For over 50 years chromium has been used as a corrosion-inhibiting element for metal surfaces. Its high solubility makes it an ideal corrosion inhibitor in paints, but can negatively impact the environment and humans if proper safety and health measures are not followed. In the aerospace industry, hexavalent chromium is used in conversion coatings and primers to protect the aluminum structure from corrosion. As long as aircraft are manufactured with aluminum, the need to protect aluminum from corrosion will be a critical issue.
Most aerospace aluminum structure is protected with chrome in two ways. First, the aluminum is treated with a chromate conversion coating. The conversion coating provides some corrosion protection and improves subsequent paint adhesion. The structure is then coated with a chromated primer. The chromated primer provides the majority of the corrosion protection.