导　　师： 龚金科

学科专业： 080201

授予学位： 博士

作　　者： ;

机构地区： 湖南大学

摘　　要： 800MPa级高强度镀锌钢板由于强度高、回弹小、成形性好和良好的抗腐蚀性等特点而成功地应用于白车身的高强度吸能件,如A-B-C柱加强板,门槛,座椅骨架,保险杠加强板,纵梁,横梁等方面。而能否解决高强度镀锌钢板的焊接问题,是关系到车身轻量化,安全性以及该钢种进一步应用的关键问题之一。所以,对其进行焊接性研究,具有重要的理论意义和工程实用价值。 激光焊接是实现高强度镀锌钢板高质量焊接的重要手段,本文首先在热传导温度场模拟研究的基础上,对高强度镀锌钢板以及高强度镀锌钢与普通冷轧钢的拼焊板进行了激光焊接的试验研究;其次在研究激光焊接热循环特征的基础上,对高强度镀锌钢板焊接接头的组织转变与晶粒长大规律进行了深入研究,着重分析了化学成分,晶粒尺寸及显微组织对焊接接头力学性能的综合影响。取得了如下主要结果: 1、建立了激光焊接的热传导数学模型,利用有限差分法对模型进行了求解。当功率较低时,激光焊接属于热传导焊接模式;随着激光功率的提高,当工件表面刚好出现汽化时,则处于热传导焊接向深熔焊接过渡的临界状态。这样,通过研究这种临界焊接状态的情况,得到了激光深熔焊接高强度镀锌钢板的下临界功率与焊接速度的关系。 2、在激光焊接高强度镀锌钢板试验研究的基础上,分析了激光焊接的工艺参数对深熔焊熔化特性的影响,得到本试验条件激光焊接的最优工艺参数。为保证拼焊板良好的机械性能,采用侧吹保护气体的方法能有效地控制镀锌层对焊接接头质量的影响,比较了N2和Ar作为侧吹辅助气体进行焊接时,其最大熔深,接头的硬度,韧性和焊接件的杯突值等方面的差异。检测焊接件的力学性能,腐蚀性能和微观组织后表明,用CO2连续激光焊接高强度镀锌钢可以有效地避免高强 High strength galvanized steel with 800MPa possesses characteristic of less spring-back, good formability, corrosion resistance. So it was extensive applied to high strength power-absorbing of initial body of car, such as A-B-C reinforced plate, door sill, seat skeleton, reinforced plate of bumper, carline, beam and so on. The welding of high strength steels is one of the critical problems to apply these steels. Therefore, research on the weld ability of high strength steels is of great signification in theoretical study and engineering practical value. laser welding is one key method to carry out the welding of high strength steels, in this paper, firstly on the base of the simulation of heat conduction temperature field, welding experiments are done to high strength galvanized steel and tailor-weld the high strength galvanized steel plate with cold-rolled plate; then based on the research of thermal cycling of laser welding, the grain growth and microstructure transformation of welding joint in laser welding of 800MPa grade high strength galvanized steel were studied, especially the combined influence of impurity element, grain size and microstructure on mechanical properties of the laser-welded joint was analyzed. The major conclusions are summarized as the followings: 1. Mathematic model of thermal conduction of laser welding was established in this paper, and it was calculated by using finite difference method /(FDM/). When laser power is lower, laser welding is belong to thermal conduction welding model; with the increasing of laser power, the surface happen to appear evaporation, then it transforms from thermal conduction welding model into deep penetration welding model. By studying the transition, the relation of critical power and welding speed in laser penetration welding of high strength galvanized steel is acquired. 2. On the basis of experiments of laser welding high strength galvanized steel, by analyzing the influence of technology parameter to laser penetration welding, optim

关 键 词： 高强度镀锌钢板 激光焊接 焊接性 显微组织 晶粒长大

领　　域： [机械工程] [交通运输工程] [交通运输工程] [金属学及工艺]