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An alloy is distinct from an impure metal in that, with an alloy, the added elements are well controlled to produce desirable properties, while impure metals such as wrought iron are less controlled, but are often considered useful. Alloys are made by mixing two or more elements, at least one of which is a metal.
Metallurgy derives from the Ancient Greek μεταλλουργός, metallourgós, "worker in metal", from μέταλλον, métallon, "mine, metal" + ἔργον, érgon, "work" The word was originally an alchemist's term for the extraction of metals from minerals, the ending -urgy signifying a process, especially manufacturing: it was discussed in this sense in the 1797 Encyclopædia ...
Of all the metallic alloys in use today, the alloys of iron (steel, stainless steel, cast iron, tool steel, alloy steel) make up the largest proportion both by quantity and commercial value. [36] Iron alloyed with various proportions of carbon gives low-, mid-, and high-carbon steels, with increasing carbon levels reducing ductility and toughness.
Fortunately some alloys are able to dissolve the surface oxides in their bulk when superheated by several degrees above their melting point; the Sn-Cu 1 and Sn-Ag 4 require superheating by 18–19 °C, the Sn-Sb 5 requires as little as 10 °C, but the Sn-Pb 37 alloy requires 77 °C above its melting point to dissolve its surface oxide.
In contrast, certain metal alloys exhibit unique properties where their size and density remain unchanged across a range of temperatures. [33] Cast iron is defined as an iron–carbon alloy with more than 2.00%, but less than 6.67% carbon. Stainless steel is defined as a regular steel alloy with greater than 10% by weight alloying content of ...
In addition, gold, copper, iron, mercury, tin, and lead may occur in alloys of this group. [8] As with gold, salts and other compounds of the platinum group metals are rare; native platinum and related metals and alloys are the predominant minerals bearing these metals.
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High-entropy alloys are difficult to manufacture using extant techniques as of 2018, and typically require both expensive materials and specialty processing techniques. [42] High-entropy alloys are mostly produced using methods that depend on the metals phase – if the metals are combined while in a liquid, solid, or gas state.