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。     

热镀锌钢板点焊工艺研究

热镀锌钢板与普通低碳冷轧钢板相比,其点焊焊接性能显著恶化。研究了三个主要焊接参数（焊接电流、点焊时间及电极压力）对热镀锌钢板点焊质量和电极寿命的影响。试验表明：热镀锌钢板点焊时,焊接电流、焊接时间和电极压力较同等厚度的低碳冷轧钢板都有不同程度的提高;热镀锌钢板的点焊焊接规范调节区较窄;焊点质量对焊接规范特别是电流变化敏感。     

HC340LAD+ZM锌铝镁镀层钢板点焊接头组织与性能研究

采用正交实验确定了锌铝镁镀层钢板HC340LAD+ZM的最佳点焊工艺,利用拉剪实验、显微镜、SEM、硬度计等方法研究了焊接接头组织、性能的变化.结果表明,焊接参数对拉剪力影响的顺序分别为焊接电流、电极压力、焊接时间,最优点焊工艺为焊接电流10 kA、电极压力2.6 kN、焊接时间14 cy-cles;此工艺下焊接接头组...     

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。     

Si-Mn系超高强度热成形淬火钢板的点焊性能

 采用不同的点焊工艺参数对研发的1700MPa级Si-Mn系热成形淬火钢板与低碳钢板DC04进行异种材料之间点焊,并对焊接接头的拉伸性能、显微硬度分布及微观组织特征等进行了分析。结果表明,焊接电流对点焊接头熔核直径和抗剪强度具有显著的影响,而焊接时间的影响相对较小。超高强度钢板侧的热影响区存在两个明显的软化区和硬化区,即在靠近母材处存在一个硬度明显低于母材的软化区,其组织为回火马氏体;在靠近熔核处存在一个硬度明显高于母材的硬化区,其组织为细小的马氏体。点焊接头熔核部位为柱状粗大马氏体组织,其硬度明显低于超高强度钢板母材且远高于低碳钢板母材。低碳钢板热影响区低的硬度和明显粗化的铁素体组织,使得点焊接头单向拉伸时均从低碳钢板的热影响区一侧破断。     

MS1300超高强钢点焊焊接工艺研究

1000MPa以上超高强钢在国内应用越来越广泛。由于该级别钢材强度极高且碳当量高,使其焊接工艺制定非常困难。而点焊参数的选取对点焊质量控制显得尤为重要,为解决此类问题,特对MS1300超高强钢进行点焊工艺参数摸索,通过调整焊接电流和焊接时间,研究了不同的电阻点焊工艺参数对接头性能的影响。观察了焊接接头的微观组织,测试了接头的显微硬度。制定出最优焊接工艺窗口,为MS1300超高强钢在汽车上的应用提供数据支撑。     

超低碳钢与奥氏体不锈钢的电阻点焊

对超低碳钢与奥氏体不锈钢进行了点焊工艺及焊点性能试验，分析了影响点焊性能的因素，结果表明：钢板表面状态对焊接性能有较大的影响。     

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。     

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。     

模拟焊后轧制工艺对345 MPa级别中厚板性能的影响

对钢板模拟焊后性能的摸索可以为钢板焊接过程提供可靠的数据,指导焊接工艺的制定,减少焊接对钢板母材基体和焊缝处的影响,以保证产品在使用过程中的性能和寿命。不同的轧制工艺对提高钢板模拟焊后的性能及钢板的力学性能十分关键。因此,文中对比分析了精轧开轧温度和精轧累计变形量对中厚板力学性能、微观组织的影响,并在此基础上讨论了钢板模拟焊后性能的改善成因。通过降低精轧开轧温度和提高精轧累计变形量,可以细化组织、减轻钢板心部偏析和带状组织,提高钢板强韧性。     

SPCC冷轧钢胶焊连接工艺研究及数值模拟

 为了研究胶焊工艺对接头力学性能的影响，并分析胶焊接头的温度场演变规律，针对1.5 mm厚的SPCC冷轧钢薄板，开展胶接点焊和电阻点焊的正交试验，并应用极差和方差分析得到最佳工艺参数，借助材料性能试验机对两种接头进行单向静拉伸试验获得接头的失效载荷，对比分析点焊和胶焊接头的力学性能，建立胶焊接头的仿真模型，分析接头熔核区温度场的演变规律，采用超声波C扫描成像检测熔核直径。结果表明，影响胶焊接头拉剪载荷的主、次因素依次为焊接电流、焊接时间、电极压力；胶焊接头和点焊接头的平均失效载荷分别为11 071.12和10 179.72 N，胶层的引入提高了接头的失效载荷；随着焊接时间的增加，熔融的金属液增多，熔核沿着径向和轴向呈椭圆形扩张，熔核中心的径向温度均高于轴向温度，模拟获得的熔核尺寸与超声C扫描测得熔核直径分别为6.17、5.61 mm。     

Comparative study of resistance spot welding performance between cold-rolled DP980 and Q&P980 steels

Advanced high strength steel (AHSS) has been widely used in the automobile industry.The resistance spot welding performance of DP980 and Q&P980 steels was studied through comparing the two steels’welding current range,tensile shear strength (TSS),cross tension strength (CTS),weld spots’microhardness,etc.The following conclusions were achieved:It is easy for both DP980 and Q&P980 steels to get a nugget size bigger than 4 mm,they all have welding current ranges exceeding 2 kA and high weld strength.     

