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1、南京航空航天大学博士学位论文颗粒增强铝基复合材料焊接工艺与机理研究姓名：王少刚申请学位级别：博士专业：机械制造及其自动化指导教师：姜澄宇;徐九华20060101南京航空航天大学博士学位论文 i 摘 要 颗粒增强铝基复合材料由于具有比强度和比模量高、耐磨、耐腐蚀、抗辐射及尺寸稳定性好等许多优点，在航空航天、兵器等国防工业和汽车、电子等民用工业具有广泛的应用前景，成为当今金属基复合材料研究和发展的主流。然而，由于复合材料的增强体与基体之间的熔点、导热性和热膨胀系数等热物理性能参量存在巨大差异，使得铝基复合材料的焊接性很差，采用常规的熔化焊方法焊接该类材料，焊缝表面成形不好，且易在焊缝金属中产生气孔
2、、夹杂和微裂纹等缺陷，对于 SiCp/Al复合材料，还会在增强体 SiC 颗粒与基体 Al 合金之间发生界面反应，生成脆性化合物 Al4C3，严重降低接头力学性能。 针对铝基复合材料焊接过程的特点，本文在全面总结铝基复合材料焊接过程中存在的问题基础上，以颗粒增强铝基复合材料 Al2O3p/6061Al、SiCp/2124Al等作为研究对象，系统研究了颗粒增强铝基复合材料的脉冲氩弧焊焊接性及氩气保护条件下 Al2O3p/6061Al炉中钎焊的可行性。通过采用不同填充材料及不同规范参数焊接工艺试验，以及对获得接头采用光学金相分析、拉伸断口扫描电镜（SEM）观察和接头 X 射线衍射（XRD）相结构分
3、析，探讨了接头形成过程的机理以及获得高质量焊接接头应采取的措施。 论文提出了在脉冲氩弧焊过程中采用合金化填充材料，通过合金元素 Ti 发生诱发反应的方法，以抑制 SiC/Al之间的界面反应，同时新生成的 TiC 粒子又可作为增强体，从而提高接头强度。焊接过程中，微量脉冲的加入，一方面可减少焊接时对熔池的热输入，有利于减轻界面反应；另一方面可增强对熔池金属的搅拌作用，改善焊缝金属的流动性，有利于气体的析出，减少焊缝金属中气孔的形成，并使焊缝表面成形良好。研究结果表明，采用脉冲诱发反应的方法焊接 SiCp/Al 复合材料，获得的接头表面成形良好。金相组织观察显示，接头内部组织致密，未发现有气孔、夹
4、杂和微裂纹等缺陷；拉伸实验及接头显微硬度测试表明，接头强度等力学性能没有大幅度下降，说明该方法用于焊接颗粒增强铝基复合材料可行。 接头 X 射线衍射相结构分析检测到焊缝金属中存在 TiC等增强相，进一步证实诱发反应的真实性。 对氩气保护条件下 Al2O3p/6061Al炉中钎焊性研究表明，采用氩气保护炉中钎焊颗粒增强铝基复合材料，具有操作简单，钎焊温度低，焊接变形小，去膜效果好等特点，通过采用合理的钎料、钎剂组合以及优化钎焊工艺参数，可以获得良好的钎焊接头质量。对钎焊接头形成过程的机理研究表明，钎焊过程中采用惰性气体 Ar 保护以及对接头施加微压力可大大改善钎料对母材的润湿性，颗粒增强铝基复合
5、材料焊接工艺与机理研究 ii 促进钎料与母材中合金元素的相互扩散，进一步提高接头性能。 关键词：铝基复合材料，脉冲氩弧焊，炉中钎焊，抗拉强度，显微硬度，X 射线衍射相结构分析，断口扫描电镜分析，焊接机理 南京航空航天大学博士学位论文 iii ABSTRACT Particulate reinforced aluminium metal matrix composites(Al- MMCs) have many excellent properties such as high specific strength and specific stiffness, resistant wear, r
6、esistant corrosion, resistant radiation, steady dimensions, etc. They will increasingly be used in many fields such as aeronautics and astronautics, weapon, automobile and electron and so on, which makes them become one of the main topics of research and development in the field of metal matrix comp
7、osites. However, the distinct parameters of thermal physical properties such as melting point, thermal conductivity and thermal coefficient of expansion between reinforcement and matrix lead to poor weldability of Al- MMCs. When the general fusion welding technology is used in welding these material
8、s, the form of joint surface become bad and defaults of porosity, inclusion and micro- crack, etc. can easily be formed in weld metal. Especially for SiC particulate reinforced Al- MMCs, the interfacial reaction between reinforcement SiC and matrix Al will occur during welding, the formation Al4C3 i
9、s very brittle which will result in great decrease of performance and toughness of welding joint. Aiming at the feature of Al- MMCs welding processing, the problems of Al- MMCs welding are fully summarized in this paper. Particulate reinforced Al- MMCs (Al2O3p/6061Al and SiCp/2124Al, etc.) taken as
10、the object of study, the weldability of pulsed TIG (Tungsten Inert Gas) welding particulate reinforced Al- MMCs and furnace brazing Al2O3p/6061Al protected by argon is researched systematically. By using different filler metals and optimizing the welding processing parameters, consequently, based on
11、 optical microscope observation of weld joint, scanning electric microscope(SEM) analysis of tensile crack section, and X- ray diffraction(XRD) analysis of the phase structure of joint, the forming mechanism of welding joint and the ways on how to improve the quality of welding joint are discussed i
12、n detail. This paper puts forward that the alloying filler metal is added to weld metal in the course of pulsed TIG, the interfacial reaction between reinforcement SiC and matrix Al can be controlled to a great extent through induced reaction of alloying element Ti, 颗粒增强铝基复合材料焊接工艺与机理研究 iv at the sam
13、e time, the newly formed TiC particles can act as reinforcement, as a result, they can increase the strength of joint. In the welding process, the micro pulse may effectively decrease the arc heat input to molten pool so as to weaken interfacial reaction, on the other hand, it strengthens the stirri
14、ng action to molten pool, and the fluidity of weld metal is greatly improved, the gas in weld metal can easily escape so as to reduce porosity in weld metal, and the weld surface formation is good. Results show that when SiCp/Al materials are welded by pulse induced reaction, the weld surface format
15、ion of joint is excellent, joint structure is dense under the metallographic structure observation, no porosity, inclusion and micro- crack etc. can be found in weld metal. Tests of tensile and microhardness demonstrate that the mechanics properties such as joint strength do not decrease greatly, wh
16、ich proves that this way to weld Al- MMCs is feasible. Through the phase analysis by XRD, TiC etc. reinforcement can be found in the weld metal, which verifies that induced reaction is true in the further. The study on brazability of Al2O3p/6061Al furnace brazing protected by argon shows that brazing Al- MMCs in this way have some advantages such as simple brazing operation, low brazing temperature, small welding deformation and more effective elimination of the oxidization films on the surfa
