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

As the lightest structure material, Magnesium alloys have many advantages, such as low density, high specific strength, damping capacity, better mechanical properties, recyclable and so on, which are attracting more attention from the domestic and foreign. It is well known that the advanced manufacturing techniques such as an appropriate bonding or joining technique play an important role in exploiting the new fields of magnesium alloys' applications.The laser-TIG hybrid welding technique, with the characteristics of high welding speed, high efficiency and quality, is being paid more attention by the domestic and foreign researchers. It is helpful to understand the physical mechanism of this welding process by numerical simulation and to achieve the goal of controlling the welding quality further.Taking wrought magnesium alloys AZ31B as the research object, this dissertation investigated the technical characteristics of laser-TIG hybrid lap welding process, systemically analyzed the influence of various welding parameters to the butt weld depth of fusion, the melt width, the surface shape, the microstructure characteristic, and finally obtained welding joint with high shear strength. The research results found that due to the energy characteristic of the hybrid welding, the lap welding joint of magnesium alloy appeared "pin shapes " and the microstructure characteristics can be divided into two parts: The top of bead was the zone acted by laser and TIG together, while the bottom of bead was acted by laser alone.Based on the study of hybrid welding technology, a new heat-source model of laser-TIG hybrid welding that based upon Rotary-Gauss body heat-source model and Gauss area heat-source was established according to magnesium alloys characteristic. In the model, the high energy laser heat-source was described by the Rotary-Gauss body heat-source, while the TIG was described by the Gauss surface heat-source. The establishment of heat-source model for laser-TIG welding process has fully considered of the physical characteristics and synergetic effects of hybrid laser and arc welding.For the limitation of the precision of the heat-source model parameters and the physical properties in high temperature zone, the accuracy of the numerical simulation was difficulty to guarantee. This dissertation proposed a new ideal that uses the temperature field dates captured by the infrared thermal imaging system in outside of the arc interference region to adjusted simulation parameters and the material physical parameters, finally to obtain theentire temperature field. Besides, the feasible and precision of this method have been confirmed by the thermocouple measuring temperature and the contrast of molten pool shapeIn the final of this dissertation, according to the former experiment results and the numerical simulation results, the forecast system of laser-TIG hybrid welding was established based on the nerve network work and the finite element analysis. This system may, according to the requirement of materials species and thickness provided by the user, present appropriate welding parameters and forecast the fusion depth, the melt width, the quasi-steady three dimensional welding temperature fields, the remaining stress and so on, which will make the laser-TIG hybrid welding process of magnesium alloys more systemic and clear.