3104铝合金热变形流变应力模型

采用等温压缩试验，研究了3104铝合金在应变速率为0．001-1s^-1、变形温度为573-773K条件下的流变应力行为。结果表明，3104合金流变应力对应变速率和变形温度十分敏感，合金高温塑性变形时存在稳态流变特征，并建立了合金热变形流变应力模型。     

变形参数对AZ31镁合金变形抗力的影响

利用Gleeble-1500热模拟试验机对AZ31镁合金在变形温度为250~400℃、变形速率为0.5~3.0s^-1下进行热变形模拟实验,得到了AZ31镁合金真实应力-真实应变曲线,并通过光学显微镜观察了试样在变形中的微观组织.结果表明,动态再结晶是该实验条件下晶粒细化的主要机制,变形参数影响了再结晶的程度.     

TiNiFe形状记忆合金热变形行为的研究

针对TiNiFe形状记忆合金,在Gleeble-3500热模拟试验机上对其进行了高温压缩实验,研究了TiNiFe合金在温度为750～1050℃、应变速率为0.01～10.00 s-1条件下的热变形行为。结果表明,流变应力受到变形温度和应变速率的显著影响,在相同变形温度条件下,流变应力随应变速率的提高而增大;在相同应变速率条件下,流变应力随变形温度的升高而降低。并采用双曲正弦模型确定了该合金的应力指数n和变形激活能Q,建立了相应的热变形本构关系。经实验验证,所建立的本构关系能够很好的反映TiNiFe合金的实际热变形行为特征。     

Mg-5.52Zn-1.73Nd-0.71Cd-0.5Zr镁合金的热变形组织和力学性能

采用Gleeble-1500热模拟机研究Mg-Zn-Nd-Cd-Zr合金在温度为300～420℃、应变速率为0.001～1S-1、最大变形程度为80％的条件下的高温变形行为.采用光学显微镜及透射电镜研究Mg-Zn-Nd-Cd-Zr镁合金在不同压缩变形条件下的组织形貌特征.结果表明:在实验条件下,合金的流变应力-应变曲线...     

新型Al-Zn-Mg-Cu合金热变形流变应力特征

采用Gleeble-1500热模拟机进行热压缩变形实验,研究了一种新型Al-7.5Zn-1.6Mg-1.4Cu-0.12Zr合金在变形温度为380-460℃、应变速率为0.001～0.1 s-1条件下的流变应力特征,并利用TEM分析了合金在不同变形条件下的组织形貌特征.结果表明,应变速率和变形温度对合金流变应力的大小有显著影响,流变应力随变形温度的升高而降低,随应变速率的提高而增大;合金平均亚晶尺寸随温度补偿应变速率Zener-Hollomon参数的升高而减小.可用Zener-Hollomon咖参数描述该Al-Zn-Mg-Cu合金热变形时的流变应力行为.     

一种新型Al-Cu-Li系合金的热压缩流变应力

采用Gleeble-1500热模拟机高温等温压缩试验,研究了一种新型Al-Cu-Li系合金在应变速率为0.01～10s^-1、变形温度为3130～500℃条件下的流变应力特征,结果表明：流变应力随变形温度的升高而降低,随变形速率的提高而增大;采用Z参数的双曲正弦函数描述该合金高温变形的峰值流变应力,获得了峰值流变应力解析式,其热变形激活能为239.02kJ·mol^-1.     

Ti-25Al-14Nb-2Mo-1Fe合金热压缩变形流变应力行为与微观组织演变的研究

在Gleeble-3500热模拟试验机上对Ti-25Al-14Nb-2Mo-1Fe合金进行了等温恒应变速率压缩试验,研究了在变形温度为950~1 100℃,应变速率为0.001~1 s-1,最大变形程度为50%的条件下合金的热压缩变形流变应力行为与微观组织演变。结果表明:Ti-25Al-14Nb-2Mo-1Fe合金的流变应力对变形温度和应变速率均较为敏感,其流变应力曲线具有应力峰值、流变软化和稳态流变的特征。在变形温度为950℃,应变速率为0.001~0.1 s-1的条件下,Ti-25Al-14Nb-2Mo-1Fe合金的热变形特性为片层组织球化,其热变形机制可用晶界分离球化模型进行解释说明;在变形温度为1 000~1 100℃,应变速率为1 s-1的条件下,材料只发生了动态回复现象;在变形温度为1 050~1 100℃,应变速率为0.001~0.1 s-1的条件下,材料发生了动态再结晶现象。     

