SAPH440酸洗板电阻点焊工艺研究

以2.0 mm厚SAPH440酸洗板为研究对象,通过检测点焊接头的抗剪性能及十字拉伸性能,综合评价接头的力学性能,并使用Axio Obersver A1m型光学显微镜观察点焊接头显微组织,测量熔核直径,分析焊接电流对熔核直径的影响,创建点焊工艺窗口。结果表明:酸洗板点焊工艺窗口为8.5 kA至12 kA,宽度3.5 kA,接头熔核直径及力学性能与焊接电流呈正相关,当出现飞溅后,熔核直径与力学性能略微下降,熔核区与热影响区组织均为马氏体,受焊接热循环的影响,熔核区组织为粗大柱状,热影响区组织为细小针状。     

1200MPa级双相钢电阻点焊接头失效原因

对厚度1.4 mm、1200 MPa高强双相钢进行了电阻点焊工艺试验,结合拉伸试验结果,分析了接头界面断裂及纽扣断裂失效的原因.结果表明:相同焊接工艺下,纽扣断裂吸能效果较好,高达45 kJ左右.缩孔类焊接缺陷的存在会导致接头结合面处可承受的极限剪切力降低,实际熔核直径变小,裂纹容易在此处萌生,倾向于界面断裂失效;焊核...     

热镀锌DP780电阻点焊工艺研究

研究了热镀锌DP780电阻点焊性能,并优化其点焊参数。通过测量焊接接头的熔核直径、熔透率、压痕深度,观察焊接接头显微组织,检测焊接接头硬度、抗剪力及正拉力等参数,综合评价热镀锌DP780点焊性能。结果表明:DP780热镀锌板因其合金含量高的特点,点焊性能良好,但焊接工艺窗口较窄。当电极压力为3.5 k N,焊接电流为9.5 k A时,最佳焊接时间为300~400 ms,当焊接电流为10.5~11.5 k A时,焊接时间在200~400 ms均可。DP780热镀锌板点焊接头显微组织为马氏体和铁素体,这种焊接接头的组织决定了其塑性比仅有8%~30%,接头硬度值稍高。焊点的失效形式均为熔核剥离失效。     

DP590双相钢电阻点焊及其动态力学性能研究

针对高强度汽车板焊接质量差的问题,本文采用电阻点焊对DP590双相钢进行焊接,研究了DP590双相钢点焊的接头组织和力学性能。实验结果表明,采用合适的点焊工艺,可以实现DP600电阻点焊。随着焊接电流的增大,DP590双相钢电阻点焊接头熔核直径和剪切力先增大后减小。加载速率越快,塑性变形速度越快,变形后材料储能越高,应变硬化率越高,接头拉剪力提高。     

电阻点焊接头力学性能的优化

利用正交试验法对CR820/1180DP钢电阻点焊电极压力、焊接电流和焊接时间3个主要因素进行了优化,并对点焊接头力学性能进行了研究。正交试验结果表明,影响点焊接头力学性能因素的优先顺序为电极压力、焊接电流和焊接时间;优化后的焊接工艺组合为:电极压力4. 1 k N,焊接电流8. 6 k A,焊接时间240 ms。优化焊接工艺下的点焊接头显微组织分析结果显示,点焊接头主要由熔核区、热影响区和母材3部分组成。其中,熔核区主要是板条马氏体,热影响区细分为H1,H2,H3和H4 4个区域,各区域组织分别为粗晶马氏体、细晶马氏体+贝氏体以及部分残奥,贝氏体+马氏体混合组织,铁素体+马氏体组织且表现回复组织特征。硬度结果表明,接头力学性能均匀,无明显的软化区和脆化点。     

TC4/6061异种金属电阻点焊接头组织与性能研究

采用2mm厚的TC4钛合金和1.5 mm厚的6061铝合金进行电阻点焊,研究焊接热量与时间对接头拉剪力与熔核直径的影响,观察接头断裂特征并对接头进行了显微组织分析.试验结果表明:热影响区和熔核区的晶粒尺寸相对母材区变得粗大,靠近熔核的6061侧热影响区出现晶粒长大,TC4侧组织出现了细小的针状α'马氏体组织,并呈一定位向排列.随着焊接热量的增加,接头的拉剪力和焊核直径逐渐增加,随着焊接时间增加,接头的拉剪力和熔核直径先增加后减小;当Q=600 J时,接头的拉剪力最高,为1.17 kN.接头靠6061侧显微硬度无明显变化,靠TC4侧熔核区与热影响区硬度分布不均匀,当Q=550 J,t=10s时硬度分布较理想.试验数据为钛/铝异种金属点焊提供理论指导.     

