7055铝合金高温压缩变形的流变应力

在Gleeble 1500热模拟试验机上,采用高温等温压缩试验,研究了7055铝合金在250～450℃温度范围内压缩变形的流变应力变化规律.结果表明,应变速率和变形温度的变化强烈影响合金的流变应力,流变应力随变形速率的提高而增大;随变形温度的提高而降低.7055铝合金高温变形时的流变应力可用Zener Hollomon参数来描述.     

TC11钛合金应变速率和温度敏感系数

采用热模拟试验方法,对TC11钛合金在温度为850℃～930℃,应变速率为0.001～1.0,最大变形程度50%条件下的高温流变应力变化规律进行了研究.在分析变形温度、变形程度和应变速率对流动应力影响规律的基础上,确定了TC11钛合金的高温应变速率敏感系数m=0.168 8,以及温度敏感性指数s=10 233,为钛合金高温变形过程的数值模拟提供了重要计算参数.     

石墨烯增强铝基复合材料的热变形本构方程研究

采用热模拟实验机对石墨烯增强7075铝合金复合材料进行高温热压缩实验,变形温度为300～450℃、应变速率为0.001～1 s^-1,分析其在不同应变速率及温度条件下的高温流变应力特征,并以实验数据为基础,通过函数拟合确定包含应变、应变速率和温度等变形参数的双曲正弦本构方程。研究结果表明：铝基复合材料热压缩变形时流变应力随应变增加迅速增大,达到峰值应力后略有下降且出现锯齿状波动;给出的双曲正弦本构方程可以较好地描述流变应力与应变、应变速率及温度之间的关系,计算值与实验值吻合良好。     

Al-10Sn-4Si合金高温塑性变形的流变应力特征

采用高温压缩试验法,测定了新型Ａｌ－１０Ｓｎ－４Ｓｉ合金高温变形过程的真应力一直应变曲线;在温度为１００－４００℃范围和应变速率为０．０１－１．０ｓ＾－１范围的变形条件下,研究了该合金的流变应力变化规律。结果表明,Ａｌ－１０Ｓｎ－４Ｓｉ合金为正应变速率敏感材料,表现出稳态流变特征：稳态流变阶段,流变应力基本保持不变;稳态流变应力随变速率的增加而增大,随变形温度的升高而降低,进一步分析表明,这种稳态     

TC11钛合金的高温变形力学行为

在G leeble-1500热模拟试验机上对TC11钛合金在温度为760~960℃,应变速率为0.001~5.0s-1,变形程度为50%条件下的高温流变应力变化规律进行了研究.在分析变形温度、变形程度和应变速率对流动应力影响规律的基础上,依据Arrhenius方程对实验数据进行回归,得到了TC11钛合金的本构关系模型,为钛合金高温变形过程的数值模拟提供了重要计算模型.     

碳化硅颗粒增强6168铝基复合材料热变形本构关系

利用Gleeble-3500热模拟试验机研究碳化硅颗粒增强6168铝基复合材料(SiCp/6168Al)在变形温度为340~540 ℃、应变速率为0.001~10 s-1、真应变为0.7的条件下的热变形行为。结果表明:应变速率和变形温度对流变应力有明显的影响,在应变速率相同的条件下,流变应力随变形温度的升高而降低,相同的变形温度下,随应变速率的增加,流变应力也随之升高。采用双曲正弦模型求解SiCp/6168Al复合材料在不同真应变ε下的材料常数,并使用5次指数函数拟合出n、lnA、α和Q与真应变ε的关系式,建立流变应力σ与真应变ε的本构方程。利用该方程可以计算任意变形条件下的流变应力,该模型能较好地反映该复合材料的实际热变形行为。       

AZ81E镁合金的高温流变应力模型及热加工图研究

在应变速率为0．003—3．0s^-1、温度为340～430℃的变形条件下,采用Gleeble-1500热模拟机对AZ81E镁合金进行高温热压缩变形特性研究。结果表明：流变应力随变形温度的升高和应变速率的降低而减小,峰值应力随温度的降低和应变速率的升高向应变较大处转移,进入稳态阶段的临界应变明显增大。结合Arrhenius方程并引入Zener-Hollomon参数,构建AZ81E镁合金的高温流变应力模型,其平均变形激活能为166．15kJ／mol。根据材料动态模型,计算并分析AZ81E镁合金的热加工图。利用热加工图确定热变形的流变失稳区,获得试验参数范围内的热变形过程最佳工艺参数：热加工温度范围为380～420℃,应变速率范围为0．01～0．03S^-1.     

