Nd:YAG laser butt welding of AA6013 using silicon and magnesium containing filler powders

Aluminium alloy 6013 sheet was butt welded using a 3 kW Nd:YAG laser and different filler powders. Two kinds of filler metals were used: gas atomised powders of the aluminium alloys AlMg5, AlSi12, AlSi12Mg5 and AlSi10Mg, as well as mixtures of powders of the elements Al and Si and the binary alloys Al-5Mg, Al-5Zr, Al-5Cr and Al-10Mn. Microstructure, hardness, tensile properties and corrosion behaviour of the welds were investigated in the as-welded T4 and T6 conditions and after a post-weld heat treatment to the T6 temper. The weld region exhibited a dendritic cellular structure in the fusion zone and a partially melted zone adjacent to the fusion boundaries. The hardness of the fusion zone depended upon the filler metals used. Post-weld artificial aging to the T6 temper improved the hardness, being associated with precipitation of strengthening phases, as confirmed by transmission electron microscopy. Joint efficiencies achieved for post-weld heat treated joints ranged from 80 to 90%. Strengths of welds in the as-welded T6 condition were lower due to the softened fusion zone and heat affected zone, being between 70 and 75 % of the ultimate tensile strength of the base alloy 6013-T6. Optimum tensile properties were obtained with joints made with the filler powder AlSi12. Reasonable tensile properties were achieved for welds made with mixtures of elemental and binary alloy powders, but they did not reach those of joints made with aluminium alloy powders. The dispersoid forming elements Zr, Cr and Mn added to a mixed Al-7Si powder did not prove beneficial effects on weld quality. When exposed to an intermittent acidified salt spray fog, joints in the as-welded T4 and post-weld heat treated T6 conditions exhibited corrosion behaviour similar to that of the base sheet in the tempers T4 and T6. As-welded 6013-T4 joints were susceptible to stress corrosion cracking when immersed in an aqueous solution of 0.6 M NaCl + 0.06 M NaHCO3 . Sensitivity to environmentally assisted cracking was associated with grain boundary precipitates in the heat affected zone. (c) 2006 Elsevier B.V. All rights reserved.