Effect of welding current on morphology and microstructure of Al alloy T-joint in double-pulsed MIG welding

The effect of current on the morphology of Al alloy T-joint in double-pulsed metal inert gas（DP-MIG） welding process was investigated by simulation and experiment.A three-dimensional finite element model and the DP-MIG heat source of double-ellipsoidal volumetric model were developed to simulate the temperature and stress fields under different welding conditions.The macro-morphology and microstructure of welding joints at the corresponding currents were observed in the experiment.The results show that the best condition is at an average current of 90 A and current difference of 40 A,when the maximum temperature is 200 °C higher than the fusion points,with the temperature difference of about 100 °C and stress change of 10 MPa between thermal pulse and thermal base.Under these conditions,Al alloy T-joint with proper fusion condition has smooth fish-scale welding appearance and finer microstructure.Furthermore,the thermal curves and stress distribution in the experiment are consistent with those in the simulation,verifying the precision of the welding simulation.

Mechanism study on electromagnetic acoustic transducer for ultrasonic generation in ferromagnetic material

Based on the proper assumptions and approximations, the coupling mechanism of the electromagnetic acoustic transducer (EMAT) for ultrasonic generation within ferromagnetic material was studied by analyzing the eddy current distribution, Lorentz force, magnetostriction force and magnetization force. Some useful numerical calculations are presented to explain the EMAT behavior with general geometric arrangements. It is indicated that for the ferromagnetic material the magnetostriction effect dominates the EMAT phenomenon for ultrasonic wave generation in low magnetic field intensity, while the material does not reach its magnetizing saturation. But, with the increase of the bias magnetic field and saturation, the magnetostrictive terms will make no contributions to the ultrasonic generation and the Lorentz force becomes the only exciting mechanism. It is important to determine both the Lorentz and magnetostriction forces and select the appropriate working manner for achieving an optimized design.

Influences of acoustic field parameters on welding arc behavior in ultrasonic-MIG welding

By applying ultrasonic-MIG welding as research object, the behaviors of welding arc were analyzed with varied ultrasonic parameters in welding using arc images recorded by high-speed camera. The influences of the current by exciting ultrasonic and the height and shape of ultrasonic radiator on welding arc were studied. Results showed that when the current was 150 mA, ultrasonic showed most distinct compressive effect on arc. The compressive volumes of arc length at different heights were calculated by adjusting the height of ultrasonic radiator continuously from 10 mm to 35 mm, there were three maximum points. The compressive degrees of them reduced successively. By utilizing different shapes of ultrasonic radiator, it revealed that ultrasonic radiator with spherical crown surface showed better compressive effect in a larger welding standard scope. When radius of radiator increased, axial compressive volume of arc enlarged, while an increasing curvature radius led to mare distinct radial compression of arc.

Automatic stabilization of velocity for ultrasonic vibration system

Describes the structure of a current feedback ultrasonic generation system with such characteristic as velocity stabilization and automatic frequency tracking, discusses the velocity stabilization principle, and points out that successful frequency tracking is precondition for velocity stabilization.

The Influence of Ultrasonic Treatment on the Properties of Schottky Diodes

The given work studies the reason of the change of a superfluous current near crystallization temperature of an amorphous αPbSb metal alloy and at the same time founds out the influence of ultrasonic processing (USP) on the properties of αPbSb-nSi solar elements (SE), made by Shottki diodes technology (ShD) with a metal alloy. It is found that occurrence of a superfluous current αPbSb-nSi ShD under the influence of thermoannealing is connected with changes of structure of an amorphous film of metal at transition in a polycrystalline condition. VAC damaged αPbSb-nSi Sh Dare very sensitive to annealing time. Eventually, even at room temperature, level of a superfluous current decreases, i.e. “the wound” put by mechanical damage sort of heals, restoration process occurs the faster, the higher the annealing temperature is. Function of γt annealing parameters changes in an interval and the influence USP on photo-electric properties αPbSb-nSi SE depends on the chosen UIT mode.

