Aluminium surface finish: mill finish, anodised or powder-coated
Anyone working with aluminium will encounter the terms mill finish, anodised and powder-coated. We explain what the different terms mean and what properties these different surface finishes have.
Mill finish
Mill finish refers to aluminium that remains largely untreated after being formed by the roller or press. This means that it has no additional surface coating.
These aluminium profiles can be recognised by their typical silver-grey appearance, as aluminium forms a thin oxide layer when it comes into contact with air. This thin layer already provides corrosion protection for bare aluminium profiles.
Aluminium profiles are extruded. Minor surface imperfections such as slight stripes, scratches, grooves, scuff marks, longitudinal lines, rolling marks or uneven surface characteristics resulting from rolling treatment, as well as machining marks, cannot be avoided or are permitted.
These so-called extrusion lines are purely visual and do not affect the quality of the aluminium. Mill finish aluminium is therefore particularly suitable when appearance plays a secondary role.
Anodised
Anodising is a very popular surface treatment for aluminium. In this process, a thin oxide layer is deliberately built up on the aluminium surface using an electrolytic process.
This layer makes anodised aluminium even more resistant than untreated aluminium. It offers better corrosion protection and a more pleasant, scratch-resistant surface feel. In addition, the surface is visually enhanced by the resulting satin-silver colour tone.
By adding special solutions and alloys, the oxide layer can also be electrolytically coloured. This creates a wide range of decorative design options in terms of colour tones.
Using the anodising process, aluminium profiles are upgraded in terms of durability and appearance and are therefore used in many different areas.
Powder-coated
Before aluminium profiles are powder-coated, the surface must be cleaned and a conversion layer applied. The powder particles are then applied electrostatically and with the help of compressed air to the surface of the workpiece and are subsequently baked at around 200 °C or fused into a paint layer.
As with anodising, this process also allows visual upgrades. A wide variety of colour tones, metallic effects and different gloss finishes can be achieved.
The result is aluminium profiles with a durable surface that also has an attractive appearance. In addition to its high resistance to corrosion, chemicals and weathering, powder coating is an environmentally friendly process.
This is because this aluminium surface treatment does not use toxic, unpleasant-smelling, flammable or explosive solvents.
Mill finish, anodised or powder-coated: the differences
- Mill finish: untreated, natural aluminium surface with a typical silver-grey appearance.
- Anodised: electrolytically reinforced oxide layer for improved feel, appearance and corrosion resistance.
- Powder-coated: durable, coloured coating with high resistance to weathering and corrosion.
Which surface suits which project?
- Technical applications: mill finish aluminium when appearance is secondary.
- Visible components: anodised aluminium for a higher-quality, satin surface.
- Outdoor use: powder-coated aluminium for additional protection and individual colour design.
- Design projects: anodised or powder-coated aluminium profiles for a decorative effect.
- Garden, terrace and balcony: powder-coated aluminium parts for durable and weather-resistant solutions.
Conclusion
As with many other materials, the choice of the right material or the right surface finish depends on the construction and the required properties.
Overall, aluminium is a popular material used in many different areas. Depending on the project, mill finish, anodised or powder-coated aluminium can be the right choice.
Frequently asked questions about aluminium surface finishes
What does mill finish mean for aluminium?
Mill finish aluminium remains largely untreated after forming. It has no additional coating and shows the natural silver-grey aluminium surface.
Is mill finish aluminium protected against corrosion?
Yes, aluminium forms a thin oxide layer when it comes into contact with air. This natural layer already provides a certain level of corrosion protection.
What is the advantage of anodised aluminium?
Anodised aluminium is more durable, more scratch-resistant and more corrosion-resistant than untreated aluminium. The surface also has a higher-quality appearance.
Why is aluminium powder-coated?
Powder coating gives aluminium additional protection against weathering, corrosion and chemicals. At the same time, it enables many colours, metallic effects and different gloss levels.
Which aluminium surface is suitable for outdoor use?
Powder-coated aluminium is particularly suitable for outdoor use, as it is durable, weather-resistant and can be individually designed in colour.
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