Effect of Al-Si and Al-Mg filler wires on microstructure and mechanical properties of bead-on-plate weld on AA6061-T6 using CMT welding

In recent times, cold metal transfer (CMT) welding has become a popular choice to weld large structures of aluminium and its alloys as it provides good quality weld beads with lesser heat input. The welded joint of AA6061-T6 achieved through CMT welding provides the desired characteristics and better mechanical performance than other fusion welding methods. In the present work, bead-on-plate experimentation has been performed on an AA6061-T6 plate with two different filler wires ER4043 and ER5356 using two combinations of welding speed and current, keeping the gas flow rate constant throughout the experiment in CMT welding. Optical micrograph and X-ray diffraction analysis have been studied from which it has been observed that bead welded with ER5356 exhibits more fine equiaxed grain structure in the fusion zone and columnar-dendritic fragmentation in HAZ than beads welded with ER4043 due to the presence of higher amount of Mg₂Si. X-ray diffraction reveals the presence of different phases with silicon found exclusively in specimens welded with ER4043. Porosity, dilution, microhardness and tensile strength have been examined over the weld bead and a comparison has been done between the filler wires at the same welding parameters. Porosity levels have notably elevated, measuring 53.69% and 55.71% higher in specimens welded with ER4043 filler than ER5356. Similarly, the dilution level is 33.33% and 17.51% higher in specimens welded with ER4043 filler than ER5356. Conversely, specimens welded with ER5356 filler exhibited a 4.02% and 20.37% increase in microhardness and a 3.42% and 8.82% improvement in tensile strength as compared to ER4043.