Investigation on Microstructures and Mechanical Properties of the Hypoeutectic Al-10Si-0.8Fe-XEr Alloy

In this paper, the effect of Er addition (0.2, 0.5, 0.65, 0.8, 1.0, and 1.5 wt. %) on the microstructure evolution and tensile properties of as-cast hypereutectic Al-10Si-0.8Fe alloy was investigated. The phases and their morphologies in these alloys were identified by XRD and SEM equipped with EDX with the help of metallographic analysis techniques; the length of the secondary phase (LSP) and secondary dendrite arm spacing (SDAS) of α-Al grain were quantified. The results indicated that the second phases (primary Si, eutectic Si, and iron-rich phases) and α-Al grain were significantly refined when the addition of Er increased from 0 to 0.8 wt. %. The mean LSP and SADS values were decreased to a minimum value when the Er addition reached 0.8 wt. %. However, the second phases and α-Al grain became coarser when the level of Er increased more than 0.8 wt. %. The analysis of XRD shows that Er mainly exists in the form of Er₂Si compound. The microstructure modification also has a significant effect on the mechanical properties of the alloy. The yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) increase from 52.86 MPa, 163.84 MPa, and 3.45% to 71.01 MPa, 163.84 MPa, and 5.65%, respectively. From the fracture surface, the promotions of mechanical properties are due to the dispersion and pinning reinforcement caused by the Er₂Si phase.