长输油气管道内检测技术

管道内检测技术是长输油气管道内检测最有效的方法之一,是长输油气管道缺陷检测、评估与完整性评价的重要手段。随着我国能源行业的高速发展,管道成为能源输送的最有效载体,这对管道内检测技术提出了新的挑战,应运而生多种新的检测方法与解决方案。梳理了长输油气管道内检测技术的发展过程,阐述了长输油气管道内检测技术的国内外研究现状,针对长输油气管道内检测现存在的问题,对新技术、新方法的原理、应用情况进行归纳总结,并提出管道内检测行业的未来展望。

电磁超声与电涡流复合线圈的数据融合及分析

以Q235钢板为研究对象,搭建了带有磁屏蔽结构的、共用螺旋线圈的、分时复用的、二维电磁超声与远场涡流复合仿真模型,分析了电磁超声对近表面缺陷检测的盲区,并从永磁体参数、接收线圈参数对复合远场涡流模型进行优化。针对Q235钢板(5~15)mm电磁超声与远场电涡流共同作用的区域,将电磁超声得到的幅值信号和时间信号,远场涡流得到的线圈感应电压和阻抗参数,利用灰狼优化算法的支持向量机进行数据融合,反演出缺陷的参数,并设计实验验证了仿真模型的准确性。研究表明:所设计的电磁超声与远场复合线圈对缺陷检测的准确率达到百分之96.14%,远场涡流能够很好地弥补电磁超声的检测盲区。

高氮钢超音频脉冲GMA增材制造熔滴过渡特性

针对高氮钢增材制造熔滴过渡过程中氮元素逸出及飞溅问题,进行超音频脉冲熔化极气体保护(Ultrasonic Frequency Pulsed Gas Metal Arc,UFP-GMA)增材制造熔滴过渡试验,研究不同超音频脉冲电流叠加模式和脉冲电流频率对高氮钢熔滴过渡稳定性的影响,获取能够实现高氮钢增材稳定熔滴过渡的工艺参数。试验结果表明:在脉冲熔化极气体保护(Pulsed Gas Metal Arc,P-GMA)增材工艺条件下可以实现一脉一滴过渡,但是过渡稳定性较差,飞溅明显;在P-GMA基值阶段或基值和峰值阶段都叠加超音频脉冲电流均不利于熔滴过渡,容易出现短路、熔滴爆炸等问题;在P-GMA峰值阶段叠加低频(20 kHz)脉冲电流时,对熔滴过渡影响较弱,叠加中频(40~60 kHz)脉冲电流能抑制高氮钢熔滴过渡中大颗粒飞溅生成,提高熔滴过渡稳定性,但是当频率超过60 kHz时在过渡中会形成许多小飞溅。

脉冲电磁式EMAT-涡流检测复合系统的研究

常规电磁超声换能器(EMAT)中永磁体难以应用于实际情况、产生的信号幅值较小,根据电磁超声检测和涡流检测在检测范围内的互补性,本文设计了脉冲电磁式EMAT—涡流检测复合传感器结构,采用多物理场耦合技术验证了复合检测方法的可行性,并讨论了影响传感器检测灵敏度的关键参数。结果表明:该复合传感器能够激发用于检测表面缺陷的涡流信号和检测深层缺陷的超声波信号,并且对不同宽度和深度缺陷具有良好的灵敏度;此外,对励磁线圈与涡流线圈进行参数优化设计,为电磁超声和涡流的复合检测应用提供思路。

基于DSP的恒流超声电源谐振频率自动识别技术研究

针对换能器在加工过程中因温度升高与负载变化导致的谐振频率偏移问题,采用最小阻抗法与相位差控制法相结合的谐振频率识别策略,利用基于DSP控制的恒流超声电源样机测试了电源谐振频率识别的精确性与一致性。结果表明超声电源识别出的换能器谐振频率与阻抗分析仪测得的谐振频率最大差值为25 Hz、误差小于0.1%;激光测振仪测得振幅最大时的谐振频率与超声电源识别的谐振频率最大相差24 Hz;使用超声电源多次测试三种负载下的换能器,相同负载下识别出的换能器谐振频率波动范围在15 Hz以内。

