Effect of Ti Addition and Electric Field on Microstructure and Mechanical Properties of the Al-Si-Fe Hypereutectic Alloy

In the present research, the Al-Si-Fe hypereutectic alloys with different Ti addition were prepared and the electric field treatment was performed on the alloys to regulate the phase morphology. The microstructure and mechanical properties of the alloys were characterized by OM, SEM, TEM, EPMA and tensile test. The results reveal that the Al-Si-Fe hypereutectic alloy prepared by conventional casting is mainly composed cubic β-Si phase, long rod-like and needle-like β-Al₅FeSi phases. In addition, there are stacking faults in the β-Al₅FeSi phase. Minor Ti addition in Al-Si-Fe hypereutectic alloy could change the needle-like phase into eutectic structure, decrease the size of β-Al₅FeSi phase and homogenize the β-Si phase size. The more Ti addition tends to coarsen the β-Al₅FeSi and β-Si phases, and moreover the needle-like phase precipitate again. The electric field treatment promotes the coarsening of β-Al₅FeSi and β-Si phases in the Al-Si-Fe hypereutectic alloy with 0-1.0 wt.% Ti addition, but results in the refinement of β-Al₅FeSi and β-Si phases in 1.5 wt.% Ti doped Al-Si-Fe hypereutectic alloy. Furthermore, the needle-like phase has been transformed into small-size eutectic structure in the 1.0 and 1.5 wt.% Ti doped Al-Si-Fe hypereutectic alloys. With the synergistical effect of Ti addition and electric field treatment, the 1.5 wt.% Ti doped Al-Si-Fe hypereutectic alloy obtains yield strength of 100 MPa and ultimate tensile strength of 113 MPa, which is about 26% and 37% higher than the conventional-cast Al-Si-Fe hypereutectic alloy.