2001 Volume 19 Issue 4 Pages 656-663
In the weld metal of A5083 welded with high energy density such as electron beam and laser beam, the amount of solute (mainly magnesium) of the primary crystals tends to increase with the increase in the welding speed. The solute concentration of solid phase tends to increase generally with the increase in the solid fraction and increases rapidly near the last stage of solidification, that is, the dendrite boundary. Though the dissolved amount of magnesium in the weld metal estimated with Xray diffraction technique becomes lower than that of the base metal, this tends to approach to that of the base metal after the weld metal was homogenized. In this paper, we examined these phenomena more precisely. First, we calculated the distributions of magnesium by applying the rapid solidification theory when the dendrite arm spacings (DAS) were changed to several steps. Then, the dissolved amount of magnesium in the dendrite was calculated by considering the distributions of magnesium and we made clear the influence of DAS on the dissolved amount of magnesium. Next, we also calculated the distributions of magnesium when the weld metal was homogenized and made clear the influence of DAS on the dissolved amount of magnesium after the homogenization. Moreover, the actual weld metals, in which DAS were changed, were obtained by changing the welding conditions with electron beam and we could experimentally confirm the same tendency as mentioned above which were simulated by the calculation. It was made clear that the Charpy impact energy of the weld metals linearly increased with the increase in the dissolved amount of magnesium.
