Corrosion Evolution Behavior of Ti/Zr/Oligomeric Epoxy Silane Composite Chemical Conversion Coatings on Multi-metals

The new energy vehicle body composed of multi-metals requires a synchronous chemical conversion coating to exhibit excellent corrosion resistance. Herein, we prepared a titanium/zirconium/water-based oligomeric epoxy silane composite chemical conversion coating on multi-metals, and conducted an investigation into its electrochemical behavior and micro-zone structural characteristics upon immersion in a 3.5% NaCl solution. The electrochemical results combined with characterization results revealed that the corrosion evolution characteristics of the composite coatings could be categorized into three stages of mild corrosion, synergistic protection, and substrate damage. Besides, Si–OH groups interact with Me–OH at the defect on the multi-metal surface to form an organic monolayer coating. This organic monolayer coating, in conjunction with the synergistic inorganic conversion layer comprising Al2O3, TiO2·2H2O, ZrO2·2H2O, effectively cooperates with the corrosion products to hinder the erosion by the corrosive medium and suppresses the progression of the anodic reaction.