B95оч铝合金的热变形行为研究

采用Gleeble-1500D热模拟试验机进行高温等温压缩变形试验,研究了B95оч铝合金在变形温度为330～450℃、应变速率为0.001～1.000 s-1条件下的热变形行为,并利用金相显微镜(OM)和透射电子显微电镜(TEM)分析了B95оч铝合金在不同变形条件下的组织特征。研究结果表明:变形温度和应变速率对B95оч铝合金的流变应力大小有着显著的影响,合金的流变应力随变形温度的升高而降低,随应变速率的增加而增大。B95оч铝合金在450℃以下热变形过程中析出大量的第二相粒子,并随着温度的降低数量显著增加。B95оч铝合金热变形后平均亚晶尺寸随Zener-Hollomon参数的升高而减小,即随着变形温度的降低、应变速率的升高而减小。B95оч铝合金热变形的流变应力行为可以用包含Arrhenius项的Zener-Hollomon参数来描述,其变形激活能为124.09 kJ·mol-1。     

微量B对铸态TiAl基合金显微组织及热变形行为的影响

采用电弧熔炼法制备含微量B元素的Ti-43Al-4Nb-1.4W-xB(x=0.2,0.4,0.6,0.8。数据为原子分数,%)合金;利用光学显微镜(OM)和扫描电镜(SEM)研究B含量对该铸态合金显微组织的影响,并通过热模拟压缩试验研究温度为1 050~1 200℃、应变速率为10 3~1 s 1的变形条件下Ti-43Al-4Nb-1.4W-0.6B合金的热变形行为,分析该合金在不同变形条件下的组织演化规律。结果表明:当B含量(质量分数)达到0.6%时,合金组织明显细化;Ti-43Al-4Nb-1.4W-0.6B合金的高温压缩流变应力随变形速率增加以及变形温度降低而增加;其峰值应力与变形条件之间的函数关系可用双曲正弦函数来描述,并以此求得高温变形激活能为580.68 kJ/mol;加入0.6%B对合金动态再结晶形核起到一定的促进作用,热变形后,合金发生明显的动态再结晶。     

真空热压烧结CuW30复合材料的热压缩变形特性

采用真空热压烧结法制备了CuW30复合材料,在Gleeble-1500D热模拟机上对该材料进行等温热压缩模拟试验.研究了温度为650～950℃、应变速率为0.01～5 S-1、最大变形量为50％条件下的流变应力行为.结果表明:CuW30复合材料存在明显的动态再结晶特征.材料的稳态流变应力随应变速率的增大而增大,在恒应变速率条件下,合金的真应力水平随温度的升高而降低.热变形过程的流变应力可用双曲正弦本构关系来描述.在给定的变形条件下,计算的热变形激活能为231.150 kJ/mol.根据试验分析,合金的热加工宜在850～950℃范围内进行,应变速率为0.01～0.1 S-1.     

Relationships between process parameters and temperature field of roll casting for wide sheet made of AZ61 magnesium alloy: Finite element method

In recent years, wide sheet made of AZ61 wrought magnesium alloys has been widely studied and applied in industry. Thin roll-casting technology for the new wrought magnesium alloy can provide acceptable quality wide and thin sheet made of AZ61 magnesium alloy. To study the influences of roll-casting process parameters on temperature field for wide and thin sheet made of AZ61 magnesium alloy plates, some simplification and assumptions have been done by characteristics of magnesium alloy. Two-dimensional FEM model for roll-casting has been established along casting direction. Simulations of temperature fields of the plates have been done by using finite element analysis ANSYS software. A series of researches on the temperature distributions under different process parameters (pouring temperature, heat-transfer coefficients and casting speeds) have been done. The simulation results and the literature about the casting process of the relevant theory are the same. The simulation results show that the process parameters of rapid-casting process for AZ61 magnesium alloy are mutual influenced on the temperature fields of wide sheet made of AZ61 magnesium alloy.     

AZ31镁合金的热变形加工图及其应用

为了确定AZ31镁合金轧制工艺参数,利用Gleeble-3500热模拟试验机进行热压缩试验以测试其热变形行为,并根据动态材料模型理论得到其热加工图.当变形温度为380~400℃、应变速率为3~12 s^-1时,功率耗散效率大于30%,属于动态再结晶峰区;在该区域进行异步轧制变形退火处理后得到平均晶粒直径为2.3μm的细晶组织,抗拉强度为322.7 MPa,延伸率为19.6%.当应变速率大于15 s^-1时,属于流变失稳区,250~300℃低温加工时合金的塑性显著降低,350~400℃高温加工时合金出现混晶组织.     