超高强热成型钢板的点焊工艺性能研究

对试验用超高强热成型钢的电阻点焊工艺进行了研究,探讨了焊接电流对点焊接头压痕深度、焊核直径、焊透率以及拉断力的影响规律,讨论了电流模式对点焊试样断裂点位置和中心偏析的影响,分析了焊接接头软化区、中心偏析的原因。研究结果表明,该钢种具有良好的点焊性能。     

TRIP600 高强钢的点焊工艺研究

对1．8mm规格的TRIP600钢进行了点焊试验、拉剪试验和接头的金相分析,研究了焊接电流、焊接时间等点焊工艺参数对接头力学性能的影响。结果表明,焊接时间为0．20、0．24、0．30S,TRIP600钢的可焊电流范围分别为11-12、10．5～12、10-11．5kA,拉剪试验失效模式为扣式或母材撕裂、且无飞溅的焊点,拉剪力达到27-30kN。     

汽车用高强TWIP980钢板点焊工艺研究

采用中频逆变点焊机对1.8 mm厚TWIP980钢板进行了点焊工艺研究,分析了焊接工艺参数对钢板点焊性能的影响规律,确定了TWIP980钢板的点焊工艺参数和焊接工艺窗口。结果表明:焊前预热200 ms的工艺可以避免产生焊接飞溅,焊后锻压工艺明显增加了熔核尺寸和焊点强度,消除了缩孔缺陷,扩大了焊接工艺参数的调节范围。     

汽车用高强TWIP980钢板点焊工艺研究

采用中频逆变点焊机对1．8mm厚TWIP980钢板进行了点焊工艺研究,分析了焊接工艺参数对钢板点焊性能的影响规律,确定了TWIP980钢板的点焊工艺参数和焊接工艺窗口。结果表明：焊前预热200ms的工艺可以避免产生焊接飞溅,焊后锻压工艺明显增加了熔核尺寸和焊点强度,消除了缩孔缺陷,扩大了焊接工艺参数的调节范围。     

Weldability Evaluation and Microstructure Analysis of Resistance‐Spot‐Welded High‐Mn Steel in Automotive Application

In this paper, resistance spot weldability of high‐Mn steels were investigated in order to get high reliability in welded joints of automotive components. Microstructural characterizations, cross‐tensile test (CTT), microhardness tests of spot welded parts were conducted. The effects of weld current on the microstructural characteristics, mechanical properties, and fracture modes were investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The hardness in the weld nugget was observed to be lower than that in the base metal (BM). In CTT, the failure initiation was observed to occur at the boundary of the weld nugget. Also welding imperfections of welded parts were investigated. Liquation cracking in heat affected zone (HAZ), porosity, and shrinkage cavity were found most common welding defects in welded parts. Furthermore, the effects of welding imperfections on weld quality and failure criteria were identified and discussed.     

A study on weldability of zinc-coated steel sheets in lap joint configuration

The weldability of Zn-coated steel sheets 0.7 mm thick was investigated using resistance spot welding process. The effect of welding current, welding time and holding time on weld nugget characteristics, microstructure, and mechanical properties was discussed. Then, the possibility of replacing this welding process with laser beam welding was outlined. In this respect, quality of weld joints as a function of zinc removal by grinding prior to welding was evaluated. It is found that resistance spot welding current and time are the most significant parameters in affecting both expulsion and Zn-induced porosity. Expulsion was avoided and Zn-induced porosity was reduced with the decrease in welding current and/or welding time. Zn-induced porosity was completely eliminated by zinc-removal by grinding prior to welding. The best weld joint concerning nugget characteristics, soundness and tensile shear strength was obtained using welding current of 10 kA, weld cycle of 20, holding cycle of 18. Unlike resistance spot welds, high quality of CO₂ laser welds free from Zn-induced porosity could be made without zinc removal by grinding before welding.     

