The high purity aluminum coatings covered by this specification are intended for use as corrosion protective coatings on ferrous and aluminum alloy parts. The requirements for coating low alloy steel, stainless steel, aluminum alloy, copper alloy, and titanium alloy parts with high purity aluminum (99 percent plus) are military unique. Control of the application process is absolutely critical because of the potential change in mechanical fatigue life or strength on aluminum substrates to which the coating is being applied. Coating may be applied by any process which produces a high purity (99 percent plus) aluminum coating. Ion vapor deposited aluminum, sputtered aluminum, and aluminum electrodeposited using an organic electrolyte are processes that meet this criteria. It can be used on high strength steel without causing hydrogen embrittlement, for high temperature applications up to 925°F (496°C), and in lieu of anodize on fatigue-critical aluminum structures. It can also be applied to copper, titanium, and stainless steel alloys to provide corrosion compatibility with aluminum structure. Type II (Chromate, see 3.4) high purity aluminum coating can also be used for applications which require an electrically conductive surface such as electrical bonding and ground, and Electromagnetic (EMI) Interference compatibility.

Class 1 and Class 2 coatings are intended as general purpose coatings where corrosion protection and/or dissimilar metal compatibility is required for structural and functional ferrous and non-ferrous alloy parts.

Class 3 coatings are intended as special purpose coatings where corrosion protection and/or dissimilar metal compatibility is required for close tolerance or threaded parts (such as bushings, pins, fastener, etc.).