Effect of retained austenite and nonmetallic inclusions on the thermal/electrical properties and resistance spot welding nuggets of Si-containing TRIP steels

Five advanced high-strength transformation-induced plasticity(TRIP) steels with different chemical compositions were studied to correlate the retained austenite and nonmetallic inclusion content with their physical properties and the characteristics of the resistance spot welding nuggets. Electrical and thermal properties and equilibrium phases of TRIP steels were predicted using the JMatPro? software. Retained austenite and nonmetallic inclusions were quantified by X-ray diffraction and saturation magnetization techniques. The nonmetallic inclusions were characterized by scanning electron microscopy. The results show that the contents of Si, C, Al, and Mn in TRIP steels increase both the retained austenite and the nonmetallic inclusion contents. We found that nonmetallic inclusions affect the thermal and electrical properties of the TRIP steels and that the differences between these properties tend to result in different cooling rates during the welding process. The results are discussed in terms of the electrical and thermal properties determined from the chemical composition and their impact on the resistance spot welding nuggets.

Characterization of electrical properties of resistance welding machines

Due to the individual electrical and mechanical characteristics of resistance welding machines, choice of the right machine and welding parameters for an optimized production is often difficult. This is especially the case in projection welding of complex joints. In this paper, a new approach of characterizing the electrical properties of AC resistance welding machines is presented, involving testing and mathematical modelling of the weld current, the firing angle and the conduction angle of silicon controlled rectifiers with the aid of a series of proof resistances. The model predicts the weld current and the conduction angle （or heat setting） at each set current, when the workpiece resistance is given.

Effects of Rare Earths on Electrical Conductivity, Melting-Welding and Corrosion Resistance by Electric Arc of Copper-Based Alloys

The effects of rare earths on electric conductivity fusion welding-resistance and erosion-resistance by electric arc of copper-based compound material by adding different amount of rare earths to copper base to get copper based compound materials were studied. Rare earths improve active ability among interfaces and optimize organizational structures. The conductivity of samples with rare earths is obviously better than that of materials without them. Moreover, wear ability and oxidization resistance of materials with rare earths can be improved greatly. For copper contact head with rare earths, electric arc corrosion resistance and welding-melting resistance are improved. Such alloys also decrease resistance change with increasing temperature. But the adding quantity of rare earths should be appropriate and formed handicraft should be properly regulated.

Mechanical behavior of electric resistance welded pipes in pipe-making process

The changes in the mechanical behavior of electric resistance welded（ERW） pipes before and after the cage roll forming process were investigated through tensile experiments. It is found that the Bauschinger effect does not exist in the pipe product, while the work hardening effect introduced by pipe-making is the direct cause of the mechanical changes. The prestrain introduced during different pipe-making processes are accumulative to the work hardening effect. And the increment of the yield strength for making Ф 244.48 × 8.94 pipe is approximately 45 MPa, higher than that of hot-rolled plates. It is verified that the strain ε=t/D-t is an efficient index representing the work hardening effect from the engineering viewpoint.

A MULTI-COUPLED FINITE ELEMENT ANALYSIS OF RESISTANCE SPOT WELDING PROCESS

A two-dimensional axisymmetric finite element model is developed to analyze the transient thermal and mechanical behaviors of the Resistance Spot Welding （RSW） process using commercial software ANSYS. Firstly a direct-coupled electrical-thermal Finite Element Analysis （FEA） is performed to analyze the transient thermal characteristics of the RSW process. Then based on the thermal results a sequential coupled thermo-elastic-plastic analysis is conducted to determine the mechanical features of the RSW process. The thermal history of the whole process and the temperature distribution of the weldment are obtained through the analysis. The mechanical features, including the distributions of the contact pressure at both the faying surface and the electrode-workpiece interface, the stress and strain distributions in the weldment and their changes during the RSW process, the deformation of the weldment and the electrode displacement are also calculated.

Relation between viscoplastic flow, periodic feature and Joule heat validity for electrically assisted friction stir welding

Electrically assisted friction stir welding is a promising way to improve liquidity of viscoplastic metal. However, this local heat source only can take into effect in a certain contact interface status. Semi-analytical model and FEM are adopted to analyze materials flow in electrically assisted FSW. Semi-analysis results show that Joule heating is validity with rotation speed 1 400 r/min and travel speed 400 mm/min. The maximum flow velocity is 0.033 m/s when travel speed is 400 mm/min, and it increases to 0.043 m/s with current assistant. Visco-plasticizing efficiency is a key factor to decide whether Joule heat is significant, and viscoplastic flow can periodically make circuit short. Periodic torque, axial force and onion rings surface show dynamic flow process, which can be used to illustrate the dynamic contact resistance feature and correct the calculation equation of Joule heat. This paper is aim to point out the potential relation between viscoplastic flow, periodic torque and Joule heating validity.

