Metallurgical characteristics of A5083-O aluminium alloy welded by high energy density welding

Summary

Since electron beam welding and laser welding have a higher energy density than GTA and GMA welding, both methods allow higher speed welding. The cooling rates estimated in the present research study range between around 500–800°C/sec and around 300–1500°C/sec under the welding conditions respectively adopted in electron beam welding and laser welding. The results of line electron probe microanalysis (EPMA) suggest that magnesium segregates near the dendrite boundaries and that the maximum content tends to decrease from around 14 to 10 mass% as the cooling rate increases. The minimum content at the dendrite cores exhibits the reverse trend. The dissolved amount of magnesium in the weld metal is estimated from the relationship between the lattice parameter and the magnesium content by the X-ray diffraction method. In laser welding, the estimated dissolved amounts of magnesium are around 0.3–0.5 mass% less than in the base metal and tend to increase with an increasing cooling rate. This phenomenon is due to the distribution of magnesium in the dendrites, the dissolved amount becoming almost the same as in the base metal when the weld metal is subjected to homogenising heat treatment. The metallurgical characteristics of aluminium alloy weld metal produced by laser welding are much the same as those produced by electron beam welding, because the cooling rate in the weld metals is much the same.