电极端面尺寸对IF钢镀锌板点焊性能的影响

对DX54D冷轧IF钢镀锌板进行点焊试验,研究了焊接工艺参数及电极端面尺寸对镀锌板点焊性能、焊点拉剪性能及熔核尺寸的影响。结果表明:随着焊接电流的增加,焊点的拉剪强度和熔核尺寸均增大,当电流过大而发生飞溅时,焊点的拉剪强度和熔核尺寸开始降低。随着电极端面半径的减小,电极与工件的实际接触面积减小,引起电流密度升高,导致在相同焊接时间条件下得到相同熔核尺寸和焊点拉剪强度所需焊接电流降低。     

High cycle fatigue behavior of DP980 steel and DP980 steel laser welded joints

For the study of the DP980 steel high cycle fatigue property, high fatigue tests of DP980 steel and DP980 steel laser welded joints were carried out with fatigue testing machine, the Basquin equation was concluded. Microstructures and fractures were analyzed by optical microscope and scanning electron microscope. The results show that DP980 steel laser welding joints have the weld concavity at the welding root and top, the quality of welded joints is medium. The fatigue limit of DP980 steel is 341MPa, the fatigue limit of DP980 steel laser welded joint is 148MPa, the fatigue limit decreases by 50% compared with the fatigue limit of the base metal. For DP980 steel, the crystal boundary of the ferrite/martensite is the main location of micro cracks initiation, the fatigue fracture of DP980 steel is the quasi cleavage fracture. For DP980 steel laser welding joints, the fatigue cracks initiation is located in the weld concavity, not in the heat affected zone, the fatigue fracture is cleavage fracture. DP980 steel and DP980 steel laser welding joints crack propagation is characterized by the obviously fatigue striations coupled with secondary cracks.     

DP980钢及DP980钢激光焊接接头的高周疲劳性能

摘要：为了研究DP980钢的高周疲劳性能,采用疲劳试验机对DP980钢和DP980钢激光焊接接头进行高周疲劳试验,得到Basquin方程,并利用光学金相显微镜和扫描电镜进行组织和断口分析。结果表明：DP980钢激光焊接接头的焊缝根部和顶部出现形状凹陷,焊接接头的质量为中等。DP980钢疲劳极限为341MPa,DP980钢激光焊接接头的疲劳极限为148MPa,激光焊接接头的疲劳极限较母材的疲劳极限降低约50%。对于DP980钢而言,铁素体/马氏体晶界是裂纹萌生的主要位置,疲劳断口为准解理断口。对于DP980钢激光焊接接头而言,疲劳裂纹源位于焊缝凹陷处,而非热影响区及母材,疲劳断口为解理断口。DP980钢和DP980钢激光焊接接头的疲劳裂纹扩展区均有明显的疲劳条带,并伴随有二次裂纹。     

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.     

Resistance spot welding of precoated steel sheet: Computational heat-transfer analysis

The heat-transfer phenomenon during the resistance spot welding of the precoated steel sheet, consisting of a thin organic coating coated on a steel sheet, has been investigated theoretically using a two-dimensional finite-element heat-transfer model. Material parameters such as the thermal conductivity of the coating and the thickness of the sheet were varied under various welding conditions in order to optimize the welding process. These welding parameters included the contact resistance at the steel/steel interface, the welding current, and the welding time. The effect of these material and welding parameters on the weldability was demonstrated; the selection criteria for the organic coating and accompanying welding conditions were proposed from this study.     

Improvement of weldability of TRIP steels by use of in‐situ pre‐ and post‐heat treatments

Low alloy TRIP‐aided steels are very interesting for the automotive industry as they combine both a high strength and an excellent formability. Though the actually developed TRIP steels can be considered as low alloyed when compared to the first generations of steels exhibiting TRIP effect, due to their chemical composition, they still exhibit a quite high carbon equivalent. This is particularly detrimental for the weldability of those materials. After solidification, welds are very hard and can show a brittle behaviour. The hardness of the heat affected zone of the welds can even exceed 500HV and cold cracking phenomena is prone to occur. In the automotive industry, spot welding is the main joining process. During spot welding of TRIP steels, the interface between the plates can act like a notch and promote fracture of the weld. This is particularly dangerous when brittle welds are submitted to peel stresses. The aim of the paper is to demonstrate that a careful choice of the process parameters can significantly improve the resistance of the welds. The selection of the welding cycle parameters is far from being an easy task as many different parameters are involved. Therefore, a design of experiment methodology (DOE) was chosen to optimise the welding cycle for a cold‐rolled TRIP steel with a tensile strength above 700 MPa. Mechanical properties of the welds were significantly improved by use of pre‐ and post‐heat treatments. Those improved welding cycles were realised without excessive extension of the total weld cycle on a conventional spot welding machine. This means that the optimised welds can be obtained in the existing production lines without any additional investment or significant decrease in productivity.