Anodizing, or anodization, is an electrolytic passsivation process. The process works by treating the component as anode electrode in an electrical circuit. The purpose is to increase the thickness of the natural oxide layer on the surface of the component. The result is an increase in resistance to corrosion and wear, and provides better adhesion for paint primers and glues than bare metal would.
Anodic surface finish are commonly applied to protect aluminum alloy die cast components. Anodizing changes the microscopic texture of the surface and the crystal structure of the metal near the surface. Anodized aluminum surfaces, for example, are harder than aluminum but have low to moderate wear resistance that can be improved with increasing thickness or by applying suitable sealing substances.
MIL-A-8625F, Black Anodize
Coatings of moderate thickness 1.8 µm to 25 µm (0.00007" to 0.001") are known as Type II in North America, as named by MIL-A-8625.
If close fits are specified in design drawings as is the case here up to .001 in tolerances, it is not feasible to control with anodize process.
Build up by anodic coating, especially Type III may results in interference on assembly and that's why we recommend machining after paint and apply chem. film.
Acid etching is performer in the pre-treatment cleaning of aluminum profiles, prior to the anodize process which will make any machining finish no better than 63 micro inch.