Effect of groove shape on laser welding-brazing Al to steel

Defocused laser welding-brazing of 2-mm-thick 6061-T6 aluminum alloy and DP590 steel in butted configuration was performed with AlSi12 flux-cored filler metal. Three different groove shapes at steel side were made: square-shape, half Y-shape and half V-shape. The experimental results indicated that inhomogeneous inter-metallics compounds (IMC) morphology along the steel appeared from top to bottom region. In top region, IMCs consisted of needle theta-Fe(Al,Si)(3) + serrated tau(5)-Fe1.8Al7.2 for three joints and their average thickness was different (10.2-mu m for square-shape, 10.1-mu m for half Y-shape while 8.6-mu m for half V-shape). In middle region, only 2.0-mu m tau(5)-Fe1.8Al7.2 was detected in joint with square-shape groove while theta-Fe(Al,Si)(3) + tau(5)-Fe1.8Al7.2 with the average thickness of 7.2-mu m and 4.9-mu m were observed in joints with half Y-shape and half V-shape grooves. In bottom region, insufficient metallurgical reaction occurred in joint with square-shape groove while tau(5)-Fe1.8Al7.2 with the average thickness of 1.2-mu m and 1.1-mu m were formed in joints with half Y-shape and half V-shape grooves, respectively. The smallest temperature gradient along the steel interface in thickness direction was noticed in joint with half V-shape groove, resulting in the least difference of IMC thickness values from top to bottom. The results of tensile test indicated that the highest tensile strength was achieved in joint with half V-shape groove because of its excellent spreading behavior of molten filler metal, largest bonding interface area and suitable interfacial IMC distribution along the steel interface.