The Difference Between Anodized and Hard Anodized

Written by lindsay pick | 13/05/2017
The Difference Between Anodized and Hard Anodized
Hard anodising is common in hydraulic parts that suffer major wear and tear. (Jupiterimages/ Images)

Anodising aluminium creates aluminum oxide, a strong and durable product used in a variety of construction projects and consumer products. Known for its environmentally safe process and long-lasting, weather-safe finish, anodised aluminium can be customised to level of durability. Hard anodising refers to an especially strong and durable form of anodised aluminium that differs in thickness and production from standard anodised aluminium.

Types of Anodizing

There are three general types of anodised aluminium. Chromic anodised -- Type I -- is the thinnest and least corrosive of anodised aluminium. It's produced using chromic acid electrolytes. Sulphuric anodised -- Type II -- and hard anodised -- Type III -- are both produced utilising sulphuric acid electrolytes. Type II is the most common anodised aluminium and doesn't share the roughened surface of Type III.


Standard anodised aluminium is sealed to close pores that occur during the conversion to aluminum oxide. Sealing gives the anodised aluminium a protective coat and prevents colour erosion in coloured products. Hard anodised aluminium is not generally sealed, as its thicker surface is considered more durable and wearproof, negating the necessity of a sealant. Waxes and silicone may be used to give hard anodised aluminium a desired finish.


Hard anodised aluminium is thicker than standard anodised aluminium. At greater than 25 microns, hard anodised is produced using low temperatures and higher current density to accomplish this thickness. A thicker surface gives hard anodised aluminium a more abrasion-resistant surface.


Standard sulphuric anodised is employed for architecture, aerospace and automotive components. Products requiring a heavy-duty, wear-resistant surface utilise hard anodised. These include various hydraulics and pistons, some food cooking surfaces and pans, and exterior surfaces of buildings.

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