Anodizing

Anodizing is an electrochemical finish for aluminum parts. The part is submerged in an acid bath and an electric current is passed through it, which grows a layer of aluminum 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 anodizing in clear or color for CNC machined aluminum parts, such as 6061-T6 and 7075-T6.

What anodizing does

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

Clear vs color anodizing

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

Color anodizing adds dye to the porous layer before sealing. Black is the most common choice for enclosures and consumer parts. Colors are decorative as well as protective.

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

Anodizing and dimensions

Type II anodizing 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.

Anodizing and electrical conductivity

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

A common combination: bead blast before anodizing

Anodizing 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 anodizing. The blast evens out the surface texture, and the anodizing then gives a consistent color across the whole part. This is the standard recipe for consumer electronics housings and visible brackets.

When to choose anodizing

• Aluminum parts that need corrosion resistance for indoor or moderate outdoor use
• Visible parts that need color 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 color or a thicker, more impact-resistant layer, look at powder coating.

Cost and lead time

Anodizing 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.