Aluminium is the main component of alloy wheels and is the main reason for their lightness and
strength. Other elements used in alloy wheels include Magnesium, Silicon, Manganese, Zinc and Copper. These different elements are added in smaller quantities for different combinations of weight and strength.
Alloy wheels are either “forged” or “cast”. Forged wheels are pressed from a single block of alloy
under very high pressure. The process is very expensive because of the equipment used but the wheels are of highest quality and usually stronger. Cast wheels are made by pouring molten alloy metal into a mould then finishing of the wheel to the right shape and dimensions. The alloy used in wheels has a crystalline structure which makes it very strong. However, if the metal becomes distorted or badly buckled it can’t easily be knocked back into shape. Forcing the metal to bend usually causes it to fracture which is why you need to take care not to cause any physical damage to the shape of the wheels.
Although the alloys used in wheels are very strong they are also quite soft. Therefore they are easily damaged when they come into contact with kerbs, stones and gravel. They are also prone to corrosion, especially from salt and brake dust, as well as other dilute acids found in nature. Most alloy wheels now come with a coating of clear lacquer or paint to protect the metal. Sometimes the damage only affects this lacquer coating which is usually easier and less expensive to repair.
Unlike steel, aluminum never goes “rusty”. Pure Aluminum will oxidise in normal atmosphere but the layer of oxidation is so incredibly thin it’s transparent. However, when mixed with other alloys, aluminum will corrode slowly in an atmosphere of oxygen and water. So corrosion takes place INSIDE alloy wheels eventually breaking the seal between the wheel and the tyre. This allows air inside the tyre to escape looking as if the tyre has a puncture. This can be common with wheels on cars more than four or five years old and means its time to refurbish the wheels.
Repairing alloy wheels is a straightforward process if you have the right tools and equipment. The good news is that most alloys can be restored to their original condition using the tools and equipment in a mobile repair workshop. More serious damage may need a certain amount of sandblasting and fillers to repair larger cracks or gaps and this needs to be carried out in a professional workshop. Either method can produce excellent results. The only downside is, if you only repair one wheel it tends to show up the others on your car so its always worth paying to have all four done at the same time.