Research On The Weldability Of ZL101/TiB₂Aluminum Matrix Composite And TiB₂Particle Behavior In Laser Welding

With the development of industry and technology, the special materialsare required in the fields of military, aerospace, aviation, automotive,electronic devices. Aluminum matrix composites with low density, highstrength and stiffness, high modulus, high structure and dimensional stability,good abrasion resistance and fatigue resistance become one of the mostpromising materials. However, the more applications in above fields will belimited due to the weldability of the aluminum matrix composite reinforcedwith particles. TiB₂reinforced particulate aluminum matrix composites havehigher strength and wearing resistance comparing with aluminum matrixcomposites reinforced with other particulates. Welding plays an importantrole in enlarging the applications, but the weldability of TiB₂reinforcedaluminum matrix composite, especially with high efficient weldingtechnology was rarely reported. The weldability and particles behavior ofTiB₂reinforced aluminum matrix composites in laser welding are researchedwith the methods of experimental and numerical simulation, such as theinteraction between laser and reinforcement, the stability of TiB₂, interactionbetween interface and TiB₂, the migration and distribution of TiB₂amongweld. The researches help to provide the guidance in theory for the weldingand application of TiB₂reinforced aluminum matrix composites.In this paper, the weldabiltiy of ZL101/TiB₂composite with thethickness of6mm in laser welding is studied. The effects of differentprocessing parameters on the microstructure and mechanical properties areresearched. The test results of hardness, tension and wearing resistance ofwelding joints indicate that the properties of weld seam are better than that ofbase metal, which is caused by refined grains and more uniform distributionof TiB₂among weld seam. The contribution to the hardness due to uniformdistribution of TiB₂is larger than that caused by refined grains and solutionsstrengthen by Si. The physical and chemical variations of TiB₂are analyzed. TiB₂particles unmelt and remain solid state in molten pool, which are pushed faraway from the keyhole by the vaporized plasma. It is found that few TiB₂particles break and some TiB₂particles close to wall of keyhole are oxidizedinto TiO₂and B₂O₃, where B₂O₃vaporizes and escapes out of the moltenpool. The interface between TiB₂and Al is bonded with semi coherentrelation based on TEM observation, which increased the strengthen effect ofthe weld seam.The effects of heat input into base metal on the solidification process arestudied in order to find out the relationship between the Si morphology andTiB₂distribution in the weld seam. The heat input has small effects on thegrain size. But the cluster size of TiB₂varies significantly from larger clusterto disperse particles or smaller clusters with the increasing of heat input. Thecritical size of TiB₂cluster is evaluated to be1.9μm when the input energy is180J/mm. When the cluster size is larger than this value, the cluster will beengulfed by the solidification front and trapped within the grain. Otherwise,the cluster will be pushed by the solidification front and distribute on thegrain boundary. The calculating results are consistent with the experimentalresults.The fluid dynamic flow and particle migration behavior in the moltenpool are deeply investigated based on fluid dynamics and thermo mechanicscalculation. In order to reveal the discipline of TiB₂migration anddistribution, the temperature field, fluid flow and keyhole dynamic variationare discussed based on above model. The calculated results show that thevelocity of molten pool is larger at full penetration in comparison withnon-penetration weld. The fluid flows changing from upward and backwardto downward and backward for process of the non-penetration to fullpenetration. When the keyhole passes by the TiB₂cluster, the TiB₂cluster isdispersed and distrubutes homogeneously in the back pool due to thedifferent velocity in particle position.There are two convective loops presentinside molten pool, upward fluid existing above the center location ofkeyhole and downward fluid below the location, which promotes the more uniform distribution of TiB₂inside molten pool. The calculation results canexplain the migration and distribution of TiB₂in laser welding.