Effect Of Cold Rolling On The Microstructures And Mechanical Porperties Of Al_0.5Cu_1.25CoFeNi_1.25 And Al_0.25CoCrFe_1.25Ni_1.25 High-entropy Alloys

High-entropy alloys (HEAs), a newly developed alloy system, wereproposed in the1990s when materials scientists explored multicomponent alloysfor enhanced glass-forming ability. They are commonly defined as solid solutionalloys that contain five or more principal elements in equal or near equal atomicratios. Recent studies have shown that HEAs possess adjustable and attractiveproperties compared to the conventional alloys, such as significantelevated-temperature strength, excellent thermal stability, and good wearresistance. In addition, it is available to obtain the combination of high strength,high hardness, high corrosion resistance, high temperature oxidation resistance,and otherwise by cold rolling or heat treatment. Because of its broad applicationprospects, to study on the phase formation, microstructure, and mechanicalproperties of HEAs will become very meaningful. In this paper, the effect ofcold rolling on the microstructures and mechanical properties ofAl0.5Cu1.25CoFeNi1.25and Al0.25CoCrFe1.25Ni1.25HEAs were studied as well astheir corrosion resistance and heat treatment effects.Alloy ingots of Al0.5Cu1.25CoFeNi1.25and Al0.25CoCrFe1.25Ni1.25HEAs werefabricated using arc-melt casting. Cold-rolling was carried out at roomtemperature with various reductions of Al0.5Cu1.25CoFeNi1.25HEAs:0(as-cast),13.3%,26.7%, and40%; Al0.25CoCrFe1.25Ni1.25HEAs:0(as-cast),13.3%, 26.7%,40%,60%, and80%. The Al0.25CoCrFe1.25Ni1.25HEAs with tworeductions of26.7%and40%were annealed at temperatures of500℃,700℃,and900℃respectively for2hours. Corrosion tests were conducted at roomtemperature in1N H2SO4. The microstructures, morphologies, and chemicalcompositions of the alloys with as-cast, cold-rolling, and heat-treated states werecharacterized by x-ray diffraction (XRD) and scanning electron microscope(SEM) equipped with an energy dispersive spectrometry (EDS). Vickershardness and tensile tests were performed with a material test systemservohydraulic mechanical testing machine. The experimental results are asfollows：1. After cold-rolling, the (111) texture was produced in theAl0.5Cu1.25CoFeNi1.25alloy, and did not steer. The alloy hardness could be up to285HV, and the increasing ratio was51.6%relative to the as-cast sample.Moreover, the maximum tensile strength of638MPa was obtained as thecold-rolling ratio was40%, which was2.7times greater than the as-castcounterpart. Fracture analyses revealed that the as-cast sample exhibited a mixedintergranular and dimple-like fracture mode, while the dimple-like fracturemode was dominated in the cold-rolled alloy.2. With increasing the rolling reduction, the hardness, yield strength andfracture strength of the Al0.25CoCrFe1.25Ni1.25HEAs distinctly increased.Similarly, the (111) texture was produced in the Al0.25CoCrFe1.25Ni1.25alloy, anddid not steer. Specially, at the reduction of80%, the tensile strength (hardness)of alloys was up to702MPa (406HV),1.62(2.43) times that in the as-castcondition. The present study also revealed that the general corrosion resistancein H2SO4solution was improved with increasing thickness reduction. Theregulation of phase formation and thermodynamic properties ofAlxCoCrFe1.25Ni1.25allys were studied by CALPHAD method, indicating thatthe Al0.25CoCrFe1.25Ni1.25HEA was single fcc solid solution structure. 3. After heat treatment, the tensile plasticity of the cold-rolledAl0.25CoCrFe1.25Ni1.25HEA was greatly improved. In particular, for the alloywith a reduction of26.7%, the maximum tensile elongation was up to52.5%atthe temperature of900℃,14.4times that in the cold-rolled condition. However,the microhardness, yield strength, and tensile strength were also relativelydecreased, indicating that the softening behavior may occur in the annealedsamples.