变形镁合金光纤激光及激光-mig复合焊接工艺特性的研究.pdf

华 中 科 技 大 学 硕 士 学 位 论 文 I 摘要镁及其合金是目前最轻的金属结构材料,在制造业具有很大的应用潜力。但是, 由于镁合金特殊的物理和化学特性导致焊接头性能下降,严重制约了其工业应用。如何提高镁合金焊接性能一直是镁工业重点研究的关键技术之一。对此,本文采用高功率光纤激光器开展了 AZ31B 变形镁合金激光焊及激光-MIG 复合焊接的工艺特性及接头性能研究,主要研究结果如下: 研究了光纤激光焊接工艺参数对 AZ31B 镁合金焊缝成形、显微组织特征和力学性能的影响。结果表明:光纤激光焊缝晶粒细小,热影响区窄。当焊接热输入小于 48J/mm 时,焊接接头均断裂于母材,焊接接头实际抗拉强度为 265MPa ,为母材的 113% 。而且,在本实验条件下,最小的接头抗拉强度也达到了母材的 % 。开展了 AZ31B 变形镁合金光纤激光-MIG 复合焊接研究,并得到了优化的工艺参数范围。研究表明:激光-MIG 复合焊通过填充材料,有效地弥补了光纤激光焊接存在的冶金缺陷。测试结果表明:光纤激光-MIG 复合焊熔深比激光焊提高了 10% , 接头强度达到母材的 104% ,高于轴快流 CO 2 激光-MIG 复合焊得到的接头强度。对 AZ31B 镁合金光纤激光焊接及其激光-MIG 复合焊接工艺进行了对比分析。结果表明:光纤激光-MIG 复合焊在减小气孔率方面更具优势,电弧的加入使得更多气泡逸出熔池,降低了焊缝气孔率。在优化的焊接参数下,可取得气孔率小于 % 的焊缝;接头断口均为准解理脆- 韧性混合断裂形式,主要表现为微孔聚合型韧性断裂及有少量准解理撕裂层。关键词: 镁合金 光纤激光 复合焊 显微组织 抗拉强度 气孔率华 中 科 技 大 学 硕 士 学 位 论 文 II Abstract Magnesium and its alloys are the wide used metallic structural materials due to the particular advantages, for example the low de nsity, high specific strength and excellent sound damping capabilities. However, some special physical and chemic characteristics such as low boiling temperature, high vapor pressure and big solidification shrinkage cause great challenges in the fusion welding of magnesium alloys. The main problems are the metallurgical defects, such as underfill, excess root ration, solidification crack, porosity and large distortion of the welded joints, which decrease the joint mechanical properties. Then, this paper aims to impr ove the welding properties of AZ31B wrought magnesium alloys by fiber laser and laser-ar c hybrid welding. The following are the main results obtained in present study. Fiber laser welding of AZ31B wrought magnesium alloy is carried out to reveal the effects of the welding parameters on bead shap e, microstructure and mechanical properties of welded joints, and the optimal welding parameters are obtaine d.. The good welds with fine grains, large aspect rati o and very narrow joints can be obtained. As the heat input reduces to 48 J/mm or lower,