Anodizing
Anodizing converts the surface of aluminium into a hard, corrosion-resistant aluminium oxide layer, typically 5–25 µm thick, that can be dyed in many colours. Standard (Type II, sulphuric acid) anodizing is the most common finish for machined and extruded aluminium parts.
What it is
The aluminium part is made the anode in an acid electrolyte. The current grows a porous oxide layer out of the metal itself, so it cannot peel off like paint. About half the layer grows outward and half penetrates into the surface.
The porous oxide can absorb dyes for colour, and is then sealed to close the pores and lock in corrosion resistance. The finish is electrically insulating.
Typical applications
- Machined aluminium housings, covers and brackets
- Aluminium extrusions and profiles
- Electronics enclosures and heat sinks
- Consumer products and architectural hardware
- Automation, fixtures and machine parts
Suitable materials
- 6061 and 6063 (excellent results)
- 6082 and 5000-series alloys
- 7075 and 2000-series (acceptable, less even colour)
- Cast alloys (high-silicon grades give grey, patchy results)
Points to consider
- Alloy choice strongly affects appearance; 6061/6063 give the most consistent colour.
- Colour can vary slightly between batches and alloys; state if colour matching across parts is critical.
- Threads and precision bores may need masking or allowance for growth.
- Anodizing is insulating, so mask areas that need electrical contact (grounding points).
- Machining marks and scratches show through; finish or bead-blast first for a uniform look.
Frequently asked questions
What colours can anodized aluminium be?
Clear/natural, black, and most dyed colours such as red, blue, gold and grey. Exact shades depend on the alloy, so we recommend approving a sample for colour-critical work.
Does anodizing change part dimensions?
Slightly. Roughly half the coating thickness is added on each surface, so a 20 µm coat adds about 10 µm per face, or about 20 µm on a diameter.
Can cast aluminium be anodized?
Yes, but high-silicon casting alloys (such as ADC12/LM24) give a grey, uneven finish. Low-silicon alloys anodize much better.