Introduction to aluminum alloy anodizing
Anodizing is one of the most common surface treatment operations performed on aluminum parts. This is an electrochemical process that involves dipping aluminum parts into a series of cans, transforming the aluminum surface into a durable and corrosion-resistant finish.
To determine whether anodizing is the right choice for a specific part, product designers must first understand how it affects the strength, thickness, color and thermal conductivity of aluminum.
This article provides answers to five frequently asked questions about anodized aluminum. If you wish to implement anodizing into your machined products.
1.Three types of aluminum anodization
Anodizing can generally be divided into three types:
Type I anodizing process
Also known as chromic acid anodizing, a chemical bath of chromic acid is used to form a coating (or oxide layer) on an aluminum surface. It produces thin coatings (up to 2.5 microns) ideal for applications requiring minimal corrosion protection and paint adhesion.
Type II anodizing process
A chemical bath of sulfuric acid is used to form an oxide layer on aluminum parts. This type of anodization produces an oxide layer up to 25 microns thick, making it more corrosion-resistant than Type I anodized aluminum parts. Additionally, because they have a thicker oxide layer (and pores), they retain dyes and colorings better than “Type I” anodized parts.
Type III anodizing process
Also known as hard coat anodizing, this produces an oxide layer that is more than 25 microns thick. It uses sulfuric acid as a chemical bath, like Type II anodizing. However, the current flows during this process for a longer period of time compared to Type II anodization. This allows them to produce thicker layers and makes them more corrosion resistant than Type I and Type II anodized parts.
2.Why should aluminum parts be anodized?
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 thin and wears off easily, especially if you scratch it or use it in areas with polluted air.
However, unlike regular aluminum, the oxide layer of anodized aluminum parts lies deep within the aluminum substrate. For example, the pores (and honeycomb oxide layer) formed during electrochemical reactions can be up to 25 microns in size. As a result, you have an aluminum component that is corrosion-resistant, scratch-resistant, and can withstand almost any chemical attack.
3.How is anodizing done?
The anodizing process involves immersing clean aluminum parts in a chemical bath of electrolyte and treating them. This chemical bath is usually made of sulfuric acid or chromic acid, a conductive solution.
Next, a direct current is applied to the chemical bath, creating a positive charge on the aluminum parts and a negative charge in the electrolyte plate. The resulting electrochemical reaction creates pores on the surface of the part. These pores combine with the negatively charged O 2 ions in 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 aluminum’s hardnessㅡ, which describes an aluminum part’s resistance to surface dents, scratches, or abrasions. For example, anodized aluminum parts may be three times harder than the original aluminum alloy.
Additionally, anodized aluminum parts are generally lighter than other metals like copper and stainless steel. This unique property makes them ideal for aerospace applications requiring lightweight metals.
5.Can anodizing improve the thermal conductivity of aluminum?
Thermal conductivity describes a material’s ability to transfer or conduct heat. This capability increases with heat flow, material thickness, and material surface area.
Because anodizing creates an additional layer of oxide on the surface of the aluminum part, you will agree that it increases the thickness and surface area of the part. Therefore, anodized aluminum will have a higher thermal conductivity than unfinished aluminum parts. This makes anodized aluminum components ideal for heat sink applications in today’s electronics and other thermal systems.
From the above article, I believe that you have at least some knowledge about anodizing, then you will agree that anodized aluminum parts have several advantages over regular aluminum parts. However, the anodizing process is not as simple as it seems: it requires special techniques and expertise.