Effects of AlCoCrFeNiTi high-entropy alloy on microstructure and mechanical properties of pure aluminum

A new kind of AlCoCrFeNiTi high-entropy alloy (HEA) as a grain refiner was prepared by vacuum arc melting. In this work, the effects of HEA (1.0 wt.%, 2.0 wt.% and 3.0 wt.%) on the microstructure and mechanical properties of pure aluminum were studied. The microstructure was characterized and examined by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), electron probe micro-analyzer (EPMA) and transmission electron microscopy (TEM) to indicate the refining abilities and mechanism of HEA on pure aluminum. Results show that the addition of HEA refined both the macrostructure and microstructure of pure aluminum. When 1.0 wt.% HEA was added, most coarse columnar grains were refined into equiaxed crystals, and as the amount of HEA increased to 2.0 wt.% and 3.0 wt.%, aluminum grains were further refined, and the grain boundaries were nearly indistinguishable. Moreover, the morphology of α-Al transformed from coarse columnar crystals to equiaxed grains, and the mean size of α-Al grains decreased from 374 μm to 27 μm. The Al3Ti, Al3Ni, and nano-phase precipitated from the aluminum alloy with HEA in the solidification. The typical rod-like nano-phases distributed interdendritic regions of α-Al. The average length of nano-phases is 2568 nm, 4372 nm, and 6907 nm and the average diameter is 112 nm, 103 nm, and 92 nm when 1.0 wt.%, 2.0 wt.% and 3.0 wt.% HEA were added to the pure aluminum, respectively. The ultimate tensile strength (UTS) and yield strength (YS) were improved in all samples, whereas the elongation (El) was decreased with increasing HEA concentration. When 3.0 wt.% HEA was added into the aluminum melt, the UTS was improved by 145.2 % from 62 MPa to 152 MPa, the YS was increased by 173.8 % from 42 MPa to 115 MPa, and the El was decreased by 33.3 % from 39 % to 26 %.