基于修正流变应力的2050铝锂合金统一本构方程和热加工图

通过热压缩模拟实验研究热轧态2050铝锂合金在340~500℃、0.001~10 s^(−1)下的高温塑性变形行为,分析了热压缩过程中的外摩擦和温度变化对合金流变应力的影响,并且对测量得到的流变应力进行了修正。基于修正流变应力构建了热轧态2050铝锂合金的流变应力统一本构方程,包括应变修正Arrhenius模型和Hensel-Spittel模型,同时还绘制了合金在不同应变量下的热加工图,并通过金相显微镜观察了不同变形条件热压缩试样的晶粒形貌。结果表明:外摩擦会导致流变应力测量值高于理想值,而绝热温升造成的温度变化会导致流变硬化或软化,使得流变应力改变。统一本构方程模型在拟合区间内都具有较高的拟合性,应变修正Arrhenius模型在稳态流变阶段的拟合程度较高,Hensel-Spittel模型能描述合金在整个热变形过程的流变应力变化。通过热加工图可以发现热轧态2050铝锂合金最佳的加工范围是温度420~500℃、应变速率0.001~0.003 s^(−1)区域。流变失稳区为温度350~480℃、应变速率3.16~10 s^(−1)和温度340~360℃、应变速率0.1~3.16 s^(−1)两个区域。合金在稳定区主要发生动态回复和动态再结晶,而在失稳区主要发生局部流变。

Constitutive equation and processing map for hot compressed as-cast Ti-43Al-4Nb-1.4W-0.6B alloy

High temperature compressive deformation behaviors of as-cast Ti-43Al-4Nb-1.4W-0.6B alloy was investigated at temperatures ranging from 1323 K to 1473 K, and strain rates from 0.001 s-1 to 1 s-1. The results indicated that the true stress-true strain curves show a dynamic flow softening behavior. The flow curves after the friction and the temperature compensations were employed to develop constitutive equations. The effects of temperature and the strain rate on the deformation behavior were represented by Zener-Holloman exponential equation. The influence of strain was incorporated in the constitutive analysis by considering the effect of the strain on material constants by a five-order polynomial. A revised model was proposed to describe the relationships among the flow stress, strain rate and temperature and the predicted flow stress curves were in good agreement with experimental results. Appropriate deformation processing parameters were suggested based on the processing map which was constructed from friction and temperature corrected flow curves, determined as 1343 K, 0.02 s-1 and were successfully applied in the canned forging of billets to simulate industrial work condition.

Hot deformation behavior and processing maps of Mg-Zn-Cu-Zr magnesium alloy

The deformation behaviors of a new quaternary Mg-6Zn-1.5Cu-0.5Zr alloy at temperatures of 523-673 K and strain rates of 0.001-1 s-1 were studied by compressive tests using a Gleeble 3800 thermal-simulator.The results show that the flow stress increases as the deformation temperature decreases or as the strain rate increases.A strain-dependent constitutive equation and a feed-forward back-propagation artificial neural network were used to predict flow stress,which showed good agreement with experimental data.The processing map suggests that the domains of 643-673 K and 0.001-0.01 s-1 are corresponded to optimum conditions for hot working of the T4-treated Mg-6Zn-1.5Cu-0.5Zr alloy.

Arrhenius-type constitutive model and dynamic recrystallization behavior of V-5Cr-5Ti alloy during hot compression

To clarify the high temperature flow stress behavior and microstructures evolution of a V-5Cr-5Ti （mass fraction, %） alloy, the isothermal hot compression tests were conducted in the temperature range of 1423-1573 K with strain rates of 0.01, 0.1, and 1 s-1. The results show that the measured flow stress should be revised by friction and the calculated values of friction coefficient m are in the range of 0.45-0.56. Arrhenius-type constitutive equation was developed by regression analysis. The comparison between the experimental and predicted flow stress shows that the R~ and the average absolute relative error （AARE） are 0.948 and 5.44%, respectively. The measured apparent activation energy Qa is in the range of 540-890 kJ/mol. Both dis-continuous dynamic recrystallization （DDRX） and continuous dynamic recrystallization （CDRX） mechanisms are observed in the deformed alloy, but dynamic recovery （DRV） is the dominant softening mechanism up to a true strain of 1.5.

