Effect of iron addition on the microstructures and properties of hypereutectic Al-20%Si alloys

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The microstructural evolution, mechanical properties and wear behaviors of hypereutectic Al-20%Si alloy with the different additions of Fe (0, 1.0, 1.5, 2.0, and 2.5 wt%) were investigated. The as-cast specimens were evaluated by scanning electron microscope (SEM), electron probe micro-analysis (EPMA) equipped with wavelength dispersive spectroscopy (WDS) and x-ray diffraction (XRD). The results indicated that the primary Si phases were significantly refined from coarse platelet-like, irregular polygonal and star-like shape to fine blocky shape when the addition contents of Fe was up to 2.5%. Meanwhile, the eutectic Si structure was modified from coarse platelet-like/needle-like to fine granular and short rod structure. The tensile test illustrated that the ultimate tensile strength and elongation firstly increased with the increasing Fe content from 0% to 1.5%, and then decreased when the concentration of Fe improved from 2.0% to 2.5%. When the addition level of Fe was 1.5%, the ultimate tensile strength and elongation were 175 MPa and 1.84%, respectively. In addition, the wear behaviors of Al-20%Si alloy with the different Fe content were investigated. The results showed that the friction coefficient firstly decreased as 1.0%Fe was added into the Al-20%Si alloy. However, the friction coefficient gradually increased with the further increasing Fe content from 1.0% to 2.5%. In addition, the wear rate decreased by 46.8% from 2.65 × 10−5 g m−1 to 1.41 × 10−5 g m−1, which showed the wear resistance of hypereutectic Al-20%Si alloy gradually increased with Fe concentration.