摘 要

激光焊接技术是20世纪80年代开始运用于汽车车身制造领域的一种技术，由于激光焊接具有热输入量精确可控、焊材变形小等优点，成为钢/铝等异种材料一种理想的焊接方法。本文首先综述了国内外钢/铝异种材料激光焊接工艺的研究进展，分析了不同工艺下接头金属间化合物的变化规律，探讨了其形成机理。通过上述方法的分析与总结，提出了恒定磁场辅助激光焊接的方法，以实现成形良好、性能优异的焊接接头。

本文采用搭接方式进行恒定磁场下钢/铝异种材料激光焊接，基于现有实验仪器搭建焊接平台，通过查阅相关的文献资料，制定出相应的实验方案。

借助金相显微镜、电子显微镜等仪器设备，研究不同磁场对1mm薄板焊接的影响规律，分析磁场下接头焊缝成形与组织变化过程，并借助于能谱分析对接头区元素分布进行研究，发现在熔合区与铝基体之间析出了多种金属间化合物如Fe₂Al₅、FeAl₃等，这些脆性金属件化合物的连续分布或半连续分布，会降低界面之间的作用力，诱导界面出现裂纹缺陷。

借助高温性能试验机进行接头力学性能进行评估，发现添加磁场后接头承载能力明显提高。接头的断口分析发现，断裂面处二次裂纹明显减少，局部出现撕裂，仅在断口处有韧性断裂，热影响区的热裂纹与界面处的富铝IMC相关。通过推测，这可能与界面处富Fe金属间化合物的形成有关，这些相具有良好的韧性，一定程度可以阻止位错的扩展，有效地提高接头的力学性能。

本文所设计的恒定磁场来辅助车身钢铝异种材料激光焊接，揭示了不同金属间化合物对接头力学性能的影响机制，可为异种材料高质量、高效率的激光焊接提供一定的理论指导。

关键词：磁场搅拌; 钢/铝异种材料; 金属间化合物; 激光焊接; 力学性能

Abstract

Laser welding technology has been applied in the field of automobile body manufacturing since the 1980s. Due to the advantages of accurate control of heat input and small deformation of welding materials, laser welding has become an ideal welding method for dissimilar materials such as steel/aluminum. In this paper, the research progress of laser welding process for steel/aluminum dissimilar materials at home and abroad is reviewed, the variation rules of intermetallic compounds in joints under different processes are analyzed, and the formation mechanism is discussed. Based on the analysis and summary of the above methods, the method of constant magnetic field assisted laser welding is proposed to realize the welding joint with good shape and excellent performance.

In this paper, laser welding of steel/aluminum dissimilar materials under constant magnetic field is carried out by means of lapping. The welding platform is built based on the existing experimental instruments, and the corresponding experimental scheme is formulated by referring to relevant literature.

By means of metallographic microscope, electron microscope and other instruments and equipment, study the effect of different magnetic field on the 1 mm thin plate welding, analysis of the magnetic field of weld joint and the organizational change process, and by means of spectral analysis of joint distribution study of the elements found in the fusion zone and precipitation between the variety of intermetallic compounds such as aluminum matrix Fe₂Al₅, FeAl₃ etc, these brittle metal compounds of continuous or semi-continuous distribution, can reduce the force of interface between the induced crack of interface defects.

The mechanical properties of the joint were evaluated by the high temperature performance testing machine. The fracture analysis of the joint showed that the secondary crack at the fracture surface was significantly reduced, and local tear occurred. Only the fracture site had ductile fracture, and the thermal crack in the heat-affected zone was related to the Aluminum-rich IMC at the interface. It is speculated that this may be related to the formation of Fe-rich intermetallic compounds at the interface. These phases have good toughness, which can prevent dislocation expansion to some extent and effectively improve the mechanical properties of the joint.

The constant magnetic field designed in this paper is used to assist the laser welding of dissimilar materials of steel and aluminum body, revealing the influence mechanism of different intermetallic compounds on the mechanical properties of joints, which can provide theoretical guidance for the high-quality and efficient laser welding of dissimilar materials.

Key words: Magnetic field stirring；Steel / Aluminum dissimilar materials；Intermetallic compounds；Laser welding；Mechanical properties

目 录

摘 要 I

Abstract II

第1章 绪论 1

1.1 研究背景与意义 1

1.1.1 研究背景 1

1.1.2 研究意义 2

1.2 国内外研究现状 2

1.3 研究内容与方法 4

1.3.1 研究内容 4

1.3.2 技术方案 5

第2章 实验平台搭建与实验方案 6

2.1 实验材料 6

2.2 实验设备 7

2.3 实验方案 9

2.3.1 实验方法 9

2.3.2 实验分析 10

2.4 本章小结 10

第3章 接头焊缝成形与显微组织 11

3.1 工艺参数对焊缝宏观成形的影响 11

3.2 接头金相组织 12

3.3 接头显微组织 14

3.3.1 接头微观形貌 14

3.3.2 接头区元素分布 15

3.3.3 接头区物相分析 16

3.4 本章小结 17

第4章 接头力学性能与断裂行为 19

4.1 接头力学性能 19

4.1.1 接头显微硬度 19

4.1.2 接头拉伸性能 20

4.2 接头断裂分析 21

4.3 本章小结 22

第5章 总结与展望 23

5.1 总结 23

5.2 展望 23

致 谢 24

参考文献 25

第1章 绪论

1.1 研究背景与意义

1.1.1 研究背景

轻量化是汽车未来的发展趋势，由于汽车车身约占整车质量的三分之一，要实现汽车轻量化应当从减轻车身质量出发。而熟知的轻质量材料铝合金则有以下几点优点：

（1）铝合金的重量相对钢材料大大减轻，在满足车身结构强度和刚度要求前提下，铝合金车辆比钢质车辆轻30%-50%；