热处理对ERW焊缝沟槽腐蚀敏感行为的影响

采用恒电位阳极极化加速腐蚀试验方法研究了不同热处理工艺对高频直缝电阻焊(ERW)钢管焊接区沟槽腐蚀敏感性的影响,通过电化学测试、显微组织分析、残余应力测试和微区成分分析探讨了沟槽腐蚀的成因和机制。结果表明,ERW焊缝区、热影响区与母材的组织和成分分布的差异是产生沟槽腐蚀的主要原因,而残余应力不是重要影响因素。焊后单纯回火处理不能降低ERW焊管焊缝区沟槽腐蚀敏感性,焊后调质处理和单纯淬火处理均可显著降低ERW焊管焊接区的沟槽腐蚀敏感性。

J55钢级电阻焊(ERW)套管的焊缝沟槽腐蚀行为

采用恒电位阳极极化加速腐蚀电化学试验,研究了J55钢级套管电阻焊(ERW)焊缝的沟槽腐蚀行为,利用激光共聚焦显微镜观察试样腐蚀后的表面形貌和三维微观特征,计算了焊缝沟槽腐蚀敏感系数,分析了沟槽腐蚀的影响因素并对比了无缝套管和ERW套管的经济性。结果表明:J55钢级ERW套管发生了选择性局部腐蚀,焊缝区域存在点蚀坑;其沟槽腐蚀敏感系数均小于1. 3,对沟槽腐蚀不敏感;相比J55钢级无缝套管,其经济性较好。

ERW焊管的超声波检测

简要介绍了ERW焊管生产过程中超声波检测的工艺过程及特点,从折射角、声束宽度和检测频率三方面对ERW焊缝超声波检测工艺参数的选择进行了讨论。在ERW焊管的超声波检测中,焊管中横波折射角的下限是33.2°,其上限范围随焊管内外径比r/R的变化而变化,r/R数值越大,其范围也就越大;45°折射横波对于焊缝及热影响区表面开口缺陷具有较高的检测灵敏度,但是为了兼顾焊缝内部的径向面积型缺陷的检测,还应采用大折射角的横波声束进行扫查;在检测中要根据横波折射角和钢管直径综合考虑入射声束宽度,既要保证声束上边缘不在焊管中激发出表面波,又要避免焊管中折射纵波的出现。

基于激光视觉的ERW焊管在线错边监测系统

设计了一种基于激光视觉的ERW管子在线错边监测系统,通过先进的结构光视觉传感器来获取ERW管子焊缝的图像,采用PC机进行图像处理和模式识别,获取焊缝的宽度和错边数据,并输出给操作者,以连续在线监测管子的错边情况,这为高质量ERW焊管的生产提供了一种有效的监控手段。

Microstructure and mechanical/conductivity properties of pure copper joint welded by friction stir welding

Copper plates with 3 mm thickness were friction stir welded at a rotation rate of 800 r/min and different welding velocity.The effects of microstructure and the mechanical/conductivity properties of the FSW joints were studied.The results indicate that the grain sizes of nugget zones are 2.49,2.13 and 5.07μm for welding speed of 100,150 and 200 mm/min,respectively.Furthermore,lower density of dislocation was obtained in the nugget zone.Under the welding speed of 200 mm/min,annealing twins had been observed.When the speed is 150 mm/min,the tensile strength of the stir welded joint is 264 MPa that can reach 98%of the base metal.The mechanical properties of the joints with the welding speed of both 100 mm/min and 200 mm/min are lower than the base metal.The corrosion resistance of weld is higher than that of base metal.Electrical resistivity measurement shows no obvious change in the welded joints compared to the base metal at the room temperature.

Microstructure and mechanical properties of dissimilar resistance spot welded DP1000–QP1180 steel sheets

In this study,the effect of welding parameters on the microstructure and mechanical properties of the dissimilar resistance spot welded DP1000–QP1180 joints was investigated.Heat affected zone(HAZ)width of QP1180 side was smaller than that of DP1000 side.HAZ width and indentation depth increased with increasing welding current and welding time.The nugget size increased with increasing welding current whereas it increased at lower currents and decreased at higher currents with increasing welding time.The lowest hardness was on the DP1000 side.On the QP1180 side,the center of HAZ had the peak hardness.With increasing welding current,hardness values throughout the weld zone decreased and the tensile shear load increased.At lower welding currents,the welding time did not affect the tensile shear load.Tensile elongation decreased with the increase of welding time,whereas there is no relationship between the welding current and elongation.The spot-welded joints having higher strength exhibited a more ductile fracture characteristic.

浅谈ERW钢管错边缺陷

对ERW焊管生产中错边产生的原因进行了较详细的论述,指出ERW焊管错边产生的主要原因是成型质量不好,挤压辊挤压量过大以及挤压辊磨损及安装不当等。给出了错边缺陷的判定方法,并提出了消除错边的方法和措施。

A New Characterization Approach of Weld Nugget Growth by Real-Time Input Electrical Impedance

The in-process changes of weld nugget growth during the Resistance Spot Welding were investigated based on the resistance of input electrical impedance. To compute the time varying resistance of input electrical impedance, the welding voltage and current signals are measured simultaneously and then converted into complex-valued signals by using Hilbert transform. Comparing with the dynamic contact resistance as reported in literature, it showed that the time varying resistance of input electrical impedance can be accurately correlated with the physical changes of weld nugget growth. Therefore, it can be used to characterize the in-process changes of weld nugget growth. Several new findings were reported based on the investigation of spot welds under no weld, with and without weld expulsion conditions.

