Study On The Properties And Process Of Pulse Laser Welding Of ?-Ti Dendritic Toughened Amorphous Alloy

As a popular material,amorphous alloy has many superior properties which are incomparable to crystalline alloy.However,the fabrication process of amorphous alloy is complicated,forming is difficult,and it is extremely difficult to obtain large volume complex structure parts.At the same time,in order to expand the application of composite amorphous alloy in industry,there are few reports on the welding experiments of crystalline alloy and amorphous alloy.To solve the above problems,a pulse laser welding method was proposed in this paper.The ?-Ti dendritic toughened composite amorphous(MGC)and TC4 titanium alloy with the thickness of 0.5mm were taken as the main research objects.By changing the welding parameters such as laser pulse width and excitation current,an efficient and stable welding process was realized.This paper characterized the microstructure,mechanical properties and grain morphology of the fusion zone(hereinafter referred to as FZ)under different welding parameters during MGC-MGC butt welding and MGC-TC4 butt welding,and revealed the influence of parameter change on grain size change.Finally,the differences of microstructure,element distribution and mechanical properties of FZ joints were compared.The details are as follows:(1)MGC-MGC butt welding.The influence of welding parameters on the microstructure,morphology,mechanical properties and grain size of MGC-MGC butt welded joint were researched.Results showed that at different welding parameter sets,there is no obvious heat affected zone in the welded joint.Identified by XRD,the microstructure of FZ is thecrystal?-Ti phase unevenly and dispersively distributing on amorphous matrix background.The crystal ?-Ti phases are in nano scale,finer than MGC base material.Element Mo trends to solute in ?-Ti phase to form a solid solution.With the increase of laser pulse energy,the shape of ?-Ti phase turns into dendritical from spherical,and the size of ?-Ti phase increases upto1?m.Domiated by the distribution of ?-Ti phase,regions with dense ?-Ti phase in FZ have lower hardness.During tensile test,the specimen fractured on MGC base material,indicating the high tensile strength of the welded joint(at least 1600MPa).(2)MGC-TC4 butt welding.Dissimilar butt weldingof MGC and TC4 Ti alloy was studied.Influences of pulsed laser welding paramters on microstructures,element distribution and mechanical performances were researched.Results showed that welded joint with good formation can be achieved at a proper heat input.No obvious heat affected zone was found between FZ and base materials.XRD tests show that the microstructure of FZ is still composed of ?-Ti dendritic phase and amorphous matrix phase.?-Ti grains were in diameters of 0.3?0.8?m at different welding paramters.Welding parameters hardly influence the hardness of FZ,and the maximum hardness in FZ is 575 HV.The specimen fractured on TC4 base material,indicating that the tensile strength of the welded joint is higher than TC4 base material(940MPa).(3)Influence of element Ti on MGC-MGC and MGC-TC4 welded joint.Compared with MGC-MGC butt welded joint,the content of Ti element in MGC-TC4 joint is higher.Ti content directly influences the morphology and size of ?-Ti grains in FZ.More and larger dendritical ?-Ti grains can be seen in MGC-TC4 FZ.Due to the extremely uneven distribution of ?-Ti grains in FZs of the two kinds of welded joints,hardness in FZ varies greatly with the regions.Tensile tests indicate that all the joints fracture on the base materials,because the amorphous background supplies the FZ with a high tensile strength.