Anodizing is an electrochemical process that makes the natural oxide layer on aluminium thicker, harder and more durable in a controlled way. Unlike paint, this layer is part of the metal itself and does not peel.
The anodizing steps
- Preparation: degreasing, rinsing and etching the surface.
- Anodizing: the part is made the anode in an electrolyte bath (usually sulphuric acid), and as current flows a porous layer of aluminium oxide grows on it.
- Colouring (optional): the pores of the oxide layer absorb dyes or metal salts, giving colours such as bronze, black and gold.
- Sealing: the pores are closed so the layer resists corrosion and staining.
Benefits
- High resistance to corrosion and wear
- A uniform, long-lasting appearance
- An electrically insulating oxide layer
- No peeling
Which alloys anodize best?
6063 and the 5xxx series give very good decorative results. High-silicon casting alloys (such as ADC12) usually end up with a darker, less even surface after anodizing — worth bearing in mind when choosing an alloy for visible cast parts.