Aerospace aluminum alloys, especially the most commonly used AA 2024 T3 alloy is often susceptible to corrosion in chloride containing environment. These alloys are phase separated, highly complex metal-in-metal composites and tend to have weakness towards local galvanic corrosion because of this microstructure. At present the coating system used for aerospace aluminum alloys involves a multi-layer system such as a pretreatment layer at the primer/Al-alloy substrate interface, primer and topcoat. Chromate conversion coatings (CCCs) are usually applied as pretreatment layer to aluminum and its alloys. Despite its efficiency and versatility, the use and emission of hexavalent chromium (Cr6+) has been under increasingly strict regulation because of its high toxicity and carcinogenic effect. For the past two decades concentrated efforts were made to develop an ecofriendly conversion coating system as an alternative to CCC and also chromate free additives in primer layer
