Anodizing is an electrochemical process that converts the metal surface into a durable, corrosion-resistant oxide layer. It is most commonly applied to aluminum but also works on titanium, magnesium, and other non-ferrous metals.
The Anodizing Process
The part is submerged in an acid electrolyte bath (typically sulfuric or chromic acid) and connected to the positive terminal of a power supply. Oxygen ions released at the anode combine with aluminum atoms to form aluminum oxide (Al₂O₃). The resulting oxide layer is integral to the substrate — it will not peel or chip like paint.
Types of Anodizing
Type I (Chromic Acid) — Thin coating (0.5-2.5μm), excellent for tight-tolerance parts and aerospace. Good corrosion resistance.
Type II (Sulfuric Acid) — Standard decorative anodizing (5-25μm). Can be dyed in various colors. Most common.
Type III (Hard Coat) — Thick coating (25-150μm), very hard and wear-resistant. Used for functional/mechanical parts.
Benefits
Corrosion resistance — protects aluminum in harsh environments
Hardness — Type III anodizing can reach 60-70 Rockwell C
Colorability — dyes penetrate the porous oxide layer for permanent coloring
Electrical insulation — anodized coatings are non-conductive
Environmentally friendly — no VOCs or hazardous byproducts