Constitutive Equation of Mg-3.5Zn-0.6Y-0.5Zr Alloy under Hot Compression Deformation
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The hot deformation behavior of Mg-3.5Zn-0.6Y-0.5Zr alloy was investigated by compressive tests of strain rate ranges of 0.002~1 s-1 and deformation temperature ranges of 300~450 °C using a Gleeble 1500D thermal simulator. The flow stresses in different deformation conditions are measured. The results show that flow stress is significantly affected by both deformation temperature and strain rate, the flow stress increases with increase in strain rate and decreases in deformation temperature during the hot compression process. The constitutive equation established on the basis of data of activation energy and stress exponent is a hyperbolic sine function.Keywords:
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The flow stress behavior of Cu-Ni-Si alloy was investigated in the temperature rang of 600～800 ℃ and at strain rate range of 0.01 s-1～5 s-1 on a Gleeble-1500D test machine.The relationship between the flow stress,strain rate and deformation temperature was studied,and the microstructure evolution of the experimental alloy was studied in the hot-compression process.The results show that both strain rate and deformation temperature have large effects on the dynamic recrystallization.The higher temperature and less strain rate easily cause dynamic recrystallization.At the same strain rate,the microstructure is strongly depended on the deformation temperature.The hot deformation activation energy of Cu-Ni-Si alloy during hot deformation is calculated by Arrhenius sinh function,which is 245.4 KJmol-1.
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Dynamic Recrystallization
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Abstract Hot deformation behavior of iron‐nickel based superalloy (multimet N‐155) was investigated by hot compression tests, carried out in the deformation temperature of 850 °C–1150 °C with strain rates of 0.001–0.1 s −1 . The results showed that during the hot deformation of the alloy, under the same temperature, the flow stress rises with the increase of strain rate. At the same strain rate, the flow stress decreases with the increase of the temperature. The constitutive equations of the alloy that describe the flow stress as a function of strain rate and deformation temperature were established and the calculated apparent activation energy was 584.996 Kj/mol. The results of metallographic analysis showed that the amount of dynamic recrystallization in the peak efficiency domain is higher than the other domains. The results also showed that by increase of deformation temperature and/or decrease of strain rate, the volume fraction of dynamic recrystallization increases. Processing maps under different strains were constructed for evaluation of flow instability regime and optimization of processing parameters. The optimum hot working window for alloy was obtained at the temperature range of 925 °C–1050 °C and strain rate of 0.001–0.003 s −1 , with peak efficiency of 28 %.
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The finite element simulation method has been becoming an useful tool for the optimization of metal-forming processes,meanwhile an accurate constitutive equation describing the deformation behavior of the workpiece material is one of the most critical factors for simulation.The hot compression tests of AZ61 magnesium alloy were performed on Gleeble 3500 at deformation temperatures of 250 ℃,300 ℃,350 ℃,400 ℃and 450 ℃and strain rates of 0.01 s-1,0.1 s-1,1 s-1,10 s-1 and 50 s-1.The results show that the flow stress increases with the decrease of deformation temperature and the increase of strain rate.At the high strain rate,the temperature rise of samples caused by the deformation is very notable.Thus,a correction of flow stress is carried out for the precision of the constitutive equation.The constitutive equation is established based on the corrected flow stress.
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The hot deformation behaviors of 30%SiCp/2024 aluminum alloy composites was studied by hot compression tests using Gleeble-1500 thermomechanical simulator at temperatures ranging from 350-500 °C under strain rates of 0.01-10 s-1. The true stress-true strain curves were obtained in the tests. Constitutive equation and processing map were established. The results show that the flow stress decreases with the increase of deformation temperature at a constant strain rate, and increases with the increase of strain rate at constant temperature, indicating that composite is a positive strain rate sensitive material. The flow stress behavior of composite during hot compression deformation can be represented by a Zener-Hollomon parameter in the hyperbolic sine form. Its activation energy for hot deformation Q is 153.251 kJ/mol. The optimum hot working conditions for this material are suggested.
