| Recently, high-entropy alloys (HEAs) which are best characterized by their inherent high mixing entropies have been studied. In comparison with the general strategy for designing alloys based on one or two principal elements, a HEA alloy contains at least five major metal elements in equimolar ratio or non-equimolar ratio whose concentration for each one ranges between 5 at% and 35 at%. After a period of research on HEAs, it is discovered that they principally consist of simple solid solution phased with FCC and BCC structures as opposed to complex structures consisting of many intermetallic compounds, which makes HEAs easy to be analyzed and understood. The HEAs open the door to unlimited research in finding novel materials. But many scientific issues involved in HEAs need to be further studied.As an exploratory research, in this paper two kinds of multi-principal alloys with Al, Co, Cr, Cu, Fe, Ni were prepared by well-developed arc melting method and medium frequency induction melting furnace. And the electromagnetic stirring was first applied to HEAs during solidification. Their microstructure, hardness and mechanical properties were studied to broaden the research scope of multi-principal alloys.All AlxCrFe1.5Ni0.5 (x=0.15,0.2,0.3,0.4,0.5) alloys present a single BCC solid-solution crystal structure. Precipitates, forming in the grain boundary of the Al0.15CrFe1.5Ni0.5 alloy, are lamellar and rich in Ni element. Besides, a vast number of nano particles are dispersedly distributed in the alloy matrix. Because of the common precipitation strengthening effect of lamellar precipitates and equiaxed particles, the Al0.15CrFe1.5Ni0.5 alloy presents very high hardness, which is Hv443.2. With Al content changing from 0.2 to 0.4, the crystal boundary of alloys tends to be quite straight. And due to the solution strengthening effect of Al atom, the hardness of alloys gradually increases from Hv303.8 to Hv450.1 with the increase of Al content. The AlCrFeNi alloy shows a simple cubic solid-solution structure, and has the highest hardness-Hv476.9.The mixing entropies of Al0.15CrFe1.5Ni0.5 and Al0.2CrFe1.5Ni0.5 alloys are not high enough to keep alloys stable when the temperature is 900℃. The microstructures of the two alloys after homogenized tend to be same. However, the microstructure of the AlCrFeNi alloy doesn't change even at the temperature of 900℃because of the high mixing entropy.The Al0.5CoCrCuFeNi alloy exhibits a simple FCC solid solution whether or not applying EMS during solidification. And the electromagnetic stirring is effective to refine grains for Al0.5CoCrCuFeNi alloy which shows a typical cast dendrite and interdendrite structure. The compressive and tensile test results show that the alloy exhibits excellent mechanical properties. The EMS can effectively enhance the alloy's compressive and tensile strength. The rod sample for compressive test does not fracture even when the compressive engineering strain is above 50%. The tensile strength of Al0.5CoCrCuFeNi alloy with EMS is 693.66MPa, while that is 616.76MPa without EMS. The Al0.5CoCrCuFeNi alloy has not only extended ductility but also the large potential for deformation strengthening. Although it is still above 25%, the tensile engineering strain of the alloy reduces a little with electromagnetic stirring. One of reasons for that is considered to be the existence of microcracks in specimens for tensile test with EMS. The microstructure of Al0.5CoCrCuFeNi alloy is well refined after homogenized at the temperature of 900℃, which is more effective than electromagnetic stirring. And the segregation of Cu element is improved, but can't be eliminated.
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