An alloy wheel is a wheel made of aluminum or magnesium alloy. Alloys are a mixture of metals and other elements. Usually more strength than pure metals, which are usually softer and more ductile. Alloys of aluminum or magnesium are usually lighter in respect to the same strength, provide better heat transfer, and often produce improved decorative appearance on the steel wheel. Although steel is the most common material used in the production of wheels, it is an alloy of iron and carbon, and the term "alloy wheels" are usually reserved for wheels made of nonferrous alloys. The earliest light alloy wheels are made of magnesium alloy.They're still popular in 60s, though they lost the favor of ordinary vehicles and the number is very limited. But in the mid to late 1960s, aluminum casting improved to allow for less brittle and more secure wheels. Until now, most aluminum tires have low ductility, usually in the elongation of 2-3%. Because the light alloy wheel is made of magnesium (usually called "Mark"), the low ductility of these early failures due to magnesium wheels later, in many cases, these wheels are cast aluminum alloy wheels. Once the improvement of these aluminum castings is more widely adopted, aluminum wheel will instead of magnesium as a low cost, high performance wheel motor vehicle.