Hard anodising is an electrochemical process that enhances the surface properties of aluminium by producing a dense, durable oxide coating. It differs from standard anodising in the sense that it is performed at lower temperatures and higher current densities, resulting in a much thicker and harder layer. This makes it particularly suitable for applications where components will be exposed to extreme wear, corrosion, or heat.
The process and its key properties
The process of hard anodising involves immersing aluminium parts in a sulphuric acid electrolyte while applying a strong electric current to it. The resulting oxide layer, which can reach up to 100 microns in thickness, is integral to the metal and provides exceptional hardness and wear resistance.
Hard anodised coatings also exhibit excellent corrosion resistance, even in harsh environments such as marine or aerospace settings. The finish is typically dark grey to black due to the processing conditions, although it can be dyed for specific aesthetic requirements. The surface’s porous structure allows for secondary treatments such as impregnation with lubricants or PTFE, further improving performance in demanding mechanical systems, as outlined at https://www.poeton.co.uk/surface-treatments/anodising/hard-anodising.
Applications across industries
Thanks to its durability, hard anodising is widely used in a number of sectors, including aerospace, automotive, defence, and industrial engineering. It is often applied to components such as pistons, gears, and hydraulic cylinders, where abrasion resistance is essential.
Hard anodising provides a helpful balance between strength, corrosion protection, and thermal performance, making it a vital treatment for enhancing the longevity and efficiency of aluminium components.
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