【作者】 孟超；

【导师】 芦凤桂；

【作者基本信息】 上海交通大学 ， 材料科学与工程， 2013， 硕士

【摘要】 随着工业技术的发展，铝基复合材料广泛地应用于航空、航天、汽车等行业。颗粒增强铝基复合材料由于其低密度、高强度、高比模量及良好的耐磨性能成为一种很有潜力的材料。颗粒增强铝基复合材料焊接性及焊接过程颗粒的稳定性等问题的解决会加速其在上述领域的推广应用。关于TiB₂颗粒增强铝基复合材料在激光深熔焊接过程中TiB₂粒子演变的相关研究较少，特别是粒子对激光深熔焊接过程中小孔稳定性的研究涉及更少。本文开展了TiB₂增强铝基复合材料的激光深熔焊接研究，采用试验研究与数值模拟相结合的方法，探讨颗粒增强铝基复合材料TiB₂/ZL101激光深熔焊接过程中TiB₂粒子的演变及TiB₂粒子对小孔稳定性的影响，揭示在激光焊接过程中TiB₂粒子与铝合金基体之间的相互作用行为，研究TiB₂粒子在焊缝中的分布特征，探讨TiB₂粒子对静态激光深熔焊接和动态激光深熔焊接过程中小孔稳定性的影响等，为理解TiB₂增强铝基复合材料的激光深熔焊接的复杂现象提供试验及理论支持。论文采用大功率激光器研究了激光焊接TiB₂/ZL101颗粒增强铝基复合材料时TiB₂粒子的演变行为。采用XRD、SEM及EDS观察并分析了焊缝内粒子的物相、热力学过程及形貌特征，发现当TiB₂团簇体积分数足够大时，焊缝中心的TiB₂粒子会熔化并聚在一起，且较大尺寸的TiB₂粒子会发生断裂；当温度足够高的TiB₂粒子被熔融的Al液体包围的时候，会发生界面反应，从而生成AlB12和Al3Ti，进而减弱了TiB₂粒子的增强效果。由于激光束的能量一般具有高斯分布特征，这使得焊缝中心的界面反应程度比焊缝边缘的界面反应程度更激烈。本文基于流体动力学、热力学理论，结合有限差分方法和VOF方法，建立了颗粒增强铝基复合材料激光深熔焊接的数学模型。特别考虑了熔池中的第二相粒子与金属流体之间的耦合作用，结合适当的边界条件，对物理方程的近似与求解给出了比较详细的论述。本文以颗粒增强铝基复合材料TiB₂/ZL101为实验材料，分别计算得出了静态激光深熔焊接与动态激光深熔焊接时熔池的流动形态、小孔形貌、温度场和速度场分布，分析了两种激光深熔焊接情况下的小孔成形过程和小孔稳定性，通过改变铝基复合材料TiB₂粒子体积分数来研究粒子对小孔稳定性的影响，发现在激光深熔焊接过程中，小孔会出现不稳定现象，小孔的不稳定与小孔壁上形成的凸起有密切关系。而且随着TiB₂粒子体积分数的增加，小孔有变得不稳定的趋势，并且小孔壁上振荡出现的时间会提前，振荡的频率和幅度都增大。更多还原

【Abstract】 With the development of industry and technology, the specialmaterials are required in the fields such as aerospace, aviation andautomobile. Aluminum metal matrix composites （MMCs） reinforced withparticles for its low density, high strength and high modulus, goodwearing resistance became one of the most promising materials. Theapplications in above fields would be promoted by solving the weldabilityof particles reinforced aluminum MMCs. The evolution of TiB₂particles,especially the keyhole stability of aluminum MMCs reinforced withparticles in deep penetration laser welding was rarely reported. Particlesevolution behavior and the keyhole stability of aluminum MMCsreinforced with particles in deep penetration laser welding are researchedwith the methods of experimental and numerical simulation, such as theinteraction between particles and alloy matrix, the distribution of TiB₂particles in the weld seam, and the influence of particles on the keyholestability of both stationary and moving laser welding. The researches arehelpful to provide guidance in theory for the deep penetration laser welding of aluminum MMCs reinforced with TiB₂particles.In the paper, the evolution behavior of TiB₂particles is studied duringlaser welding on aluminum MMCs reinforced with TiB₂. XRD, SEM andEDS are used to analyze the phase, thermodynamics and appearancecharacteristics of particles in weld seam and the interface reactionbetween TiB₂particles and aluminum matrix are also discussed. Thestudy results show that TiB₂particles would melt and get together in themiddle of the weld seam and that fracture could be found in larger oneswhen the scale of TiB₂cluster is bigger than the spot size of laser. Theanalysis also indicates that Al3Ti and AlB12are produced by the interfacereaction between TiB₂particles and Al matrix. And also the interfacereaction of broken TiB₂particles in the middle of the weld seam isstronger than that at the edge of weld seam.Fluid dynamics, thermodynamics, finite difference method and VOFmethod are employed to analyze the deep penetration laser welding ofaluminum MMCs reinforced with TiB₂particles. The particle-fluidcoupling effect is considered in the model. Numerical approximations ofphysical equations are descripted in detail.The formation and stability of keyhole in both stationary and movinglaser welding on aluminum MMCs reinforced with particles are studiedbasing on numerical simulation method. In order to study the effect ofdifferent mass fraction on the keyhole stability and fluid flow inside molten pool, keyhole formation process, variation of free surface,temperature distribution and fluid flow are calculated respectively basingon the model built in this paper. The calculation results show that keyholeis stable at the beginning for different conditions and then fluctuationoccurs inside keyhole with increasing calculation time for the emergenceof hump on the wall of keyhole. The flow behavior of molten poolaffected by particles and forces acting on the surface could explain theforming of humps inside keyhole, which directly causes the variation ofkeyhole. As the mass fraction of TiB₂particles increases, the keyhole ismore likely to be instable and oscillation occurs at earlier time. At thesame time, the frequency and magnitude of oscillation become larger.更多还原