Effect of Different Fluxes on the Weld Bead Formed on AZ91 Magnesium Alloy Using Activated Gas Tungsten Arc Welding

In this study, A-TIG was employed to deposit the bead on plate (BOP) on AZ91 sheet having thickness of 5 mm using different layers of MgO, MgF2, CdCl2 and Cr2O3. In order to have comparison, uncoated sample also was used. Visual analysis of cross section of weld beads showed that the bead made with the help of MgO flux has porosity, while other weld beads were without any porosity-like defects. The bead obtained with the implementation of MgF2 flux layer has the highest depth of penetration of 2.67 mm with a width of 6.78 mm. The bead formed with Cr2O3 flux showed the highest depth to width ratio which is 0.417 in contrast to ratio of 0.196 obtained with uncoated bead due to focusing of welding arc on narrow region. Analysis suggests that the improved depth of penetration in different fluxes is a result of the increased arc energy due to interaction of arc with dissociated Cr and Cd from Cr2O3 and CdCl2. While in case of MgF2 flux, mechanism responsible for deeper penetration is probably the arc constriction because halides are electronegative and attract the free electrons through inner region of welding arc resulting in concentrated and hotter arc. The bead obtained with CdCl2 has coarsest secondary phase precipitates in contrast to all other deposited beads, but these are finer as compared to precipitates in base metal region.