Influence of axial magnetic field on shape and microstructure of stainless steel laser welding joint

The morphology and microstructure of the weld joint have significant influence on mechanical properties of welded specimens. In this paper, the mechanism on how the external magnetic field affected weld profile and microstructure was discussed by applying the longitudinal steady magnetic field to laser welding for SUS301 stainless steel. The optimal and scanning electron microscopes were used to measure the shape of the cross section and observe the microstructure after welding. The results showed that the shape of the cross section and microstructure could be significantly changed using the external magnetic field. Moreover, joint shape changed distinctly with the magnetic field intensity changing. With the increasing of magnetic flux density, the weld profile of the full penetration model changed from funnel to X type; meanwhile, the bottom weld width increased by 40%. In addition, the partial fusion zone occurred, and the weld width decreased by 20% while penetration increased by 18% when magnetic flux density turned into 380 mT. As far as microstructure of weld joint was concerned, it appeared that application of axial magnetic field led to indistinct fusion line and blocky austenite in big size rather than columnar grain in the center of the cross section. This phenomenon could be explained by numerical simulation results.     

Deviations from Parameters of Thermal Cycle of Electric-Arc Welding of 12Kh1MF Heat-Resistant Steel Detected in Magnetic Characteristics of the Affected Zone

On the base of investigations of magnetic characteristics of the 12Kh1MF heat-resistant steel in the zones of melting and thermal transformations in various regimes of electric-arc welding, a new approach to estimating the quality and service lives of welded joints in steam pipelines has been developed on the basis of magnetic structural analysis. Fields due to residual magnetization in the affected zone are measured locally along the direction towards the unaffected metal with a step width of 1–2 mm by the MS-1 magnetic sorter after removing the bead. Deviations from the prescribed regime of welding are detected and the service life of the joint is predicted using the maximal and minimal measurements or magnetic parameters along the line of measurements.     

基于DSP控制的交变磁场装置的研究

本文研制一套以DSP为控制核心的变频电源装置,采用新型单相SVPWM调制技术,激励铁氧体线圈可产生频率、场强均可独立调节的交流磁场。主电路部分采用桥式拓扑电路结构,磁场输出部分采用带气隙的回形磁芯,在气隙中产生交变磁场,用于研究磁场对细胞的生物效应。实验效果比较理想,测量结果较精确,系统稳定可靠,数字化界面操作简洁方便。     

Characteristics of metal magnetic memory signals of different steels under static tension

To study the characteristics of metal magnetic memory (MMM) signals of different steels during tensile test, static tension tests were applied to 30 pieces of Q235 and 16MnR base metal and welded specimens. During the various deformation periods, MMM signals are tested, and micrometallographic is observed. Furthermore, the derivative of magnetic intensity (dH_p/dx) is analyzed by mathematical and statistical methods to study the macro and micro corresponding relationships and difference among magnetic signals. Results show that despite the different magnetic intensity (H_p) curves of different materials, their dH_p/dx patterns in the yielding and necking stages are the same; welded specimens have the similar magnetic signal curves with their base metal, and the welded structure does not interfere with its H_p distribution; different materials have their unique zero point (H_p＝0) before being fractured, which is independent of the fracture location; there is a direct relationship between the intragranular slip and the changes of magnetic signals, which indicates the uneven plastic deformation.     

Thermal imaging investigations of the temperature fields on the surface of a welded item during manual arc welding with coated electrodes

The possibility of using thermal imaging equipment (a thermal imager) for determining the pattern of the temperature field distribution on the surface of welded items is considered. This allows evaluation of a region that is subjected to thermal action in the real-time mode and predicting the strength characteristics and the chemical composition of the welded joint.     

热压对镁合金焊接接头拉伸性能的影响

通过拉伸试验机、光学显微镜、扫描电镜等研究了热压对AZ31B镁合金钨极氩弧焊焊接接头拉伸性能和断口形貌的影响。结果表明:热压后焊接接头的抗拉强度和伸长率分别可达200MPa和10%,比焊态的分别提高了18%和67%;焊态接头拉伸断口以解理断裂为主,呈现出较多的脚印状小平台,同时伴随有少量韧窝;而热压后焊接接头的断口具有平台撕裂畸变现象,可以观察到热压塑性变形流变线,晶界表现出一定的滑动协调现象。     

电磁轴承磁场计算的磁路法优化

介绍电磁轴承磁场计算和转子受力特性分析的磁路法和有限元法。基于上述两种方法,详细地计算了考虑铁磁材料磁阻及其非线性因数的电磁轴承磁场,讨论了两种方法计算结果的差异。参考有限元法的计算结果,对计算电磁轴承磁场的磁路法进行了优化。优化后的电磁轴承磁路法简单、准确,具有工程应用价值。     

