Magnesium has a special place in the hearts of VW enthusiasts. We all know (or SHOULD know) that the engine case of the Type I and 3 air-cooled motor is made of an alloy of it, as is the gearbox casing. We might also know that it burns. If we're good at trivia, we could say that Volkswagen once used 38,000 tonnes per annum, nearly one sixth of the entire world's output.
In actual fact, one Beetle contains about 22 kg of magnesium castings, because the air-cooled engine design was ideally suited for ultra-light alloy. The trend to front-mounted water-cooled engines has now reduced VW's magnesium consumption considerably, although it still finds uses mainly in gearboxes and other transmission components. The pressure diecasting plants operated by Volkswagen remain prime examples of highly developed technology.
Magnesium is known as the lightweight champion of the metals. It is the lightest of all metals used in general engineering, with a relative density only 1.7 times that of water! Aluminium is more than half as heavy again, iron and steel are four times heavier, and copper and nickel are five times heavier. Perhaps not unexpectedly though, magnesium is also relatively weak in the pure state, with a tensile strength of only 110 newtons per square millimetre. However, when alloyed with various other metals it can be strengthened two or even three times over, yet still remain very light. Aluminium, zinc and thorium are common alloying metals.