Abstract
The effects of the gas tungsten arc (GTA) welding process on the microstructure and microhardness of two Mg-5Al-3RE and Mg-5Al-5RE experimental alloys (RE-rare earth elements) are presented. Both alloys were gravity-cast in a steel mould and GTA-welded in the same conditions. Analyses of the alloys' microstructure were carried out by scanning electron microscopy (SEM+EDX) as well as X-ray diffraction (XRD). In as-cast conditions; both alloys were mainly composed of α-Mg; Al(11)RE(3); and Al(10)RE(2)Mn(7) intermetallic phases. Additionally; α+γ eutectic (where γ is Al(12)Mg(17)) in the Mg-5Al-3RE alloy and an Al(2)RE phase in the Mg-5Al-5RE material were revealed. The same phase composition was revealed for both alloys after the GTA welding process. The results of the dendrite arm size (DAS) and Vickers microhardness measurements were also described. Both welded materials exhibited an intensive size reduction of the structural constituents after GTA welding. About 75% smaller values of the dendrite arm spacing were revealed in the fusion zones of the investigated materials than in the as-cast conditions. The GTA welding process also influenced the microhardness of the experimental alloys and increased them by about 21% compared to the base metal; which was the consequence of the refinement of the structural constituents.