Mg-2.5Nd-1.0Zn-0.5Zr合金的热变形行为及微观组织

本文采用Gleeble-1500B热模拟试验机研究了铸造Mg-2.5Nd-1.0Zn-0.5Zr稀土镁合金在变形温度为200~400℃、应变速率为0.001~0.1 s~(-1),变形程度为30%条件下的高温压缩变形行为,分析了实验合金在高温变形过程中应力与应变速率和变形温度之间的关系。结果表明,Mg-2.5Nd-1.0Zn-0.5Zr镁合金热变形时,变形温度和应变速率是影响合金热变形性能的重要因素。应变速率越低,温度越高时更容易发生再结晶。提高变形温度和变形量、降低应变速率,均使动态再结晶程度增加,晶粒尺寸加大。     

Mg-3.5Zn-0.6Y-0.5Zr合金高温压缩变形行为

采用Gleeble-1500D热模拟实验机,研究了Mg-3.5Zn-0.6Y-0.5Zr合金在变形温度为300~450℃、变形速率为0.002~1s-1及变形量为50%的条件下的高温压缩变形行为,分析了流变应力与应变速率、变形温度的关系,计算了高温变形时变形激活能和应力指数,建立了该合金的本构方程。结果表明:Mg-3.5Zn-0.6Y-0.5Zr合金在热变形过程中真应力随着温度的升高而降低,真应力随着应变速率的升高而升高。该合金的流动应力可以用双曲正弦函数来描述。     

Mg-5Zn-1Mn合金高应变速率热压缩过程中的组织演变和流变行为

采用Gleeble-3500热模拟试验机对Mg-5Zn-1Mn镁合金进行大变形(变形量为80%)热压缩实验,研究变形温度为250~400℃、应变速率为1~40 s-1范围内变形过程中合金的组织演变规律和流变行为。结果表明:该合金在上述工艺条件下进行热压缩变形时均发生了明显的动态再结晶,且高应变速率下获得的再结晶组织在较低应变速率下更为均匀、细小。通过分析流变应力变化过程中对应的微观机理,表明高应变速率更利于Mg-5Zn-1Mn镁合金实现大塑性变形。Mg-5Zn-1Mn合金的变形激活能随着变形温度的升高和应变速率的增大而减小。     

Mg-7Gd-2.5Nd-0.5Zr耐热镁合金热变形行为

采用Gleeble-1500D型热模拟试验机,在变形温度为623~773 K、应变速率为0.002~1 s~(-1)、最大变形程度为50%条件下,研究Mg-7Gd-2.5Nd-0.5Zr耐热镁合金的热压缩变形行为。分析合金在不同变形条件下流变应力的变化规律,并观察合金变形过程中显微组织的变化,建立具有双曲正弦关系的流变应力本构方程。结果表明:该合金的流变应力随变形温度的升高而减小,随应变速率的增大而增大;而且合金在773 K热压缩变形时发生完全动态再结晶,整个组织呈现为均匀细小的等轴晶,有细小颗粒状第二相在动态再结晶的晶界分布;计算出了合金的热变形激活能为235.958 k J/mol;合金适合的热加工温度为723~773 K。     

Mg-9Y-3Zn-0-5Zr合金的热变形行为

用Gleeble-1500热／力模拟机研究Mg-9Y-3Zn-0、5Zr镁合金在应变速率为0.001～0.1／s,变形温度为543～743K下的热变形行为,分析实验合金在高温变形时的流变应力和应变速率及温度之间的关系,计算变形激活能和应力指数,并讨论热压缩过程中的组织变化。结果表明：在同一变形温度下,实验合金的真应力水平随应变速率的增加而增加,随温度的提高而降低且表现出明显的再结晶特征。当变形温度在643～693K时,激活能变化不大;当温度大于693K时,激活能随温度升高而增大。当温度达到693K时,合金发生了完全再结晶。Mg-9Y-3Zn-0．5Zr合金在693K挤压后的抗拉强度为340．0MPa,伸长率为16．2％;该合金在时效后的抗拉强度为396．4MPa,伸长率为6％,时效抗拉强度明显上升。     

