高频群脉冲电解加工的极间平衡间隙

给出了脉冲电解加工极间平衡间隙的数学模型，并据此讨论了高频群脉冲电解加工极间电压、阴极进给速度和电源脉冲频率与平衡加工间隙(极限平衡间隙)间的关系。模拟和实验表明：极限平衡间隙随极间电压升高而升高，它们呈近似的线性关系；随阴极进给速度增加，极间平衡间隙非线性地降低；而极限平衡间隙与脉冲频率则呈严格的线性关系，即随频率增加平衡间隙线性减小。极限平衡间隙与初始加工间隙无关，即一定的阴极进给速度和极间电压对应的稳定平衡间隙是不变的。     

钛合金叶栅套料电解加工表面质量研究

针对TC4钛合金叶栅套料电解加工易点蚀、表面质量差的问题,开展了直流和脉冲电解加工对比研究,设计了脉冲电解加工正交试验,优化了脉冲电压、频率、占空比和加工速度等参数。试验结果表明:脉冲电解加工能减少钛合金点蚀凹坑,提高表面质量,在22 V电压、80%占空比和1000 Hz频率时,加工叶型表面完整无点蚀,加工效率高。     

MOSFET高频窄脉冲电解加工工程化电源研制

气门模具的试生产表明,高频窄脉冲电解加工工艺是提高电解加工精度的有效技术途径。介绍了MOSFET高频窄脉冲电解加工工程化电源的性能指标及样机研制方案,解决了矩形波畸变、反向电流影响、瞬时过压击穿、功率管过热烧损、快速短路保护等研制中的主要技术难题。     

不同波形电压信号对电解加工表面质量的影响

为研究不同波形电压信号对电解加工工件表面质量的影响,以直流、正弦、三角和脉冲四种不同波形的电压信号对6061铝合金进行电解加工,以表面粗糙度表征电解加工的表面质量。实验结果表明:三角和正弦电压信号所加工的工件表面粗糙度介于直流和脉冲电压信号之间,且能同时提高加工效率和所得工件的表面质量。     

纳秒级脉冲电流电解加工定域性的试验研究

利用纳秒级脉冲电源、毫微秒级脉冲电源和直流电源,进行了电解加工试验。并对不同电源加工出的微小孔进行了分析、比较,研究了影响电解加工定域性的工艺因素。结果表明：采用纳秒级脉冲电源能显著提高电解加工的定域性,优化纳秒级脉冲电源脉冲宽度和加工电压可进一步提高加工定域性。     

微小孔的电解加工工艺研究

为了研究微小孔的电解加工工艺,采用在线加工的微细电极和超短脉冲电压,以及复合电解液电解加工微小孔.通过在线加工电极,避免了电极的二次装夹,提高了加工孔时的定位精度.实验中,分析了不同种类的电解液及其浓度、加工电压以及脉冲宽度对微小孔加工精度的影响.实验结果表明,添加络合剂的钝化电解液既能溶解阳极的电解产物,避免发生短路,提高了加工的稳定性,又不会增大加工间隙.而超短脉冲电压能明显减小微小孔加工的侧面间隙,并保证孔直径的一致性.     

电解加工技术的新发展——高频窄脉冲电流电解加工

综述了国内外脉冲电流电解加工研究和应用概况 ,重点介绍了 MOSFET脉冲电源高频窄脉冲电流电解加工 ( HSPECM)特性及加工精度、表面质量的试验研究。研究表明 HSPECM较大地改善了阳极溶解过程理化特性 ,可以较大幅度地提高电解加工精度 ,具有广阔的应用前景     

高频脉冲耦合铝合金激光-MIG复合焊接熔滴过渡及其熔覆特性

文中采用高频脉冲电源与单脉冲MIG焊电源并联叠加的方式与激光热源复合,形成高频脉冲耦合激光-MIG复合焊接方法.在A7N01铝合金板材上进行堆焊试验,用高速摄像研究高频脉冲耦合后电弧及熔滴过渡行为的变化,并通过金相观察研究高频脉冲耦合对熔覆层成形及组织的影响.结果表明,高频脉冲耦合后弧长增大,电弧电压增大、基值电流减小,峰值电流变化不大;熔滴由部分亚射流过渡转变成完全射流过渡;熔覆金属表面光滑,“鱼鳞纹”特征消失,无“指状”熔深问题;熔覆层晶粒大小变化不明显,但晶粒内部强化相颗粒变小,分布更加均匀.     

电火花线切割加工脉冲电源介绍

电火花线切割加工的工件表面容易产生电解现象,影响工件的使用寿命,且不同的放电波形对电极丝的振动会产生不同的影响。针对上述问题,早在70年代就出现了双极性脉冲电源,或者平均电压为零伏的交变脉冲电源。最近日本三菱公司申请了采用7～30MHz的交流高频脉冲电源的发明专利。图1为该电源的等效电路图。     

多孔金属工具阴极电解加工微坑阵列试验研究

采用多孔金属工具阴极电解加工方法,在磷青铜表面加工微坑阵列以增大超声电机摩擦副接触面的摩擦系数,试验研究了脉冲频率、脉冲占空比、加工电压和有效加工时间对微坑阵列尺寸及加工定域性的影响。结果表明:微坑阵列尺寸及加工定域性随脉冲频率的变化而影响很小;微坑阵列加工定域性及微坑深度随脉冲占空比的增大而减小;微坑阵列尺寸随脉冲电压和有效加工时间增大而增大。在磷青铜表面加工时,高电压、短时间、低占空比、高脉冲频率参数时的加工定域性略高。     

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.