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

Abstract

The present study deals with the structural characterisation of welds produced in the particulate composite 6061/Al₂O₃/10p by means of gas tungsten arc welding. Specimens of the composite were welded under various conditions and the structure of the welds obtained was analysed using optical microscopy, electron probe microanalysis, and scanning electron microscopy. It appears that, during welding, a thin particle free (denuded) zone is formed below the upper surface of the weld. The formation of this zone results from a combination of Marangoni flow and arc plasma drag. Furthermore, it was found that, during solidification of the weld metal, particle pushing takes place, which results in redistribution of the particles. This phenomenon is particularly apparent in the vicinity of the fusion boundary. It was also shown that, during welding, Mg₂Si precipitates are formed in the interfacial zone between the particle and the matrix. Welding experiments were also carried out with filler wire addition. It was found that only limited mixing occurs in the weld pool between the filler wire material and the composite.^a The degree of mixing increases with increasing travel speed and is independent of wire feed rate.