corrosion in the form of pitting. The Ti-Cd coating acts as a sacrificial anode when coupled to Al 2024. Although there is a large difference in corrosion potentials of Al 7075 or Al 2024 and the anodized Ti alloy, there is practically no increase of dissolution rates of the Al alloys due to coupling to the more noble metal. A combination of weight loss and galvanic current data seems most promising for investigating the effect of coatings on galvanic corrosion, since galvanic current measurements are a convenient way of following the time dependence of the corrosion process and weight loss measurements provide quantitative measure of average corrosion rates.