The Study Of Activating Flux Welding For Magnesium Alloy

For the characteristics of low density, high specific strength, good electromagnetic shielding and recycleable, Mg alloys are praised of the green engineering material in 21st century, which have recently attracted great attention in academic research and industry application. Applications in aerospace vehicle, automobile, consumer electronic productions have been widely and rapidly extended. As a country with abundant Mg resource, the industrialization of Mg has been become the one of tactic aims of science and technology in our country. However, the welding technique of Mg and its alloy can't meet the demands of manufacturing at present and it has been the main problem which limits the application of magnesium alloy structural components. Hereby, the research on Mg welding technology is becoming a focal topic all over the world in order to acquire the advanced joining technique with advantages of high quality, high efficiency and energy saving. A-TIG (activating flux -Tungen Insert Gas) was a method to increasing weld penetration which could improve the productivity, reduce the production costs and reduce the welding deformations. So the A-TIG welding method for the magnesium alloy welding could increase the quality and efficiency of the magnesium alloy welding. In this paper, the weld penetration, microstructure, mechanical property, arc image and molten pool behavior have been studied and the mechanisms of weld penetration increase are discussed profoundly.1. The effects of an activating flux on AZ31B alloy TIG, Plasma arc and laser welding were investigated. Results show that applying the activating flux on the AZ31B alloy surface leads to an increase in weld penetration depth in all three welding methods. However, the different kinds of fluxes have a different effectiveness in weld penetration increased. It found that various welding conditions such as welding current, welding arc length, welding shielding gas flowrate, welding speed, and flux thickness, influence the effectiveness of the activating flux on weld penetration increasing in different levels. The maximum increase level is the 300% of the weld penetration without flux. There is always a saturation point on the curve of coating quantity to penetration.2. The microstructure and mechanical property of the TIG welding seam was studied. The results showed that the fluxes can increase the weld penetration effectively and grain size in the weld seam of ACTIG welding of Mg alloy. The mechanical property of the weld joint with fluxes was correspondence to the weld joint without fluxws not only in the butt welding with the same weld penetration under different welding current but also in the bead welding with the different weld pentration under the same welding condition. The used of fluxes did not change the phase composition of the weld seam, which is composed with Mg-matrix andβ-Mg₁₇(Al,Zn)₁₂. The fractographs are similar in weld joint for with and without fluxes. There were some oxide particle in the weld seam when the oxide fluxes was used, which approve that the oxide fluxes enter into the weld seam following the convection of weld pool.3. The mechanism of weld penetration increase with activating flux was investigated with arc voltage measurement, arc images observation, arc spectrum analysis, temperature measurement, elements distributing analysis and weld pool convection verification.The chloride flux (CdCl₂) increase the arc voltage, change the arc images. The Cd atom and Cd⁺ ion were detected in weld arc. There was not Cd element in the weld seam. The convection of weld pool with CdCl₂ flux was not changed. So the chloride flux effect the weld arc mainly, increasing the arc energy and heat input so as to increase the weld penetration. The oxide flux (TiO₂) decrease the arc voltage, change the arc images a little. A small amount Ti atom were detected and Ti⁺ ion were not detected in weld arc. There was large quantity Ti element in the weld seam. The convection of weld pool with TiO₂ flux was changed. So the oxide flux effect the weld pool mainly, changing the Convection of weld pool into the mode for increasing the weld penetration.4. The complex formula which is composed of oxide fluxes is designed with the uniform design. The results of experiments showed that the optimally compound could increase the weld penetration in more efficiency than that of with single oxide flux. The optimally compound could refine the crystal grain while the optimally single oxide had opposite effect on the crystal grain of the welding seam. So the mechanical property of the optimally compound oxide sample is superior to the single oxide sample.In conclusion, the A-TIG welding method is a optimal welding technology for magnesium alloy welding.