Study On The Influence Of Oxidation Treatment On Corrosion Resistance Of Pure Titanium Welded Joints

In this paper,on the basis of the oxidation of industrial pure titanium welded jointssamples by TIG welding at different temperatures(550?,650?,750?,850? and950? for 4h)and at different times(550? for 2h,4h,6h and 8h),the oxidation kinetic behavior was analyzed.The microstructure,surface morphology and phase composition of the materials after thermal oxidation under different conditions were analyzed by means of scanning electron microscope((SEM)),energy dispersive spectrometer((EDS)),X-ray diffractometer((XRD))and optical microscope((OM)).The variation of oxidation rate,microstructure and phase with oxidation temperature and time was obtained,and the oxidation mechanism was discussed.Potentiodynamic polarization technique and electrochemical impedance spectroscopy were used to test the electrochemical properties of unoxidized industrial pure titanium welded joints and industrial pure titanium welded joints treated under different conditions.The relevant electrochemical parameters were obtained,and their electrochemical corrosion property in 15%HCl solution was studied.The uniform corrosion rate of unoxidized and oxidized industrial pure titanium welded joints was obtained by using gravimetric method.The corrosion behavior of the welded joints in 15%HCl solution was studied.The results show that after the industrial pure titanium welded joint was oxidized at550? for different time(0h,2h,4h,6h,8h),the oxidation rate and time showed a parabolic law.The oxidation rate of the welded joint increases with the prolonging of time,but the increment of oxidation rate decreases accordingly.The oxidation treatment time has little effect on the oxidation behavior of the welded joint.Only slight oxidation reaction occurred on the joint surface,and the weight gain per unit area and the rate of oxidation weight gain were too small,and the oxidation was not obvious.The industrial pure titanium welded joints were oxidized for 4 hours at different temperatures(550?,650?,750?,850? and 950?).With the increase of oxidation temperature,the oxidation rate and temperature increased exponentially,that is,the oxidation rate of welded joints increased with the increase of temperature.The surface oxidation reaction is small at 550? and 650?,and the content of Ti on the surface of the matrix is much higher than that of the oxidation product Ti O2.The oxidation reaction is more obvious at 750?.The content of Ti on the surface of the matrix is less than that of the oxidation product Ti O2,but the oxidation reaction is not sufficient.The oxide film does not completely cover the surface of the joint.At 850? and 950?,the Ti element on the surface of the matrix disappears and all changes to Ti O2,that is,the surface of the joint is completely covered by the oxide film.However,the oxide film on the surface of the joint is thicker and denser at 950?.In the electrochemical corrosion system of 15%HCl solution,the polarization resistance of industrial pure titanium welded joint is higher than that of base metal,the self-corrosion current density is lower than that of base metal,and its corrosion resistance is better than that of base metal.After oxidation treatment at 650?,850? and 950? for 4h,with the increase of oxidation temperature,the polarization curve of pure titanium welded joint first moved to the right and then to the left.When the oxidation temperature was 950?,the corrosion resistance of pure titanium welded joint was the best.In 15% HCl solution,the corrosion resistance order of industrial pure titanium welded joint was 950?4h>850?4h > unoxidized welded joint > base metal > 650?4h.In the immersion corrosion system of 15%HCl solution,the uniform corrosion rate of unoxidized pure titanium welded joints is the largest.After being oxidized at 650?,850?and 950? for 4h,the uniform corrosion rate of industrial pure titanium welded joints in15%HCl solution decreases.However,with the increase of oxidation treatment temperature,the corrosion rate of industrial pure titanium welded joint in 15%HCl solution increases.In15%HCl solution,the uniform corrosion rates order of the unoxidized and the industrial pure titanium welded joint was 650?4h<850?4h<950?4h< unoxidized welded joint.