Editing Materials science (section)

===Metal alloys===
{{Main|Alloy}}
[[File:Steel wire rope.png|thumb|upright|Wire rope made from [[steel]] alloy]]
The alloys of iron ([[steel]], [[stainless steel]], [[cast iron]], [[tool steel]], [[alloy steel]]s) make up the largest proportion of metals today both by quantity and commercial value.

Iron alloyed with various proportions of carbon gives [[Carbon steel#Mild or low-carbon steel|low]], mid and [[high carbon steel]]s. An iron-carbon alloy is only considered steel if the carbon level is between 0.01% and 2.00% by weight. For steels, the [[hardness]] and tensile strength of the steel is related to the amount of carbon present, with increasing carbon levels also leading to lower ductility and toughness. [[Heat treatment]] processes such as [[quenching]] and [[tempering (metallurgy)|tempering]] can significantly change these properties, however. In contrast, [[Invar|certain metal alloys]] exhibit unique properties where their size and density remain unchanged across a range of temperatures.<ref>{{Cite journal |last1=Lohaus |first1=S. H. |last2=Heine |first2=M. |last3=Guzman |first3=P. |last4=Bernal-Choban |first4=C. M. |last5=Saunders |first5=C. N. |last6=Shen |first6=G. |last7=Hellman |first7=O. |last8=Broido |first8=D. |last9=Fultz |first9=B. |date=2023-07-27 |title=A thermodynamic explanation of the Invar effect |url=https://www.nature.com/articles/s41567-023-02142-z |journal=Nature Physics |volume=19 |issue=11 |language=en |pages=1642–1648 |doi=10.1038/s41567-023-02142-z |bibcode=2023NatPh..19.1642L |osti=1993279 |s2cid=260266502 |issn=1745-2481}}</ref> 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 [[chromium]]. [[Nickel]] and [[molybdenum]] are typically also added in stainless steels.

Other significant metallic alloys are those of [[Aluminium alloy|aluminium]], [[Titanium alloys|titanium]], [[copper]] and [[Magnesium alloy|magnesium]]. [[Copper alloys]] have been known for a long time (since the [[Bronze Age]]), while the alloys of the other three metals have been relatively recently developed. Due to the chemical reactivity of these metals, the electrolytic extraction processes required were only developed relatively recently. The alloys of aluminium, titanium and magnesium are also known and valued for their high strength to weight ratios and, in the case of magnesium, their ability to provide electromagnetic shielding.<ref>{{Cite journal |last1=Chen |first1=Xianhua |last2=Liu |first2=Lizi |last3=Liu |first3=Juan |last4=Pan |first4=Fusheng |date=2015 |title=Microstructure, electromagnetic shielding effectiveness and mechanical properties of Mg–Zn–Y–Zr alloys |url=http://dx.doi.org/10.1016/j.matdes.2014.09.034 |journal=Materials & Design  |volume=65 |pages=360–369 |doi=10.1016/j.matdes.2014.09.034 |issn=0261-3069}}</ref> These materials are ideal for situations where high strength to weight ratios are more important than bulk cost, such as in the aerospace industry and certain automotive engineering applications.