Research On The Mechanism Of Horizontal VPTIG Forming For Aluminum Alloy

With the increase of the ratio of the tank diameter to the wall thickness in launchvehicles and spacecraft, the stiffness of tank will decline in the flat position welding.In further, the roundness and straightness will have a larger deviation. Thedeformation is hard to correct and stress concentration becomes worse. Horizontalposition welding meets characteristic of the in-situ fabrication with a smaller tankdistortion, a short production cycle, and it is safe and reliabe. Variable polaritytungsten inert gas (VPTIG) in horizontal position experienced an asymmetric heat andforce, which make it’s forming deserve a research issue in this field.In the paper, a systematic study on the mechanism and characteristics ofhorizontal VPTIG forming for5083aluminum alloy: the force and heat acted on weldpool, microstructures, mechanical properties have been investigated.Firstly, workpiece received more heat in DCEP stage of a cycle. With theincrease of the proportion of direct current electrode positive(DCEP) time in areasonable range, the weld width, the depth-to-width ratio, the volume of the weldpool de. And the same results can be obtained with the increase of current DCEP.Secondly, the radial distribution and influencing factors of arc pressure forVPTIG were studied. Experiment results showed that it’s a hyperbolic distribution.Under the same root mean square current, arc pressure will decrease gradually withthe increase of the duty ratio of DCEP at one cycle and the integrated arc force isdirectly proportional to the square of the current. The results of orthogonal experimentshow that the effects of the direct current electrode negative (DCEN), the DCEPcurrent, the frequency of alternating polarity, the duty ratio of the positive polaritycurrent, the distance between tungsten and workpiece on the arc pressure decreases.Then, the force acted on the weld pool and the effects of the working angle of thetorch on the weld forming were analyzed at horizontal VPTIG. A relationship betweenthe working angle of the torch, the force acted on the weld pool and the weld formingwere obtained.Finally, microstructure and mechanical properties of horizontal VPTIG werestudied. Experiment results showed that the microstructure for weld was as-castequiaxed crystal, and for the zone near the base metal was directional coarse columnar dendrites. The relationship between microstructure and mechanical properties wasalso obtained.