铝合金7050高温流变应力特征及本构方程

在高温分离式Hopkinson压杆装置进行高温冲击压缩试验，研究航空铝合金7050—77451在温度范围200—550℃及应变率范围1400—2800s’内压缩变形时的流变应力变化和特征。结果表明，流变应力随着温度的升高而降低，随应变率的升高而增大。温度对流动应力的影响较应变率对流动应力的影响更为显著。用修正的Johnson—Cook模型建立7050-T7451铝合金的本构方程，描述了该合金材料高温下流变应力、应变与应变率之间的关系。     

GH4169合金热轧过程流变应力模型

以GH4169合金应变温度在950~1 100℃,应变速率在0.1~100.0 s-1范围的应力-应变曲线为研究对象,基于Arrhenius方程和Zener-Hollomom参数构建合金的流变应力模型,采用此模型对GH4169合金在等温等速压缩过程中变形温度、变形速率、变形程度与流变应力的关系进行数值仿真分析。结果表明,除流变失稳区域(950℃和100.0 s-1)的曲线外,在其他应变速率和温度范围,模拟所得应力-应变曲线与实测曲线取得较高的拟合精度,能较好地反映GH4169合金在不同热力学参数下的变形特征。本文构建的流变应力模型适用于合金热轧过程的基于有限元法的数值仿真分析。     

Al-Si-Cu-Mg-Ni活塞合金热压缩变形行为研究

针对高功率柴油发动机活塞在高温下变形和烧蚀严重,导致活塞早期失效,使用寿命不能满足设计要求的问题,文中采用光学显微镜(OM)、透射电子显微镜(TEM)和热模拟实验机等实验仪器,研究了在不同热压缩变形参数下,Al-Si-Cu-Mg-Ni活塞合金显微组织以及流变应力的变化规律,利用Zener-Hollomon参数的双曲正弦函数来描述Al-Si-Cu-Mg-Ni活塞合金热压缩变形流变应力行为。研究结果表明:该合金在高温压缩变形过程中存在动态回复和动态再结晶现象,流变应力值随应变速率的增大而增大,随温度的升高而减少;在高温低应变速率下,组织形貌由于动态再结晶而形成完整的亚晶结构;该合金的热变形激活能Q=294.08 kJ·mol~(-1),建立了Al-Si-Cu-Mg-Ni活塞合金热压缩变形条件下的流变应力本构方程。     

Deformation behavior and microstructural evolution during hot compression of an α+β Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy

The effect of processing parameters on the flow response and microstructural evolution of the α+β titanium alloy Ti-6.5Al-3.5Mo-1.5Zr-0.3Si has been studied by conducting isothermal hot compressive tests at a strain rate of 0.01-10 s-1 at 860-1100℃.The true stress-true strain curves of the sample hot-compressed in the α+β phase region exhibit a peak stress followed by continuous flow softening,whereas in the β region,the flow stress attains a steady-state regime.At a strain rate of 10 S-1,the alloy exhibits plastic flow instabilities.According to the kinetic rate equation,the apparent activation energies are estimated to be about 674-705 KJ/mol in the α+β region and 308-335 kJ/mol in the β region,respectively.When deformed in the α+β region,the globularization process of the α colony structure occurs,and α dynamic recrystallized microstructures are observed to show bimodal.Dynamic recrystallization can take place in the β region irrespective of starting deformed structures.     

