Aluminum Alloy Anodic Oxidation Common Problems

Anodizing is one of the most common metal surface treatment operations performed on aluminum parts. It is an electrochemical process that involves immersing aluminum parts in a series of tanks to transform the aluminum surface into a durable and corrosion-resistant finish.

To determine if anodizing is the right choice for a particular part, product designers must first understand how it affects the strength, thickness, color and thermal conductivity of aluminum.

This article provides answers to five common questions about anodized aluminum. If you are looking to implement anodizing in your machined products

1. Three Types of Aluminum Anodizing

Anodizing can usually be categorized into three types:

Type I Anodizing
 Type II Anodizing
 Type III Anodizing

Type I Anodizing Process

Also known as chromic acid anodizing, a chromic acid chemical bath is used to form a coating (or oxide layer) on the aluminum surface. It produces thin coatings (up to 2.5 microns) and is ideal for applications requiring minimal corrosion protection and paint adhesion.

Type II Anodizing Process

Uses a sulfuric acid chemical bath to form an oxide layer on aluminum parts. This type of anodizing produces an oxide layer up to 25 microns thick, making it more resistant to corrosion than Type I anodized aluminum parts. In addition, because they have a thicker oxide layer (and pores), they retain dyes and coloration better than "Type I" anodized parts.

Type III Anodizing Process

Also known as hard coat anodizing, this process produces an oxide layer thicker than 25 microns. It uses sulfuric acid as the chemical bath, as in Type II anodizing. However, the current flows for a longer period of time in this process than in Type II anodizing. This allows them to produce thicker layers and makes them more resistant to corrosion than Type I and Type II anodized parts.

2. Why anodize aluminum parts?

When you expose regular aluminum parts to the atmosphere, a layer of aluminum oxide forms on the surface of the part. However, this layer is usually very thin and wears off easily, especially if you scratch it or use it in places where the air is polluted.

Unlike regular aluminum, however, the oxide layer in anodized aluminum parts is located deep within the aluminum substrate. For example, the pores (and honeycomb oxide layer) formed during the electrochemical reaction can be up to 25 microns. As a result, you will have an aluminum part that is corrosion and scratch resistant and can withstand virtually any chemical attack.

3. How is anodizing done?

The anodizing process involves immersing and treating clean aluminum parts in an electrolyte chemical bath. This chemical bath is usually made of sulfuric acid or chromic acid (a conductive solution).

Next, a direct current is applied to this chemical bath, creating a positive charge on the aluminum part and a negative charge in the electrolyte plates. The resulting electrochemical reaction creates pores on the surface of the part. These pores combine with the negatively charged O 2 ions of the electrolyte to form a honeycomb oxide layer (aluminum oxide) on the component.

4. Does anodizing make aluminum parts stronger?

Anodizing does not make aluminum parts stronger or weaker. Instead, it increases the hardness of the aluminum ㅡ, which describes the resistance of an aluminum part to surface indentations, scratches, or abrasion. For example, an anodized aluminum part may be three times as hard as the original aluminum alloy.

In addition, anodized aluminum parts are typically lighter than other metals such as copper and stainless steel. This unique property makes them ideal for aerospace applications that require a lightweight metal.

5. Does anodizing improve the thermal conductivity of aluminum?

Thermal conductivity describes the ability of a material to transfer or conduct heat. This ability increases with heat flow, material thickness, and material surface area.

Because anodizing creates an additional oxide layer on the surface of an aluminum part, you will agree that it will increase the thickness and surface area of the part. As a result, anodized aluminum will have higher thermal conductivity than unfinished aluminum parts. This makes anodized aluminum parts ideal for heat sink applications in today's electronics and other thermal systems.

When choosing the right anodized finish for your application, be sure to consider your product needs as well as the desired performance characteristics. Whichever type of anodizing your project requires - Type I, Type II, or Type III - can make your aluminum alloy parts more corrosion-resistant, robust, and available in a variety of optional colors. At the same time, the thermal conductivity of aluminum alloys is critical for some applications, and anodizing can also help increase the material's ability to conduct heat.

To ensure the success of your project, we recommend that you choose an experienced company to perform anodizing and other surface treatment processes. Founded in 2008, Richconn is a professional rapid prototyping company that offers anodizing services, surface finishing services, and plating services for a variety of materials. No matter what your needs are, we will provide you with superior technology and service to ensure that your products are the best they can be in terms of performance and appearance. We look forward to working with you to add color to your projects and inject more value and competitiveness into your products.