Peak load and energy absorption of DP600 advanced steel resistance spot welds

The paper aims at investigating the microstructure, failure mode transition, peak load and energy absorption of DP600 dual phase steel during the tensile-shear test. It was found that the welding current has profound effect on the load–displacement characteristics. In the low welding current, welds failed in interfacial failure mode. Increasing welding current resulted in sufficient weld nugget growth to promote double-sided pullout failure mode with improved mechanical properties. Further increase in the welding current caused expulsion and failure mode was changed to single-sided pullout with reduced energy absorption capability. It was found that the fusion zone size is the key parameter controlling the mechanical properties of DP600 resistance spot welds in terms of peak load, maximum displacement and failure energy.     

A Study on Friction Stir Multi Spot Welding Techniques to Join Commercial Pure Aluminum and Mild Steel Sheets

To achieve significant improvement in the shear strength of dissimilar joints between aluminum and mild steel sheets, four methods of friction stir multi-spot welding processes, were investigated. Initially, in all these methods, plasticized aluminum layer was deposited on the steel side by friction surfacing. Subsequently, the deposited aluminum was compacted by friction forming. After dressing, spot welding with different tool configurations was performed. Tool rotational speeds of 900, 1120, 1400 and 1800 rpm were used to analyze their effects on the weld nugget. Different mechanical and metallurgical characterizations were done on the welds thus made. The process with aluminum layer on grooved mild steel followed by friction stir multi-spot welding using concave tipped welding tool resulted in welds. These welds had better metallurgical bonding characteristics and higher shear strength, which at a rotational speed of 1120 rpm was more than twice that of the welds made with conventional friction stir spot welding.     

Effect of Welding Current and Time on the Microstructure,Mechanical Characterizations,and Fracture Studies of Resistance Spot Welding Joints of AISI 316L Austenitic Stainless Steel

This article aims at investigating the effect of welding parameters, namely, welding current and welding time, on resistance spot welding (RSW) of the AISI 316L austenitic stainless steel sheets. The influence of welding current and welding time on the weld properties including the weld nugget diameter or fusion zone, tensile-shear load-bearing capacity of welded materials, failure modes, energy absorption, and microstructure of welded nuggets was precisely considered. Microstructural studies and mechanical properties showed that the region between interfacial to pullout mode transition and expulsion limit is defined as the optimum welding condition. Electron microscopic studies indicated different types of delta ferrite in welded nuggets including skeletal, acicular, and lathy delta ferrite morphologies as a result of nonequilibrium phases, which can be attributed to a fast cooling rate in the RSW process. These morphologies were explained based on Shaeffler, WRC-1992, and pseudo-binary phase diagrams. The optimum microstructure and mechanical properties were achieved with 8-kA welding current and 4-cycle welding time in which maximum tensile-shear load-bearing capacity or peak load of the welded materials was obtained at 8070 N, and the failure mode took place as button pullout with tearing from the base metal. Finally, fracture surface studies indicated that elongated dimples appeared on the surface as a result of ductile fracture in the sample welded in the optimum welding condition.     

Metallurgical and Mechanical Characterization of Laser Spot Welded Low Carbon Steel Sheets

This paper aims at investigating metallurgical and mechanical characterization of low carbon steel laser spot welds. Microstructural examinations, microhardness tests and quasi‐static tensile‐shear tests were preformed. Mechanical properties of the welds were described in terms of peak load and failure mode. The effects of laser spot welding parameters including pulse frequency, laser energy, welding speed, pulse width and welded circle diameter, on low carbon steel laser spot weld performance were studied using the Taguchi design of experiment method. It was found that the effective laser pulse energy is the controlling factor in the determination of mechanical strength of laser spot welds.     

