Nd: YAG laser welding of aluminium to low carbon steel

Abstract

The lap-welding of 6000 aluminium alloys to low carbon steel was investigated in key-hole mode with a Nd:YAG cw laser in 2 configurations: aluminium upon steel and steel upon aluminium. The influence of 3 main parameters was examined: the focal length (150 mm and 200 mm), the spot regime (single spot and dual spot welding), and the use -or not- of a brazing flux. For each welding condition, different welding speed (3 to 7 m.min−1) and laser power (2 to 3.5 kW) were used to vary the penetration depth in the lower plate.To analyze the effect of each parameter on the welds, welds were observed by optical microscope, X-ray radiography and scanning electronic microscope, the phase composition was characterized by energy dispersive spectrometry and the microhardness by Vickers hardness test. Also, the mechanical properties of the welds were determined by tensile tests. In addition, the process was analysed with a 4000 Hz fast camera to investigate the melt pool stability during welding for each welding condition.The first results show that the best welds were obtained when welding steel upon aluminium and for a limited penetration depth. In this configuration, most of the weld is made of a solid solution of aluminium in iron with a limited layer of FexAly intermetallics at the interface, and a rather small hardening effect on the weld. In the case of aluminium upon steel, the intermetallics layer was shown to be larger, and their stoechiometry (mainly Fe2Al5) seemed to be detrimental to the resistance of the welds, which presented large transverse cracks. Last, the use of a dual spot configuration allowed to stabilize the melt pool dynamics, and to optimise the Al-Fe mixing.The lap-welding of 6000 aluminium alloys to low carbon steel was investigated in key-hole mode with a Nd:YAG cw laser in 2 configurations: aluminium upon steel and steel upon aluminium. The influence of 3 main parameters was examined: the focal length (150 mm and 200 mm), the spot regime (single spot and dual spot welding), and the use -or not- of a brazing flux. For each welding condition, different welding speed (3 to 7 m.min−1) and laser power (2 to 3.5 kW) were used to vary the penetration depth in the lower plate.To analyze the effect of each parameter on the welds, welds were observed by optical microscope, X-ray radiography and scanning electronic microscope, the phase composition was characterized by energy dispersive spectrometry and the microhardness by Vickers hardness test. Also, the mechanical properties of the welds were determined by tensile tests. In addition, the process was analysed with a 4000 Hz fast camera to investigate the melt pool stability during welding for each welding conditio...