Laser beam welding of Al–Mg–Si–Cu alloy 6013 sheet using silicon rich aluminium filler powders

Abstract

Butt welds of 1.6 mm thickness sheet of the Al–Mg–Si–Cu alloy 6013 were produced using a 3 kW Nd : YAG (neodymium : yttrium–aluminium–garnet) laser. The sheet was welded in the T4 and T6 temper conditions using filler powders of alloys Al–5%Mg, Al–12%Si, Al–20%Si and Al–40%Si. Microstructure, hardness profile, tensile properties and corrosion behaviour of the welds were investigated in the as welded conditions and after a post-weld heat treatment to the T6 temper. Pores were observed in the fusion zone, which exhibited a dendritic microstructure. Post-weld artificial aging increased the hardness in the fusion zone owing to precipitation of strengthening phases. Joint efficiencies between 80 and 90% were achieved for 6013 alloy welds in the as welded T4 condition. After a post-weld heat treatment to the T6 temper, the strength approached 90% of the ultimate tensile strength of the base material 6013-T6 for welds made with silicon rich filler powders. Joints in the as welded T4 and post-weld heat treated T6 temper conditions suffered pitting when exposed to an intermittent acidified salt spray fog. In the as welded T6 condition, welds exhibited zones adjacent to the fusion boundaries that were not corroded. These corrosion free zones were not observed after alternate immersion tests in 3.5%NaCl solution. As welded 6013-T4 joints were susceptible to stress corrosion cracking in the heat affected zone when immersed in an aqueous chloride–bicarbonate solution.