Effect of welding parameters on surface formation and microstructure for TC4 titanium alloy joint welded by CMT

Low heat input, less spatter and low deformation after welding are some of the advantages of joining titanium alloys using CMT welding. However, few systematic studies about the effects of welding parameters on joint formation and microstructure characteristics have been conducted. In this paper, a numerical model for CMT based on time interval loading and double ellipsoid volume heat flow distribution is established by using APDL language in ANSYS software. The effects of wire feed speed and welding speed on the temperature field, stress field and deformation cloud distribution characteristics of CMT welding for TC4 titanium alloy are studied. The numerical simulation results in a high degree of coincidence with the experimental weld, with an average error of no more than 7%. At the same time, the influence of wire feed speed and welding speed on the surface formation and microstructure of the weld is experimentally studied in this paper. The results of numerical simulation show that with the increase of wire feed speed, the area of high temperature zone of the joint enlarges. The peak temperature at the arc closing position changes from 2858 ${}^{\circ }$C to 4182 ${}^{\circ }$C. As the welding speed increases, the area of high temperature zone of the joint shrinks. The peak temperature at the arc closing position decreases from 4722 ${}^{\circ }$C to 2133 ${}^{\circ }$C. When the wire feed speed is 5.5 m/min and the welding speed is 0.45 m/min, the maximum von Mises residual stress on the upper surface is relatively small, 730 MPa, and the maximum deformation is relatively small, 0.869 mm. The experiment results show that with the increase of the wire feed speed, the melt width on the front side gradually increases and the formation of the back side gradually changes from discontinuous to continuous and uniform. The average grain size in the weld increases from 10.0 $\mu$m to 16.7 $\mu$m. With the increase of welding speed, the melt width on the front side gradually decreases and the formation of the back side gradually changes from continuous and uniform to discontinuous. The average grain size in the weld decreases from 14.3 $\mu$m to 9.1 $\mu$m.