生物医用镁锌钇钕合金热变形行为的研究

采用GLEEBLE 1500热模拟机对挤压Mg-2.3Zn-0.5Nd-0.4Y生物医用镁合金在温度为200~400℃、应变速率为0.001~0.100 s-1、最大变形程度为60%的条件下,进行压缩模拟实验研究,分析了实验合金在热变形时的流变行为。实验表明此合金是正的应变速率敏感材料。合金的峰值流变应力随应变速率的增大而增加,随温度的升高而降低;应力-应变曲线以动态再结晶软化机制为特征,热变形应力指数n为4.0035,变形激活能Q为108.04 kJ/mol,流变应力行为满足双曲正弦关系,本构方程为:??=A[sinh(ασ)]nexp[–Q/(RT)]=1.1498×107[sinh(0.0133σ)]4.0035exp[–108.04/(RT)],该本构关系模型的计算结果与实验值间相对误差小于10%,为确定该医用镁合金的后续热加工提供了理论依据。     

Mg-13Gd-4Y-2Zn-0.5Zr合金形变软化行为及本构方程建立

使用型号为Gleeble-3500的热压缩实验机进行热压缩实验,在实验中调控温度和应变速率,绘制流变应力曲线图并进行分析。对Mg-13Gd-4Y-2Zn-0.5Zr合金在温度为360~480℃、应变速率为0.001~1 s^-1、并且热压缩试样的最大变形程度为60%条件下的形变软化现象进行了研究。经研究发现,Mg-13Gd-4Y-2Zn-0.5Zr合金的形变软化行为主要受其在不同变形条件下的动态再结晶行为的影响。设定材料常数α、n、A和Q与应变构建影响关系,将应变考虑在内后,建立了Mg-13Gd-4Y-2Zn-0.5Zr合金本构方程,其平均变形激活能为232.54 kJ·mol^-1。进行了误差检验,得到的峰值应力的实验值与计算值的平均相对误差的绝对值仅为5.5%,说明了建立的本构模型精度较高。     

Mg-13Gd-4Y-2Zn-0.5Zr合金热压缩行为及晶粒尺寸的研究

采用Gleeble-3500热压缩实验机对Mg-13Gd-4Y-2Zn-0.5Zr合金在温度360～480℃、应变速率0.001～1 s-1、最大变形程度为60%的条件下进行高温压缩实验研究。分析了应变速率和变形温度对该合金在高温变形时流变应力的影响,引入温度补偿应变速率因子Z构建合金高温流变应力的本构方程;研究了合金在不同压缩条件下的组织变化及动态再结晶晶粒尺寸,为后续有限元组织模拟提供了实验依据。结果表明:该合金的真应力-真应变曲线具有动态再结晶曲线的特征。动态再结晶的再结晶晶粒尺寸随温度的降低、应变速率的增大而减小;而且峰值应力也随再结晶晶粒尺寸的减小而增大。     

Mg-5Sn-2.5Pb镁合金的热变形行为及加工图

采用Gleeble-3500热模拟试验机研究Mg-5Sn-2.5Pb镁合金在变形温度250~450℃、应变速率为0.001~10 s~(-1)条件下的热压缩变形行为,并基于动态材料模型(DMM)建立了Mg-5Sn-2.5Pb镁合金在应变为0.6时的热加工图。结果表明,Mg-5Sn-2.5Pb镁合金的高温流变应力对应变速率和温度的变化敏感,随变形温度的降低和应变速率的增大而增大;Mg-5Sn-2.5Pb镁合金的最佳加工区域:变形温度为375~450℃、应变速率为0.01~0.3 s~(-1)。在此区域Mg-5Sn-2.5Pb镁合金的显微组织为动态再结晶组织。     

Mg-Zn-Zr-Ce合金高温变形行为与热加工性能研究

采用Gleeble 3800热模拟机对Mg-6Zn-0.5Zr-0.5Ce镁合金进行了高温压缩变形实验,分析了该合金在变形温度为523—673 K,应变速率为0.001—1.0 s^-1条件下的流变应力变化规律.结果表明,变形温度和应变速率对流变应力具有显著影响,流变应力随变形温度的升高和应变速率的降低而减小;在较高变形温度和较小变形速率下,流变应力随真应变的增加至峰值后即呈稳态流变特征.采用双曲正弦函数拟合曲线.确定了该合金的变形表观激活能为145.76 kJ/mol;建立了可用于描述该镁合金的流变应力的单隐层前馈误差反向传播人工神经网络模型.利用动态材料模型构建了热加工图,结合组织观察认为,该合金在648—673 K,应变速率为0.1 1.0 s^-1条件下发生动态再结晶;而同样应变速率下,温度低于573 K时材料在变形过程中由于机械孪生导致开裂.由交滑移所产生的机械回复位错控制着界面的形成,且动态再结晶模型表明该合金再结晶主要受界面迁移所控制.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。