Microstructure and magnesium burning loss behavior of AA6061 electron beam welding joints

Full penetration butt welding with different parameters was performed on 4 mm thick AA6061 plates. The microstructural characteristics, element burning loss behavior and their effects on the mechanical properties of the weld beams were studied. It revealed that the weld porosity could be effectively controlled with a lower welding velocity and the crystal enlargement is rather obvious near the weld upper surface. The secondary-precipitated phase AlFeSi was observed at the crystal boundaries, whereas the strengthening phase Mg2Si within the welds is undetectable by SEM. The magnesium burning loss behavior of the welds embodies in two aspects: the decrease in magnesium content compared to the original alloy and the uneven distribution of magnesium with a decrease tendency as close to the weld surface and a symmetric growth as further away from the seam center line. The welded joints with a higher burning loss degree of magnesium are performed at a lower Vickers hardness, tensile strength, plasticity and toughness. The characteristic isotherm and convection within the molten pool during EBW were considered as the key factors that dominated the microstructure and magnesium distribution.