焊接钢管高频感应加热的残余应力和组织演变

 随着中国钢铁、冶金与电磁等交叉学科的快速发展，焊接钢管产量及质量日益提升。高频感应加热是生产焊接钢管的核心工序，获取更加精确的焊管高频加热过程的应力分布和微观组织演化规律，是进一步提升焊管品质的关键要素和学者们关切的问题。综合考虑热传导和微观组织转变对应力的影响，针对高频焊管特有的沙漏形热源形貌，定量分析了焊接热影响区微观组织演变过程和残余应力的分布规律，获得了考虑热应力和组织应力的残余应力分布。发现该应力特点为在焊缝附近轴向残余应力较大，最大等效残余应力出现在距焊缝中心1/2壁厚处的热影响区，在壁厚方向管材内部的中间层的残余应力较大，且应力分布与反映高频焊接热源形貌特征的加热温度峰值和加热温度宽度相关。而在焊缝中心处，未考虑组织变化的等效残余应力值是考虑组织变化的1.3倍。掌握焊管高频焊接应力和组织演变的特点和规律，可为优化高频焊接工艺提供理论依据，对提升高频焊管质量具有重要意义。     

Characterization Method of Mechanical Properties of Dissimilar Steel Resistance Plug Welding Joints

A novel resistance plug welding process has wide prospects for dissimilar steel. However, until present, there is no effective method to characterize the mechanical properties of resistance plug welding joints. In this paper, the influence factors such as diameter of filler, diameter of surface plastic ring, and diameter of nugget were first used for analysis. Slug ratio and indentation depth (height) ratio were designed to characterize the mechanical properties of the resistance plug welding joints. The results show that smaller the slug ratio, better the mechanical properties of the joint. The tensile shear load of the joint is higher when the indentation depth (height) ratio is 92–102%, and the joint has the best tensile shear load when the indentation depth (height) ratio is 96% or 97% in this study. Slug ratio and indentation depth (height) ratio are suitable for characterizing mechanical properties of dissimilar steel resistance plug welding joints.     

Comparing Properties of Adhesive Bonding, Resistance Spot Welding, and Adhesive Weld Bonding of Coated and Uncoated DP 600 Steel

 Zinc coated dual phase 600 steel (DP 600 grade) was investigated, utilisation of which has gradually increased with each passing day in the automotive industry. The adhesive bonding (AB), resistance spot welding (RSW), and adhesive weld bonding (AWB) joints of the zinc coated DP 600 steel were investigated. Additionally, the zinc coating was removed using HCL acid in order to investigate the effect of the coating. The microstructure, tensile shear strengths, and fracture properties of adhesive bonding (AB), resistance spot welding (RSW), and adhesive weld bonding (AWB) joints of the coated and uncoated DP 600 steel were compared. In addition, a mechanical-electrical-thermal coupled model in a finite element analysis environment was utilised. The thermal profile phenomenon was calculated by simulating this process. The results of the tensile shear test indicated that the tensile load bearing capacity (TLBC) values of the coated specimens among the three welding methods were higher than those of the uncoated specimens. Additionally, the tensile strength of the AWB joints of the coated and uncoated specimens was higher than that of the AB and RSW joints. It was determined that the fracture behaviours and the deformation caused were different for the three welding methods.     

Characterization of Loading Responses and Failure Loci of a Boron Steel Spot Weld

Boron steel, classed as an ultra high-strength steel (UHSS), has been utilized in anti-intrusion systems in automobiles, providing high strength and weight-saving potential through gage reduction. UHSS spot welds exhibit unique hardness distributions, with a hard nugget and outlying base material, but with a soft heat-affected zone in-between these regions. This soft zone reduces the strength of the weld and makes it susceptible to failure. Due to the interaction of various weld zones that occurs during loading, there is a need to characterize the loading response of the weld for accurate failure predictions. The loading response of certain weld zones, as well as failure loci, was obtained through physical simulation of the welding process. The results showed a significant difference in mechanical behavior through the weld length. An important result is that instrumented indentation was shown to be a valid, quantitative method for verifying the accuracy with which weld microstructure has been recreated with regard to the target weld microstructure.