【作者】 张海涛；

【导师】 王敏；

【作者基本信息】 上海交通大学 ， 材料加工工程， 2008， 硕士

【摘要】 双相钢是兼有高强度和良好成型性的理想汽车用钢,已成为未来发展轻质量高安全性汽车的主要材料。在汽车制造中,电阻点焊是主要的连接技术。与普通低碳钢相比,双相钢中加入了较多的Si、Mn等合金元素,在焊接时可能会出现成份偏析、淬硬脆化、易产生焊接缺陷等问题,因此通过实验确定合适的点焊工艺参数,制定合理的点焊规范将对双相钢在今后的广泛使用产生重要影响。而由于点焊熔核形成过程的不可见性,计算机模拟技术已经成为电阻点焊研究的主要方法。本文介绍了近年来国内外学者对双相钢电阻点焊的研究现状,以及计算机数值模拟技术用于点焊技术的发展。此外,还简单介绍了针对电阻焊特点开发的专业有限元软件SORPAS的特点和理论基础。基于SORPAS软件,针对DP590双相钢建立了描述点焊熔核形成过程的轴对称有限元模型,并实测了DP590双相钢的多项热物理性能参数。通过数值模拟定量揭示了双相钢点焊中温度场、电场、接触电阻等过程量的变化规律,并计算出双相钢点焊熔核直径、接头区域硬度、冷却速度及焊后组织的分布。对DP590双相钢板采用不同焊接规范进行多组点焊实验,测出不同规范下熔核直径大小、硬度分布,并通过拉剪、正拉实验得出焊点的力学性能,研究了焊接电流、焊接时间、电极压力对焊点熔核直径以及力学性能的影响规律,并对熔核进行宏观及微观金相分析,最后实测了DP590双相钢的焊接CCT曲线。将计算结果与实测结果进行了比较,验证了本文所建模型和计算结果的可靠性。应用SORPAS软件模拟各种参数组合下缓冷及回火过程,将计算所得到的最佳参数应用到实际中。通过拉伸实验、显微硬度实验以及断口扫描分析结果表明:对DP590双相钢附加恰当的缓冷或回火脉冲规范会使点焊接头的韧性有较大程度的提高。更多还原

【Abstract】 The dual-phase steel is the ideal automotive steel for its combination of high strength and excellent formability. It has being the main steel used in the automobiles of light weighting and high safety in the future. Resistance spot welding is the main jointing technique in the automobile manufacturing. Compared with normal low-carbon steel, the dual-phase steel is added to more alloying elements such as Si and Mn, so it is possible for the welding joint zone to result in problems like segregation, quench hardening embrittlement and prone to welding defects. Therefore, to be able to widely use the steel, it is very important to confirm suitable welding parameters and establish optimum spot welding specification. Numerical simulation has been the main research method in resistance spot welding since the forming process of nugget is hard to observe.The recent development of the research on the spot welding of dual phase steel and the application of numerical simulation on spot welding are introduced in this paper. Furthermore, characteristic and theoretical background of finite element software SORPAS which is specially designed for resistance welding are also briefly introduced.Based on the environment of software SORPAS, an axial symmetric finite element model for the spot welding process of DP590 dual-phase steel is established. Thermophysical properties parameters of DP590 are tested for this simulation. By researching numerical simulation, the variation rules of temperature field, electrical field and contact resistance are discovered quantitatively, and nugget diameter, distribution of hardness, cooling rate and microstructure of weld joint zone are calculated.Many groups of spot welding experiments of DP590 dual-phase steel with different welding specification are carried out. Nugget diameters and hardness distribution are measured under different combination of welding parameters, and mechanical properties of weld joint are gained by cross-tensile test and tensile-shear test. The effect rule of welding time, welding current and electrode force to nugget diameter and mechanical properties are researched. The SH-CCT curve of DP590 dual-phase steel is determined by practical experiment. Finally, the simulative results with the experimental results are compared, and the computational nugget diameter, shape and penetration agree well with those from experiments, which show that the models and simulation results in this paper are reliable.Using the software SORPAS to simulate slow cooling and tempering process under different combination of welding parameters, then put the optimum combination of parameters into practical spot welding experiment. By means of tensile test, hardness test and fracture scanning analysis, the results show that the toughness of spot weld joint of DP590 can be obviously improved by attaching suitable slow cooling impulse or tempering impulse specification.更多还原