Aluminium-copper alloys (AlCu) are aluminum alloys that consist largely of aluminum (Al) and traces of copper (Cu) as the main alloying elements. Important grades also contain additives of magnesium and silicon (AlCu(Mg,Si)), often manganese is also included to increase strength (see ). The main area of ​​application is aircraft construction. The alloys have medium to high strength and can be age-hardened. They are both . Also available as cast alloy. Their susceptibility to corrosion and their poor weldability are disadvantageous. Duralumin is the oldest variety in this group and goes back to Alfred Wilm, who discovered it in 1903. Aluminium could only be used as a widespread construction material thanks to the aluminium-copper alloys, as pure aluminium is much too soft for this and other hardenable alloys such as (AlMgSi) or the naturally hard (non-hardenable) alloys. Aluminium-copper alloys were standardised in the 2000 series by the international alloy designation system (IADS) which was originally created in 1970 by the Aluminum Association. 2000s series includes 2014 and 2024 alloys used in airframe fabrication. History Duralumin s a trade name for one of the earliest types of age-hardenable aluminium alloys. The term is a combination of Dürener and aluminium. Its use as a trade name is obsolete. Duralumin was developed by the German metallurgist Alfred Wilm at Dürener Metallwerke AG. In 1903, Wilm discovered that after quenching, an aluminium alloy containing 4% copper would harden when left at room temperature for several days. Further improvements led to the introduction of duralumin in 1909. The name is mainly used in pop-science to describe all Al-Cu alloys system. Aluminium-copper alloys were standardised in the 2000 series by the international alloy designation system (IADS) which was originally created in 1970 by the Aluminum Association. 2000s series includes 2014 and 2024 alloys used in airframe fabrication. Pure AlCu wrought alloys All AlCu alloys are based on the system of pure AlCu alloys. Solubility of copper and phases Aluminum forms a eutectic with copper at 547 °C and 33 mass percent copper, which also corresponds to the maximum solubility. At lower temperatures, the solubility drops sharply; at room temperature it is only 0.1%. At higher copper contents, Al2Cu is formed, an intermetallic phase. It is present in a tetragonal structure, which is so different from the cubic crystal system of aluminium that the -phase exists only as an . There are also the partially coherent ones -