Chemical film, also referred to as iridite or alodine, is a chromate conversion coating primarily used for the protection of aluminum and aluminum alloys from corrosion and as primer for paint adhesion. It can be applied as a thin “clear” coating or as a heavier “gold” coating as specified by the class designation of Mil-C-5541.
Class 1A “gold” chemical film provides the maximum protection against corrosion when items are left unpainted and can be used to improve paint adhesion.
Class 3 “clear” chemical films are intended for use as a corrosion preventative film for electrical and electronic applications where lower resistant contacts are required. Because
class 3 coatings are thinner, they are more susceptible to corrosion than Class 1A.
Neither class results in any dimensional change to the part after processing. ROHS and ELV compliant chemical films are now available that do not contain any cadmium, lead, hex chromium or mercury compounds. They are all clear to light gray in color.