Traditionally, conversion coatings based on metal phosphates and chromium based species were extensively used in industrial coating processes to provide anti-corrosion properties to metal substrates (e.g. AA6111, steel). Due to increasing environmental constraints, new solutions based on titanium and zirconium species are currently being commercialized around the world.

The growth of conversion coatings on metal alloys exhibits oxidation reactions at the alloy surface (e.g. M → Mⁿ⁺ + ne^‒). These electrons are consumed in the reduction of solution species (e.g. H⁺ + e^‒ → ½ H₂) leading to gaseous evolution and deposition of solid species at the alloy surface. At this step, a higher pH in the vicinity of alloy surface causes decomposition of the passivating ion, which in turn leads to initiation and growth of the coating layer. Interfacial properties, such as adhesion and anti-corrosion behavior, are dependent on the chemical bonding, thermodynamic stability, uniformity, and continuity of this coating layer along the metal surface. This presentation will show our recent studies on the effect of various additives in the conversion coating solutions using electrochemical tools, thermodynamic stability measurements, and electron microscopic analysis.