超声-电阻复合焊接方法及界面行为

有色金属微型零件超声焊接时,由于焊头面积小,输入焊接区域能量少,界面有效连接面积不足,影响焊接接头的力学性能. 针对这一问题,结合超声焊接与电阻焊的特点,研制了超声-电阻复合焊接系统. 对铜、铝异种金属进行了超声-电阻复合焊接工艺试验,并与相同工艺条件下的超声焊接进行了对比. 结果表明,电流对超声能的输出有促进作用,使换能器的峰值功率有明显的增加;超声使焊接起始阶段界面接触电阻迅速减小并消失;在复合能量的作用下,输入焊接区域总能量有较大提高,焊接区域温度和加热速率显著增加.     

电子束焊-钎焊复合焊T形接头组织性能分析

实现了TA15钛合金T形接头的电子束焊-钎焊复合焊接.采用扫描电镜、能谱分析仪和X射线衍射分析仪等测试手段,对接头的微观组织形貌、元素成分分布和界面反应产物等进行分析研究.并分别对复合焊接头和电子束焊接头的弯曲性能进行了比较分析.结果表明,在适当的工艺条件下,可以实现TA15钛合金T形接头的电子束-钎焊复合焊接.在电子束焊缝和钎焊缝的界面处存在Cu,Ni元素的扩散和界面反应.复合焊接头的塑性要优于电子束焊,其所承受的最大压强略低于电子束焊.     

压焊

AZ31镁合金电阻点焊中焊接电流对接头组织和强度的影响;电阻点焊动态电阻的测量;高频脉冲变极性焊接工艺性能研究;扩散连接Al／Ni／0Cr18Ni9Ti复合材料的界面组织;Cr、Ni元素对Fe3Al／钢扩散焊界面组织结构的影响;真空扩散焊时在钢制工装与钛接魅区氧化物的还原;TC4合金线性摩擦焊摩擦时间与变形量的关系。     

电阻法用于扩散焊接头微孔缺陷评价的数值模拟

从扩散焊接头界面微孔实际形貌和分布特征出发,提出了界面微孔周期性分布的二维有限元模型,应用ANSYS电磁场分析模块,考察了界面焊合率、界面微孔宽度和长度对电阻增量的影响.结果表明,扩散连接接头的界面焊合率与电阻增量之间呈双曲线变化规律,界面微孔的宽度和长度对电阻增量均有影响.当界面焊合率在20%～80%范围内时,电阻增量与界面焊合率之间表现出更高的敏感性.基于Lodge等人提出的扩散焊界面焊合率与电阻增量关系式,建立了能够包含界面微孔几何尺寸影响的修正方法.     

压焊

AZ31镁合金电阻点焊中焊接电流对接头组织和强度的影响;电阻点焊动态电阻的测量;高频脉冲变极性焊接工艺性能研究;扩散连接Al／Ni／0Cr18Ni9Ti复合材料的界面组织;Cr、Ni元素对Fe3Al／钢扩散焊界面组织结构的影响;真空扩散焊时在钢制工装与钛接魅区氧化物的还原;TC4合金线性摩擦焊摩擦时间与变形量的关系。     

双温工艺瞬时液相扩散连接45MnMoB地质钻杆

采用瞬时液相扩散连接技术进行了45MnMoB地质钻杆焊接试验,探讨了两种焊接工艺下接头的组织和力学性能.结果表明,在两种焊接工艺下,焊缝区晶粒已实现跨界面连续生长,焊缝区组织与母材组织相同,都为回火索氏体.与传统单温焊接工艺相比,1 250～1 230 ℃双温焊接工艺获得的接头无异质界面、焊合率高,接头抗拉强度为890 MPa,弯曲180°不裂,达到了地质钻杆焊接接头技术要求.另外,采用瞬时液相扩散连接工艺获得的地质钻杆接头成形好,焊后无需机械加工,降低了钻杆的制造成本.     

Cu/Al异种材料真空扩散连接研究

采用真空扩散连接工艺对Cu/Al异种材料进行连接,焊后利用扫描电镜和EDS对焊接接头的微观组织及元素扩散行为进行了研究.在焊接温度为540℃、扩散时间为60 min、焊接压力为5MPa的工艺下,焊接接头最高抗拉强度为185 MPa.     

304L不锈钢夹层扩散连接研究

采用Nb做中间层对304L不锈钢进行了真空扩散连接研究,焊后利用扫描电镜和EDS对焊接接头的微观组织及元素扩散行为进行了研究.在焊接温度750℃,扩散时间20 min,焊接压力10 MPa的工艺下,接头最高抗拉强度为185 MPa.     

