Anodizing is a common way to finish the surface of rapid prototypes. Chromate conversion is less common, but it's a similar process. It's easy to get these two mixed up. This article will explain the difference between anodizing and chromate conversion.
What Is Anodizing?
Anodizing is a process that creates an aluminum oxide layer on the surface of aluminum materials by applying an external voltage in an electrolyte solution. Different thicknesses of the oxide film can be achieved by adjusting parameters like voltage, current, and time. This aluminum oxide layer is known for its high hardness and wear resistance and can also undergo various electrochemical coatings that further enhance surface adhesion and corrosion resistance.
Key Features of Anodizing
Increased Surface Hardness: Anodizing forms a uniform and dense oxide layer on the metal surface, increasing hardness by 5-10 times compared to the original material. This makes it ideal for manufacturing high-strength, wear-resistant metal parts.
Enhanced Surface Adhesion: The anodized surface can receive various electrochemical coatings, ensuring strong adhesion between the coating and the base material.
Improved Corrosion Resistance: The anodized surface forms a fine oxide layer, significantly boosting the material's resistance to corrosion.
What Is Chromate Conversion?
(image from the Internet)
Chromate conversion involves applying a chromate solution to a metal surface, resulting in a dense and uniform oxide layer. This layer significantly enhances the material's corrosion resistance and adhesion, giving the surface a smoother and more attractive appearance.
Key Features of Chromate Conversion
Broad Applicability: Chromate conversion is effective for various metals, particularly ideal for aluminum and aluminum alloy surfaces.
Consistent Results: Treated metal surfaces develop a uniform, dense oxide layer, offering excellent corrosion resistance and adhesion.
Cost-Effective: Chromate conversion is economical, making it suitable for small to medium-scale production.
The Difference Between Anodizing and Chromate Conversion
Anodizing and chromate conversion are surface treatment processes used to enhance the properties of metals, particularly aluminum. Here are the key differences between the two:
Anodizing | Chromate Conversion | |
Process |
Getting anodized involves immersing the metal in an acid electrolyte bath and passing an electric current through it.
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Chromate conversion, or chromating, is a chemical process that applies a chromate-based coating to the metal surface. |
Purpose |
Anodizing is primarily used to increase corrosion resistance and wear resistance. |
Chromate conversion aims at improving corrosion resistance and providing a base for paint or other coatings. It also provides some degree of electrical conductivity, unlike anodizing. |
Properties |
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Chromate conversion produces a thinner coating compared to anodizing. |
Applications | Anodizing is commonly used in aerospace, automotive, consumer electronics, and architectural applications. |
Chromate conversion is commonly used in the aerospace, military, and electronics industries. It is often used for parts that require electrical conductivity. |
Environmental Impact | Anodizing is generally considered environmentally friendly, but the process generates some waste products that must be handled properly. |
Chromate conversion coatings contain hexavalent chromium. It is toxic and poses environmental and health risks. |
Challenges for Prototype Manufacturers in Surface Treatment
In the prototype stage, they also use anodizing and chromate conversion for the surface treatment. But it's different from mass production. Since there are only a few prototypes, taking them to get anodized or chromate converted in a factory would be very expensive to do just for them. Instead, the prototypes have to get processed along with the regular big batches of products. Whatever the factory is doing for their main orders, that's what the prototypes have to go through too. So it's hard to fully match the customer's high standards for the mass-produced version.
This is a common problem that prototype makers face. Luckily, in the prototype stage, customers are usually more flexible and don't demand things to be as perfect. They can generally accept the results, even if the prototypes don't reach the full quality level of mass production.
Conclusion
Here is a simpler conclusion of the difference between anodizing and chromate conversion.
Anodizing: Electrochemical process, a thicker non-conductive oxide layer, used for corrosion resistance and aesthetics, environmentally friendly.
Chromate Conversion: Chemical process, thinner conductive coating, used for corrosion resistance and as a primer, contains toxic hexavalent chromium.
Both processes have specific advantages and are chosen based on the application's needs. In rapid prototyping, they often fail to meet the standards required for mass production.