Study On Process Of Fiber Laser Welding Of TC4 Titanium Alloy And Mechanical Property Of Joints

Titanium alloy with many excellent properties have been widely used in aerospace field for aircraft?the key components of engine blade etc.,and optical fiber laser welding is the main connection method.The application environment of the fiber laser welding head leads to the unidirectional axial stress as well as the cyclic loading,so the quality and mechanical properties of the welded joint is the bottleneck of the safe application.The study on mechanical properties of titanium alloy and its optical fiber laser welded joint based on infrared thermal imaging can analysis the nature ofmechanical properties experimentfrom the perspective of energy transformation.This method has the characteristics of direct,accurate and real-time,.It has great theoretical significance and practical significance,and provide reference for further development of titanium alloy and fiber laser welding joint.This paper has conducted a series of optical fiber welding process tests of titanium alloy,through the analysis of weld width,reinforcement,undercut and porosity of different welding line energy data,obtaining the relationship between welding joint structure? welding quality and welding line energy;Analyzing the temperature revolution of titanium and its fiber laser welding joints under axial tension force and axial cyclic alternating load with infrared thermal imaging technology,understanding the influence of fiberlaser welding process and welding defects on thetensile mechanical properties and fatigue mechanics behavior.Studies have shown that welding 2.5mm titanium alloy with fiber laser welding parameters of 2.5Kw welding laser power?-10 defocus and protect gas of Ar or He would getthe best welding joint structure,and the weld width would increase with the increase of welding line energy,the key influence factor of weld reinforcement and undercut is welding line energy.Using partial focus welding,the change law of weld width with welding line energy has not changed greatly.But it can significantly improve the undercut defect of fiber laser welding joint of TC4 titanium alloy,but partial focus will also cause weld penetration problem with low welding line energy,it needs higher welding line energy to obtain the same weld penetration.Welding with the protect gas of He would appropriately increase the stability of molten pool,having a optimistic influence on the control of weld reinforcement and undercut,but when weld line energy is low,the influence of Ar is more significant,when weld line energy is proper,the deference of influence between Ar and He is small.When the energy of welding line energy is greater than 80J/mm,the stomata in laser welding joint of titanium alloy disappeared,the effect is very significant;Changing the type of protection gas and the defocus,the appearance and distribution of stomata changes with welding line energy,which is similar with former experiment,it has no obvious effect in refraining the stomata.The study on mechanical properties of titanium alloy and its optical fiber laser welded joint based on infrared thermal imaging shows that:the welded joint has similar strength but of which the elongation rate just reached 59.53%of base material.The specimen temperature field test results show that: when the axial loads is below the load corresponds to the yield strength,larger yield strength area appears in the heat affected zone of welded joint,but significant plastic strain did not appear.When the load is equal to the load corresponding to yield strength,the micro plastic deformation appears before macroscopic yield point;when the load is higher than the load corresponding to yield strength,the length of severe plastic deformation zone reaches only 35% of the base metal,and the length of severe plastic deformation zone gradually increases with the stretching process.The stomata and undercut defects will greatly increase the stress concentration phenomenon exists in the joint,and the plastic deformation zone length is further reduced.The study on fatigue properties of titanium alloy and its optical fiber laser welded joint based on infrared thermal imaging shows that: fiber laser welding can reduce the fatigue properties of titanium alloy,initial heating stage,the temperature drop stage and temperature strongly elevated stage.