The microstructure and mechanical strength of Al-6061-T6 GMA welds obtained with the modified indirect electric arc joint

Plates of Al-6061-T6 with a thickness of 12.7 mm were welded with a non-heat treatable ER4043 electrode in four welding passes using the typical single V groove butt joint (at room temperature) and in one pass using the novel modified indirect electric arc (MIEA) joint (at 50, 100 and 150 °C). Microstructural characterization of the weld metal revealed that the MIEA joint design yielded microstructures in which columnar growth was restricted and a grain refining effect occurred without the addition of inoculants, even with preheating of the joints. The self-refining effect in the MIEA joint was discussed in terms of the cooling behavior and the large dilution of base material. Vickers microhardness profiles revealed that the high dilution rates obtained with the MIEA joint caused alloying of the weld pool with magnesium producing a weld metal composition sensible to heat treating due to the precipitation of Mg₂Si precipitates. The grain self-refining effect of the MIEA joint along with alloying of the weld metal were found to have a profound impact on the mechanical properties of the welded joints.