不同型砧下大型轴类锻件倒棱滚圆过程的数值模拟研究

根据大型轴类锻件的锻造特点,针对平砧、90°V砧和120°V砧分别确立了每种型砧下大锻件的倒棱滚圆锻造工艺,并运用Deform软件对多工步锻造过程进行数值模拟,得到了不同型砧下大锻件倒棱滚圆成形后的尺寸精度和锻件内部应力应变状态。模拟结果表明,运用120°V砧倒棱滚圆可以得到成形质量和力学性能最佳的大型轴类锻件。     

轴类大锻件倒棱滚圆后内部质量及尺寸精度研究

轴类大锻件的锻造过程分为压方、拔长和倒棱滚圆三大步骤。为制定准确的倒棱滚圆工艺参数以提高锻件质量并指导实际生产,应用有限元软件Deform-3D建立相应的分析模型,对倒棱滚圆过程进行模拟。从锻件的尺寸精度和锻件内部应力应变状态两个方面对比分析了平砧、90°V型砧和120°V型砧3种工艺方法。模拟结果表明,运用120°V型砧倒棱滚圆可以得到质量更佳的轴类大锻件。     

大型轴类锻件倒棱滚圆过程的数值模拟研究

在钛合金长方体锻件的锻造中,倒棱滚圆长方体锻件是最后一道成形工序,也是整个锻造工艺过程中非常重要一道工序。利用Dform软件,研究钛合金长方体锻件的倒棱滚圆过程,不同的砧形对锻件尺寸精度及其内部应力、应变大小分布的影响。     

不同型砧下方柱体倒棱工艺研究

利用有限元软件模拟了120°的V型砧和梯型砧的锻造倒棱过程,分析了在不同型砧上倒棱后锻坯塑性变形区的内应力、应变分布和变形规律。结果表明:与120°的V型砧相比,采用梯型砧倒棱提高了锻坯内部的压应力,使锻坯心部和内外表层金属均获得较大的均匀变形,避免了表面裂纹的产生,提高锻件的内部质量;它为正确制定倒棱工艺提供理论依据,对大型锻件的生产实践提供指导。     

圆弧砧结构尺寸对列车车轴成形质量影响

基于实测的50钢高温应力-应变曲线和热物性参数,建立了列车车轴圆弧砧快速锻造的DEFORM-3D有限元模型,并对车轴锻造过程进行了热力耦合模拟。基于毛坯成形过程中材料应力应变和金属流动模式研究,分析了砧子的结构尺寸对车轴成形质量的影响。从锻件的内部应力应变状态和表面缺陷等方面分析了圆弧砧有效工作面长度、预成型段与有效工作面过渡圆角及圆弧砧弧度对车轴成形质量的影响。进行了生产试制,验证了圆弧砧结构的合理性。     

轴类大锻件压方时锻件表面质量和内部应力状态的影响因素研究

轴类大锻件的锻造过程分为压方、拔长和倒棱滚圆三大步骤。目前对锻造工艺的研究集中在拔长工艺优化上,忽略了压方和倒棱滚圆对锻件质量的影响。为制定准确的压方工艺参数以提高锻件质量并指导实际生产,应用有限元软件DEFORM_3D建立相应的分析模型,对压方过程进行模拟,从锻件内部应力状态、锻透性及锻件裂纹3个方面对比分析了平砧压方和90°V型砧压方2种工艺方法,结果显示:采用90°V型砧压方时,锻件质量显著提高。     

压方圆角对长轴类大锻件质量影响研究

长轴类大锻件的锻造过程一般分为压方、拔长和倒棱滚圆三大步骤,目前对锻造工艺研究较多的是拔长和倒棱滚圆的优化,很少有对压方工艺优化的研究。本文从V型砧边缘的圆角半径的大小来对长轴类大锻件的压方过程进行模拟优化,从锻件内部应力、应变及破坏因子三个方面进行对比分析。结果表明,适当增大V型砧边缘的圆角半径可以有效防止锻件裂纹的产生,为锻件的质量提高和结构设计提供一种有效、可靠的分析方法。     

车轴倒棱成形工艺及型砧设计

在车轴的锻造生产过程中,型砧的几何尺寸和锻造工艺参数是影响车轴锻件表面质量和力学性能的主要因素。通过几何分析,研究了车轴倒棱时的圆形砧弧面半径与压下量的关系和车轴旋转锻造过程中的变形规律,发现不同的圆形砧弧面半径对应不同的最大倒棱压下量,为保证车轴旋转锻造过程中的尺寸精度,旋转角度、步进量和圆形砧工作带长度之间需满足一定的关系。将上述设计的约束应用于260 mm×260 mm方形坯料的锻造工艺参数设计,同时结合微观组织数值模拟,确定了圆形砧的几何尺寸和相应的车轴倒棱成形工艺参数,为实际生产提供了有力的指导。     

平砧倒棱方柱体的数值模拟研究

应用ANSYS有限元分析软件 ,对方柱体在平砧间倒棱进行了数值模拟。研究了倒棱时内部应力应变分布情况和变形规律 ,为正确制定倒棱工艺提供了理论依据 ,对大锻件的生产有意义———过去被忽略之处得到了新的认识     

不同工艺参数下锻件倒棱的研究

通过物理试验对锻件进行倒棱,在不同型砧倒棱过程中改变其边界条件,观察试件的变形情况,结果表明当梯形凸面砧中间凸起与坯料接触后,在油润滑的情况下,利用梯形凸面砧倒棱可使成形质量和力学性能达到最佳。     

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.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

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.