5052铝合金-HC420LA高强钢磁脉冲焊接接头盐雾腐蚀性能

对5052铝合金-HC420LA高强钢的磁脉冲焊接接头进行了盐雾腐蚀试验，揭示了磁脉冲焊接接头的腐蚀机理。研究结果表明，铝-钢磁脉冲焊接接头的力学性能在盐雾腐蚀环境中的退化较为明显，腐蚀首先从焊缝两侧尖端开始，当腐蚀时间达到48h时，焊接接头强度已下降为原来的20%。断口微观分析表明，钢较低的电化学电位加快了腐蚀，接头的腐蚀行为具有自催化作用。     

Characteristics of metal magnetic memory signals of different steels under static tension

To study the characteristics of metal magnetic memory (MMM) signals of different steels during tensile test, static tension tests were applied to 30 pieces of Q235 and 16MnR base metal and welded specimens. During the various deformation periods, MMM signals are tested, and micrometallographic is observed. Furthermore, the derivative of magnetic intensity (dH _p/dx) is analyzed by mathematical and statistical methods to study the macro and micro corresponding relationships and difference among magnetic signals. Results show that despite the different magnetic intensity (H _p) curves of different materials, their dH _p/dx patterns in the yielding and necking stages are the same; welded specimens have the similar magnetic signal curves with their base metal, and the welded structure does not interfere with its H _p distribution; different materials have their unique zero point (H _p = 0) before being fractured, which is independent of the fracture location; there is a direct relationship between the intragranular slip and the changes of magnetic signals, which indicates the uneven plastic deformation.     

Rapid rise time pulsed magnetic field circuit for pump-probe field effect studies

Here we describe an electronic circuit capable of producing rapidly switched dc magnetic fields of up to 20 mT with a rise time of 10 ns and a pulse length variable from 50 ns to more than 10 micros, suitable for use in the study of magnetic field effects on radical pair (RP) reactions. This corresponds to switching the field on a time scale short relative to the lifetime of typical RPs and maintaining it well beyond their lifetimes. Previous experiments have involved discharging a capacitor through a low inductance coil for a limited time using a switching circuit. These suffer from decaying field strength over the duration of the pulse given primarily by the ratio of the pulse width to the RC constant of the circuit. We describe here a simple yet elegant solution that completely eliminates this difficulty by employing a feedback loop. This allows a constant field to be maintained over the entire length of the pulse.     

Choice of place of magnetic-flux registration in the magnetic core of an attachable electromagnet for inspection of articles using their coercive force

The demagnetizing current I _dc is measured in different areas of an electromagnet-article magnetic circuit at the moment of zero crossing of the magnetic flux as the gap between the electromagnet and article changes. The weaker dependence of the I _dce magnitude measured in close proximity to the article on the gap width and the possibility of using the parameter in measuring the coercive force of the article with an attachable transducer (in particular, with a Hall sensor) are demonstrated.     

The UMD-101M plant for automated bulk magnetic nondestructive testing of quality of electric-welded pipes

The optimal structural scheme and special features of the new automated plant for magnetic nondestructive testing of electric-welded pipes in a technological industrial line, which meets contemporary demands, are considered. It has been shown that the use of computer technologies and thin-filmed high-resolution transducers provides significant improvement of operating possibilities of a flaw detector and makes it possible to detect, not only such flaws as discontinuities in metal and displacement of edges, but also flaws caused by failures in welding regimes, such as burns and cohesion of edges near a welded joint.     

A setup for measuring the magnetic characteristics of soft magnetic materials and articles

An automated setup for measuring the normal magnetization curve, the major and minor magnetic-hysteresis loops, and the main (initial permeability, maximum permeability, residual magnetic induction, induction coercive force, and saturation induction) and additional (the permeability at a field equal to the coercive force, the field strength at which the saturation induction is reached, and the induction at fields equal to the coercive force and the double coercive force) magnetic parameters of soft magnetic materials and articles produced from them is described. Measurements are performed in an open or closed magnetic circuit at a magnetization-reversal frequency of 0.05–0.5 Hz. The block diagram of the setup and its main parameters and characteristics are presented. The operation of the setup and the possibilities of its application are considered.     

Acoustic-emission study of the possibilities of localizing flaws of a welded joint during cooling

A method of localizing acoustic-emission signals from flaws of a welded joint during its cooling is considered. Aluminum and titanium inserts were used to simulate flaws of the welded joint. The developed technique of clustering made it possible to exclude noise accompanying the processes of welding and cooling the welded joint. The welded specimens were tested on an MTS-50 loading machine. At the finishing stage, specimens with double-sided welded joints containing titanium inserts were subjected to metallographic analysis.     

