Effect of Substrate Preparation and the Conversion Coating on the Corrosion Resistance in Ringer's Solution of 304L Stainless Steel Coated with Alumina Film

This work aims to determine the best substrate preparation and conversion coatings that may enhance the anti-corrosive performance of alumina film/stainless steel substrate systems in Ringer’s solution. Boehmite, silica, silica/boehmite, and boehmite/silica conversion coatings were deposited on sanded or sandblasted 304L stainless steel samples, and the best results were further covered with alumina film for a long-time exposure evaluation. The best anti-corrosive performances for each substrate preparation were observed for the sandblasted sample covered with silica/boehmite conversion coating (JSB500) and the sanded sample covered with silica (LS500), which showed the highest global resistance (Rg) values (828 Ω.cm2 and 1837 Ω.cm2, respectively) and the smallest values of global capacitance, Cg (2.19 X 10-6 F.cm-2 and 3.37 X 10-9 F.cm-2, respectively). After covering with the alumina film and evaluating for 216 h in the corrosive medium, it was noted an increase in the Rg values for both systems (JSBA500 and LSBA500), likely due to the presence of a corrosion products layer. The presence of iron oxides in these conversion coatings led to a more stable alumina film. Comparing the selected coating systems, the LSBA500 exhibited an improved performance, reaching an increase of 85% in Rg and a decrease of 94% in Cg.