Influence of welding on structure of Al-Mg-Si matrix composites

The present study deals with the structural characterisation of welds produ ced in the particulate composite 6061/Al2O3/10p by means of gas tungsten ar e welding. Specimens of the composite were welded under various conditions and the structure of the welds obtained was analysed using optical microsco py, electron probe microanalysis, and scanning electron microscopy. It appe ars that, during welding, a thin particle free (denuded) zone is formed bel ow the upper surface of the weld. The formation of this zone results from a combination of Marangoni flow and are plasma drag. Furthermore, it was fou nd that, during solidification of the weld metal, particle pushing takes pl ace, which results in redistribution of die particles. This phenomenon is p articularly apparent in the vicinity of the fusion boundary. It was also sh own that, during welding, Mg2Si precipitates are formed in the interfacial zone between the particle and the matrix. Welding experiments were also car ried out with filler wire addition. It was found that only limited mixing o ccurs in the weld pool between the filler wire material and the composite. The degree of mixing increases with increasing travel speed and is independ ent of wire feed rate. MST/3923.