Research On The Evolution Of TiB₂Particles And Keyhole Stability In Laser Welding On ZL101Aluminum Matrix Composite

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.