The Plasma Arc Welding Process Optimization And Microstructure And Mechanical Performance Of TC4 Titanium Alloy

TC4 titanium alloys is bi-phase alloy with equiaxial martensite crystal.With the development of economy,science and technology,TC4 titanium alloys has gradually become common titanium alloy around the world.As a typically bi-phase of ?+? titanium alloys,TC4 titanium alloys have been wildly used to manufacte the aircraft fuselage,engine,and all kinds of bearing components,pressure vessel and other large engine support missile rudder and fin structure.The application of TC4 titanium alloys accounted for 80%in airline and aerospace industry.With the greatly application of titanium and titanium alloy in various fields of our industries,the welding process of TC4 titanium alloys are becoming more and more mature.Previous research has shown that the welded joint of TC4 titanium alloys have a good performance when it was welded by high energy beam welding.But,there are little researches about plasma arc welding of TC4 titanium alloys.Hence,in this paper,research was done on 3mm thick TC4 titanium alloy using TC4 titanium alloys.Firstly,by using response surface methodology,the plasma arc welding process parameters were optimized and the effective extent of every parameter could be decided with considering tension strength and bending strength as controlling indexes.And then the microstructures and properties of welded joint of TC4 titanium alloys by plasma arc welding process were analyzed.The range of parameters of the response surface methodology were determined by respectly observing the self fluxing welded and butt welded shape.The welding parameters were optimized by using response surface methodology and the optimization welding parameters were got.When the welding speed is 14mm·s^-1,the welding current is 160 A,gas flow is 3 L·min^-1,tensile strength of TC4 titanium alloy plasma arc welded joint is1080 MPa.when the welding speed is14.4mm·s^-1,the welding current is 161 A,gas flow rate is 3 L·min^-1,bending strength of TC4 titanium alloy plasma arc welded joint is1426 MPa.The regression equations can be determined by using the response surface methodology which are available.The results show that the prediction values of tensile strength of TC4 titanium alloy plasma arc welded joint well accord with the measured values,and the actual value of bending strength of TC4 titanium alloy plasma arc welded joint and the predicted value's error is 2.983%.C₁ and C₃ are significant difference in the first degree term,C₃² is more significant difference in the quadratic term and C₁C₂ also is more significant difference in interaction terms of the regression equation of H1.C₁,andC₂,C₃ are more significant difference in the first degree term,C₂2 is more significant difference in the quadratic term and C₁C₃ also is more significant difference in interaction terms of the regression equation of H₂.After analysis of significance,welding speed is a high significance parameter.Therefore,the effect of welding speed as a singer variable on the microstructure of the welded joints was studied.It is found that When the welding current is 160 A,gas flow is 3L·min^-1,the range of welding speed is 14mm·s^-116mm·s^-1,the microstructure of weld center mainly consist of ??phase the microstructure of HAZ which is close to the weld center consist of original ? phase and acicular ??phase,the microstructure of weld center mainly consist of ??phase the microstructure of HAZ which is close to the base metal consist of original ? phase,original ? phase and acicular ??phase.