Study Of Laser-TIG Hybrid Welding Process For Magnesium Alloy And Its Numerical Simulation

Due to the energy characteristic of the hybrid welding, the welding joint of magnesium is like a “pin” in geometry. The top of weld has the appearance acted by TIG alone while the bottom of weld has the appearance acted by laser alone. The common welding heat source modes such as the Gauss plane heat source,double-elliptic heat source, inverted conical heat source, Rotary Gauss heat source and so on can not be used to describe the characteristics of laser-TIG hybrid welding weld with “keyhole” geometry. Further study must be carried out to propose adaptive volumetric heat source mode which fully takes account of the features of the process and the weld geometry. Based on the above issues, the main research contents and results are as follows:(1) The influence of the parameters(welding speed, laser power, the spacing of the heat sources and welding current) of hybrid welding experiment on the weld shows that: laser has a great influence on weld penetration while arc has a great influence on weld width. Arc can improve the absorption rate of laser while laser can attract, compress and improve the stability of arc.(2) Based upon the "keyhole effect" in the process of laser-TIG hybrid welding, a new type of heat source model(C-G model) which consists of Rotary Gauss and inverted conical heat source model is built. This C-G heat source model adopts Inverted conical heat source model in the workpiece’s surface to solve the problem that the molten pool becomes wider owing to the rapid heating of laser and arc; While it adopts Rotary Gauss heat source model in the molten pool’s bottom to solve the problem that a narrow and long keyhole forms in the weld owing to the penetrating power of laser. The new heat source model is as follows:(3) Laser-TIG hybrid welding experiments on AZ31 B magnesium alloy workpiece are carried out, and weld geometry and dimension are measured. The experimental results and the predicted ones are compared together, and the results show that: For the hybrid welding process with holes not forming, the inverted conical heat source is appropriate; For the hybrid welding process with holes forming, they are in good agreement, especially in the mutation appearance of the "keyhole" position. Therefore it provides an effective way for the selection of heat source model and a prediction of weld shape in different welding conditions.