Abstract
Since both electron beam welding and laser welding have higher energy density than GTA and GMA welding, higher speed welding is possible in these welding methods. The cooling rates estimated by the dendrite arm spacings are from 500 to 800°C/s in the welding conditions used in electron beam welding, and from 300 to 1500°C/s in laser welding. According to the result of EPMA line analysis, magnesium segregates near boundaries of dendrites and the maximum content tends to decrease from about 14 mass% to 10 mass% as cooling rate increases, while the minimum content at the dendrite cores has the reverse tendency. The dissolved amount of magnesium in the weld metal is estimated using the relation between lattice parameter and magnesium content by X-ray diffraction technique. In laser welding, the dissolved amounts estimated are less by about 0.3 to 0.5 mass% than that of the base metal and tend to increase as the cooling rate increases. This phenomenon is due to the distribution of magnesium in the dendrites, because the dissolved amount becomes almost the same as the base metal when homogenizing heat treatment is performed on the weld metal. Metallurgical characteristics of aluminum alloy weld metal made by laser are almost the same as those by electron beam, because the cooling rate in the weld metal is almost the same.
