The Relationship Between Anodic Oxide Film Thickness and Laser Marking Color

Experiments were used to verify the effect of different thicknesses of anodic oxidation film on the color of laser marking, revealing the corresponding rules for the thickness of anodic aluminum oxide film and the color of markings.The focus of the article is on how to control the thickness of the oxidation layer to achieve specific colors in products such as electronic casings and metal nameplates, providing practical technical references for the surface treatment industry.

Why is the thickness of the oxide layer important?

When we give metal a surface treatment, anodizing is like putting on a shirt.The thickness of the coating directly relates to the protective qualities of the "coat of armor.Recently a lot of metal engravers have been asking: Why do some laser-engraved metal signs come out black, and others gray? The answer has to do with the thickness of the metal's oxide layer.

A hands-on experiment.

We prepared six 6063 aluminum alloy samples, and used an automatic thickness tester to control the thickness of the coating.

Setting experimental parameters.

- First group: 5μm (standard construction aluminum thickness).

2. 10μm (standard industrial parts).

Group 3: 15μm (commonly used in 3C electronics).

Class 4: 20 microns (precision instrument standard).

- Class 5: 25μm (military grade).

- Group 6: 30μm (special application).

Laser engraving.

After using the same 30W fiber laser to mark the two types of material, they found that the laser was able to mark the glass but was unable to mark the metal.

At 5 to 10 microns, the marks are light gray, like pencil marks.

- 15μm: A black color becomes visible.

The purest black was obtained at 20 microns.

The coating is 25 micrometers thick.

The science behind it.

This is actually related to the way light plays hide and seek.Oxide films are like multi-layer mirrors, and the tiny holes that are produced in the laser marking process cause light to interfere.If the film is too thin, too much light is reflected, and the color becomes lighter. When the thickness is just right, the film "captures" more light, resulting in a black appearance. If the film is too thick, however, the scattering of light becomes disordered, and the effect is lessened.

Practical techniques.

Based on our own experience, we have a few practical suggestions for everyone.

1. The most dependable thickness for dark color marking is 18-22 μm.

2. The thickness of the film is checked with an eddy current tester before the film is applied.

3. The holes must be sealed properly, or else the colors will be uneven.

4. Laser parameters: frequency 20kHz, speed 800mm / s.

What must be noted is that one should not blindly pursue a thick coating.A customer once demanded that we produce a 30-micron coating, but the result was that the characters looked as if they had grown a fringe, and the cost of oxidation was 30 % higher.

Frequently Asked Questions.

Q: What happens if the thickness of the film is uneven?

This kind of problem is usually caused by fluctuations in the temperature of the oxidation tank.The temperature should be kept within a range of ± 1 ℃.A quick fix is to use a marking liquid in the lighter areas.

Q: Can you print out color marks?

So far, we've been able to produce three shades: gray-black, dark brown, and navy blue.The colorful effects of the traditional dyeing process are still needed.

Q: Do different materials have different effects?

After trying the common aluminum alloys 6061, 7075, and 5052, he found that the basic principles were consistent.But magnesium and titanium alloys are a whole different ball game.