镁合金激光焊接焊缝微观组织分析（本科毕业论文设计）.doc

摘 要

本试验用光学显微镜，扫描电镜以及能谱分析对变形镁合金AZ61ND:YAG脉冲激光焊接接头微观组织和缺陷进行了详细的研究。结果表明:脉冲激光焊接焊接镁合金AZ61能够得到缺陷较少的焊缝，同时焊接线能量对微观组织的变化和缺陷的形成有很大的影响。
实验结果表明：热影响区的宽度在焊接线能量较小时很窄，但是随着线能量的增加热影响区的宽度也随着增加，而且在焊缝区还存在着具有一定宽度的层状偏析。另外焊缝中也出现了热裂纹和气孔等缺陷：镁合金AZ61的脉冲激光焊接焊缝对热裂纹敏感性很强，几乎每个焊缝都出现了不同程度的热裂纹，而气孔则主要为氢气孔，并且随着线能量的增加凝固裂纹减少液化裂纹增多气孔也随着减少，在焊接线能量为87J/mm时焊缝中缺陷较少。


关键词：镁合金，激光焊接，微观组织

ABSTRACT

Optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to analyze the microstructure and defect of wrought AZ61magnesium alloy joint welded by ND:YAG pulse laser. The results show that defect-free welding seam of the AZ61magnesium alloy can be achieved by use of pulse laser welding and the welding heat input influenced the microstructure and the defect distribution of alloy joint greatly.
The experiments show that the width of the heat affect zone (HAZ) was narrow when the heat input was low while it increased with the increase of heat input. Layer-like segregations were presented in the weld seam. In addition, hot cracks and pores were formed in the weld seam. The presence of hot cracks almost in every weld seam indicated hot cracks were easy to form in AZ61magnesium alloy joint during pulse laser welding. The number of the hydrogen pores, which is the major pore formed in alloy joint, reduced with the increase of heat input in pulse laser welding. The best alloy joint with most few defects was obtained when the heat input of pulse laser welding about 87 J/mm.


Key words: magnesium alloy, laser welding, microstructure

目 录

中文摘要 Ⅰ
ABSTRACT Ⅱ
1绪论 1
1.1镁及镁合金性能与应用前景 1
1.2 镁合金加工（成型）技术的现状与发展 3
1.3 激光技术及激光焊接 5
1.4 激光焊接技术发展趋势和展望 6
2 实验 9
2.1 实验材料 9
2.2 实验设备 9
2.3 实验原理 11
2.3.1 激光焊接原理 11
2.3.2 扫描电子显微镜（SEM）及工作原理 13
2.4 实验工艺及样品的制备 14
2.4.1 实验工艺 14
2.4.2 样品的制备 15
3 实验结果的分析及讨论 16
3.1激光焊接焊缝成型分析 16
3.1.1 焊接接头的宏观结构 16
3.1.2 焊接接头的微观组织 17
3.1.3 线能量对微观组织的影响 19
3.2激光焊接焊缝微观组织缺陷分析 20
3.2.1 气孔 22
3.2.2 裂纹 23
3.2.3 元素损耗 24
3.2.4 层状偏析 25
3.3关于缺陷的预防的讨论 25
4 结论 28
参考文献 29