Effect Of Heat Treatment On Microstructure And Mechanical Properties Of Al_0.5CoCrFeNiSi_0.25 High Entropy Alloy With Cold Rolling

The emergence of high entropy alloy(HEA)provides a new concept for the design of structural materials.Due to the special ingredients,structural and performance of high entropy alloys,becoming a preface topic in the current alloy field.Plastic deformation is the main method of material processing and modification,accounting for an important role in alloy modification.At present,the high-entropy alloy field is in the rapid development stage.More and more people have begun to extend various traditional processes to high entropy alloy design and performance optimization.This paper utilizes X-ray diffraction,scanning electron microscopy and transmission electron microscopy.The effects of plastic deformation on the tissue and performance of Al_0.5CoCrFeNiSi_0.25 high entropy alloy were studied,and the effects of recrystallization annealing process on the mechanical properties of alloys were studied.The experimental results show:The as-cast and solution treated phases of Al_0.5CoCrFeNiSi_0.25 high entropy alloy are FCC/BCC dual-phases structure.Compared with the cast alloy,the tensile properties of alloy samples after solid solution treatment have significantly enhanced,and the rolling amount also has a very obvious influence on the tensile strength of the alloy.After rolling 20%,the tensile strength of the alloy can reach 1398 MPa.Samples of the rolling amount of more than 20%are directly broken in the linear hardening stage.And after rolling deformation of 20%,the micro Vickers hardness reaches 527 HV,which is 42.4%higher than that of as-cast and 78.6%higher than that of solution samples.However,the hardness of the alloy does not continue to rise when the rolling amount is increased.Cold-rolled samples were treated at 900?for 1 h,Cr-rich phase precipitated at the phase boundary,a small amount of ordered L1₂ phase appeared in FCC phase and ordered B2 phase dispersed and precipitated in BCC phase.Further analysis shows that the composition of Cr-rich phase can be determined as Cr₁₅Co₉Si₆,L1₂ phase is Ni₃Al intermetallic compound,B2 phase is Al Ni-rich phase.After treatment at 1100?for 1 hour,the tensile strength of the alloy rolled 40%reached 1267.8 MPa,and the maximum ductility increased to 43.3%,which achieved the experimental goal of high strength and high toughness.The average grain size of rolled 40%alloy was kept at micron level after different recrystallization time treatment,and the average grain size was only 4.745?m after 20 h treatment.The recrystallization time has little effect on the phase ratio of the alloy,and the hardness value is stable between 321 HV and 419 HV.Different annealing time has great influence on the static tensile properties.The tensile strength of 40%rolled samples annealed for 5 h is 1146.6 MPa,and the ductility is 46.7%,which shows the best comprehensive mechanical properties.After more than 5 h,the tensile strength of the alloy decreases,and the plasticity increases first and then decreases.Combined with EBSD analysis results,it is shown that the partially recrystallized structure plays a key role in maintaining high strength and toughness of the alloy...