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 α-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.