Mechanism and microstructure of nickel-ceria composite coatings prepared by pulse current deposition under the ultrasonic field

In recent research, a novel method combined with pulse current （PC） deposition and the ultrasonic （U） field was used to fabricate pure nickel and nickel-ceria composite coatings, respectively. Morphology, crack propagation, and crystal texture were observed and analysed by using environment scanning electron microscopy （E-SEM） and transmission electron microscopy （TEM）. Orthogonal experiment [L16 （45）] was designed to optimize the parameters of pulsed power and the appropriate amount of RE addition based on microhardness. Effect of RE addition and pulsed current on the mechanism of co-electrodeposition was also investigated and compared. Experimental results indicated that it produced the alloying coatings, exhibiting compact grain and amorphous state. Nano-sized RE would preferentially occupy and pad at the edge of cracked gaps and micropore to limit the growing location and space for coarse Ni grain. Furthermore, during annealing at 480 ℃ for 2 h, a solid-solution precipitated phase named NiCexO1-x （0

水下无损外检测技术研究进展

无损检测技术用于发现水下结构物结构性损伤以避免发生重大事故,对保障海上油田安全和可靠运行至关重要。外检测技术广泛应用在水下结构物检测中,如导管架和海底管道。本文总结归纳包括涡流检测、超声检测和射线检测在内的水下无损外检测的技术特点以及相应的水下检测设备的技术参数。通过对比分析各检测技术,掌握各检测技术的优点和适用范围,期望为我国水下无损检测技术的工程化应用提供技术参考。

电脉冲轧制6061Al电热耦合模型及电弧加热机理分析

通过COMSOL Multiphysics仿真软件模拟高频脉冲电流激励时两板间界面处电弧的产生。讨论了在高频脉冲电流激励下,两块具有一定角度的金属板在电脉冲辅助轧制过程中界面处产生电弧的条件,并结合电磁学分析了电弧的形成机理。结果表明,在电脉冲辅助轧制过程中,除了焦耳加热外,还存在电弧加热现象,当加载300 A电流和10 kHz频率时,可以产生电弧并使两块铝板结合形成焊点。随着电流的增加,电弧温度和电势差也相应增加。在800 A电流下,电弧温度可达4 210 K,电势差可达54.5 V,已达到电弧形成的条件,但产生的电弧并不稳定。电弧的存在不仅瞬间加热了板材,提高了界面结合强度,而且在电弧力的作用下更容易形成波纹界面。模拟结果显示,加载800 A电流下可以产生超过4 000 K的电弧,并且在第一个脉冲周期内形成;并拟合了电弧产生的热源方程;为电脉冲辅助轧制研究提供了新思路。

基于时差法的低功耗超声波三维海流测量系统

声学时差海流计具有高精度、高采样率、无盲区和不受海洋散射条件限制的优点,目前国内尚无时差海流计系统样机以及核心部件(四声道双晶换能器)的报道。为了实现对海洋矢量流速的长期精确测量,设计并研制了基于时差法的低功耗超声波三维海流测量系统,构建了四声轴三维矢量流速测量模型,通过有限元仿真设计并制备了小体积异形异构V形双晶换能器。系统采用低功耗STM32L431和MSP4306288为主控芯片,由TDC-GP22高精度时间测量模块、换能器驱动电路、低功耗放大滤波电路、SD卡存储模块等组成测量电路,通过测量换能器4个声轴上的超声波飞行时间差,得到海水的三维矢量流速。系统采用低功耗硬件系统设计,配合软件低功耗管理降低系统功耗。经实际测试,所研制的三维海流测量系统具有测量准确、低功耗、存储方便等优点。