Mg/Cu异种材料共晶反应钎焊连接研究

采用共晶钎焊工艺对Mg/Cu异种材料进行连接,焊后利用扫描电镜和EDS对焊接接头的微观组织及元素扩散行为进行了研究.在焊接温度为500℃,焊接时间为5min,焊接压力为2MPa的工艺下,焊接接头最高抗拉强度为42 MPa.     

扩散焊技术的研究进展

从扩散焊元素扩散传输规律、影响扩散焊焊接接头性能的因素及新型扩散焊焊接技术等几个方面对国内外研究现状进行了综述,并探讨了扩散焊技术应用的发展趋势。认为开发新材料的扩散焊技术、优化工艺及工艺标准的完善、数值模拟及仿真以及扩散焊质量验收标准的建立和完善等方面是今后的主要研究重点。     

Electrode life of aluminium resistance spot welding in automotive applications: a survey

Short electrode life has been one of the crucial issues for aluminium resistance spot welding in high-volume automobile manufacturing. A fair amount of heat may be generated at the electrode/workpiece interface because of the high electrical contact resistance of the aluminium oxide layers. Correspondingly, rapid electrode degradation is observed due to severe Cu–Al alloying, pitting and cavity during welding. This issue has not yet been fully addressed. This survey focuses on the current studies of understanding and development of electrode life improvement specifically on those that extend electrode life via optimising the electrical contact resistance at the interface, including altering the surface conditions of the workpiece, weld parameters development and weld equipment selections, and new electrode designs, and etc.     

Some Tribological Influences on the Electrode-Worksheet Interface During Resistance Spot Welding of Aluminum Alloys

In this study, the effect of worksheet surface characteristics on the electrical contact resistance of electrode-worksheet interface during resistance spot welding of aluminum alloy (AA5182) was discussed. The electrical contact resistance was influenced by both the oxide layer and surface roughness of the worksheet. However, the effect of oxide layer was more dominant, and the effect of surface roughness was likely to be linked with the damaging of oxide layer and not the contact area. The oxide layer on AA5182 was non-uniform with Mg-rich small spots dispersed on the surface. Grinding and scratching the worksheet surface was effective in reducing the oxide layer thickness and, hence, reduced the electrical contact resistance. It was observed that the surfaces with higher electrical contact resistances at this interface showed faster pitting rate of electrode. The study also suggested that the static electrical contact resistance measured before resistance spot welding could be useful for predicting materials likely behavior during the actual resistance spot welding process of AA5182.     

Empirical model of effects of pressure and temperature on electrical contact resistance of metals

Abstract

An important input property in the development of process models for resistance spot welding is electrical contact resistance. A model for the pressure and temperature dependence of electrical contact resistance was developed from established concepts of contact resistance. The key to developing the desired relationship is determining surface roughness characteristics, which is experimentally problematic. To overcome this difficulty the electrical resistance of contacting interfaces was measured as a function of the pressure applied across the interfaces. Using known information about the temperature dependence of bulk resistivity and mechanical properties, a curve fitting procedure was used to establish the desired relationship of contact resistance to pressure and temperature. This empirical model agrees well with experimental measurements in the regime of low applied pressure. At high pressures, predictions underestimate contact resistance, and this was attributed to strain hardening of asperities at the contacting interface. The model also predicts that the competing effects of bulk resistance and contact resistance will produce a peak in the variation of contact resistance with temperature. The model provides a suitable means for incorporating the pressure and temperature dependence of contact resistance into process models of the resistance spot welding process.     

Numerical and experimental study on nugget formation in resistance spot welding for three pieces of high strength steel sheets

A resistance spot welding for three pieces of high strength steel sheets was selected as a research subject and the nugget formation processes at the various welding conditions were investigated by both experimental measurement and FEM simulation. The FEM program developed by the authors considered the coupling of the electrical field, thermal field and mechanical field. The interface elements were used to model the transient contact states between two worksheets or between a worksheet and an electrode. The electrical resistance and thermal–mechanical properties of the interface elements change with the contact state, and can have different values from the worksheets and electrodes. The nugget sizes and its formation process predicted by FEM agreed very well with experimental results. The welding conditions (current, cycles and force) to produce sound nuggets for both two pieces and three pieces of high strength steel sheets were accurately estimated by the simulation.     

