Evolution of nickel-rich phases in Al–Si–Cu–Ni–Mg piston alloys with different Cu additions

Evolution of nickel-rich phases (Ni-phases) in Al–Si–Cu–Ni–Mg piston alloys is investigated. The qualitative results show that, with the increasing of Cu content, Ni-phases translate from Al3Ni (ε-phase) or Al3CuNi (δ-phase) to Al7Cu4Ni (γ-phase), and their morphologies change from short-strip to reticular and then annular or semi-annular shape. Moreover, the quantitative calculations by Thermo-Calc software are in accordance with that of experiments’. The evolutions have a great effect on the mechanical properties. The tensile strength at room temperature decreases from 263.8 MPa to 229.6 MPa, and then increases to 278.9 MPa. Otherwise, the elevated temperature tensile strength increases about 19.7%. But the coefficient of linear expansion decreases constantly.