Microstructure Control And Corrosion Resistance Of Titanium Alloy After Welding By Local Induction Heat Treatment

Titanium alloys have outstanding mechanical and physical properties in all aspects,so they are often used in significant fields such as aerospace,biomedicine,national defense and petrochemicals.However,the welded joints of thin-walled titanium alloys have coarse grain structures and are easy to deform.This article aims to improve the microstructure of TC4 titanium alloy and control welding deformation through the technical means of local induction heat treatment.With the help of various specific characterization methods,the effects of specific induction heat treatment processes on the microstructure,corrosion resistance and mechanical properties of titanium alloys were studied,and the application of titanium alloys in the fields of national defense and aerospace was expanded.A model of TC4 titanium alloy thin-walled parts was established through finite element simulation software ANSYS,finite element meshing was performed,Gaussian moving heat source was applied,and the temperature of TC4 titanium alloy thin-walled parts during laser welding and local induction heat treatment was simulated.Field changes.The effects of local induction heat treatment temperature and cycle times on the microstructure of welded seam,mechanical properties and corrosion resistance of welded parts are studied,and the mechanism of microstructure changes in titanium alloys during laser welding and local induction heat treatment is analyzed.The study found that the temperature of TC4 titanium alloy during laser welding can reach 2849.2?,which is far beyond the phase transformation point and melting point of titanium alloy.The simulated local induction heat treatment temperature field results are in good agreement with the experimental results.During laser welding,the transformation reaction of ? phase and ? phase to high temperature ? phase occurred at the weld.Due to the extremely fast welding cooling rate,the high temperature ? phase was too late to transform into the equilibrium ? phase through diffusion,forming densely distributed?'needles.Martensite.In the process of local induction heat treatment,the decomposition of the supersaturated solid solution ?'phase occurs,that is,the transformation reaction of?'phase to ? phase and ? phase,forming a transformation ? phase and lath ? phase similar to the base material,and The ? phase and the ? phase are distributed alternately.With the increase of the induction heat treatment temperature,the reaction proceeds to the right,the phase content of the transformed ? phase shows an increasing trend,and the phase composition and microstructure are more uniform;with the increase of the number of thermal cycles,the product of the reaction transformation ? phase The phase content increases first,and will keep fluctuating within a certain range after increasing to a certain number of times.The research results show that the current density of the base metal is greater than that of the weld,and its corrosion rate is faster than that of the weld.The self-corrosion potential of the weld is higher than the self-corrosion potential of the base metal,and the modulus is also higher than that of the base metal.The corrosion performance is better.However,the strength and plasticity of the welded parts are worse than those of the base metal.The corrosion potential of welded parts first increased and then decreased with the increase of temperature,and the impedance modulus value also showed a trend of first increase and then decrease,indicating that the corrosion resistance decreased with the increase of temperature.The reason is that both the ?'acicular martensite microstructure and the high-temperature ? phase are factors that affect the corrosion resistance,so there will be an inflection point.When changing the number of cycles,4 cycles of heat treatment can improve the corrosion resistance of welded parts to the greatest extent.The overall microhardness of the weld decreases as the temperature increases.As the induction heat treatment temperature increases,the strength of the welded parts after heat treatment increases first and then decreases,while the plasticity first decreases and then increases,showing the opposite trend.As the number of cycles increases,the overall microhardness of the weld also decreases.The strength decreases as the number of cycles increases,and the plasticity increases.The tensile fracture morphology of the welded parts after different heat treatment processes is full of dimples,which all have the characteristics of ductile fracture.