New technology for measuring resistance of electrical contact and estimating welding quality

Incomplete penetration is a common defect in the welding gap of large size (welding area is over 100 mm²) electrical contact, which leads to an instability of welding quality. Nevertheless, there was limited research dealing with non-destructive quality inspection of electrical contact. In this research, the resistance of CJ400 electrical contact was measured with the device medium frequency inverter resistance spot welding (MFI-RSW) machine. Multipulse measuring method was designed and proved efficient to reach a higher accuracy by restraining the influence of the contact resistance between electrodes and electrical contact. Moreover, the error of resistance caused by temperature rising in the measuring process is also eliminated effectively. Therefore, more accurate resistance of electrical contact could be extracted compared to the method of single pulse measuring. Then, the relationship between resistance and welding quality was studied and a new quality inspection method was proposed.     

铝/铜异种金属电阻热辅助超声波缝焊工艺特性

1060纯铝箔作为中间层,通过电阻热辅助超声波缝焊的方式实现1 mm厚度6061铝合金和T2紫铜异种金属焊接,分析了焊接过程中电阻热对铝/铜焊接接头焊缝成形、界面形貌、温度场以及力学性能的影响. 结果表明,采用单独超声波缝焊焊接铝/铜异种金属时,因产生的焊接能量较小,接头连接界面处仅局部区域位置形成连接,接头拉剪强度为45 MPa. 但在电阻热辅助超声波缝焊过程中,电阻热的加入能够有效预热工件,令待焊材料表面发生软化,在高频振动作用下,接头连接界面处形成有效连接. 同时,引入电阻热提高了铝/铜界面处温度,由单独超声波缝焊的140 ℃增加至190 ℃,界面处原子扩散距离增加,获得焊接接头的拉剪强度增加至75 MPa,相对前者接头拉剪强度提高67%.     

Prediction of nugget development during resistance spot welding using coupled thermal–electrical–mechanical model

Abstract

An axisymmetric finite element model employing coupled thermal–electrical–mechanical analysis of resistance spot welding is presented. The welding parameters considered include: heat generation at the faying surface and the workpiece–electrode surface; Joule heating at the workpiece and the electrode; and the thermal contact conductance between the electrode and the workpiece. The latent heat of phase change due to melting is accounted for. The effect of friction coefficient on the workpiece interface is also studied. The computed results agree well with the experimental data. Heat generation at the faying surface in the initial stages of welding dominates the nugget development, and Joule heating at long times governs the weld nugget growth. A parametric study is carried out for the nugget growth with specific consideration of resistance spot welding of Al alloys. Process control and modelling of resistance spot welding of Al alloys is more difficult than that for steel because of their high electrical and thermal conductivity and low melting point.     

纳米和微米 WC / 12 Co 涂层的电接触强化研究

分别以微米和纳米WC-12Co粉末为原料配制液态涂料,喷涂于45钢表面形成预喷涂层,再利用电接触表面强化技术对预喷涂层进行强化,获得强化层。观察了强化层的微观形貌,测定了强化层的硬度,分析了强化层的相组成和元素组成、抗热震性能。结果表明:强化层组织致密,硬度高,抗热震性能优异;强化过程中,预喷涂层与基材间发生了元素扩散,从而形成了冶金结合;与微米粉末制备的强化层相比,纳米粉末制备的强化层有更高的硬度和更好的抗热震性能。     

AgSnO2/Cu材料焊接钎着率及界面的组织研究

以AgSnO2电接触复合材料为触点材料、紫铜为底板、银铜锌为钎料,通过火焰焊接实现触头和底板的联接。采用超声波成像无损探伤检测仪、金相显微镜、扫描电子显微镜(SEM)等测试手段,研究焊料及焊缝的显微组织形貌对钎着率的影响。结果表明,在焊接过程中触头材料会出现气孔、裂纹、夹杂等微观缺陷,该缺陷主要存在于铜与AgSnO2的结合界面层,采用AgCuZn作为钎焊材料,结合界面具有良好的焊接性能。     

新型银稀土电接触材料的研究及应用

银基电接触材料具有优异的导电性和导热性,接触电阻低而稳定,加工性能优良,耐电弧熔焊和烧蚀,是低压电器、汽车电器和家用电器中广泛使用的电工材料。在银及银合金材料中添加稀土元素,可以抑制材料的自然时效和软化过程,提高材料的抗熔焊性、耐电弧烧蚀性、抗氧化能力以及力学性能,并且能够防止显微组织的长大,克服金属的迁移。阐述了稀土元素在银基电接触材料中的工作机制,以及银稀土新材料的应用情况。