A new Zr-rich intermetallic phase in an Al-14Si-3Cu-4.5Ni casting alloy with trace additions of Zr

A trace addition of Zr to a multicomponent Al-14Si-3Cu-4.5Ni casting alloy has often been found to form a coarse plate-like Zr-rich intermetallic compound with a size of a few tens of μm at the beginning of solidification. Evaluation of the phase composition has confirmed that the Zr-rich intermetallic phase consists of multicomponent constituent elements, mainly Al, Si, Ni and Fe, and is present in a form of (Al,Si)₃(Zr,Ni,Fe). The existence of such a complex (Al,Si)₃(Zr,Ni,Fe) phase has not yet been predicted by phase equilibria calculation of the multicomponent Al-14Si-CuNiMg systems. In this paper, transmission electron microscopy studies combined with electron backscattered diffraction pattern analysis reveals the crystallography information of the (Al,Si)₃(Zr,Ni,Fe) phase for the first time and identifies it as a modified Al₃Zr-D023 crystal (tetragonal, I4/mmm(139)) with slightly changed lattice parameters of a = b = 3.275 Å and c = 15.475 Å. The primary (Al,Si)₃(Zr,Ni,Fe) phase is found to nucleate directly onto AlP particles. The mechanical properties of the Zr-rich intermetallics were also investigated using nanoindentation at both room and elevated temperatures and were compared to those of the Si phase.