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毕业论文网 > 毕业论文 > 机械机电类 > 汽车服务工程 > 正文

车身薄板铝钢异种金属磁场辅助激光熔钎焊工艺研究毕业论文

 2021-11-06 20:14:57  

摘 要

随着人类汽车工业的发展,能源问题也日渐凸显,降低车身质量可以有效减少汽车的能耗,实现铝/钢异种金属的有效可靠连接能够大幅度的减少整车质量,从而达到节能减排的目的。但是由于铝、钢两种金属在物理和化学性质上有着较大差异,并且在冶金反应时会生成金属间化合物(IMCs),这种脆性相会使接头性能恶化。因此,如何调控金属间化合物的形成和生长就成为了铝/钢异种金属研究的重点之一。国内外的研究表明,在进行铝/钢异种金属焊接时,使用激光熔钎焊并添加合金元素能够有效调节界面反应层的微观结构和成分,但无法有效解决焊缝区的组织偏析。基于此,提出磁场辅助激光熔钎焊方法,利用磁场对熔池的搅拌作用解决上述问题。

本文介绍了利用外加辅助磁场将铝合金与钢材进行激光熔钎焊的实验。利用扫描电子显微镜、能量衍射谱和X射线衍射仪等设备对界面的形貌、微观结构和相变进行了深入的研究,在此基础上讨论了钢/铝焊缝的强化机理。

研究发现,填充金属中Zn元素不仅可以提高熔融金属在钢表面的润湿铺展性,而且还可以在钢界面处生成η-Al5Fe2Zn0.4相和δ-FeZn10相。这些非脆性相具有良好的延展性,可以有效降低焊缝区热裂纹敏感性,改善界面连接行为。研究还发现,由于Al基体的溶解和安培力的调控,在钢界面处形成带状组织,而在Al基体附近形成了细小的柱状组织以及少量的等轴晶组织。界面处的冶金反应主要分为三个阶段:溶质迁移过程、非脆性相的萌生和生长。磁场对熔池的驱动效应可以有效地控制Zn-Al共晶相等非脆性相的尺寸和分布,大大提高了界面力学性能。

关键词: 激光熔钎焊;磁场;铝/钢焊缝;强化机理;界面结构

Abstract

With the development of the human automobile industry, energy problems are becoming more and more prominent. Reducing the quality of the body can effectively reduce the energy consumption of the car, and achieving the effective and reliable connection of aluminum / steel dissimilar metals can greatly reduce the quality of the vehicle, thereby achieving energy saving purpose. However, due to the large difference in physical and chemical properties of aluminum and steel, and the formation of intermetallic compounds (IMCs) during metallurgical reactions, this brittle phase will deteriorate the performance of the joint. Therefore, how to regulate the formation and growth of intermetallic compounds has become one of the focuses of the research on aluminum / steel dissimilar metals. Research at home and abroad shows that when welding aluminum / steel dissimilar metals, the use of laser brazing and the addition of alloy elements can effectively adjust the microstructure and composition of the interface reaction layer, but cannot effectively solve the structural segregation of the weld zone. Based on this, a magnetic field assisted laser fusion brazing method is proposed, which utilizes the magnetic field to stir the molten pool to solve the above problems.

This paper introduces the experiment of laser welding of aluminum alloy and steel by using an external auxiliary magnetic field. Scanning electron microscope, energy diffraction spectrum and X-ray diffractometer were used to conduct in-depth study on the interface morphology, microstructure and phase transition, and the strengthening mechanism of the steel / aluminum weld was discussed again. The study found that the Zn element in the filler metal can not only improve the wettability of the molten metal on the steel surface, but also generate η-Al5Fe2Zn0.4 phase and δ-FeZn10 phase at the steel interface. These non-brittle phases have good ductility, which can effectively reduce the thermal crack sensitivity of the weld zone and improve the interface connection behavior.

The study also found that due to the dissolution of the Al matrix and the adjustment of the ampere force, a band structure was formed at the steel interface, and a small columnar structure and a small amount of equiaxed crystal structure were formed near the Al matrix. The metallurgical reaction at the interface is mainly divided into three stages: solute migration process, initiation and growth of non-brittle phase. The driving effect of the magnetic field on the molten pool can effectively control the size and distribution of the Zn-Al eutectic equivalent non-brittle phase, which greatly improves the interface mechanical properties.

Key words: Laser fusion brazing; Magnetic field; Aluminum/steel weld; Strengthening mechanism; Interface structure

目 录

摘 要 II

Abstract III

第1章 绪论 1

1.1选题背景及研究意义 1

1.1.1 选题背景 1

1.1.2 选题意义及目的 2

1.2 国内外研究现状 2

1.2.1 国内研究现状 2

1.2.2 国外研究现状 3

1.3 研究内容及方法 3

1.3.1 研究内容 3

1.3.2 研究方案 4

第2章 实验方案及实验平台搭建 5

2.1 实验材料 5

2.2 实验设备 5

2.2.1 焊接设备 5

2.2.2 交变磁场辅助装置 6

2.3 试验方案 7

2.3.1 焊前准备 7

2.3.2 实验方法 7

2.3.3 实验分析 8

2.4 本章小结 10

第3章 铝/钢异种金属接头焊缝成形与显微组织 11

3.1 焊缝宏观成形 11

3.1.1 工艺参数对焊缝宏观形貌的影响 11

3.1.2 工艺参数对焊缝润湿性的影响 12

3.2 接头的金相组织 13

3.3 接头的显微组织 14

3.3.1 接头的微观型貌 14

3.3.2 接头区元素分布 15

3.3.3 接头区的物相分析 18

3.4 本章小结 19

第4章 接头力学性能与断裂分析 20

4.1 接头拉伸性能 20

4.2 接头断裂分析 21

4.3 接头强化机理 21

4.4 本章小结 23

第5章 总结与展望 24

5.1 总结 24

5.2 展望 24

致 谢 25

参考文献 26

第1章 绪论

1.1 选题背景及研究意义

1.1.1 选题背景

汽车轻量化研究正受到越来越多的人关注,目前主要有两种途径来减轻车身重量[1]:第一种是借助先进的车身制造工艺,如液压成型、激光焊接等,第二种是在车身上应用轻量化材料,如镁、铝合金、复合材料、高强度钢等。铝合金因为其优异的比强度、良好的塑性和优良的耐腐蚀性等特点,被认为是可以代替传统车身钢材的理想材料[2]。当前,使用6000系列铝合金作为车身材料已成为主流趋势。但是,所有铝制车身框架的设计和制造成本都很高,并且安全系数不如钢制车身。因此,综合考虑经济和安全性时,便出现了铝-钢一体化车身结构的愿景。

铝与钢在熔点、密度、热导率等诸多物理性能上存在差异(表1.1),这就容易导致焊接过程不稳定,产生热应力以及变形等问题;此外,在化学性能方面,铝和钢在在焊接中会形成金属间化合物(简称IMCs),导致接头力学性能大幅下降,难以形成Al-Fe异种金属的有效连接。

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