With the continuous development of 3D printing technology, it has been widely used in industrial manufacturing, aerospace, medical care and consumer electronics. However, 3D printed metal parts usually have rough surface, low precision and easy oxidation corrosion after molding, so a series of post-treatment processes are needed to improve their performance and appearance quality. Anodizing is a common metal surface treatment technology, especially suitable for metal materials such as aluminum alloy. This paper will introduce how to anodize 3D printed metal parts.

First, the basic principle of anodic oxidation

Anodizing is an electrochemical treatment process, which is mainly used for aluminum and its alloys. The basic principle is that the metal workpiece is used as the anode in the electrolytic cell, and a dense aluminum oxide film is formed on the metal surface through the action of current. This oxide film has good wear resistance, corrosion resistance and insulation, and can also absorb dyes or coatings to achieve beautiful surface decoration effect.

Second, the material selection of 3D printed metal parts

Not all metals are suitable for anodizing, and common anodizable materials mainly include some kinds of aluminum alloy, magnesium alloy and titanium alloy. In 3D printing, commonly used anodic oxidation materials include AlSi10Mg, 6061 aluminum alloy, etc. Therefore, it is necessary to confirm whether the material is suitable for the process before anodizing.

3. Pretreatment of 3D printed parts before anodic oxidation

Because there are usually problems such as lamination, unmelted particles and oxide scale on the surface of 3D printed parts, a series of pretreatment steps must be carried out before anodic oxidation to ensure the quality of oxide film:

1. De-oiling cleaning: Use alkaline or neutral cleaning agents to remove grease, cutting fluid and other pollutants on the surface of parts.
2. Polishing treatment: mechanical polishing or chemical polishing is adopted to remove the surface roughness and improve the smoothness.
3. Sandblasting (optional): used to obtain a uniform matte surface effect.
4. Acid washing or alkali washing: remove impurities such as surface oxides and metal chips.

Iv. anodic oxidation process flow

After pretreatment, anodic oxidation can be carried out, and the basic process is as follows:

1. Electrolyte preparation: Sulfuric acid is usually used as electrolyte, with the concentration controlled at 15%~20% and the temperature controlled at 18~22℃.
2. Electrification oxidation: the parts are hung at the anode position, and the lead plate is used as the cathode. After electrification, the voltage is controlled at 12~20V, and the time is adjusted according to the requirements of film thickness, usually 30~60 minutes.
3. Dyeing treatment (optional): After the oxide film is formed, it can be soaked in dye to achieve color effect.
4. Sealing treatment: sealing the pores of the oxide film with hot water or chemical sealing agent to improve corrosion resistance and stability.

V. Matters needing attention

There may be tiny pores or residual stress in the 3D printed parts, which may lead to uneven or partial shedding of the oxide film during anodic oxidation. Therefore, heat treatment is suggested to eliminate internal stress.
-Anodized parts should not withstand high temperature or strong acid and alkali environment, so as not to damage the oxide film structure.
-For 3D printed parts with complex shapes, the mounting method should be designed reasonably to ensure uniform current distribution.

VI. Conclusion

Anodizing, as a mature metal surface modification technology, provides an important means to improve the performance and appearance of 3D printed metal parts. Although the microstructure of 3D printed parts is different from that of traditional casting or forging parts, as long as the material selection, pretreatment and operation process are controlled, high-quality anodic oxidation effect can also be obtained. With the further integration of 3D printing technology and surface treatment technology, more 3D printing products with high performance and high value will be applied to high-end manufacturing fields in the future.