Microstructure and Property Relationships in Resistance Spot Weld between 7114 Interstitial Free Steel and 304 Austenitic Stainless Steel

Due to the differences in physical, chemical and mechanical properties of the base metals, the resistance spot welding of dissimilar materials is generally more challenging than that of similar materials. The influence of the primary welding parameters affecting the heat input such as peak current on the morphology, microhardness, and tensile shear load bearing capacity of dissimilar welds between 304 grades austenitic and 7114 grade interstitial free steel has been investigated in this study. The optimum welding parameters producing maximum joint strength were established at a peak current of 9 kA, where the electrode force is kept 6×10-5 Pa and weld time is kept constant 17 cycles, respectively. The primary cause of weakening the weldment is identified as the excessive grain growing region of heat affected zone (HAZ) in case of 7114 grade interstitial free steel.     

Deformation at Room and Low Temperatures and Martensite Transformation in Resistance Spot Welding Duplex γ & α(δ) Materials of 301L Stainless Steel

Transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) effects had been widely studied in single austenite steel. But in duplex γ& α(δ) phase, such as welding materials of stainless steel,they had been less studied. Tensile shear loading experiment of resistance spot welding specimens prepared with 2 mm 301L sheets, was carried out at 15℃ and -50℃. Optical microscopy and scanning electron microscopy (SEM) as well as X-ray diffraction (XRD) were used to investigate the microstructure of weld nugget, and specimens fracture surface. The results showed that the initial weld nugget was composed of 8.4%α(δ) ferrite and 91.6% austenite. Tensile shear load bearing capacity of spot welding specimen at -50℃ was 24.8 kN, 17.7% higher than that at 15℃. About 78.5 vol. pct. martensite transformation was induced by plastic deformation at -50℃, while about 67.9 vol. pct transformation induced at 15℃. The plasticity of spot welding joint decreased with the decline of experimental temperature.     

Deformation at Room and Low Temperatures and Martensite Transformation in Resistance Spot Welding Duplex γ ＆ α（δ） Materials of 301L Stainless Steel

Transformation induced plasticity （TRIP） and twinning induced plasticity （TWlP） effects had been widely studied in single austenite steel. But in duplex γ ＆ α（δ） phase, such as welding materials of stainless steel, they had been less studied. Tensile shear loading experiment of resistance spot welding specimens prepared with 2 mm 301L sheets, was carried out at 15℃ and -50℃. Optical microscopy and scanning electron microscopy （SEM） as well as X-ray diffraction （XRD） were used to investigate the microstructure of weld nugget, and specimens fracture surface. The results showed that the initial weld nugget was composed of 8.4% α（δ） ferrite and 91.6% austenite. Tensile shear load bearing capacity of spot welding specimen at -50℃ was 24.8 kN, 17.7% higher than that at 15℃. About 78.5 vol. pct. martensite transformation was induced by plastic deformation at -50℃, while about 67.9 vol. pct transformation induced at 15℃. The plasticity of spot welding joint decreased with the decline of experimental temperature.     

Microstructure development in resistance spot welded galvannealed IF steel sheet

Abstract

Interstitial free (IF) steels having excellent drawing and forming characteristics find extensive use in autobody panels. Although, resistance spot welded joints are widely used in the automobile industry, little is known about the metallurgical changes which occur during the spot welding process. The investigation of the metallurgical changes is very important for the safety strength of the welded joints. In the present research work, microstructures of the different zones of spot welded interstitial free steels have been characterised by optical, scanning electron and transmission electron microscopes. Microstructural changes at weld and heat affected zone have also been correlated with welding heat input and microhardness values.     

PHS1800热成形钢电阻点焊接头截面特性及工艺优化

目的 研究不同参数下PHS1800热成形钢电阻点焊接头截面特性及其工艺。方法 利用金相显微镜、扫描电子显微镜和万能试验机,对点焊接头的焊点熔透率、压痕率、熔核直径、压痕直径及拉伸性能进行测试。结果 随着焊接时间的增加,各截面特性总体呈线性增长的趋势,当焊接时间超过0.6 s时,接头熔核直径减小;随着焊接电流的增大,各截面特性整体呈上升的趋势,当焊接电流为11.5 kA时,熔透率达到峰值,继续增大焊接电流,压痕率迅速上升;随着焊接压力的增大,熔透率增至59.17%后不断减小,压痕率不断增大,熔核直径与压痕直径无明显变化。基于三因素八水平正交实验,确定点焊接头最大拉伸载荷为16.54 kN,其断口为脆性断裂。结论 焊接时间和焊接电流对点焊接头截面特性的影响较为显著,拉伸性能受焊接电流的影响最大。实验得到了成形良好的焊接接头,最优参数如下：焊接时间为0.6s,焊接电流为11.5 kA,焊接压力为2.0 kN。本实验可为热成形钢在汽车加工中的应用提供理论基础和技术支持。     

Microstructure and failure behavior of dissimilar resistance spot welds between low carbon galvanized and austenitic stainless steels

Resistance spot welding was used to join austenitic stainless steel and galvanized low carbon steel. The relationship between failure mode and weld fusion zone characteristics (size and microstructure) was studied. It was found that spot weld strength in the pullout failure mode is controlled by the strength and fusion zone size of the galvanized steel side. The hardness of the fusion zone which is governed by the dilution between two base metals, and fusion zone size of galvanized carbon steel side are dominant factors in determining the failure mode.     

