Ferris metals (alloys) include iron (often mostly iron) while non-ferrous alloys include very little or no iron. Alloys of copper and aluminum for example may not include more than a trace of iron. Iron alloys (steel) are usually cheaper than aluminum or copper and have superior strength for structures. Copper and aluminum are better electrical conductors and resist corrosion. Stainless steels are expensive and more difficult to fabricate but also resist corrosion.