Effects of Sc and Zr addition on the solidification and mechanical properties of Al–Fe alloys

The effects of Sc and Zr on the microstructure and properties of Al–3Fe alloys were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and mechanical property testing. The results show that the Al3(Sc, Zr) phases with a L12 structure are formed with the addition of Sc and Zr, which promotes the heterogeneous nucleation, reduces the segregation and improve columnar grains. In the process of iron-rich phase nucleation and growth, Sc and Zr atoms are adsorbed around iron-rich phases, which prevents the growth of iron-rich intermetallics and makes the needle-like primary Al3Fe phases gradually change to short rod-like, butterfly-like and flower-like morphologies. Additionally, the fibrous eutectic Al6Fe phases are also observed. With increasing the Sc and Zr contents from 0 to 0.35 wt% and 0 to 0.14 wt%, respectively, the strength of the alloy increases and the elongation decreases. The Al–3Fe alloy with the addition of 0.16 wt% Sc and 0.06 wt% Zr has a tensile strength of 160.8 MPa and a yield strength of 132.4 MPa. During aging process, fine, dispersed and coherent nanoscale secondary Al3(Sc, Zr) (L12 structure) phases are formed in the α-Al matrix to promote precipitation strengthening. When the addition of Sc and Zr is 0.35 wt% and 0.14 wt%, respectively, the refinement effect on the macrostructure and the second phase is most obvious. After aging, the tensile strength reaches 233 MPa and the yield strength reaches 200 MPa.