脉冲涡流-电磁超声复合检测方法的可靠性评估

金属结构广泛应用于现代工业的各种领域,在其从生产、制造到服役各个阶段都有可能产生各类复杂缺陷。例如金属结构的表面和底部都出现复合缺陷的情况,单一的电磁无损检测方法难以满足所有需求。而使用两种或多种具有针对性的电磁无损检测方法进行检测,又存在检测效率低、成本高等问题。为解决这一难题,本文开发了一种新型的脉冲涡流-电磁超声一体化复合检测方法。该复合检测方法仅需使用一套检测系统和检测探头,基于同时解调出的电磁成分和超声成分,即可同步检测出金属结构的表面缺陷和底部缺陷,大大简化了实验系统,提高了复合缺陷的检测效率。此外,基于检出概率开发了一种可靠性评估方法,对脉冲涡流-电磁超声复合检测方法的检测能力进行评估。通过数值模拟和实验对脉冲涡流-电磁超声复合检测方法进行检出概率分析,以确定复合缺陷检测的最小可检尺寸。

焊缝质量离线检测技术的研究现状与发展前景

针对焊后焊缝成形缺陷存在的技术问题,对目前比较常用的几种无损检测技术,即结构光视觉检测、超声波检测、涡流检测、磁光成像检测和红外检测进行了深入研究。对上述检测方法的基本原理、系统结构、检测特点和各自的适用范围进行了讨论。研究结果表明:单种检测技术各有各的优势与短板,不能满足焊缝的全面检测要求,可以采用多种检测手段相结合的方法,实现优势互补。

无患子皂苷连续管式逆流超声辅助提取的釜式微分模拟研究

借助工业生产(行业)公认的“萃取”扩展定义,以尊重原理、“化繁为简”、“实施可行”的理念,对无患子皂苷连续管式逆流超声辅助提取的工艺过程展开了“釜式微分提取”的模拟研究。结果表明,不同提取阶段的提取液皂苷含量与其相对应的进料液皂苷含量之间的函数关系为Y=0.0188x^(4)-0.0389x^(3)-0.2866x^(2)+0.6108x+1.4536,R^(2)=0.7108。从数理统计学的角度,可以将它看作是“连续管式逆流超声辅助提取无患子皂苷的动力学行为关系”。

LNG管道在线检测技术现场应用研究

针对液化天然气(LNG)管道在线检测,采用红外热成像、脉冲涡流、数字射线成像(DR)、电磁超声测厚等检测技术,对LNG管道进行了现场验证测试,并对各技术现场检测存在的主要问题进行分析,提出相关的建议。对目前LNG管道在线检测法规标准方面存在的问题进行了讨论,提出了制定和完善LNG管道在线检测相关法规标准的建议。

大型石化装备无损检测技术应用进展

无损检测技术在石油化工行业具有不可或缺的重要地位,是保障大型石化设备产品质量安全的重要技术支撑手段。回顾了石化行业中无损检测技术的发展现状与进展,介绍了无损检测技术在大型石化装备相关领域中的重要作用。同时从实际工作出发,探讨分析了目前无损检测新技术的应用进展,讨论了未来石油化工行业无损检测技术的主要发展趋势与方向。

500 kV变压器无励磁分接开关放电故障诊断分析

无励磁分接开关出现放电性故障会严重危害变压器安全运行。介绍了一起500 k V变压器交接试验过程中脉冲局部放电试验异常的案例,应用脉冲电流法、特高频法、超声波法等多维局部放电检测技术进行时差定位,成功诊断了变压器无励磁分接开关内部异物放电故障;通过材质成分分析判断异物为动触头旋转轴压环的机加工碎屑,异物位于无励磁分接开关动触头旋转轴位置,随挡位切换而移动,导致各个挡位均可检测到局部放电,且脉冲局部放电量随挡位变化而变化。