A Study On Microstructure And Properties Of Al_0.2Co CrFe₂Ni Alloy During Rolling And Recrystallization Annealing

The Al_0.2CoCrFeNi high-entropy alloy in the as-cast state has a single-phase face-centered solid solution structure and has excellent comprehensive properties such as high work hardening ability and high-temperature stability.However,the relatively high material cost will limit its use in many fields.By adding low-priced Fe element,Al0.2CoCrFe2Ni high-entropy alloy was designed.Calculate its mixing entropy,mixing enthalpy,atomic radius difference and other parameters,predict the crystal structure of the alloy,and study the microstructure and mechanical properties of the alloy as-cast.Subsequently,the 80%rolled high-entropy alloy was heat treated to study the changes microstructure and mechanical properties at different annealing temperatures in alloy.Using the JMAK equation to fit the alloy recrystallization fraction,the alloy’s recrystallization activation energy is finally calculated.1.Using mixed entropy,mixed enthalpy,atomic radius difference,equilibrium valence electron number and other parameters to design a single-phase FCC solid solution structure alloy.Using XRD diffractometer,it is found that there is no dispersed phase structure in the crystal structure of the alloy.In the as-cast state,the alloy has a coarse dendrite structure,and the composition distribution in the structure is relatively uniform,and there is no obvious segregation phenomenon.The alloy has excellent plasticity,the plasticity can reach 46%,but the hardness is only 120HV,and the tensile strength is only 360Mpa.It can be known from the stress-strain curve that it has a large elastic modulus and excellent uniform plastic deformation ability.The strain hardening index value is n=0.5 obtained from Hollomon equation,indicating that the as-cast alloy can withstand large plastic deformation without cracking.2.80%rolled Al_0.2CoCrFe₂Ni high-entropy alloy was annealed at 700°C,800°C,900°C,and 1000°C for one hour respectively.It was found that the alloy still maintains the single-phase FCC solid solution structure after rolling and heat treatment,.The diffraction peaks of the later crystals in 80%cold reduction were broadened,and a larger dislocation density(ρ=0.021nm^-2)was generated.The grain orientation distribution of the alloy after rolling and annealing was measured using EBSD technology,and it was found that there was a large（111）texture after rolling,the texture strength of the annealed sample was weakened,and annealed at 800°C for 1h complete recrystallization is obtained.The rolled alloy forms higher strength（1005Mpa）,but the plasticity（10%）is lower.As the annealing temperature increases,the strength of the alloy gradually decreases,and the plasticity increases accordingly.Good mechanical properties were obtained when annealed at 700°C,its yield strength was 640 Mpa,and the elongation after break was 25%.3.Observed the microstructure changes at different annealing times during heat treatment at 700°C,800°C,and 900°C using a metallographic microscope.The alloy has similar recrystallization rules at different annealing temperatures.At 700°C annealing,the alloy requires a longer annealing time to achieve complete recrystallization.As the annealing temperature increases,the time for the alloy to achieve complete recrystallization is shortened,and annealing at 900°C for 30 min achieves complete recrystallization.The alloy exhibits a high recrystallization temperature and a relatively long recrystallization time at low temperatures.A digital microhardness tester was used to measure the hardness value of samples treated at different annealing times.As the annealing time increases,the hardness of the alloy changes in the same pattern,and the hardness decreases rapidly in a short time,and then tends to be gentle.When annealing at 900°C,the hardness value decreases to a large extent,mainly because the alloy first completes recrystallization and grain growth occurs at this temperature.The hardness value method is used to characterize the recrystallization rate of the alloy,and its shape is S-shaped.The JMAK equation was used to calculate the Avrami index n and recrystallization activation energy of the alloy.It is found that the Avrami index n of the alloy at three temperatures is less than 1,and the smaller value of n is mainly related to the uneven nucleation and growth of the alloy during annealing.The alloy has a large recrystallization activation energy,the value of which is 420.13KJ/mol.The larger activation energy is related to the larger initial grain size of the alloy and the dispersed phase during annealing.