are similar in lightness and strength, are cheaper and much more widely used. Additions of erbium and zirconium have been shown to increase the coarsening resistance of Al-Sc alloys to ~400 °C. This is achieved by the formation of a slow-diffusing zirconium-rich shell around scandium and erbium-rich precipitate cores, forming strengthening precipitates with composition . Additional improvements in the coarsening resistance will allow these alloys to be used at increasingly higher temperatures. Applications The main application of metallic scandium by weight is in aluminium–scandium alloys for minor aerospace industry components. These alloys contain between 0.1% and 0.5% (by weight) of scandium. They were used in the Russian military, specifically the Mikoyan-Gurevich MiG-21 and MiG-29. The increased operating temperature of Al-Sc alloys has significant implications for energy efficient applications, particularly in the automotive industry. These alloys can provide a replacement for denser materials such as steel and titanium that are used in 250–350 °C environments, such as in or near engines. Replacement of these materials with lighter aluminium alloys leads to weight reductions which in turn leads to increased fuel efficiencies. Some items of sports equipment, which rely on lightweight high-performance materials, have been made with scandium-aluminium alloys, including baseball bats, tent poles and bicycle frames and components. Lacrosse sticks are also made with scandium. The American firearm manufacturing company Smith & Wesson produces semi-automatic pistols and revolvers with frames of scandium alloy and cylinders of titanium or carbon steel. References Further reading Dorin, Thomas; Ramajayam, Mahendra; Vahid, Alireza; Langan, Timothy (2018), "Aluminium Scandium Alloys", Fundamentals of Aluminium Metallurgy, Elsevier, pp. 439–494 Røyset, J.; Ryum, N. (2005-02-01). "Scandium in aluminium alloys". International Materials Reviews. 50 (1): 19–44. doi:10.1179/174328005X14311. ISSN 0950-6608 Shevchenko, M. O.; Kudin, V. G.; Berezutskii, V. V.; Ivanov, M. I.; Sudavtsova, V. S. (2014-07-01). "Thermodynamic Properties of Al–Sc Alloys". Powder Metallurgy and Metal Ceramics. 53 (3): 243–249. doi:10.1007/s11106-014-9610-6. ISSN 1573-9066