多孔质电极电火花加工极间流场仿真

为研究多孔质电极电火花加工中分布式冲液对加工过程的作用机制,建立了多孔质电极极间流场模型,采用固液两相流数值方法模拟电极间冲液和蚀除产物的两相流动过程,与单孔电极进行了对比研究,并进行了电火花加工实验验证。仿真结果显示:多孔质电极的极间流场流速由于分布式冲液出口的存在而呈现分布式特征,且流场外围流速大于中心流速;采用多孔质电极后,由于分布式冲液出口的存在,能够将固相蚀除产物沿一定的通道有效排出加工区域。与仿真结果相对应,电火花加工实验结果表明:由于冲液对蚀除产物良好的排出作用,多孔质电极能够获得更高的加工效率,且加工速度随加工深度变化不大;但由于冲液影响了炭黑向工具电极的附着行为,导致工具电极相对损耗率增大。     

多孔质电极电火花加工方法及实验

为克服传统电火花加工的复杂形状电极制备周期长、大面积复杂型腔加工效率低的弊端,提出了一种用于粗加工的多孔质电极电火花加工新方法。采用紫铜颗粒高温烧结的方式实现多孔质电极的快速制备,利用多孔质电极中的孔隙实现内冲液,以达到电火花粗加工过程中快速去除材料的目的。并可采用电极端部、侧部冲液相结合的方式,提高复杂型腔电火花加工的效率。通过对多孔质电极烧结制备的实验研究,初步确定了多孔质电极的烧结工艺参数。通过加工实验证明了多孔质电极电火花加工的可行性。     

侧铣式高速电弧放电加工工艺研究

侧铣式高速电弧放电加工利用电极侧面放电蚀除工件材料,能加工复杂的型腔、沟槽及直纹面等。为了探索这种新型电弧放电加工的工艺特性,探讨了峰值电流、脉宽和冲液压力等条件对工件材料去除率和相对电极损耗率的影响。实验结果表明:提高冲液压力和峰值电流均能增大工件材料去除率;相对电极损耗率随冲液压力的提高而增大,随峰值电流的提高而减小。在一定范围内,工件材料去除率随脉宽的提高而增大,相对电极损耗率随脉宽的提高而减小。     

水下电火花加工工艺研究

采用自行研制的水下电火花加工装置,选用石墨或紫铜作为电极材料、去离子水作为工作液,通过正交试验,利用水下电火花来加工不锈钢;讨论峰值电流、脉冲宽度对于水下电火花加工性能的影响。结果表明:采用石墨作为电极可获得较大的材料加工速度;峰值电流和脉冲宽度对水下电火花加工速度影响最为明显。     

电火花加工电极材料蚀坑的有限元热分析

工件材料蚀除的主要动力来源于放电通道等离子体中的热源。从放电加工过程中能量分配、传导和转换的角度,建立放电加工过程的物理模型;借助热传导理论,建立基于电火花放电去蚀除工件过程的数学模型。为研究不同峰值电流和脉冲宽度条件下放电蚀坑半径和深度以及深径比的变化规律,通过ANSYS仿真软件,模拟了20Mn23Al V无磁钢电极材料的温度场分布。分析了峰值电流和脉冲宽度对蚀坑径向和轴向温度场变化和凹坑几何尺寸分布的影响。结果表明:峰值电流和脉冲宽度对电极材料表面凹坑大小和深度均有较大影响且对凹坑半径的影响大于深度方向,导致深径比下降。     

慢走丝线切割单点放电温度场有限元分析

建立了慢走丝电火花线切割单脉冲放电模型,利用有限元分析了单脉冲放电温度场分布。计算出该条件下工件放电凹坑几何特征,与实际切割条件下的材料去除率进行了对比,并根据电火花线切割的加工特点进行了修正。讨论了不同峰值电流和脉冲宽度条件下,蚀除凹坑体积与材料去除率(MRR)的变化规律,并分析了峰值电流和脉冲宽度对MRR的交互作用。分析结果表明:考虑实际加工的相关因素,模拟的单脉冲放电的MRR经修正后可以近似表征实际连续切割时的MRR;单个凹坑的蚀除量随着电流和脉宽的增大而增大,并且电流和脉宽的交互作用随着它们取值的增大而更加明显。     

SiC/Al功能梯度材料的电火花多脉冲温度场仿真

为探索Si C/Al功能梯度材料的电火花加工特性,建立了电火花加工连续多脉冲放电温度场仿真模型,开展了连续多脉冲放电蚀除动态模拟仿真研究,应用生死单元法分析了放电凹坑位置的随机分布情况,研究了峰值电流、脉冲宽度对放电凹坑和材料去除率的影响规律,并进行了实验验证。结果表明:随着峰值电流和脉冲宽度的增大,材料去除率逐渐提高,仿真结果与实验结果具有相同的变化趋势;误差分析显示,理论值与实验结果最大误差为9.84%,最小误差为5.10%。     

基于流体动力断弧的高速电弧放电加工

提出了一种可用于难加工材料大余量高速蚀除的新的放电加工方法——基于流体动力断弧的高速电弧放电加工。与传统的电火花加工方法相比,高速电弧放电加工采用具有更高能量密度的电弧放电而不是火花放电来实现材料的蚀除;与其他利用电弧进行材料去除的工艺方法相比,高速电弧放电加工可使用特殊设计的成形电极实现强制多孔内充液,从而获得三维复杂型腔的沉入式加工能力,因此具有更广泛的应用前景。初步实验表明,对于镍基高温合金等难切削材料,高速电弧放电加工的材料去除率(MRR)远高于传统的电火花加工,甚至高于铣削加工。例如:加工镍基高温合金(GH4169)的材料去除率可达11 300 mm3/min,而电极损耗率(TWR)低于3%。由此可见,高速电弧放电加工在难切削材料的高效去除加工方面具有明显的技术优势。     

电火花磨削非导电工程陶瓷实验研究

针对非导电工程陶瓷的加工难题,提出了双电极同步伺服电火花磨削新方法,并用不导电的Al2O3工程陶瓷进行了加工实验,研究了脉冲宽度、脉冲间隔、峰值电压、峰值电流等电参数对材料去除率和表面粗糙度的影响规律,并进行了理论分析.实验结果表明,在实验加工的范围内,脉冲宽度的增加、峰值电压的升高、峰值电流的增大、脉冲间隔的降低都能使材料去除率升高,而对表面粗糙度的影响则不尽相同.     

SiCp/Al复合材料电火花加工多目标参数优化

针对SiC_p/Al复合材料电火花加工设计了工艺试验,并从复合材料的蚀除特性角度分析了峰值电流、开路电压、脉冲宽度对加工速度和表面粗糙度的影响,最后利用多目标遗传算法获得了加工电参数的最佳组合。结果表明：峰值电流、开路电压对加工速度的提升影响较大,而峰值电流对表面粗糙度的影响最显著;以多目标遗传算法获得的最优加工参数进行工艺试验,预测值与试验值误差小于10%,验证了模型的有效性。     

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.     

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.