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The hot deformation behavior, hot workability and dynamic recrystallization evolution of Zr–1.0 (wt%) Be alloy in single α phase were investigated by conducting hot compression tests. The strain rates ranging from 10–3 s–1 to 10° s–1 and testing temperatures varying from 650 °C to 850 °C were used. Flow stress was found to increase with increasing strain rate and decrease with the increment of the deformation temperature. A constitutive equation of flow behavior was established to describe the dependence of flow stress on strain rate and deformation temperature. The activation energy for deformation of Zr–1.0Be alloy was determined to be Q=301 kJ/mol. The processing map of Zr–1.0Be alloy was constructed at strain rates ranging from 10–3 s–1 to 10° s–1 and deformation temperatures varying from 650 °C to 850 °C at the true strain of 0.7. A processing map was used to identify the best domains of thermal processing, including a domain at a temperature of 650 °C and strain rate of 10–3 s–1, as well as another domain at deformation temperatures ranging from 800 °C to 850 °C and strain rates varying from 10–3 s–1 to 10–1 s–1. Microscopic analysis of Zr–1.0Be alloy showed that the flow instability and kink were very obvious at low temperatures and high strain rates. At high temperatures and low strain rates, the dynamic recrystallization became the main softening mechanism during hot working.
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The hot deformation behaviors of Aluminum alloy C919 were studied in the present investigation. The hot compression tests for C919 were carried out in the temperature range of 350°C~470°C and strain rates range of 0.001s -1 ~1s -1 using GLEEBLE-1500 thermal simulate testing machine. Optical microscopy (OM) was used for the microstructure characterization. The experimental results showed that the flow stress of C919 aluminum alloy decreased with increasing temperature and decreasing strain rates and the flow stress curves tended to increase at a strain rate of 1s -1 with increasing strain, while the flow stresses kept with increasing strain at lower strain rate. The alloys were more prone to dynamic recrystallization with decreasing strain rates during hot deformation. The hot compression behavior of C919 aluminum alloy can be described as hyperbolic sine function corrected Arrhenius relation. The processing maps for the alloy were built at a strain of 0.6. The instability deformation domain occurred at temperatures range from 350°C and 380°C and at a strain rate of 0.1-1s -1 . Based on the processing maps and microstructure observations, the optimum hot-working parameters were determined to be at a temperature of 470°C in the strain rate range from 0.1-0.01s −1 for the C919 aluminum alloy.
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The deformation response of magnesium alloy AZ91 was investigated by means of hot compression tests. The flow curves were obtained in the temperature and strain rate range of 300–500°C and 0.001–1 s - 1 , respectively. The processing maps of the studied material were obtained by interpreting them on the basis of the dynamic material model. The activation energy maps were developed based on Lyapounov’s function and the safe processing zones were confirmed by comparing both the maps taking into account the largely accepted conclusions in the form of the constitutive equation that correlates flow stress, strain rate, and temperature in these materials. The flow instability between strain rates 0.31–1.0 s - 1 and temperature range between 300 and 480°C were studied. The optimum domains and instability zone were obtained for the hot workability of the material.
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The hot deformation behaviors of 30%SiCp/2024 aluminum alloy composites was studied by hot compression tests using Gleeble-1500 thermomechanical simulator at temperatures ranging from 350-500°C under strain rates of 0.01-10 s-1. The true stress-true strain curves were obtained in the tests. Constitutive equation and processing map were established. The results show that the flow stress decreases with the increase of deformation temperature at a constant strain rate, and increases with the increase of strain rate at constant temperature, indicating that composite is a positive strain rate sensitive material. The flow stress behavior of composite during hot compression deformation can be represented by a Zener-Hollomon parameter in the hyperbolic sine form. Its activation energy for hot deformation Q is 183.251 kJ/mol. The optimum hot working conditions for this material are suggested.
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