Study On Microstructure And Tensile Properties Of TC4 Titanium Alloy By A-TIG Welding

Ti-6Al-4V is a medium-strength ?+? double-phase titanium alloy.It has been widely applied in the fields of aerospace,ship manufacture,chemical,medical and etc.because of its small density,high strength,excellent corrosion resistance,high-temperature creep and etc..TIG has been used widely as one of welding methods with low cost,better form of welding,and its simple operation.But TIG has low arc energy density,low depth-to-width ratio,and wide softened zone in the joint,which decrease the mechanical property of joint.In recent years,A-TIG has received more attention.The microstructure and mechanical property of Ti-6Al-4V joints welded by TIG coating with NaF,MgF₂,Na₃AlF₆ of different single component flux,Na₂SiF₆ was studied.Ti-6Al-4V was welded by TIG coating NaF,MgF₂,Na₃AlF₆,Na₂SiF₆ with the optimized parameter.Micromorphology and microstructure of the weld were investigated through observing the form of arc and measuring the voltage of arc,then analysis the effect of the different flux on phase composition.The effect of different flux on orderliness of mechanical property through testing mechanical property of joints welded by TIG and A-TIG,SEM,and EDS was investigated.The depth-to-width of weld with no flux,NaF,MgF₂,Na₃AlF₆ and Na2AlF6 is 0.224,0.315,0.398,0.200,0.200 respectively.Coating NaF and MgF₂ increase the penetration of weld,and decrease the width of weld obviously.Coating Na₃AlF₆ and Na2AlF6 decrease the penetration and width of weld slightly.The arc of coating NaF and MgF₂ was contracted obviously during welding,the arc of coating Na₃AlF₆ and Na2AlF6 was not contracted obviously.The voltage of arc with no flux,NaF,MgF₂,Na₃AlF₆ and Na2AlF6 was 15.0V,15.7V,15.9V,14.9V,and 14.9V respectively.The microstructure of base metal of Ti6-Al-4V is the mechanical mixture,which is composed of equiaxed ? and ?.The microstructure of joints consists mainly of widmanstatten and basket-weave microstructure.The basket-weave microstructure of weld coating NaF and MgF₂ was more than basket-weave microstructure,and the size of ?' was small.The widmanstatten of weld coating no flux,Na₃AlF₆ and Na2AlF6 was more,the size of ?' was large.The flux had almost no effects on phase composition.The strength coefficient of joint with no flux,NaF,MgF₂,Na₃AlF₆ and Na2AlF6 was 0.75,0.88,0.92,0.91,0.94 respectively.The bending strength of joint with no flux,NaF,MgF₂,Na₃AlF₆ and Na2AlF6 was 1436.67 MPa,2231.36 MPa,1843.91 MPa,1613.0MPa,1888.54 MPa respectively.The fluxes increased the tensile strength and bending strength of joint obviously.