Effect of post weld aging treatment on tensile properties of electron beam welded AA2219 aluminum alloy

Aluminum alloy 2219 (Al-6.5%Cu) is a favourite age hardenable alloy for aerospace applications because of its excellent welding characteristics. Though AA2219 has got an edge over its 6000 and 7000 series counterparts in terms of weldability, it also suffers from poor joint strength when welded. In this investigation an attempt has been made to improve the welded joint strength through post weld aging treatment. This paper presents the effect of post-weld aging treatment on tensile properties of electron beam welded AA2219 aluminum alloy. Square butt joints were fabricated using an electron beam welding (EBW) machine of 100 kV capacity. The joints were given post-weld artificial aging treatment. Tensile tests were carried out using 100 kN, electro-mechanical controlled universal testing machine. It is found that the post-weld aging treatment is beneficial for improving weld metal hardness and tensile properties. This is mainly due to the uniform distribution of CuAl₂ precipitates in the weld metal region in post-weld aged joints compared to as welded joints as evident from weld metal microstructure.     

Optimization of the magnetic circuit in the MFL inspection system for storage-tank floors

Magnetization is the key to inspection of a tank floor via the magnetic-flux-leakage (MFL) technique. In order to optimize the magnetic circuit of the MFL detector and obtain the best detection effects, the influences of the magnet size on the floor magnetization condition, the gap magnetic flux density, and the magnetic force were studied with the help of the finite element method (FEM) and the effects of some other parameters, such as the magnet pole spacing and pole-piece thickness, on the signal-to-noise ratio were analyzed. The simulation results indicate that variation of the magnet width affects the magnetization much more than variation of the magnet thickness and that the detector can reach a trade-off between the magnetization effects and the driving force when the magnet is about 30 mm thick and 40 mm wide. On condition that the floor has reached its magnetizing saturation, an increase in the magnet-pole spacing and the pole-piece thickness can improve the testing sensitivity and the signal-to-noise ratio. The text was submitted by the authors in English.     

Q355NE+SUS304异种金属焊接接头组织与腐蚀疲劳性能研究

以Q355NE+SUS304异种金属焊接接头为研究对象,对其显微组织、3.5%NaCl+0.5%Na2SO4(质量分数),PH=5溶液腐蚀疲劳和腐蚀疲劳断裂特征进行了研究,分析了异种金属焊接接头腐蚀疲劳性能和断裂过程。结果表明:试验级腐蚀疲劳极限在170MPa左右,腐蚀疲劳裂纹起源于Q355NE侧的热影响区,逐渐扩展最终断裂于接头焊缝区,异种金属焊接接头构件级腐蚀疲劳通过4吨极限加载条件下的200万次试验,未发生破坏。     

一种磁流变液性能测试用的凹字型磁路结构设计与研究

剪切屈服应力是反映磁流变液流变特性的主要参数之一,稳定可控的磁场直接影响磁流变液剪切屈服应力的测量精度,因此磁场设计是否合理对磁流变液的流变性能测试具有重要的影响。针对外置式线圈产生的磁场强度较低且存在漏磁现象、对称式线圈中磁流变液装载不便导致测量过程持续性差等问题,设计了一种凹字型磁路,通过调整线圈位置来改变磁场结构,使磁力线垂直穿过磁流变液流动方向,同时可拆卸的组合式磁路设计在保证磁场强度需要的前提下实现了磁流变液的连续性测量。此外,还分析了不同电流下的磁场强度分布规律,并基于优化的磁路开展了磁流变液剪切屈服应力等力学性能参数的测试。与主流标准测试仪器相比,具有凹字型磁路结构的磁流变液测试系统所测得的剪切屈服应力平均相对偏差值约为10%,重复误差在6.34%以内,说明该磁路结构是磁流变测试中磁场装置设计的一种可行方法。     

力学不均匀性对焊接接头动态J积分影响的实验研究

用真空电子束焊的方法建立焊接接头的“软夹硬”非均匀体模型。用示波冲击的试验方法测出试件的动态断裂韧性,用该模型研究了焊接接头的力学不均匀性对其动态J积分的影响。结果表明,裂纹位于硬区材料,断裂韧性值理接近硬区材料,与软区材料的断裂韧性值差别较大;随夹层宽度增加,断裂韧性值减小,夹层宽度到某一值时,断裂韧性值趋于稳定。     

Modelling the bioelectric behaviour of halo pin-patient structures during magnetic resonance imaging

Bioelectric compatibility of electrically conductive halo fixation devices and magnetic resonance (MR) imaging has been largely based on resulting image quality. Previous studies have focused primarily on improving image quality and, although the electrical characteristics of the system during imaging may have been noted, they have not been studied in depth. Utilizing both a theoretical and experimental approximation, this study focuses on the bioelectric characteristics of the pin-patient structures typically enountered in clinical halo fixation systems. Results indicate that the halo pin-patient system can be modelled using a resistor-inductor-capacitor circuit and that simple attempts at improving compatibility through increasing interface resistance by the use of insulated pins may not be an effective approach to improving halo instrumentation compatibility with new, stronger magnetic and higher-frequency resonance imaging systems.