Experimental and Numerical Study of Electromagnetic Forming of AZ31B Magnesium Alloy Sheet

Wrought magnesium alloys are interesting materials for automotive and aeronautical industries due to their low density in comparison to steel and aluminium alloys, making them ideal candidates when designing a lower weight vehicle. However, due to their hexagonal close‐packed (hcp) crystal structure, magnesium alloys exhibit low formability at room temperature. For that reason, in this study a high velocity forming process, electromagnetic forming (EMF), was used to study the formability of AZ31B magnesium alloy sheet at high strain rates. In the first stage of this work, specimens of AZ31B magnesium alloy sheet have been characterised by uniaxial tensile tests at quasi‐static and dynamic strain rates at room temperature. The influence of the strain rate is outlined and the parameters of Johnson‐Cook constitutive material model were fit to experimental results. In the second stage, sheets of AZ31B magnesium alloy have been biaxially deformed by electromagnetic forming process using different coil and die configurations. Deformation values measured from electromagnetically formed parts are compared to the ones achieved by conventional forming technologies. Finally, numerical study using an alternative method for computing the electromagnetic fields in the EMF process simulation, a combination of Finite Element Method (FEM) for conductor parts and Boundary Element Method (BEM) for insulators, is shown.     

A New Constitutive Strain-Dependent Garofalo Equation to Describe the High-Temperature Processing of Materials—Application to the AZ31 Magnesium Alloy

A new strain-dependent equation derived from that of Garofalo is developed in this work. This equation describes mathematically the deformation behavior of materials as a function of strain, strain rate, and temperature and is valid over a wide range of strain with good statistical accuracy. An explicit expression s( e) = f( e,T,[(e)\dot] ) \sigma \left( \varepsilon \right) = f\left( {\varepsilon ,T,\dot{\varepsilon }} \right) is introduced that reproduces stress-strain curves. Statistical tools for determining the validity of the equation have been applied. Predictions from this expression were compared with torsion data obtained in AZ31 magnesium alloy that was deformed at various temperatures and strain rates. Analysis of the strain dependence of the Garofalo parameters allowed us to establish a steady state at strains of about 0.6. It also allows drawing conclusions about the microstructural changes that occur during deformation of the alloy. In addition, the characteristic points in the evolution with strain of the parameters of the equation are related to the most significant values that characterize the microstructural processes occurring during deformation of the AZ31 alloy. The observed decrease of Q and n as a function of strain is attributed first to a softening process due to dynamic recrystallization and grain size refinement and finally to flow localization. The predicted values obtained with the new constitutive equation and the experimental values for the AZ31 alloy are in good agreement with an average relative error of about 6.5 pct.     

Study of High Temperature Deformation and Recrystallization in W9Mo3Cr4V Steel

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Deformation mechanisms responsible for the high ductility in a Mg AZ31 alloy analyzed by electron backscattered diffraction

The microstructural evolution during tensile deformation of an AZ31 alloy with grain size ranging from 17 to 40 μm, at intermediate temperatures, has been studied using electron backscattered diffraction (EBSD) and optical microscopy (OM) as the main characterization tools. Two deformation regimes could be distinguished. In the high-strain-rate regime, the stress exponent was found to be about 6, and the activation energy is close to that for Mg self-diffusion. These values are indicative of climb-controlled creep. In the lower strain rate range, elongations higher than 300 pct were measured. In this range, significant dynamic grain growth takes place during the test, and thus, the predominant deformation mechanisms have been investigated by means of strain-rate-change tests. It was found that the stress exponent varied during the test between 1.7 and 2.5, while the activation energy remains close to that for grain-boundary diffusion. The EBSD analysis revealed, additionally, the appearance of low to moderately misoriented boundaries that tend to lay perpendicular to the tensile axis. The enhanced ductility of this AZ31 alloy in this regime is attributed to the operation of a sequence of deformation mechanisms. Initially, grain-boundary sliding governs deformation; once dynamic grain growth occurs, dislocation slip becomes gradually more important. Dislocation interaction gives rise to the appearance of new interfaces by continuous dynamic recrystallization (CDRX).     

7085铝合金的高温压缩流变应力及软化行为

对均匀化炉冷态7085铝合金进行高温压缩实验,研究该合金在变形温度为350~450℃、变形速率为0.001~0.1 s 1和应变量为0~0.6条件下的流变应力及软化行为。结果表明:流变应力在变形初期随着应变的增加而迅速增大,出现峰值后逐渐软化进入稳态流变;随着变形温度的升高和应变速率的降低,峰值流变应力降低。采用包含Zener-Hollomon参数的Arrhenius双曲正弦关系描述合金的流变行为。分析和建立了应变量与本构方程参数(激活能、应力指数和结构因子)的关系,研究发现本构方程参数随应变量的增加而减少。合金的流变行为差异与动态回复再结晶和第二相粒子相关。