When a customer is hesitating between several treatments, the right question is: what do you expect from the surface? Colour, hardness, protection against rust lasting several decades? Each process meets a different need.
Anodizing: for aluminum only
Anodizing does not add a layer: it thickens, by electrochemistry, the natural oxide of aluminum. The result is part of the metal, explains the Aluminum Anodizers Council. The layer is thin, very hard, and it keeps the metallic look. Its limits: a narrower choice of colours and textures than powder, notes Products Finishing, and a surface that is hard to touch up once damaged.
Galvanizing: the zinc that sacrifices itself
Hot-dip galvanizing immerses steel in a bath of molten zinc, at around 450 °C. The zinc bonds to the steel and covers it everywhere, including inside tubes. Its advantage is unique: where there is a scratch, the zinc corrodes in place of the steel, according to the American Galvanizers Association. Its look, grey and uneven, is that of an industrial product. Zinc electroplating, which is much thinner, is suited to fasteners and indoor parts.
Powder coating: colour and barrier
Powder forms a film that isolates the metal from water and air. It can be applied to steel as well as aluminum, in almost any colour, in matte, gloss or textured. It is barrier protection: as long as the film is intact, the metal is protected. Its sensitive points are sharp edges and impacts. Hence the importance of pretreatment, which limits corrosion under the film.
The best of both: the duplex system
For highly exposed steel, powder can be applied over galvanizing. The zinc protects if the film is pierced, and the film protects the zinc. The galvanizers' association claims that a duplex system lasts 1.5 to 2.3 times the sum of the lifespans of the two protections taken separately. That is its own figure, but the principle is recognized. Preparation is more demanding: galvanized steel must be pre-baked to prevent outgassing. We coat galvanized steel: mention it in your quote request.
In summary
- Anodizing: aluminum only, thin and hard layer, few colours.
- Galvanizing: sacrificial protection for steel, industrial look.
- Powder coating: colour and barrier, on steel as well as aluminum.
- Galvanizing and powder can be combined for highly exposed steel.
