General Motors Company

Anodic Oxidation Coating on Aluminum - Issue 3; English
 N GMW14665

Annotation

This specification covers basic requirements for anodic coatings on aluminum and aluminum alloys.

Material Description. The anodic coating is an oxide layer produced by an electrolytic oxidation process. The oxide layer provides improved corrosion protection. This coating can be transparent or colored. Anodic coatings must be either sealed or painted to maintain their appearance.

Symbols. Not applicable.

Applicability. Anodic coatings are used for:

Decorative Parts For:

Interior Applications.

Exterior Applications.

Exterior parts, whether clear or colored, are further classified for chemical resistance and application as follows:

• Class A – Extreme alkaline resistance to pH 13.5. For Class A, a supplemental coating is mandatory. Refer to GMW16209 (organic topcoat) or GMW16929 (inorganic topcoat) for requirements.

• Class B – High alkaline resistance to pH 13.0.

• Class C – Alkaline resistance to pH 12.0. This performance level may be usable in emerging markets or other areas where environments are known to be mild. It is only usable via special drawing note for parts that are not shared among other regions.

Note: If no decorative exterior class is listed on the drawing, Class B is assumed. Exterior applications should be limited to above beltline. Applications below beltline are subject to a special release and specific requirements of a higher level must be defined. The corrosion severity in that area is much higher than above beltline because of copper (etc.) containing brake dust.