Anodizing Corrosion Resistant Coatings
Anodizing corrosion resistant coatings offer exceptional means for enhancing corrosion protection in the aluminum or magnesium finishing industry. These electrolytic-based films, oxide-based, are highly stable and guard well against atmospheric corrosion.
Property enhancements are made filling the coating's micro porosity. Imagine a deep cellular structure extending inward, through much of the coating formation. Individual cells, with pores down their centers, can total millions per square inch. This makes for excellent absorptive processes.
Once the anodize aluminum is sealed it is, in effect, non-absorptive. For general corrosion protection, sealing solutions for the ceramic, like de-ionized water, are known ideally for their ability to react with anhydrous aluminum in the outer layers of the film. A mono-hydrate of the oxide is formed, which occupies greater volume than the alumina from which it was formed. The result is a reaction to close down and plug the pore structure.
Other sealing products for anodized aluminum can include steam or sacrificial corrosion inhibitors like nickel acetate or chromate. Keep in mind materials and processing methods vary. Be sure your service provider fully understands your performance needs.
Today, Teflon (PTFE) and a host of other compounds can be integrated for enhancements in corrosion protection. And, while chemical resistance of hard anodize (also known as ‘hardcoat’) is typically poor beyond mild acids and weak bases, performance can be improved.
Surface finish can be equally instrumental in preventing corrosion. There is a correlation with corrosion. Consequently, the original finish may require polishing or, minimum, be examined for surface flaws or imperfections.
Post finishing of the alumina oxide (also referred to as aluminum oxide) may also be desirable for enhanced corrosion protection.
Anodic coatings can be excellent protectors against galvanic coupling corrosion. Though homogeneous forms of aluminum are ideal, since alloying constituents can form undesirable products, less stable oxides. If dimensional builds are no issue, additional layering may be accomplished through topical paints or other corrosion inhibiting coatings, as they will be well anchored for mechanical bond strength.
These coating processes are compatible with alloys of aluminum or magnesium, only. Consequently, work pieces should be free of dissimilar metal. Masking may be feasible. Though there is always risk for ‘burning’, irrecoverable loss in parent material from catastrophic dissolution.
Anodizing corrosion resistant coatings are well suited for atmospheric conditions, salt spray resistance, marine environments, and, chemically, in the presence of many compounds.