Bare, non-anodised aluminium only marks with a fibre: a diode or CO2 simply skims over it. It gives a very legible grey-to-white mark and clean recessed engraving, but it conducts heat so well that thin parts distort.
Settings: what really matters
Starting point with a 20 W fibre: 90% at 400 mm/s, 30 to 40 kHz. The mark comes out light grey on the metal; for a whiter result, raise the frequency and run two fast passes rather than one slow pass.
Do not chase black: on bare aluminium, true black is only possible with a MOPA source, by tuning pulse duration. A standard fibre gives a lighter or darker grey.
To dig in (ID plates, serial numbers), drop to 150 mm/s and stack 5 to 15 passes, blowing the dust away between runs.
Common thicknesses and pitfalls
Common thicknesses: 0.5 to 3 mm sheet, plus machined solid parts. Cutting remains impossible with a marking fibre.
Pitfall number one: distortion. A 0.5 mm sheet marked over a large area warps under the heat. Split the marking into zones and let it cool, or clamp the part to a metal support that draws heat away.
Pitfall number two: aluminium is reflective. Check your machine accepts reflective metals, and never work a mirror-polished surface without lens protection.
Risks and finishing
The aluminium dust produced by deep engraving is fine and flammable: keep extraction running, vacuum rather than blow, and do not deep-engrave next to combustible material.
For finishing, marked aluminium can be anodised afterwards: the mark stays visible and becomes far more resistant. Without anodising, a matt varnish protects the surface from tarnishing.
Every figure on LaserSettings comes with the machine, the laser source, the material and the thickness it was tested on. A setting published for a 10 W diode says nothing about a 40 W CO2, and a setting for 3 mm says nothing about 6 mm: check those four things before you copy any number.
Settings are confirmed or disputed by the members who reproduce them, so reliability comes from cross-checking rather than popularity. Photos of the result — cut edges, engraving shades, scorching — tell you more than a single number found on a forum.
Whatever the material, treat a published setting as a starting point: run a small power/speed test grid on an offcut, clean the lens, redo the focus, work with fume extraction and air assist, wear glasses rated for your wavelength and never leave the machine unattended.