7XXX铝合金搅拌摩擦焊焊接接头组织与性能研究

发布时间：2018-03-04 12:15

本文选题：7XXX铝合金　切入点：搅拌摩擦焊　出处：《北京交通大学》2017年硕士论文　论文类型：学位论文

【摘要】：某7XXX铝合金具有比强度高、力学性能好等特点,是高速列车侧墙、枕梁等结构件常用材料。目前国内外关于该7XXX铝合金组织性能的研究较少,然而接头组织性能的研究可以为工艺参数的选择提供理论支持,从而提高企业焊接产品质量。本文将对15mm厚度的某7XXX铝合金搅拌摩擦焊焊缝成形机理、焊接接头组织形貌及第二相特征进行研究,并分析组织对焊接接头力学性能的影响。本文研究内容及成果如下:(1)从焊接热输入和材料流动行为两方面对焊缝的成形机理进行了研究,并探讨了焊接工艺参数对焊缝成形质量的影响。(2)通过目视检验和X射线检测法比选出了无焊接缺陷的工艺参数。焊接速度为200 mm/min,转速为 300 rpm、400 rpm;焊接速度为 300 mm/min,转速为 400 rpm,两组参数下均能得到无缺陷焊接接头。(3)利用光学显微镜,分析了无焊接缺陷的焊接接头不同区域组织形貌特点。沿水平方向,焊接接头各区域组织形貌差别较大,焊核区为细小等轴晶,热机影响区组织发生明显的弯曲变形,热影响区为粗化的板条组织。(4)利用扫描电镜和能谱仪,分析了无焊接缺陷的焊接接头不同区域第二相特征。母材第二相包括大量不溶杂质相AlMnSiFe、固溶体Al6(FeMn)和少量强化相T(Al2Mg3Zn3)、η(MgZn2),焊核区强化相发生析出。(5)基于显微硬度计测试结果,分析了焊接接头的显微硬度特征。焊核区硬度与母材区硬度值大致相当,平均值约121HV;热影响区硬度值125HV～140HV左右。以焊缝中心为界,AS侧热机影响区硬度值有突变现象;RS侧硬度值从焊核区到热影响区方向逐渐升高。(6)基于万能拉伸试验机、断口形貌分析、残余应力等测试结果,分析了焊接接头的拉伸性能。焊接接头平均拉伸强度为403MPa,断后伸长率为16.3%。焊接接头断裂位置位于AS侧热影响区,沿45°方向切断,断口呈纤维状,属于韧性断裂。本文主要研究了某7XXX铝合金搅拌摩擦焊焊接接头组织和力学性能。通过理论与试验相结合的方法,分析了接头工艺参数对焊缝成形的影响;焊接接头组织形貌特点和第二相特征;组织对力学性能的影响。研究成果对指导企业选择出合理的焊接工艺参数,提高搅拌摩擦焊焊缝质量具有重要意义。
[Abstract]:A certain 7XXX aluminum alloy has the characteristics of high specific strength, good mechanical properties and so on. It is a common material for the side wall and pillow beam of high-speed train. At present, there are few researches on the microstructure and properties of the 7XXX aluminum alloy at home and abroad. However, the study of the microstructure and properties of the joints can provide theoretical support for the selection of process parameters and improve the quality of welding products in the enterprise. In this paper, the mechanism of weld formation of a 7XXX aluminum alloy with 15mm thickness friction stir welding is studied. The microstructure and phase characteristics of welded joints were studied. The effect of microstructure on the mechanical properties of welded joints is analyzed. The research contents and results are as follows: 1) the mechanism of weld forming is studied from the aspects of welding heat input and material flow behavior. The influence of welding process parameters on the quality of weld formation was also discussed. (2) the parameters without welding defects were selected by visual inspection and X-ray inspection. The welding speed was 200 mm / min, the rotational speed was 300 rpm, and the welding speed was 300 rpm; the welding speed was 300 mm / min; the welding speed was 300 mm / min; the welding speed was 300 mm / min; the welding speed was 300 mm / min. Mm / min, at a speed of 400 rpm, and both sets of parameters can be used to obtain a defect free welded joint. The characteristics of microstructure in different regions of welded joints without welding defects are analyzed. Along the horizontal direction, the microstructure of welded joints varies greatly, the nugget zone is small equiaxed crystal, and the microstructure of the zone affected by heat engine has obvious bending deformation. The heat affected zone (HAZ) is a roughened lath structure, which is characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The second phase characteristics in different regions of welded joints without welding defects are analyzed. The second phase of the base metal consists of a large amount of insoluble impurity phase AlMnSiFeFe (solid solution Al6FeMn) and a small amount of strengthening phases TnAl2Mg3Zn3Zn3ZN, 畏 _ (2) MgZn2ZN _ (2), and the strengthened phases in the nugget zone are precipitated. 5) based on the results of microhardness measurement, The microhardness characteristics of welded joints are analyzed. The hardness of the nugget zone is approximately the same as the hardness value of the base metal area. The average value is about 121 HVV, and the hardness value of heat affected zone is about 125 HVN 140 HV. The hardness of RS side increases gradually from the direction of nuke zone to heat affected zone, and the hardness value of RS side increases gradually from the direction of nuke zone to heat affected zone.) based on the universal tensile testing machine, the fracture morphology is analyzed. The tensile properties of the welded joints were analyzed by the residual stress test results. The average tensile strength of the welded joints was 403MPa, and the elongation after breaking was 16.3.The fracture position of the welded joints was located in the heat affected zone of as side, which was cut in the direction of 45 掳, and the fracture was fibrous. This paper mainly studies the microstructure and mechanical properties of a 7XXX aluminum alloy friction stir welding joint. By combining theory with experiment, the influence of welding process parameters on weld forming is analyzed. The microstructure and second phase characteristics of welded joints, the effect of microstructure on mechanical properties, and the research results are of great significance to guide enterprises to select reasonable welding process parameters and improve welding quality of friction stir welding.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG407

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