to lighter components, which is particularly advantageous in aviation. See aluminium-lithium alloy for details. Cast Alloys Cast alloys contain about 4% copper and small amounts of other additives that improve castability, including titanium and magnesium. The starting material is primary aluminum; In contrast to other cast aluminum alloys, secondary aluminum (made from scrap) is not used because it reduces elongation at break and toughness. The AlCu cast alloys are prone to hot cracking and are used in the T4 and T6 hardening states. The following table shows the composition of some grades according to DIN EN 1706. All data in percent by mass, the rest is aluminum. Wrought alloys AlCuMg(Si,Mn) wrought alloys The AlCuMg alloys represent the most important group of AlCu alloys. Many other phases can form in them: Al8 Mg5 (-phase, see ) Al2 CuMg, the S phase Al6 Mg4 Cu, the T phase Additions of magnesium accelerate cold hardening. Which phases are formed depends primarily on the ratio of copper to magnesium. If the ratio is less than 1/1, clusters containing Cu and Mg are eliminated. At a ratio above 1.5/1, which is the case with most engineering alloys, the forms preferentially-Phase. These alloys have significantly higher hardness and strength. Mechanical properties Conditions: O soft (, also hot-formed with the same strength limit values). T3: solution annealed, quenched, work hardened and naturally aged T4: solution annealed, quenched and artificially aged T6: solution heat treated, quenched and artificially aged T8: solution annealed, cold worked and artificially aged 2000 series 2000 series were formerly referred to as duralumin. Applications Aluminum-copper alloys are mainly used in , where their low corrosion resistance plays a subordinate role. Corrosion resistance can be greatly enhanced by the metallurgical bonding of a high-purity aluminium surface layer, referred to as alclad-duralum. Alclad materials are commonly used in the aircraft industry to this day. The alloys are processed by rolling, forging, extrusion and partly by casting. Typical uses for wrought Al-Cu alloys include: 2011: Wire, rod, and bar for screw machine products. Applications where good machinability and good strength are required. 2014: Heavy-duty forgings, plate, and extrusions for aircraft fittings, wheels, and major structural components, space booster tankage and structure, truck frame and suspension components. Applications requiring high strength and hardness including service at elevated temperatures. 2017 or Avional (France): Around 1% Si. Good machinability. Acceptable resistance to corrosion in air and mechanical properties. Also called