Effect of Yttrium on Iron-Rich Phases and Mechanical Properties of As-Cast Al-Fe Alloy with Low Si Concentration

In Al–Fe alloys, the mechanical properties are determined by the morphology of iron-rich phases. In this work, AA8176(Al-1Fe)-nY (n = 0, 0.3, 0.5, 0.7, and 0.9 wt.%) alloys were prepared by the cast method. The effects of yttrium (Y) addition on the microstructure and mechanical properties of AA8176 alloy were studied using various techniques including optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), cooling curve analysis and tensile tests. The results revealed that the optimal refinement effect was achieved when the amount of Y content was 0.5 wt.%. When the Y content increased from 0 to 0.5 wt.%, the coarse needle-like Al13Fe4 phases were gradually transformed into short rod-like morphology and some fine Al10Fe2Y phases were formed around the Al13Fe4 phases. The average length of iron-rich phases was decreased from 10.01 μm to 2.65 μm. Additionally, as the Y content increased from 0 to 0.5 wt.%, the secondary dendrite arm spacing (SDAS) of AA8176 alloy was reduced from 31.33 μm to 20.24 μm. Furthermore, the mechanical properties of the AA8176 alloy were improved due to the modified microstructure. With the addition of 0.5 wt.% Y, the ultimate tensile strength, yield strength, elongation, and Vickers hardness were improved to 96.86 MPa, 57.21 MPa, 23.1%, and 30.55 HV, respectively, compared to 84.47 MPa, 50.71 MPa, 18.6%, and 27.28 HV for the unmodified AA8176 alloy. It is proposed that the growth of α-Al dendrite and Al13Fe4 phases were effectively inhibited by segregation of Y atoms around α-Al dendrite and Al13Fe4 phases during solidification. And the Al10Fe2Y phases were formed by these Y atoms with Al and Fe elements. However, the formation of coarse Al10Fe2Y phases was promoted by excessive Y content, resulting in a substantial degradation in mechanical properties.