Deformation behavior and microstructural evolution of Al-Zn-Cu-Mg-Sc-Zr alloy during high temperature compression

The deformation behavior of a new Al-Zn-Cu-Mg-Sc-Zr alloy was investigated with compression tests in temperature range of 380–470 °C and strain rate range of 0.001–10 s⁻¹ using Gleeble 1500 system, and the associated microstructural evolutions were studied by metallographic microscopy and transmission electron microscopy. The results show that true stress—strain curves exhibit a peak stress, followed by a dynamic flow softening at low strains (ɛ<0.05). The stress decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener-Hollomon exponential equation with the activation energy for deformation of 157.9 kJ/mol. The substructure in the deformed specimens consists of few fine precipitates with equaixed polygonized subgrains in the elongated grains and developed serrations at the grain boundaries. The dynamic flow softening is attributed mainly to dynamic recovery and dynamic recrystallization. Foundation item: Project(2006AA03Z523) supported by the National High-Tech Research and Development Program of China     

Deformation behavior and microstructure of an Al-Zn-Mg-Cu-Zr alloy during hot deformation

The hot deformation behavior and microstructures of Al-7055 commercial alloy were investigated by axisymmetric hot compression at temperatures ranging from 300°C to 450°C and strain rates from 10-2 to 10 s-1,respectively.Microstructures of deformed 7055 alloy were investigated by transmission electron microscopy (TEM).The dependence of peak stress on deformation temperature and strain rate can be expressed by the hyperbolic-sine type equation.The hot deformation activation energy of the alloy is 146 kJ/mol....     

Flow stress behavior of Al-Cu-Li-Zr alloy containing Sc during hot compression deformation

The flow stress behavior of Al-3.5Cu-1.5Li-0.25（Sc＋Zr） alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermal-mechanical simulator. Compression tests were preformed in the temperature range of 653-773 K and in the strain rate range of 0.001-10 s^-1 up to a true plastic strain of 0.7. The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature,and decreases with increasing temperature at a given imposed strain rate. The relationship between the flow stress and the strain rate and the temperature was derived by analyzing the experimental data. The flow stress is in a hyperbolic sine relationship with the strain rate,and in an Arrhenius relationship with the temperature,which imply that the process of plastic deformation at an elevated temperature for this material is thermally activated. The flow stress of the alloy during the elevated temperature deformation can be represented by a Zener-Hollomon parameter with the inclusion of the Arrhenius term. The values of n,α and A in the analytical expressions of flow stress σ are fitted to be 5.62,0.019 MPa^-1 and 1.51×10^16 s^-1,respectively. The hot deformation activation energy is 240.85 kJ/mol.     

Flow stress behavior of Cu13Zn alloy deformed at elevated temperature

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Flow stress behavior and processing map of Al-Cu-Mg-Ag alloy during hot compression

The hot deformation behavior of Al-Cu-Mg-Ag was studied by isothermal hot compression tests in the temperature range of 573-773 K and strain rate range of 0.001-1 s^-1 on a Gleeble 1500 D thermal mechanical simulator. The results show the flow stress of Al-Cu-Mg-Ag alloy increases with strain rate and decreases after a peak value, indicating dynamic recovery and recrystallization. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate and temperature, the flow stress equation is estimated to illustrate the relation of strain rate and stress and temperature during high temperature deformation process. The processing maps exhibit two domains as optimum fields for hot deformation at different strains, including the high strain rate domain in 623-773 K and the low strain rate domain in 573-673 K.     

A phenomenological constitutive equation for Rene 95 PM alloy and its application to isothermal forging process of turbine disk

The flow behavior of Rene 95 PM alloy was studied from 1050 to 1150℃ with strain rate of 1x10-3, 1x102,1x101and 1 s-2. At a given temperature and strain rate, flow curves exhibit a peak followed by flow softening up to a steady state. Moreover, at constant strain, flow stress increases with increasing strain rate and decreasing temperature. An equation relating hyperbolic sine of flow stress to hot working parameters, such as strain, strain rate and temperature, was established by using multiple nonlinear regression method. A very good agreement was found between predicted and experimental flow stress in all the strain range investigated. Application of the constitutive equation in predicting forming loads and flow behavior and temperature distribution in both upper and lower dies in an isothermal forging process of turbine disk of large dimension (about 630 mm) by means of a finite element code was systematically analyzed.     

稀土对4145H钻铤钢动态再结晶的影响

应用Geeble-1500D热模拟试验机分别对稀土含量为6×10-6和16×10-6的钻铤钢进行单道次压缩实验,测定其不同终轧温度下的真应力-真应变曲线,采用应变速率0.01 s-1,变形量60%,终轧温度为850,950,1050,1150℃,研究不同稀土含量,不同终轧温度对钻铤钢再结晶的影响。结果表明,稀土含量为16的钻铤钢能显著地抑制形变奥氏体的动态再结晶。