外加磁场对铝合金电阻点焊质量的影响

分析了外加磁场对铝合金电阻点焊接头质量的影响,包括熔核尺寸、接头力学性能和微观组织. 结果表明,外加磁场增大了熔核直径、提高了点焊接头的剪切力和吸收能. 在不同工艺参数下,熔核直径增长在5%~25%,剪切拉伸力可提高10%~30%. 在一些焊接参数下,外加磁场可以降低焊接电流、减短焊接时间,从而提高焊接效率、降低能耗. 外加磁场可促进点焊熔核内等轴晶的生成和细化晶粒.当焊接电流很小或很大、焊接时间过短或过长时,都会降低外加磁场的效应. 因此当对点焊施加外磁场时,应在合理的工艺参数下进行,以最大限度地发挥外加磁场的作用.     

外加磁场对轨道车辆不锈钢点焊组织性能的影响

以轨道车辆用SUS301L不锈钢为研究对象,研究了外加磁场对不锈钢点焊的熔核尺寸、拉伸强度和微观组织的影响。结果表明,在外加磁场的作用下,不锈钢点焊的熔核直径增长效果明显,拉伸强度得到不同程度的提高,且外加磁场强度越大,作用的时间越长,性能提高的效果越明显。在相同焊接参数下磁控电阻点焊比普通点焊拉伸强度最大提高16. 7%,宽高比提高47%,点焊凹坑降低62%,熔核组织明显细化,点焊过程中外加磁场能够有效改善不锈钢电阻点焊接头性能。     

三层板6061铝合金点焊接头形式对其力学性能的影响

文中研究了三层板6061铝合金电阻点焊接头的失效行为.设计了6种形式的三层板铝合金点焊搭接接头,并对其进行了剪切拉伸试验.通过剪切拉伸测试中获得的峰值载荷和吸收能研究不同接头形式下的力学性能.结果表明,不同的搭接形式的接头具有不同的接头峰值载荷和能量吸收能.在剪切拉伸测试中,熔核的旋转程度对接头的峰值载荷和能量吸收具有重要影响.熔核旋转程度越大,峰值载荷越小,能量吸收能越低;而对于纯剪切情况下,峰值载荷和吸收能最高.     

外加磁场对非等厚铝合金电阻点焊熔核偏移的影响

针对两层板及三层板组合下的5052铝合金进行了外加磁场与常规情况下的电阻点焊,研究了外加磁场对铝合金点焊熔核偏移影响. 结果表明,外加磁场改善了两层板及三层板非等厚度铝合金的熔核偏移情况,尤其是针对熔核偏移较严重的板材厚度组合下,外加磁场改善熔核偏移的作用更加明显. 之后针对外加磁场和常规点焊情况的不同两层及三层板铝合金板厚组合式样进行了剪切拉伸测试. 结果表明,外加磁场在改善点焊熔核偏移的同时,提高了点焊接头的强度. 因此,外加磁场是一种改善非等厚度铝合金点焊熔核偏移及提高接头剪切拉伸性能的有效方法.     

三层板铝合金电阻点焊搭接接头的弹塑性模拟

建立了1.5 mm等厚5052铝合金三层板电阻点焊接头在拉剪载荷作用下的弹塑性有限元模型.有限元模型的计算结果与试验结果吻合良好.结果表明,不同的接头设计形式导致不同的峰值载荷和断裂模式.熔核旋转对控制峰值载荷及断模式起重要作用,熔核旋转角度增加导致峰值载荷降低.断裂模式不仅与熔核旋转有关,也受接头应力分布影响.当点焊接头在拉伸过程中发生旋转时,熔核周围受到的剪切应力增大,断口形貌呈现拉长的椭圆形韧窝.当点焊接头在拉伸过程中不发生旋转时,熔核周围受到的较大拉应力,断口形貌呈等轴韧窝.     

