Anodising is a widely used electrochemical surface treatment applied to metals such as aluminium, titanium, and magnesium. The process enhances corrosion resistance, surface hardness, and paint adhesion while offering aesthetic improvements.
By submerging a metal component into an acidic solution and applying an electrical current, a durable oxide layer forms on the surface. Different anodising methods offer various properties, depending on the application needs. The three most common types are chromic acid anodising, sulphuric acid anodising, and hard anodising.
1. Chromic acid anodising
Chromic acid anodising differs in its chemistry and is often chosen when minimal oxide thickness is essential, typically producing coatings of one to ten microns. This makes it ideal for use on castings or aerospace components, where maintaining fatigue strength is critical
Although it produces a thinner layer, it offers good corrosion resistance and is electrically conductive, making it well-suited to electronic applications. It is less common but remains important in highly specialised industries.
2. Sulphuric acid anodising
Sulphuric acid anodising is the most widely used anodising method due to its versatility and cost-effectiveness. It creates an oxide layer typically between 5 and 25 microns thick. This layer provides improved wear and corrosion resistance and enhanced surface hardness.
When sealed, the oxide layer resists moisture and environmental exposure, although it may be vulnerable in chemically aggressive environments. It is also suitable for dyeing, often requiring 10 to 15 microns for colour uniformity. Sometimes called natural anodising, this process balances functionality with decorative potential.
For anyone interested in learning more about sulphuric acid anodising, specialists such as www.poeton.co.uk/surface-treatments/anodising/sulphuric-acid-anodising/ can help.
3. Hard anodising
Hard anodising is designed for demanding applications requiring superior wear resistance and durability. Using a stronger sulphuric acid solution at lower temperatures and higher voltage, it produces coatings between 25 and 100 microns thick. These dense layers can withstand mechanical and chemical stress, making them ideal for engineering components. Although primarily functional, the surface can still be dyed for aesthetic purposes
Each anodising type offers unique advantages, helping industries meet specific technical and regulatory demands as coating performance expectations increase.