Anodised aluminium plates: techniques and durability

What aluminium anodising is

Anodising is a controlled electrochemical process that converts the aluminium surface into a layer of aluminium oxide (Al₂O₃) integrated into the metal itself. Unlike a coating, this layer is not a paint or a laminate: it is part of the aluminium. This gives it unique properties: surface hardness far superior to untreated aluminium, natural corrosion resistance, chemical stability and the ability to incorporate colour durably.

In industrial identification, natural anodising (silver colour, undyed) is the most versatile substrate because it allows all subsequent marking techniques: photo-anodising, UVI printing and laser marking. Base-colour anodising is used when a coloured plate is required without adding extra layers (warning red, tooling orange, corporate blue).

The quality of the starting anodising conditions everything that follows: poorly anodised aluminium produces inconsistent finishes and compromises the plate's final durability.

Structure of the anodic layer

The freshly formed anodic layer has a porous structure: small channels perpendicular to the surface that can absorb dyes or finely ground materials. This is what enables photo-anodising: the image is introduced into the pores before they are closed.

The final step of anodising is sealing, which hydrates the layer and closes the pores. Once sealed, the layer is chemically stable and practically inert. That is why the order of processes matters: photo-anodising and anodic dyeing are applied before sealing, on open pores. Standard UVI printing and laser marking, by contrast, are applied to the already-sealed layer (or without pre-anodising, in some cases).

This difference explains why photo-anodising has durability equivalent to the metal: the information is not on the surface but inside the subsequently sealed oxide, protected by the very structure of the anodised aluminium.

Photo-anodising: information inside the oxide

Photo-anodising, also known as anodic printing, is the technique in which the image and text are introduced into the aluminium's anodic layer before final sealing. It is applied with an in-house screen-printing process on unsealed natural anodised aluminium (open pore) and closed with a subsequent sealing bath.

The result is a plate where the information is physically lodged within the aluminium oxide, with the same durability as the base material: decades outdoors with continuous resistance to UV, thermal cycles, normal abrasion, common chemicals and intensive cleaning. It does not fade, peel or scratch with normal use.

It is the reference technique for regulatory manufacturer plates, aeronautical identification and any application where the information must outlast the component's service life. It is applied exclusively to natural anodised aluminium with open pores.

UVI printing: multicolour coverage

UVI printing uses inks cured instantly by ultraviolet light. The ink polymerises as it passes under the UV lamp, anchoring chemically to the substrate. The result is a layer with anchoring far superior to that of conventional inks and high mechanical and chemical resistance, while maintaining multicolour coverage.

On aluminium it is applied both on sealed anodising and in its distinctive photo-anodised UVI variant, where the ink is applied to open anodising and becomes partially integrated into the oxide on subsequent sealing. The photo-anodised variant significantly raises durability over standard UVI for demanding environments.

It is the usual technique for technical plates with complex graphics, control panels with colour coding, multicolour overlays, corporate logos and any application where the visual result is part of the product's value.

Laser marking: physical alteration of the material

Fibre laser marking physically alters the surface of anodised aluminium through a controlled thermal effect: the optical beam locally heats the anodic layer, creating contrast through oxide or local discolouration, with no physical contact, no ink and no consumables. The information becomes permanently integrated into the material.

On anodised aluminium, laser marking typically produces light contrast on a dark background (on colour-anodised) or dark contrast on silver (on natural anodised). The resolution reaches fine technical typefaces and DataMatrix codes readable by industrial scanners.

Its distinguishing value is the ability to apply an individual variable: each plate can carry its own unique P/N, S/N or DataMatrix with no tooling cost. It is the reference technique for traceable serialisation, marking of calibrated tooling and any part-by-part identification requirement.

The three techniques, side by side

Differences relevant to the technical decision. The assessments are qualitative: each project is matched to the client's specific specification.

Photo-anodising · UVI · Laser marking comparison

• UV resistance: Excellent | High | Excellent · physical alteration
• Abrasion resistance: Excellent · information beneath the oxide | Medium-high | Excellent · physical alteration
• Common chemical resistance: High | High | High
• Thermal resistance: High | Medium | High
• Multicolour coverage: Limited | Yes · wide range | No · dark/light contrast
• Individual variable (S/N): Not on its own | Yes (at a cost) | Yes · no cost per variable
• Relative run cost: Medium | Medium | Medium · no tooling
• Reference application: Long-life manufacturer plates | Multicolour technical plates, panels | Serialisation, DataMatrix, individual marking

When to choose each technique

Photo-anodising: when the information is fixed (manufacturer data, CE marking, aeronautical identification) and the plate must survive several decades outdoors or in demanding environments. It is the reference option for long-life regulatory plates.

Photo-anodised UVI: when multicolour coverage is needed (corporate logos, colour-coded scales, overlays with graphics) with reinforced durability similar to that of pure photo-anodising. It is the usual combination for multicolour technical plates with a demanding service life.

Standard UVI: when multicolour is needed indoors or in moderate outdoor conditions and the unit cost must be controlled. Suitable for control panels, overlays and emblems with an expected service life of several years to a decade, depending on the environment.

Laser marking: when an individual variable per unit is needed (P/N, S/N, DataMatrix) at zero tooling cost. It can be combined with photo-anodising or UVI for plates mixing fixed and variable information.

Recommended combinations: photo-anodising base + laser for serialisation, photo-anodised UVI + laser for multicolour plates with S/N. The combination is common and adds no production complexity.

Expected durability by environment

Indoors (offices, industrial buildings with controlled conditions): any of the three techniques offers a service life of more than a decade with normal use. The choice is decided by visual requirements and cost.

In moderate outdoor conditions (industrial roofs, transport, installations exposed to standard climate): photo-anodising and photo-anodised UVI keep the information for decades. Standard UVI keeps legibility for several years, varying with the pigment.

In demanding outdoor conditions (continuous UV over years, extreme thermal cycles, marine weathering, continuous abrasion): pure photo-anodising is the option that guarantees a service life equivalent to the asset. In marine environments, stainless steel with laser marking is also considered when aluminium is not viable.

In environments with specific chemicals: compatibility is assessed case by case. For occasional aggressive chemicals, a specific substrate (stainless steel) or an additional finish may be necessary. Any project of this profile is qualified with a prior test.