Anodizing

Anodising is an electrochemical finish for aluminium parts. The part is submerged in an acid bath and an electric current is passed through it, which grows a layer of aluminium oxide on the surface. That oxide layer is part of the metal itself, not a coating sitting on top, so it cannot chip or peel.

OpusFab offers Type II anodising in clear or colour for CNC machined aluminium parts, such as 6061-T6 and 7075-T6.

What anodising does

• Corrosion resistance: the oxide layer protects the aluminium from oxidation and staining, which bare aluminium is prone to over time.
• Harder surface: anodised aluminium is more resistant to scratches and light wear than bare metal.
• Colour: before the oxide layer is sealed, it is porous and can absorb dye. This is how black, red, blue, and other colours are added.
• Appearance: anodising gives a uniform, slightly metallic look. The underlying surface texture still shows through, so tool marks that were visible before anodising remain visible after, only coloured.

Clear vs colour anodising

Clear anodising adds the protective oxide layer without dye. The part keeps its natural aluminium colour with a slightly more satin, uniform look. Choose clear when you want corrosion protection and surface hardness without changing the appearance.

Colour anodising adds dye to the porous layer before sealing. The options in the editor are Clear, Black, Blue, Red, Green, Gold, Purple, and Orange, with black the most common choice for enclosures and consumer parts. Colours are decorative as well as protective.

One thing to know about colour: because the dye sits in the oxide layer and the layer is thin, anodised colours can vary slightly between batches and can fade under long, direct UV exposure. If you need a precise, opaque, UV-stable colour match, powder coating is the better option.

Anodising and dimensions

Type II anodising adds a very thin layer, on the order of a few microns to a few thousandths of an inch, and roughly half of that growth goes into the surface rather than on top of it. For most parts the change is negligible. For press-fit holes, tight bores, or precision mating surfaces, mention it: those features can be masked or you may prefer to leave the part as-machined. See Tolerances explained for how tolerance choices interact with finishes.

Anodising and electrical conductivity

The oxide layer is an insulator. An anodised aluminium part no longer conducts electricity through its surface. If your part needs to be grounded or used for EMI shielding, anodising works against you: leave contact areas unanodised (masked) or choose a different finish.

A common combination: bead blast before anodising

Anodising does not hide tool marks, it follows them. If the part is visible in a final product and you want a uniform matte look, specify bead blast before anodising. The blast evens out the surface texture, and the anodising then gives a consistent colour across the whole part. This is the standard recipe for consumer electronics housings and visible brackets.

When to choose anodising

• Aluminium parts that need corrosion resistance for indoor or moderate outdoor use
• Visible parts that need colour with a metallic look
• Parts that are handled often and would otherwise scratch and stain
• Precision parts, where a thick coating like powder coat would disturb the fit

If the part needs extreme wear resistance instead, look at PVD coating. If you need an exact Pantone colour or a thicker, more impact-resistant layer, look at powder coating.

Cost and lead time

Anodising adds cost per part and a few days of lead time, since parts go to a finishing line after machining. You will see the price update in the quote table as soon as you select it, and the batch lead time reflects the longest part in the batch. See Lead times for details.