钛—铝异种金属电子束熔钎复合焊接研究

发布时间：2018-07-10 13:33

本文选题：Ti/Al异种合金 + 电子束熔钎焊　；参考：《南京理工大学》2017年硕士论文

【摘要】：铝锂合金和钛合金在航空、航天工业有着广泛的应用,由于近年来制造业都在追求结构轻型化、结构功能一体化和低成本设计与制造,所以铝锂合金和钛合金的复合结构具有巨大的应用前景,但是由于钛、铝的物理化学性质相差较大,而且二者化学反应极容易形成脆性金属间化合物,所以这就给Ti/Al的焊接造成了一定的困难。本试验采用了电子束熔钎焊接方法,利用电子束的高深宽比、能量的精确可控性得到了可靠地Ti/Al异种合金焊接接头,该方法有效地控制了过渡层的组成。设计焊接接头设计试验、焊接参数的调整试验、偏束量的调整试验和焊缝根部强化焊试验等对照组试验进行工艺优化,分析了各组对焊缝成形规律的影响。并对某些对照组采用金相显微镜、扫描电镜(SEM)及附带的能谱分析仪(EDS)、X射线衍射仪(XRD)研究微观组织分布、元素分布规律和物相组成,最后采用静载拉伸试验和显微硬度测试对不同接头进行了力学性能评价。铝锂合金熔焊部分主要分为母材、热影响区、细晶区、柱状晶区、等轴晶区,在焊接过程中接头软化导致了焊缝强度降低。熔钎焊界面金属间化合物主要有棒状、锯齿状和胞状三种生长形态,生长情况受偏束量和界面位置决定,其中棒状金属间化合物对界面结合强度有增强,胞状结合强度最差。由线扫描可以发现,偏束量越大界面反应层越薄,同一焊缝从上至下反应层越来越薄。结合线扫描和区域扫描结果发现单相的棒状和锯齿状金属间化合物原子比例不稳定,所以做出了反位缺陷的猜想。通过焊缝物相分析发现,不同偏束距离的物相组成有部分差异,这跟界面反应温度有关,界面温度决定物相的转换是否彻底。经过工艺优化的焊接接头物相由TiAl3、Ti5Al11、TiAl、Ti3Al四种相组成,其中棒状、锯齿状和胞状金属间化合物组织的大部分是TiAl3,而这些组织的根部连续过渡层则存在Ti5Al11、TiAl、Ti3Al等金属间化合物。对工艺优化后的焊接接头通过静载拉伸试验拉伸强度可以达到260MPa。焊缝的拉伸断面可以分为韧性断裂面和脆性断裂面,韧性断裂面出现大量的韧窝和第二相粒子,脆性断裂面呈现解理刻面。断裂过程是由焊缝中下部区域开始出现断裂缝隙,随着延伸长度的变化,断裂面扩张最终韧性区域断裂。对于断口不同区域组织构成,脆性断裂部分主要是TiAl3,而韧性断裂部分主要是铝锂合金组织。
[Abstract]:Al-Li alloy and titanium alloy have been widely used in aviation and aerospace industry. In recent years, the manufacturing industry has been pursuing structural lightweight, structural and functional integration and low-cost design and manufacture. Therefore, the composite structure of Al-Li alloy and titanium alloy has a great application prospect, but the physical and chemical properties of Ti and Al differ greatly, and the chemical reactions between them are easy to form brittle intermetallic compounds. So this caused some difficulties for the welding of Ti / Al. In this experiment, the welding method of electron beam fusion brazing is adopted. The high aspect ratio of electron beam and the precise controllability of energy are used to obtain the reliable Ti / Al dissimilar alloy welding joint. The composition of transition layer is effectively controlled by this method. Design welding joint design test, welding parameter adjustment test, offset beam adjustment test and weld root reinforcement welding test were optimized. The influence of each group on weld forming law was analyzed. The microstructure, element distribution and phase composition of some control groups were studied by metallographic microscope, scanning electron microscope (SEM) and EDS X-ray diffractometer (XRD). Finally, mechanical properties of different joints were evaluated by static load tensile test and microhardness test. The melting and welding parts of Al-Li alloy are mainly divided into base metal, heat-affected zone, fine-grained zone, columnar zone and equiaxed zone. During the welding process, the joint softening results in the decrease of weld strength. The intermetallic compounds in the fusion-brazing interface are mainly rod-shaped, sawtooth and cellular, and the growth is determined by the amount of skew beam and the position of the interface, among which the intermetallic compounds of rod-shaped intermetallics enhance the interfacial bonding strength, and the cellular bonding strength is the worst. It is found from the line scanning that the reaction layer of the interface is thinner with the increase of the skew beam amount, and the reaction layer of the same weld is thinner from top to bottom. In combination with the results of line scanning and region scanning it is found that the atomic ratio of single-phase rod-like and sawtooth intermetallic compounds is unstable so the conjecture of counterposition defects is made. It is found that there are some differences in phase composition between different beam distances, which is related to the interfacial reaction temperature, and the interfacial temperature determines whether the phase transition is complete or not. The phase of the welded joints optimized by the process is composed of four phases: TiAl _ 3C _ 3C _ 5AL _ (11) Al _ (11) Ti _ (3AL) Al _ (3AL), among which the rod-shaped, sawtooth and cellular intermetallics are mostly TiAl3, and the intermetallic compounds such as Ti5Al11TiAlTiAlTi3Al exist in the continuous transition layer at the root of these structures. The tensile strength of the welded joint can reach 260 MPA by static load tensile test. The tensile section of the weld can be divided into ductile fracture surface and brittle fracture surface. A large number of dimples and second phase particles appear on the ductile fracture surface and the brittle fracture surface presents cleavage surface. The fracture process begins with the crack in the middle and lower part of the weld, and with the change of the extension length, the fracture of the fracture surface expands to the final ductile zone. The brittle fracture is mainly TiAl3 and the ductile fracture is Al-Li alloy.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.1

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