Laser welding of AA 6082 by superimposing a pulsed Nd:YAG laser with a continuous wave diode laser was investigated in order to reduce the hot cracking susceptibility in bead on plate and butt welds. Conventional pulsed laser welds exhibit severe solidification cracking when a conventional rectangular laser pulse shape is employed. Due to the superposition of an Nd:YAG and diode laser beam crack free welds can be realized without the use of an additional filler material in the case of a sheet thickness of 0.5 mm. The diode laser beam simultaneously heats the base metal and weld metal during the melt pool solidification and compensates solidification shrinkage and thermal contraction. By means of an additional diode laser with a low output power of approximately 300W hot cracking could be eliminated in bead on plate welding. With an adapted clamping device and beam arrangement crack free butt welds could be realized in AA 6082-T6 for the first time. The major impact of the diode laser superposition on the hot crack suppression is expected to be achieved by compensating internal stresses resulting from the welding process as proven with the aid of a thermo-mechanical model.

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