What’s Anodizing? Process, Types, Benefits, and Uses
Anodizing is a type of surface finish known for enhancing sturdiness, corrosion resistance, wear resistance, and the aesthetic of non-ferrous...
RapidDirect Anodizing Services
Explore our Type II and Type III anodizing service and experience quality surface finish solutions to improve your metal parts' performance and appearance.
Anodizing Overview
Anodizing is an electrochemical process that improves a metal’s corrosion and wear resistance and cosmetic appearance. It is primarily for aluminum and involves connecting the part to the anode before submerging it in a sulfuric or chromic acid bath.
When a metal electrode is attached to the cathode, and current passes through the circuit, the cathode attracts positive ions from the aluminum part. In contrast, the aluminum part attracts O2 ions from the solution.
The anodic part (aluminum) becomes porous due to the loss of cations and reacts with O2 ions. As a result, this forms the oxide layer on anodized parts. There are several anodizing types depending on the voltage and the electrolyte.
Type II anodizing’s electrolyte is sulfuric acid, producing parts with a thin anodizing thickness of 8-12μm, ensuring good corrosion resistance. Therefore, aluminum anodizing services recommend it for parts that need aesthetics and moderate protection.
Type III anodizing, or hard anodizing, produces a thicker oxide layer (35 to 50μm), offering higher wear and corrosion resistance. Furthermore, Type III anodic films are hard (70 Rockwell C). Hence, an anodizing service can recommend it for parts used in extreme conditions.
Anodizing Type II Specifications
Type II anodizing produces metal parts with a thin oxide layer and moderate corrosion resistance. As a result, the quick turn anodizing process is ideal for parts requiring aesthetics and moderate protection.
| Color | Glossiness | Visual Appearance | Thickness |
|---|---|---|---|
| Clear | Glossy | It yields a clear, glossy finish that enhances the metal's natural luster without significantly altering its color. | Range from 8-12μm |
| Clear | Matte | It imparts a clear, matte finish to the metal, giving a subdued and uniform appearance without high reflectivity. | Range from 8-12μm |
| Black | Glossy | It produces a deep, glossy black finish that adds an attractive and protective layer to the metal. | Range from 8-12μm |
| Black | Matte | Provides a subdued, matte black finish for those seeking a non-reflective and uniform appearance. | Black |
Advantages
- Enhanced corrosion resistance due to the formation of an unreactive oxide coating
- Improvement in aesthetic appeal as it offers a beautiful finish with different anodizing colors
- Insulative properties for parts that need dampening of electrical conductivity
- Anodized parts are easier to clean
Notes
- Use sandblasting (#120) as a pre-treatment, or the machining marks on the surface cannot be completely covered.
- Different materials, thicknesses, and lots will have a certain degree of color difference.
- Non-standard and custom colors are available upon request.
Anodizing Type III Specifications
Type III anodizing parts with a thicker oxide layer which offers higher wear and corrosion resistance and surface hardness
| Color | Visual Appearance | Thickness |
|---|---|---|
| Clear | Introducing a non-conductive, thicker, and more wear-resistant oxide layer than standard anodizing. | Typical thickness range 35 - 50 μm |
| Black | It produces a deep, consistent black finish that is both durable and visually appealing. | Typical thickness range 35 - 50 μm |
Advantages
- High corrosion resistance
- The anodic film is harder than base aluminum
- Improvement in aesthetic appeal as it offers a beautiful finish with different color options
- Insulative properties for parts that need dampening of electrical conductivity
Notes
- Different series of aluminum will show different colors.
- Default mask fine holes and fine threads only. Special notes are required for other masking needs.
- The workpiece needs to hook up a tiny substrate that is exposed after anodizing. RD defaults to hooking up threaded or countersunk holes. Specify if there is a specific hooking-up place.
Standard Anodizing Color Options
At RapidDirect, we offer a selection of standard colors for your projects. Should you require a specific RAL or Pantone color, do not hesitate to contact your sales engineer or us at [email protected] for personalized assistance.
Anodizing Type II vs Type III
| Properties | Type II | Type III |
|---|---|---|
| Corrosion Resistance | Moderate | High |
| Wear Resistance | Moderate | High |
| Coating Thickness | 8-12μm | 35-50μm |
| Appearance | Glossy and Matte finishes | More matte, highly durable |
| Environment Friendly | Yes | Yes |
Anodizing Design Considerations
- Anodizing involves suspending parts via a “jig” or “rack.” This will leave marks on the parts. Therefore, indicate any areas where these marks are unacceptable in your technical drawing and follow our cosmetic procedure.
- Anodizing reduces part conductivity.
- Masking is not required by default, as anodizing does not significantly increase part thickness. However, you can specify areas you want masked or plugged in your CAD file.
- Type III anodizing adds significant thickness. We recommend plugging and masking threaded/reamed holes or other critical surfaces.
FAQs
The anodized coating is highly durable, second only to diamond. It is also corrosion resistant, with Type III anodizing producing a higher hardness and corrosion resistance.
The durability is due to the thick oxide layer being highly resistant to harsh environmental factors such as sunlight, saltwater, and various chemicals. Overall, anodizing a workpiece will increase its lifespan and performance, ensuring it remains functional and aesthetically pleasing for extended periods.
Consider the aluminum alloys because they react differently to anodizing, which can affect the final part color and finish. The desired thickness will determine the level of protection, but thicker coating also requires longer processing times.
Since anodized parts can be dyed, color choices are very important. Furthermore, the desired final appearance, including matte or glossy finishes, will influence the pre-treatment methods with techniques such as sandblasting or chemical etching, affecting the overall quality and aesthetics of the anodized part
A common issue with anodizing is the presence of grooves due to the machining process, which can lead to more pronounced surface imperfection. There can also be inconsistent coloring due to alloy composition, thickness, or dyeing process variations. Lastly, uneven anodizing can result in exposed areas, and inadequate cleaning or improper pre-treatment can result in poor adhesion of the anodized layer
Yes, anodizing can cause color loss due to UV exposure and environmental factors. However, the time taken to lose color depends on the process, the quality of the sealing, and the die choice.
The cost of anodizing aluminum varies based on the part size, type of anodizing, color, and other specific requirements. For example, Type III is the costlier anodizing method due to the quality and characteristics of the final part. Contact us for a detailed quote tailored to your project needs.
Surface Finishing Resources
A Guide to Aluminum Anodizing
Aluminum is a go-to material in many part manufacturing industries because of its excellent mechanical properties, myriads of alloys, low...
Anodized Aluminum Colors: Coloring Aluminum Products
At the end of the manufacturing process, the next stage is applying the surface finish. There are different methods, but...
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