先进高强钢电阻点焊接头的断裂模式分析与预测

研究了先进高强钢(advanced high strength steel, AHSS)两层板电阻点焊接头的断裂模式，不同的断裂模式会影响点焊接头断裂时的机理、力学性能及断裂位置，基于不同组合下的临界熔核尺寸、最大载荷、断口宏观形貌、初始断裂位置、宏观金相组织以及微观硬度曲线等试验结果，阐明了板材厚度和板材强度两类因素对于断裂模式的影响规律. 结果表明，板材强度因素会直接影响断裂模式、初始断裂位置以及最大载荷；板材厚度因素影响断裂模式但不改变初始断裂位置及最大载荷. 临界熔核尺寸的影响因素有板材厚度、板材强度、熔核中缺陷以及拔出断裂位置距熔合线的距离. 在此基础上，文中提出了临界熔核尺寸(D_CR)的预测模型及预测方法，该方法与试验值符合较好，为实际工业应用中的临界熔核尺寸判定提供了理论依据.     

301L/Q235B异种钢电阻点焊显微组织及拉剪性能

对等厚2 mm+2 mm的301L不锈钢冷轧板和Q235B低碳钢热轧板进行电阻点焊试验,通过显微组织分析、显微硬度分析和拉伸剪切试验,研究了点焊接头拉剪性能的影响因素,基于抗剪强度和断裂模式确定了最佳的电阻点焊工艺。结果表明,二者点焊熔核向不锈钢侧偏移,熔核中由于马氏体的产生其显微硬度最高;当界面熔核直径大于6.8 mm时,在拉剪载荷下可发生301L钢侧熔核拔出断裂;在焊接电流11 kA,电极压力11 kN,通电时间350 ms的工艺参数下,可获得拉剪性能最优的点焊接头。     

双相钢电阻点焊接头断裂形式研究

针对双相钢电阻点焊过程焊接工艺窗口窄、易出现熔核断裂的问题,文中通过焊点力学性能与微观金相试验,研究了不同焊接工艺参数变化时对双相钢焊点质量的影响规律,建立其焊接工艺窗口,分析了双相钢熔核断裂的成因及焊接参数对熔核断裂的影响规律.研究表明,对于一定板厚的试件,临界熔核直径将是决定双相钢点焊接头是否出现熔核断裂的重要参数之一,并给出避免熔核断裂的合理焊接工艺参数.     

铝合金胶接电阻点焊工艺研究与优化

按照正交试验方案对6111铝合金进行胶接电阻点焊,通过拉伸试验机对焊点的剪切强度进行测量,并利用Matlab软件对试验数据进行分析。试验结果表明:电流对焊点剪切强度影响最大,焊接时间对焊点剪切强度影响次之,压力影响最小。熔核直径和焊点剪切强度在一定范围内呈正相关关系, 6111铝合金的胶接点焊熔核直径(mm)与剪切强度(kN)的回归模型是:y=0.7718x-1.8385;根据试验结果,实现了对6111铝合金胶接电阻点焊工艺的优化,优化结果验证了模型的正确性。     

冷轧DP980电阻点焊接头断裂模式特征与组织分析

采用中频逆变点焊机对1. 2 mm厚冷轧DP980进行电阻点焊试验,确定球形电极下焊点的断裂模式,对不同断裂模式下的熔核直径、剪切力、破坏能量及断裂位移等参数进行表征。此外,针对典型熔核组织和显微硬度进行分析。结果表明,球形电极下焊点断裂模式表现为界面断裂和熔核拔出两种。两种断裂模式下,熔核处组织均为板条马氏体+孪晶马氏体,在热影响区中存在软化区域,该组织为回火马氏体+铁素体。界面断裂模式下,熔核直径、剪切力及断裂位移均呈现为数值较小的特点,破坏能量随焊接电流的增加呈快速增长的特征。熔核拔出模式下,熔核直径、剪切力和断裂位移均呈现为数值较大的特点,破坏能量随焊接电流的增加呈稳定状态。     

永磁体磁场对双相高强钢电阻点焊质量的影响

以1对中空圆柱形永磁体为磁场源,系统地分析了外加恒定磁场作用下,2.25mm厚热镀锌双相高强钢板(HDG-DP600)电阻点焊接头的力学性能、熔核尺寸及宏观晶粒组织走向.试验发现:在永磁体磁场作用下,热镀锌双相高强钢点焊接头的拉剪力较无外加磁场情况下提高了11.01%,接头的晶粒组织得到一定程度的细化,熔核形状"长而扁...     