Influence of Surface Condition on Expulsion in Spot Welding AZ31B Magnesium Alloy

Experiments were carried out to study the influence of surface condition on expulsion during the spot welding of AZ31B Mg alloy. A general electrical contact resistance theory for conductive rough surfaces and the relation between maximum temperature Tm in the contact and voltage-drop V across interface of two surfaces were employed to understand the reason of expulsion in Mg alloy spot welding. The main reason of expulsion is that the high electrical contact resistance induced by large roughness of the surface and oxide film covered on the surface leads to local melting of metal in the interface of two surfaces, and liquid metal of the local area ejected from the specimen under electrode force forms expulsion.

不锈钢城轨车辆电阻焊疲劳性能研究

不锈钢城轨车辆多采用SUS301L冷轧不锈钢薄板,结构以电阻焊连接为主,车辆运行过程中电阻焊接头会受到复杂载荷作用而失效,疲劳断裂是其主要的失效形式。研究电阻焊接头受力情况,对于改善和优化焊接结构设计、电阻点焊工艺及使用寿命评估具有重要意义。文章针对不同强度等级、不同厚度组合的电阻点焊接头进行疲劳试验,分析疲劳性能与SUS301L不锈钢强度和厚度的关系,结果表明:SUS301不锈钢板厚≤4 mm时,板厚的增加有助于疲劳强度的提高;奥氏体不锈钢板SUS301强度等级分别为DLT、ST、MT、HT,在材料板厚一致的条件下,电阻点焊疲劳极限随着材料抗拉强度增加呈现先上升再降低的趋势,与强度等级无直接的正比关系。对不锈钢电阻焊疲劳断裂微观分析,发现试样受力发生偏转,热影响区形成应力集中,电阻点焊试样疲劳裂纹在热影响区萌生并向母材区扩展,疲劳断口呈脆性断裂特征。

应力对直缝高频电阻焊管沟槽腐蚀的影响

对处于0 MPa、100 MPa、200 MPa和300 MPa恒定拉应力下的直缝高频电阻焊管(ERW)进行阳极极化,并测定了其焊缝沟槽腐蚀敏感性。测定结果表明,随拉应力增大沟槽腐蚀敏感系数增大,腐蚀电流增大。但焊管经整管热处理后,焊缝处沟槽腐蚀敏感系数明显减小。

银金属氧化物触头材料的表面劣化及抗熔焊性能分析

阐述了电触头材料表面劣化的分类，对ＡｇＮｉ，ＡｇＣ－ｄＯ，ＡｇＳｎＯ２及其不同配对时的抗熔焊性能进行了对比实验；分析了交流电弧作用下材料成分含量分布变化规律与金属θｍＣｐρｍλ间的关系。研究了电弧对ＡｇＣｄＯ等材料微观形貌的影响规律及其与熔焊概率的关系；指出了由于金属氧化物在高温下分解而使ＡｇＣｄＯ和ＡｇＳｎＯ２表现为ＡｇＣｄ和ＡｇＳｎ的抗熔焊特性，且材料非对称配对时抗熔焊能力表现出“中间效应”

基于ANSYS的高频直缝焊管主要控制参数模拟

基于高频直缝焊管的焊接温度是影响高频直缝焊管焊缝质量的首要因素,为提高高频直缝焊管的质量,重点研究了在高频感应加热中,高频焊接的主要控制参数焊接速度、焊接电流和焊管厚度对高频直缝焊管焊缝温度场的影响.依据高频焊接过程中的热源方程,利用ANSYS有限元热分析模块,建立适当的线热源模型,编写APDL程序.通过对3个主要控制参数的调节,得到在不同参数条件下的高频焊管焊缝温度场的分布云图,发现沿着高频焊管运动方向焊缝处温度是均匀递减的.在其中一组参数一定的状态下,对金洲集团Φ219 mm高频焊接机组的焊缝温度场进行测温,结果发现模拟温度场与实际温度场基本一致.

高频焊管残余应力的测量及三维有限元数值模拟

高频焊接是利用高频电流特有的集肤效应和邻近效应,使焊接电流聚集于接触处表层,表层接合面上的温度上升很快,使待焊面加热至熔化或接近熔化的塑性状态,随后迅速被挤压成接头的一种压焊方法。研究在现有条件下利用盲孔法测量了高频焊管接头焊缝的残余应力,并且采用ANSYS有限元分析程序,分析管道焊缝在焊接过程中的焊接残余应力。实测的轴向和环向残余应力,与用三维有限元模型计算得到的数值结果分布规律基本一致。同时发现高频焊管的残余应力分布与普通电弧焊基本一致,但是其残余应力值比普通电弧焊偏小,这对于指导实际焊接工程问题具有重要意义。