Study On Rigid Restraint Thermal Self-compressing Bonding Of Ti6Al4V Alloy By Local Induction Heating

Titanium alloy has the characteristics of low density,high specific strength,excellent low temperature performance and excellent corrosion resistance so it is widely employed in the aeronautical industry.In comparison with other welding method,the materials to be joined do not melt during diffusion bonding.Welding in a vacuum ensures that the surface of the material is not contaminated or oxidized and defects such as incomplete penetration,porosity,oxide inclusions,and other disadvantages will not exist and the comprehensive mechanical properties of the joint are better.The conventional vacuum diffusion bonding needs external forces and integral heating in furnace,which limits its practicability.In this paper,a new type of diffusion bonding method—Rigid restraint thermal self-compressing bonding by localized induction heating(TSCB)is proposed.The fundamental principle is to produce a thermal elastic–plastic stress-strain field which compresses the high temperature thermoplastic metal at the bonding surface by localized heating.The thermal elastic–plastic stress-strain field is achieved by locally heating the rigidly constrained zones with induction heating,and thus atom diffusion across the bonding interface is occurred.Because of the high temperature and pressure,atomic diffusion across the interface is facilitated and solid-state bonding is achieved.Experiments were conducted on Ti6Al4 V plates using TSCB in the range of holding time 2.5min-7.5min and heating temperature 900-990 ?.After welding,the joint was annealed at 650 ? / 3H.Joint with uniform structure and good mechanical properties was obtained.The bonding interface almost disappeared;the microstructure and mechanical properties of the joint were equivalent to that of the base metal.Theplastic deformation through extensive thermal compression effect was massive.The feasibility of rigid restraint thermal self-compressing bonding by local induction heating was verified.By using ANSYS software,the finite element model was established based on the experiment to numerically investigate the thermal elastic-plastic stress-strain cycle during TSCB.The results showed that an internal elasto-plastic stress-strain field is developed which makes the bond interface subjected to thermal compressive action.This thermal self-compressing action combined with the high temperature on the bond interface promoted the atom diffusion across the bond interface to produce solid-state joints.On the basis of thermal stress-strain evolution,the void closure process of atom diffusion across the bond interface was analyzed.The results showed that: Atom diffusion during TSCB bonding is significantly improved due to the occurrence of mechanism,interface source mechanism and creep mechanism that are promoted because of the plastic deformation through extensive thermal compression effect.In comparison with conventional diffusion bonding,bonding time of TSCB is shorted.In order to study the element diffusion behavior,experiments were conducted on TA0/TC4 plates using TSCB.The diffusion characteristics of elements on both sides of the interface and the effect of holding time on diffusion were analyzed.The results showed that when the holding time is short,the diffusion of elements on both sides of the interface is not sufficient,the diffusion depth of elements is limited,and the bonding quality is poor.With the increase of holding time,the diffusion depth of elements increases and the bonding quality improved.