Constitutive equations for high temperature flow stress prediction of 6063 Al alloy considering compensation of strain

In order to develop the appropriate constitutive equation which can precisely model high temperature flow stress of 6063 Al alloy, a series of isothermal hot compression tests were performed at temperatures from 573 to 773 K and strain rates from 0.5 to 50 s?1 on a Gleeble?1500 thermo-simulation machine. Zener–Hollomon parameter in an exponent-type equation was used to describe the combined effects of temperature and strain rate on hot deformation behaviour of 6063 Al alloy, whereas the influence of strain was incorporated in the developed constitutive equation by considering material constants (α,n,Q andA) to be 4th order polynomial functions of strain. The results show that the developed constitutive equation can accurately predict high temperature flow stress of 6063 Al alloy, which demonstrates that it can be suitable for simulating hot deformation processes such as extrusion and forging, and for properly designing the deformation parameters in engineering practice.

Prediction of flow stress of Mg-Nd-Zn-Zr alloy during hot compression

Isothermal hot compression tests were carried out on Mg-3.0Nd-0.2Zn-0.4Zr （mass fraction, %, NZ30K） alloy using a Gleeble-3500 thermo-simulation machine at temperatures ranging from 350 to 500 ℃and strain rates from 0.001 to 1 s^-1. A correction of flow stress for deformation heating at a high strain rate was carried out. Based on the corrected data for deformation heating, a hyperbolic sine constitutive equation was established. The constants in the constitutive equation of the hyperbolic sine form were determined as a function of strain. The flow stresses predicted by the developed equation agree well with the experimental results, which confirms that the developed constitutive equations can be used to predict the flow stress of NZ30K alloy during hot deformation.

Flow behavior of Al-6.2Zn-0.70Mg-0.30Mn-0.17Zr alloy during hot compressive deformation based on Arrhenius and ANN models

The hot deformation behavior of Al?6.2Zn?0.70Mg?0.30Mn?0.17Zr alloy was investigated by isothermal compressiontest on a Gleeble?3500machine in the deformation temperature range between623and773K and the strain rate range between0.01and20s?1.The results show that the flow stress decreases with decreasing strain rate and increasing deformation temperature.Basedon the experimental results,Arrhenius constitutive equations and artificial neural network(ANN)model were established toinvestigate the flow behavior of the alloy.The calculated results show that the influence of strain on material constants can berepresented by a6th-order polynomial function.The ANN model with16neurons in hidden layer possesses perfect performanceprediction of the flow stress.The predictabilities of the two established models are different.The errors of results calculated by ANNmodel were more centralized and the mean absolute error corresponding to Arrhenius constitutive equations and ANN model are3.49%and1.03%,respectively.In predicting the flow stress of experimental aluminum alloy,the ANN model has a betterpredictability and greater efficiency than Arrhenius constitutive equations.

Flow stress and dynamic recrystallization behavior of Al-9Mg-1.1Li-0.5Mn alloy during hot compression process

