Strength improving mechanism of laser arc hybrid welding of wrought AA 2219 aluminium alloy using AlMg5 wire

Laser arc hybrid welding of wrought AA 2219 aluminium alloy was studied. The cross-weld tensile strength of the joint using AlMg5 wire was 20% higher than that using AlCu7 wire. The reasons for strength improvement were analysed by microstructure observations via scanning electron microscopy, transmission electron microscopy and electron backscattering patterns. The results showed the strength improvement of the joint using AlMg5 wire depended on two reasons. One is the formation of large amount of fine S-Al2CuMg precipitates. The other is the preformed pinning effect of the precipitates on the dislocations. Finally, the formation of the fine S-Al2CuMg precipitates of the joint using AlMg5 wire was discussed by thermodynamic calculation, and the formation of the preformed dislocation pining effect was discussed by the collision theory of adjacent dendrites during solidification.