This article describes an extensively employed laser technique known as laser black marking on anodized aluminum. We will discuss the properties of anodized aluminum and design an experiment to explore the principle behind laser black marking on anodized aluminum.

What is Anodized Aluminum?

Anodized aluminum is a favored material in the construction and digital 3C (computers, communications, and consumer electronics) fields. Anodized aluminum curtain walls have been successfully used for nearly 20 years. In recent years, anodized aluminum single panels have become popular as a new type of curtain wall material.

Anodized aluminum sheet

In the digital 3C field, it is most commonly used for flat panels and laptop casings.

Advantages of Anodized Aluminum

Let’s first take a look at the structure of anodized aluminum.

The anodized film is a two-layer structure. The inner layer is high-purity aluminum trioxide, which forms a dense and thin glass-like film with a thickness of about 0.01 to 0.05mm and high hardness. The outer layer is hydrated aluminum trioxide (Al2O3·H2O) film.

The anodized film is essentially colorless and transparent, with a nano-scale porous structure. The pores are shaped like tapered capillary tubes, with increasing pore size from the inside out. As a result, it has excellent adsorption capabilities and can be easily dyed into various colors.

Due to this oxide film, anodized aluminum enhances the advantages of aluminum and offers additional benefits:

• Matte texture while retaining a strong metallic appearance
• Can be colored with a wide range of colors, particularly decorative
• Resistant to oxidation, corrosion, ultraviolet radiation, and weathering; does not fade, powder, peel, and is durable
• High heat resistance and fire resistance, with a melting point greater than 2000°C after anodizing

Laser Marking Black Effect on Anodized Aluminum

In practical processing, laser black marking is widely used on the surface of anodized aluminum materials for product identification, anti-counterfeiting, statistics, and traceability purposes.

As shown in the figure below, laser black marking offers controllable depth and excellent visual effects, enhancing the product’s high-end appearance.

Overall rendering

200X

Compared to traditional silk-screen printing, laser black marking has significant advantages:

1.Permanence: The black marking effect does not fade due to touch, temperature variations, acidity, or alkalinity.

2.Anti-counterfeiting: Laser black marking is a physical process, and the marked information cannot be altered, providing strong anti-counterfeiting properties.

3.Low cost: Laser black marking is a one-time process that requires no additional materials or extensive manual labor, resulting in minimal consumption.

Analysis of Laser Black Marking Principle on Anodized Aluminum (SEM)

Two identical samples were taken, with sample 1# not subjected to laser black marking and sample 2# having a portion subjected to laser black marking. The planar regions of the two samples were analyzed and compared using scanning electron microscopy (SEM), and the cross-sectional analysis was performed using SEM.

1# Sample appearance and test position

2# Sample appearance and test position

Comparing the SEM images at 1000X and 10000X magnification, no significant differences were observed in the appearance and structure between the normal anodized aluminum region and the region subjected to laser black marking. The laser treatment did not cause apparent damage to the surface region.

Analysis of Laser Black Marking Principle on Anodized Aluminum (EDS)

Two identical samples were taken, with sample 1# not subjected to laser black marking and sample 2# having a region subjected to laser black marking. The planar regions of the two samples were analyzed and compared using energy-dispersive X-ray spectroscopy (EDS).

1# EDS analysis position

2# EDS analysis position

Through planar EDS analysis of the surface of both samples, quantitative analysis of the elemental composition was performed. Comparing the results of two measurements for samples 1# and 2#, no significant differences were found in the elemental composition, indicating consistency. Therefore, the laser black marking process did not cause any chemical reaction or loss of components in the anodized film.

Summary of the Principle Analysis

1.Comparing the planar and cross-sectional SEM images of samples 1# and 2#, no differences in shape and appearance were observed, suggesting that laser black marking did not damage the anodized aluminum film.

2.Comparing the planar EDS results of samples 1# and 2#, no significant changes in the composition ratios of the elements were observed, indicating that the chemical properties of the anodized film were not altered by laser black marking.

3.Based on the deductions from points 1 and 2, after laser black marking on anodized aluminum, there is a significant color change in the appearance. Through SEM and EDS analysis, it can be concluded that there are no major structural changes or chemical reactions on a macroscopic level. According to the principle of an object turning black, which is the absorption of light without reflection, we believe that laser black marking on anodized aluminum utilizes the high-energy density of laser irradiation on the material surface to induce a nano-effect. The particle size of the oxide is reduced to the nanoscale, resulting in increased light absorption characteristics. As a result, visible light is absorbed, and the reflected visible light is minimal, leading to the perception of black color by the human eye. This process is a physical modification.