Development of aluminum alloys for high-temperature applications

Al-Ni alloys are promising aluminum alloys for high-temperature applications because of their many good properties, partly due to the high stability of the Al₃Ni eutectic fibers at elevated temperatures. The Al-Ni alloy comprises very fine rod-like Al₃Ni eutectic structure, which has high chemical stability and excellent thermal properties up to 500 °C. In spite of these, the mechanical properties of Al-Ni are insufficient for use in high-temperature engineering structures. The matrix of eutectic Al-Ni is relatively weak because the solubility limit of Ni in Al is low. Therefore, alloying addition to Al-Ni plays an essential role not only in improving the mechanical properties of the alloys by the precipitation mechanism but also in preserving the thermal stability and structure of eutectic Al₃Ni. Moreover, precipitates that result from the alloying elements should have high thermal stability to improve the high temperature properties of the Al-Ni alloy as well. Additions of Sc or Zr to the Al-Ni alloy could form the stable Al₃Sc and metastable Al₃Zr L12-nanoprecipitates, respectively. Such nanoprecipitates have excellent thermal stability and excellent coarsening resistance due to the low diffusivity of Sc and Zr in aluminum. Better coarsening- and creep resistance are achieved when Zr and Sc are added together rather than separately because of the combination of fast L12-precipitation from Sc and slow L12-coarsening from Zr. Therefore, this alloy has the potential to be a new aluminum alloy for the challenging applications.