电阻点焊技术在行波管电子枪研制中的应用

电阻点焊技术是行波管电子枪研制过程中的关键工艺技术。本文首先从行波管电子枪常用的点焊材料、点焊结构与方法、检验方法几个方面,详细描述了电阻点焊技术的应用现状;然后从行波管电子枪的电子光学设计要求、热力学性能等分析了产生这种应用的技术背景;最后,针对上述应用中一些典型的困难,基于一些团队的研究成果,提出了部分解决方案、技术方向和可能被忽略的技术空白。希望从业人员能够从中学到经验,提升行波管电子枪的电阻点焊水平。     

低碳钢板镀铅层在电阻点焊过程中的行为

本文研讨了镀铅钢板电阻点焊时,镀铅层的变化和它对接头性能的影响。试验结果表明,镀铅使焊接区的电流密度下降,析热量减少;焊后镀铅以片状或以“膜”的形式残留,在接头中这些均对接头的拉剪强度有影响。当采用大电流、短时间的强规范焊接时,能显著降低这种影响。     

Resistance spot welding of AISI 430 ferritic stainless steel: Phase transformations and mechanical properties

The paper aims at investigating the process–microstructure–performance relationship in resistance spot welding of AISI 430 ferritic stainless steel. The phase transformations which occur during weld thermal cycle were analyzed in details, based on the physical metallurgy of welding of the ferritic stainless steels. It was found that the microstructure of the fusion zone and the heat affected zone is influenced by different phenomena including grain growth, martensite formation and carbide precipitation. The effects of welding cycle on the mechanical properties of the spot welds in terms of peak load, energy absorption and failure mode are discussed.     

SUS304不锈钢板点焊接头超声成像及力学性能EI北大核心CSCD

利用超声波水浸聚焦入射法,对1mm厚的SUS304奥氏体不锈钢板点焊接头进行超声C扫描成像检测,研究不同焊接工艺参数下接头的C扫描图像特征,检测分析点焊的熔核直径,并对点焊接头进行拉伸-剪切实验。结果表明：超声波水浸聚焦C扫描成像法能够有效检测点焊熔核直径,为4．76～5．25mm,比金相实测值大2．6％～5．3％;随着焊接电流的增加（4-8kA）,接头的失效载荷均值从7116．8N增加到9707．1N,能量吸收均值从66．3J增加到196J,同时反映在C扫描图像上的熔核直径也从4．76mm增加到5．11mm;当焊接电流增加至9kA时,接头的失效载荷均值下降至6799．5N,能量吸收均值下降至41．3J,此时在C扫描图像上反映出飞溅、焊穿等典型的焊接缺陷。     

Dissimilar Resistance Spot Welding of Q&P and TWIP Steel Sheets

Dissimilar resistance spot welding of twinning induced plasticity (TWIP) and quenching and partitioning (Q&P) steel grades has been investigated by evaluating the effects of clamping force, welding current, and welding time on the microstructure, shear tension strength, and fracture of welded samples. The spot welding of TWIP and Q&P steels promotes the occurrence of an asymmetrical weld nugget with a greater dilution of TWIP steel because of its lower melting temperature and thermal conductivity. As a result, weld nuggets exhibit an austenitic microstructure. TWIP steel undergoes a grain coarsening in the HAZ, whereas Q&P steel undergoes some phase transformations. Welded samples tend to exhibit higher shear tension strength as they are joined at the highest welding current, even though an improper clamping force can promote excessive metal expulsion, thereby reducing the mechanical strength of the welded joints. Shear tension welded samples failed through interfacial fracture with partial thickness fracture mode for a low welding current, while partial thickness with button pull fractures were observed when a high welding current was used. The weld spots predominantly failed at the TWIP side. However, as TWIP steel can work harden significantly in the more resistant welded joints, the failures occur, instead, at the Q&P side.     

