Laser marking anodized aluminum,
bare alloy included.

An anodized part carries a porous aluminum oxide layer that has been dyed and sealed. At 1064 nm the fiber laser bleaches and removes the dye in that layer, and the marked area turns bright white to silver against the surrounding color. The shop-floor name is laser etching anodized aluminum. Strictly it is ablation of the dye: on Type II anodize the anodic layer itself stays largely in place, so corrosion protection is largely preserved.

Edges are sharp because the dyed layer is thin and uniform. Small text, fine logos, graduated scales, and dense Data Matrix codes all hold up, which is why black anodize is the usual specification for nameplates, panels, and housings that carry a lot of information. When a drawing calls for the mark to go through to bare metal, more energy removes the anodic layer entirely. State that requirement explicitly, because it is not the default.

Dyed Type II anodize (MIL-PRF-8625, formerly MIL-A-8625, Type II, Class 2) is the best-case substrate. Black gives the most contrast; dark blue, red, and green also mark well. Light dyes such as gold narrow the difference between mark and background, so confirm with a sample when a Data Matrix must be graded.

Type III hardcoat is thicker and harder. Black-dyed hardcoat marks with high contrast, though the mark may show a slight step. Undyed hardcoat is naturally gray to bronze depending on the alloy, and the mark on it is lower in contrast. Clear anodize marks poorly on any alloy: there is no dye to remove, so the result is a pale mark on a pale background. If a part will be marked, specify a colored anodize at the design stage.

Mark after anodize, dye, and seal. A light etch made before anodizing is largely lost in the anodize line’s own pre-treatment and under the coating. The exception is deep engraving, which survives anodize as a recessed feature and suits parts that will be stripped and re-anodized in service.

Aluminum does not grow a dark oxide under the laser the way stainless steel and titanium do, so bare aluminum is not annealed. The standard mark is a light gray to white frosted etch a few microns deep. It is permanent and crisp, but contrast against a bright machined surface is low to medium. Tuned MOPA pulse parameters can produce a darker gray mark. How dark depends on the alloy and the surface finish, and it stays lower in contrast than a mark on steel.

Data Matrix readability on bare aluminum is good when the finish is uniform. Bead-blasted and fine-machined surfaces grade more consistently than surfaces with heavy tool marks, where the lay of the cut competes with the code. When a bare part needs a reliably dark mark, the options are deep engraving with paint or epoxy fill, anodizing the part, or a laser-marked label: see asset tags and UID labels.

Chem-film (chromate conversion) parts can be marked; the laser removes the thin conversion coating inside the mark. If the drawing requires unbroken coverage, raise it on the RFQ so the mark can be sequenced ahead of conversion coating. Codes on either surface are read back 100% and graded per ISO/IEC 15415, or AIM DPM-1-2006 for direct part marks. Quality describes the verification step, and the material marking guide compares aluminum with ten other substrates.