Aluminum-copper alloys

Current economic and environmental crises in the global markets require an effective material solution for reducing the emission of CO2 and simultaneously increasing the fuel efficiency of aircraft and automobiles. Though many composites are in the race, aluminum-based alloys have been the first choice of aeronautical and automobile sectors for low-weight, high-strength applications and service life extension. The precipitation-strengthened Al-Cu (2xxx series) alloys can meet the current challenges to increase fuel efficiency where the operating temperatures are around 200 °C. Extensive attempts are currently being made to improve the high-temperature properties of these alloys. It can be achieved in multiple ways, among which two methods have acquired a particular interest. The first approach is improving high-temperature properties (200-300 °C) by alloying additions. For instance, the addition of transition elements (TM = Sc, Zr, Hf) forms L12-ordered Al3TM precipitates in the α-Al matrix. These precipitates are coherent with α-Al matrix and thermally stable up to 400 ℃. The other approach is stabilizing the primary strengthening phase (θ' plates) in Al-Cu alloys since the plates coarsen rapidly above 200 °C. Therefore, attempts can be made to restrict the coarsening. Segregation of alloying addition like Sc or Zr at the coherent interface can improve the Al-Cu alloys' creep properties. A smart approach is combining both to explore new possibilities in developing the next-generation Al alloys. The microstructure engineering by transition element additions to Al-Cu alloys and heat treatment route shows enhanced yield strength and better resistance against the coarsening of the strengthening phase (θ' plates) at elevated temperatures (250 °C). (Image: From Ref. [1])