Anodising is a popular method for enhancing the durability, appearance, and corrosion resistance of aluminium. It involves an electrochemical process that thickens the natural oxide layer on the metal’s surface. There are several different types of aluminium anodising, each offering unique benefits depending on the intended application.
1. Chromic acid anodising
Chromic acid anodising, often referred to as type I anodising, produces a thin, flexible oxide layer. The process uses chromic acid as the electrolyte and is typically carried out at lower voltages compared to other methods. Although the coating is thinner, it provides excellent corrosion resistance and is less likely to alter the dimensions of the treated parts. This makes it ideal for components used in aerospace and precision engineering. Chromic acid anodising is particularly suited for critical applications where preserving metal fatigue strength is essential.
2. Sulphuric acid anodising
Sulphuric acid anodising, or type II anodising, is the most commonly used method for aluminium. It involves immersing the metal in a sulphuric acid bath and applying an electrical current to form a thicker oxide layer than chromic acid anodising. This process offers a good balance of wear resistance, corrosion protection, and the ability to accept dyes for aesthetic purposes. The resulting finish is versatile, making it suitable for architectural, automotive, and consumer goods applications. Colouring options are vast, as the porous surface created by sulphuric acid anodising readily absorbs dyes before sealing, providing long-lasting decorative finishes.
3. Hard anodising
Hard anodising, also known as type III anodising, produces an exceptionally thick and dense oxide layer, significantly enhancing surface hardness and wear resistance. This method uses colder and more concentrated sulphuric acid solutions, with higher voltages and current densities. Hard anodising is often chosen for parts that must withstand extreme conditions, such as hydraulic components and aerospace fittings. Specialist treatments, which are offered by surface treatment companies such as poeton.co.uk/surface-treatments/anodising/hard-anodising/, provide surfaces capable of withstanding demanding mechanical and environmental stresses.
Choosing the appropriate anodising type for your needs depends on factors such as the required durability, appearance, and the operating environment of the finished component.
