Effects of AlCrFeNiTi HEA Addition on Microstructure and Mechanical Properties of Hypereutectic Al-20Si Alloy

The effects of different AlCrFeNiTi high-entropy alloy (HEA) addition amounts on the microstructure and mechanical properties of Al-20Si alloy were investigated. The microstructure evolution has been observed and analyzed using optical microscopy (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and electron probe micro-analysis. The phase composition of HEA was analyzed by X-ray diffraction (XRD). The results demonstrated that the microstructure of the Al-20Si alloy was significantly refined and modified after the addition of HEA. Among them, the morphology of alpha-Al changed into the equiaxed crystals, and the morphology of primary Si transferred from large star-like shape and irregular polygonal shape to small block-like shape. Meanwhile, the long needle-like and flake-like eutectic Si transferred into short rod-like shape. Moreover, the ultimate tensile strength (UTS) of the alloy was enhanced by 45.8% from 131 to 191 MPa when the 3.0 wt% HEA was added to Al-20Si alloy. In addition, when the adding amount of HEA was up to 1.5 wt%, the ductility of the alloy was the best among the alloys, and the elongation value (El) was enhanced by 73% from 1.15 to 1.99%. However, as the added amount of HEA further increased, the El occurred to decrease. Hence, the refinement microstructure of Al-20Si alloy was beneficial for improving mechanical properties, and the precipitated nanoparticles distributed in the matrix also played a crucial role.