If you are manufacturing aluminium components that will eventually be deployed in areas susceptible to pollution, you may find that these parts are subject to more than their fair share of corrosion. In many cases, aluminium manages to provide its own protection through its almost constant desire to oxidise. This oxidation forms a hard skin over the surface of the aluminium that is almost as hard as a diamond.
Of course, if it is subject to heavy pollution, the aluminium will not get the chance to oxidise itself, which is where it may need a little extra protection.
Otherwise known as hardcoat, the process of hard anodising gives aluminium an electrochemically produced protective layer of aluminium oxide over the surface. This process is used to provide a thicker, harder and far more corrosion-resistant coating to a range of aluminium components.
Benefits of hardcoat
One of the biggest benefits of hard anodising is the fact that the thickness can be controlled incredibly tightly, enabling components to be given just enough protection without impacting too much on their dimensions. This makes the process fantastic for precision engineering projects in which pieces are produced with exacting tolerances. Similarly, hardcoating is especially effective when utilised for tough engineering applications in which high levels of wear are expected and the parts will be exposed to high temperatures.
Other benefits of hardcoating include an attractive appearance, an environmentally-friendly process, and a long life span – usually over 80 years. Hardcoating aluminium provides a highly durable surface that is resistant and colourfast; in fact, colours should stay fast for a good 20 years. Finally, hardcoated products are very easy to clean and maintain.
Processes of hardcoating
The hardcoating process uses a similar process to the common or garden variety of anodising. When anodising aluminium, the oxide skin is grown on aluminium by immersing it in an acid bath. This coating provides great protection against scratches in addition to providing excellent chemical resistance.
Hardcoating works in a similar manner to regular anodising; however, a denser and more hardwearing outer aluminium oxide layer is grown both into and out of the surface. This is achieved by lowering the temperature of the acid into which the aluminium is submerged. The coating is more durable due to the narrower pores. In addition to increased durability, corrosion resistance is increased by hardcoating.
The thickness of the hardcoat
Generally speaking, the hardcoat thickness is usually between 25 micrometres and 50 micrometres, with great control afforded by the process. Hardcoating is used to provide great wear resistance when surface contact loads are on the light side. Common applications include the low-stress abrasive wear often encountered in pharmaceutical or food products. In addition to the aforementioned corrosion protection, hardcoating provides great electrical insulation.
It is possible to produce hardcoated pieces with high levels of control and a uniform structure, which both improves the hardness and the ability to be honed.