The flow stress behavior of spray-formed Al-9Mg-1.1Li-0.5Mn alloy was studied using thermal simulation tests on a Gleeble-3500machine over deformation temperature range of300-450℃and strain rate of0.01-10s^-1.The microstructural evolution of the alloy during the hot compression process was characterized by transmission electron microscopy(TEM)and electron back scatter diffractometry(EBSD).The results show that the flow stress behavior and microstructural evolution are sensitive to deformation parameters.The peak stress level,steady flow stress,dislocation density and amount of substructures of the alloy increase with decreasing deformation temperature and increasing strain rate.Conversely,the high angle grain boundary area increases,the grain boundary is in serrated shape and the dynamic recrystallization in the alloy occurs.The microstructure of the alloy is fibrous-like and the main softening mechanism is dynamic recovery during steady deformation state.The flow stress behavior can be represented by the Zener-Hollomon parameter Z in the hyperbolic sine equation with the hot deformation activation energy of184.2538kJ/mol.The constitutive equation and the hot processing map were established.The hot processing map exhibits that the optimum processing conditions for Al-9Mg-1.1Li-0.5Mn alloy are in deformation temperature range from380to450℃and strain rate range from0.01to0.1s^-1.

Comparison of flow behaviors of near beta Ti-55511 alloy during hot compression based on SCA and BPANN models

The flow behavior of Ti-55511 alloy was studied by hot compression tests at temperatures of 973−1123 K and strain rates of 0.01−10 s^(−1).Strain-compensated Arrhenius(SCA)and back-propagation artificial neural network(BPANN)methods were selected to model the constitutive relationship,and the models were further evaluated by statistical analysis and cross-validation.The stress−strain data extended by two models were implanted into finite element to simulate hot compression test.The results indicate that the flow stress is sensitive to deformation temperature and strain rate,and increases with increasing strain rate and decreasing temperature.Both the SCA model fitted by quintic polynomial and the BPANN model with 12 neurons can describe the flow behaviors,but the fitting accuracy of BPANN is higher than that of SCA.Sixteen cross-validation tests also confirm that the BPANN model has high prediction accuracy.Both models are effective and feasible in simulation,but BPANN model is superior in accuracy.

Hot compressive deformation behavior and constitutive relationship of Al-Zn-Mg-Zr alloy with trace amounts of Sc

Abstract： The hot deformation behaviors of AI-Zn-Mg-Sc-Zr alloy were investigated in a temperature range of 340-500℃ and a strain rate range of 0.001-10 s 1 using uniaxial compression test on Gleeble-1500 thermal simulation machine. The results show that the flow stress increases with increasing strain and tends to be constant after a peak value. The flow stress increases with increasing strain rate and decreases with increasing deformation temperature. The phenomenon of dynamic recovery and dynamic recrystallization can be observed by microstructural evolutions. Based on the hyperbolic Arrhenius-type equation, the true stress-true strain data from the tests were employed to establish the constitutive equation considering the effect of the true strain on material constants （α, β, Q, n and A）, which reveals the dependence of the flow stress on strain, strain rate and deformation temperature. The predicted stress-strain curves are in good agreement with experimental results, which confirms that the developed constitutive equations are suitable to research the hot deformation behaviors of Al-Zn-Mg-Sc-Zr alloy.

Fe-1.3C-5Cr-0.4Mo-0.4V超高碳钢的热变形行为与再结晶组织研究

采用Gleeble-3500热模拟机对Fe-1.3C-5Cr-0.4Mo-0.4V超高碳钢在温度为950~1150℃,变速率为0.01~5s^-1,变形量为40%条件下进行热压缩模拟试验。研究Fe-1.3C-5Cr-0.4Mo-0.4V超高碳钢在热压缩过程中变形温度和应变速率对超高碳钢真应力-应变曲线,以及对再结晶组织演变的影响规律,并构建出超高碳钢本构方程。结果表明,在升高变形温度和降低应变速率的情况下,超高碳钢更容易发生再结晶。在应变速率一定时,流变应力随着温度的升高而降低;在温度一定时,流变应力随应变速率的减小而降低。通过流变应力曲线获得本构方程,能够准确地描述超高碳钢的流变行为,同时获得超高碳钢的激活能为Q=729.37kJ/mol。在微观组织方面,变形温度为1050℃时,应变速率由0.01s^-1增加到5s^-1时,晶粒尺寸降幅5.21μm。因此,超高碳钢应该在温度为1000~1050℃和应变速率在1~5s^-1下进行热变形。