Microstructure and properties of friction stir butt-welded AE42 magnesium alloy

The aim of the present work was to develop a friction stir joint and to investigate the microstructural and mechanical properties of magnesium (AE42 Mg alloy) sheets joined by friction stir welding (FSW). The two sheets, aligned perpendicular to the welding directions, have been successfully welded. Light optical microscopy was used to observe and study the weld zone characteristics. Dynamic recrystallisation was observed in the weld region as well as in the thermo-mechanical heat-affected zone (TMAZ). There was a clear decrease in the precipitate size from the base material through the TMAZ and into the weld zone. The precipitates observed were β-Mg17Al12, Al11Ce3 and Al2Ce. The welds were free of porosities. XRD, SEM and TEM characterization performed on the weld region showed the presence of intermetallic phases. Vickers micro-hardness testing was done along the thickness (transverse direction) of the plate in the weld region to study and understand the variation of hardness with thickness. A good correlation between the precipitate size and micro-hardness was observed.