电阻点焊质量Hopfield神经网络在线评估方法

目的 电阻点焊广泛应用于汽车、家电等领域,但目前少有准确的无损质量评价方法。为此,研究一种基于低碳钢板焊接功率信号的焊接质量在线评估方法,并探索利用该信号来评价电阻点焊焊点质量的可能性。方法 对焊接电流、电压信号进行测量和分析,研究功率信号表征焊接质量的可靠性,提出一种有效的模式特征提取方法,将动态功率信号转换为二值图像并用二值矩阵表征,该方法避免特征提取和选择,且尽可能保留焊点质量信息。通过拉剪试验将焊接样本分为6种不同的焊接等级,利用Hopfield关联记忆神经网络建立焊接质量分类器,将具有不同焊接质量水平的焊接样本模式特征矩阵记忆为稳定状态。结果 将焊接样本的模式特征矩阵输入分类器,通过Hopfield网络关联记忆将其收敛到最相似的稳定状态,最终锁定了稳定状态对应的焊接质量。60个测试样本中59个样本都可以被正确分类,该分类器的分类准确率达到98%。结论 分类性能试验结果表明,所提出的模式特征提取方法快速、有效,并能可靠地在线评估低碳钢板的焊接质量。     

Q-switch Nd:YAG laser welding of AISI 304 stainless steel foils

Conventional fusion welding of stainless steel foils (<100 μm thickness) used in computer disk, precision machinery and medical device applications suffer from excessive distortion, formation of discontinuities (pore, void and hot crack), uncontrolled melting (melt-drop through) and poor aesthetics. In this work, a 15 ns pulsed, 400 mJ Nd:YAG laser beam was utilized to overcome these barriers in seam welding of 60 μm thin foil of AISI 304 stainless steel. Transmission electron microscopy was used to characterize the microstructures while hardness and tensile-shear tests were used to evaluate the strengths. Surface roughness was measured using a DekTak profilometer while porosity content was estimated using the light microscope. Results were compared against the data obtained from resistance seam welding. Laser welding, compared to resistance seam welding, required nearly three times less heat input and produced welds having 50% narrower seam, 15% less porosity, 25% stronger and improved surface aesthetics. In addition, there was no evidence of δ-ferrite in laser welds, supporting the absence of hot cracking unlike resistance welding.     

汽车电阻点焊分析仪的校准方法及不确定度评定

汽车电阻点焊分析仪是一种便携式、易于操作的设备,该设备可以清晰的成像点焊内部的结构,并且可以评估焊点直径,以及焊点厚度。广泛用于机械制造、铁路汽车工程等行业。     

Weldability,microstructure and mechanical properties of laser-welded selective laser melted 304 stainless steel joints

Laser welding is a promising process for joining small components produced by selective laser melting (SLM) to fabricate the large-scale and complex-shaped parts. In the work, the morphology, microstructure, microhardness, tensile properties and corrosion resistance of the laser welded stress-relieved SLMed 304 stainless steel joints are investigated, as the different sections of stress-relieved SLMed 304 stainless steel are joined. Results show that the SLMed 304 stainless steel plates have a good laser weldability. The microstructure of laser-welded joints consists of the cellular dendrites in austenite matrix within columnar grains, exhibiting a coarser dendrite structure, lower microhardness (∼220 HV) and tensile properties (tensile strength of ∼750 MPa, and area reduction of ∼27.6%), but superior corrosion resistance to those of SLMed plates. The dendrite arm spacing of the joints varies from ∼3.7 μm in center zone, to ∼5.0 μm in fusion zone, to ∼2.5 μm in epitaxial zone. The SLMed anisotropy shows a negligible effect on the microstructure and performance of the laser-welded joints. The laser welding along the building directions of the SLMed base plates can induce a slightly finer dendritic structure and higher tensile properties.     

Resistance spot welding joints of AISI 316L austenitic stainless steel sheets: Phase transformations,mechanical properties and microstructure characterizations

In this paper, we aim to optimize welding parameters namely welding current and time in resistance spot welding (RSW) of the austenitic stainless steel sheets grade AISI 316L. Afterward, effect of optimum welding parameters on the resistance spot welding properties and microstructure of AISI 316L austenitic stainless steel sheets has been investigated. Effect of welding current at constant welding time was considered on the weld properties such as weld nugget size, tensile–shear load bearing capacity of welded materials, failure modes, failure energy, ductility, and microstructure of weld nuggets as well. Phase transformations that took place during weld thermal cycle were analyzed in more details including metallographic studies of welding of the austenitic stainless steels. Metallographic images, mechanical properties, electron microscopy photographs and micro-hardness measurements showed that the region between interfacial to pullout mode transition and expulsion limit is defined as the optimum welding condition. Backscattered electron scanning microscopic images (BE-SEM) showed various types of delta ferrite in weld nuggets. Three delta ferrite morphologies consist of skeletal, acicular and lathy delta ferrite morphologies formed in resistance spot welded regions as a result of non-equilibrium phases which can be attributed to the fast cooling rate in RSW process and consequently, prediction and explanation of the obtained morphologies based on Schaeffler, WRC-1992 and Pseudo-binary phase diagrams would be a difficult task.     

