Unique Duplex Microstructure and Porosity Effect on Mechanical Properties of AlCoCrFeNi2.1 Eutectic High-Entropy Alloys Processed by Selective Laser Melting

Selective laser melting (SLM) was performed on AlCoCrFeNi2.1 eutectic high-entropy alloys (EHEAs), and the unique duplex microstructure and porosity were investigated as well as the negative effect on mechanical properties. SLM printed AlCoCrFeNi2.1 EHEAs is composed of face-centered cubic and BCC/B2 phases, and the surface texture of samples perpendicular to and parallel to the building direction is different. From the bottom of the molten pool to the inside, the structure changes from dendrites to columnar crystals and then to cellular crystals, the distribution of elements in and around the molten pool is uniform, and there is no element segregation. The surface hardness of as-printed AlCoCrFeNi2.1 EHEAs is higher than that of as-cast ones due to the grain refinement strengthening, and there is anisotropy in different surface hardness, the highest hardness is 580 HV (X–Y plane) and 560 HV (X–Z plane). The reduction of bearing area and tip stress concentration caused by pores have adverse effects on the tensile strength and elongation of the alloy, the ultimate tensile strength increased from 1060 to 1289 MPa.