Study On Pulsed Laser Welding Characteristics Of Ti-based Amorphous Alloys

Ti-based amorphous alloys possess many excellent features,but industrial application of bulk alloys with large dimensions is restrained by its hard preparation condition.Laser welding is an effective method to solve the problem in manufacturing of large and complicated structures made by the Ti-based amorphous alloys.In this paper,the Ti-based amorphous alloy and the ?-Ti dendrite enhanced amorphous alloy are chosen as the welding materials,and the characteristics of these two materials during pulsed Nd:YAG welding are experimentally researched.Laser remelting and welding experiments under different conditions are conducted,and the welded joints and specimens for the analysis are prepared.The microstructures,the element distributions and the mechanical properties of the joints are examined by optical microscopy,scanning electron microscopy(SEM)and hardness tester.After research,the following conclusions can be achieved:(1)During laser remelting of Ti-based amorphous alloys(defined as MG),there are no porosities or cracks found in fusion zone(FZ),heat affected zones(HAZ)and FZ-HAZ transition zones of the joints.The microstructures in FZ and HAZ are strongly influenced by the heat input from the laser beam.When given small heat input,no crystallization can be found in FZ,and the microstructure in FZ are similar with that in base material(BM),and there is hardly HAZ between FZ and BM.With the increase of laser heat input,coarse Cu-rich phases in needle shape(about 10 ?m in length)appear in FZ.When the laser heat input increase further,Zr-rich phases with bar shape(about 5 ?m in length).Cu-rich phases can be observed in HAZ,and the shape of the phases changes with the increase of laser heat input.(2)After laser remelting of ?-Ti dendrite enhanced amorphous alloy(defined as MGC),no porosities and cracks are found in the joints.Meanwhile,there is no obvious HAZ between FZs and BMs.In FZs,the microstructures mainly consist of spherical ?-Ti grains and amorphous background.The ?-Ti grains in FZ are in the nanometer scale(0.1?1 ?m),obviously finer than those in BM(6?10 ?m).Lager laser pulse energy always leads to increased ?-Ti grains.Great laser pulse exciting current bring laser impacting effect to the liquid molten pool,which results in the finer microstructures in the FZ.Element analysis shows the Mo atom trends to enter into the lattice of ?-Ti grains to form substitutional solid solutions.Hardness tests exhibit that the darker regions in FZ have the highest hardness(as high as 531 HV).While,in BM the hardness greatly fluctuates in range of 448?572 HV,depending on the testing position.(3)Butt welding of dissimilar MGC-MG can achieved by pulsed laser.With proper welding parameters(laser pulse exciting current 100 A,laser pulse width 1 ms,pulse frequency 30 Hz,and welding speed 400 mm/min),good weld formation can be obtained,and no cracks,porosities and inclusions are found in the welded joints.The FZ is amorphous alloy with unevenly distributing small(0.5?2 ?m)?-Ti grains.No obvious HAZs are found in the joints.Depending on the distribution of the ?-Ti grains,the microhardness in FZ is between the hardest MG BM and the softest ?-Ti grains.