Microstructure and Mechanical Properties of a Dissimilar Friction Stir Weld between Austenitic Stainless Steel and Low Carbon Steel

Dissimilar fusion welding of austenitic stainless steels to carbon steels has some metallurgical and technical problems.It was suggested that the solid-state nature of friction stir welding(FSW) can overcome these problems and produce a sound weld with reliable mechanical properties.In this study,plates of 304 stainless steel and st37 steel were welded together by FSW at tool rotational speed of 600 r/min and welding speed of 50 mm/min.In the stir zone(SZ) of 304 stainless steel,the results showed a refined grain structure with some features of metadynamic recrystallization.In the SZ of st37 steel,the hot deformation of material in the austenite region produced small austenite grains.These grains transformed to fine ferrite and pearlite by cooling the material after FSW.The production of fine grains increased the hardness and tensile strength in the SZ of both sides with respect to their base metals(BMs).     

钛铝异质材料插销增强搅拌摩擦点焊接头组织与力学性能

目的开发一种无针搅拌头,以解决传统搅拌摩擦焊产生的匙孔和Hook缺陷问题。方法钛板预制通孔,铝板预制盲孔,插销置于孔中,进行搅拌摩擦点焊。采用无针搅拌头对厚度为2mm的TC1钛合金板和厚度为4 mm的2A12铝合金板(钛上铝下)进行了异种金属搭接搅拌摩擦点焊试验,试验采用旋转速度为950 r/min,焊接时间为100 s,下压量为0.2 mm的工艺参数,对焊接接头的抗拉剪力及接头组织进行评估。结果添加插销获得的焊接接头,钛、铝板与销之间实现固相连接,有效解决了有针搅拌摩擦焊产生的匙孔和Hook缺陷问题,且接头的抗拉剪力达到了6.42 kN。结论提出的插销增强搅拌摩擦点焊的新方法,采用的搅拌头具有较低的制造成本,工艺简单,提高了焊接效率,同时确保了焊接接头的质量。     

马氏体含量对合金化热镀锌双相钢电阻点焊接头组织与性能的影响

目的 研究在双相钢电阻电焊过程中马氏体含量对点焊接头组织、性能的影响规律。方法 使用电阻点焊机对DP780、DP980、DP1180 3种马氏体含量不同的锌铁合金化热镀锌双相钢进行焊接,利用欧姆表、光学显微镜、扫描电镜、拉伸机和显微硬度计等设备,对基板的电阻率、工艺窗口、接头力学性能、焊点断裂模式、金相组织进行表征。结果 在AWS D8.9M-2012焊接标准体系下,DP780、DP980、DP1180焊接电流窗口依次减小,DP780、DP980、DP1180 3种材料在最大焊接电流下的焊核直径基本一致;熔核区硬度呈增大趋势,DP780点焊接头软化不明显,DP980和DP1180的热影响区出现明显的软化现象,这主要是由母材热影响区中的马氏体回火造成的。DP780、DP980、DP1180的最大剪切力分别为23 062、27 317、28 183 N。DP780为拔核断裂模式,DP980和DP1180为部分拔核断裂模式。结论 双相钢中马氏体含量的增加会使焊接电流窗口降低,整体向焊接电流减小的方向偏移,但是会提高上限电流的焊点承载强度。     

6061铝合金/DP600钢电阻点焊接头特征及力学性能

目的 提升6061-T6铝合金/DP600双相钢电阻点焊接头的力学性能,以满足该焊接结构在汽车工业中的应用。方法 对6061-T6铝合金与DP600双相钢分别进行了直接电阻点焊试验及添加Ni中间层的电阻点焊试验,采用光学显微镜、扫描电子显微镜及能谱仪分析了接头界面宏微观组织、化学成分、元素分布等,此外还采用接头拉剪试验进行了2种接头的力学性能测试,并对接头的断口形貌及断裂模式进行了分析。结果 直接点焊接头熔核界面形成了厚度约为2.5μm的金属间化合物层,主要金属间化合物为靠近铝合金侧的Fe₂Al₅及靠近高强钢侧的Fe₄Al₁₃。直接点焊接头的拉剪载荷为3.1 kN,失效形式为界面断裂,断口呈以脆性为主的混合断裂特征。添加Ni中间层的点焊接头界面形成了Ni₄Al₁₃、Ni₂Al₅金属间化合物,抑制了焊接过程中Al-Fe互扩散并降低了Al-Fe金属间化合物的形成以及硬脆性Al-Fe金属间化合物对接头力学性能的影响,使...