Failure Behavior of Three-Steel Sheets Resistance Spot Welds: Effect of Joint Design

There is a lack of comprehensive understanding concerning failure characteristics of three-steel sheet resistance spot welds. In this article, macro/microstructural characteristics and failure behavior of 1.25/1.25/1.25?mm three-sheet low carbon steel resistance spot welds are investigated. To evaluate the mechanical properties of the joint, the tensile-shear test was performed in three different joint designs. Mechanical performance of the joint was described in terms of peak load, energy absorption, and failure mode. The critical weld nugget size required to insure pullout failure mode was obtained for each joint design. It was found that the joint design significantly affects the mechanical properties and the tendency to fail in the interfacial failure mode. It was also observed that stiffer joint types exhibit higher critical weld size. Fusion zone size along sheet/sheet interface proved to be the most important controlling factor of spot weld peak load and energy absorption.     

Modelling the effect of welding current on resistance spot welding of DP600 steel

Experiments were made for welding current variation between 6 kA and 12 kA. Microstructure and mechanical performance under tensile-shear tests were recorded and compared. Welding current effect on micro-properties was very slight while nugget size was highly dependent on welding current. Expulsion phenomenon existed at 12 kA welding current and the unsatisfactory partial interfacial failure was detected. Nugget formation and temperature distribution were analysed numerically. Comparisons with experimental results showed that the nugget size deviation was within 10% and the nugget shape was well predicted.     

Nugget formation and its mechanism of resistance spot welded joints in DP600 dual-phase and DC54D ultralow carbon steel

Resistance spot welded joints in different configurations of DP600 and DC54D were investigated to elucidate the nugget formation process and mechanical properties of the resultant joints. Results show that, when the welding time was less than 4 cycles, the fusion zone (FZ) was not formed, but the heat-affected zone (HAZ) occurred with a “butterfly” shape. In 4 cycles, the FZ in dissimilar sheets occurred with an “abnormal butterfly” shape because of nugget shift. When the welding time increased to 14 cycles, the FZ exhibited a “bread loaf” shape and the weld shifted to “dog bones.” The nugget can be divided into three regions, namely, FZ, HAZ1, and HAZ2, and the FZ consisted of lath martensite. The micro hardness of DP600 FZ was lower than that of HAZ because of the dilution of DC54D. The failure mode of B changed from interfacial failure to plug failure during the nugget formation process. The tensile-shear load of sound weld is 6.375, 6.016, and 19.131 kN.     

管板单边电阻点焊环状焊点力学性能分析

电阻点焊接头的焊接强度由母材和熔核的材料属性及几何特征决定.管板单边电阻点焊由于其焊接结构的特殊性,生成熔核的外形为环状,其强度不能用传统的圆形焊点强度经验公式计算.环状熔核的特征影响因素复杂,物理试验存在不确定性,通过大量试验方法难以建立焊接强度和影响因素之间的关系.基于拉剪试验原理,采用计算机模拟试验和试验设计方法,设计试验并统计得出低碳钢焊接强度和环状熔核几何特征因素之间的关系,并对其影响规律做了深入研究,为环状熔核质量的评估提供了依据.     

Optimization design of resistance spot welding parameters of magnesium alloy

By means of the quadratic regression combination design process, the regression equations of nugget diameter and tensile shear load of spot welded joint were established. Effects of welding parameters on the nugget diameter and the tensile shear load were investigated. The results show that effect of welding current on nugget diameter is the most evident. And higher welding current will result in bigger nugget diameter. Besides, interaction effect of electrode force and welding current on tensile shear load is the most evident compared with others. The optimum welding parameters corresponding to the maximum of tensile shear load have been obtained by programming using Matlab software, which is 4, 7 kN electrode force, 28 kA welding current and 4 cycle welding time. Under the condition of the optimum welding parameters, the joint having no visible defects can be obtained, nugget diameter and tensile shear load being 6. 8 mm and 3 256 N, respectively.     

Prediction of the failure mode of automotive steels resistance spot welds

ABSTRACT

In this study, the critical nugget size, at which the failure state in tensile shear test changed from the interfacial failure mode to the pull-out failure one, was estimated as a function of nugget and base metal hardness. The proposed approach could address the effect of various parameters involved in resistance spot welding process, such as sheet thickness, base metal chemical composition and physical properties of electrodes and sheets. The reliability of the present model was evaluated using independent experimental results. Based on the obtained results, the effect of steel composition on critical nugget diameter was found to be more important, especially for the sheets thicker than about 1?mm, whereas predicted nugget sizes by previous models could not guarantee the pull-out failure mode.