Mechanical properties of rapidly solidified Mg-Al-Zn alloys

Rapid solidification of magnesium alloys composed of low cost elements such as aluminium (8-20 at%) and zinc (1-3 at%) has been carried out by centriugal atomization The resulting powders exhibited cellular/dendritic microstructures based on a supersaturated alpha-Mg solid solution matrix with beta- Mg17Al12 precipitates. Consolidation by extrusion and dynamic recrystallization leads to a duplex fine grained (similar to 1 mu) alpha-beta microstructure, which exhibited yield strength and ultimate tensile strength as high as 380 to 440 MPa in some alloys. Ductility is probably controlled by the phase distribution, but, for heavily alloyed compositions, the high volume fraction of beta-phase leads to brittleness. The result is that for industrial application, the concentration in aluminium must be kept below 15 at% and that of zinc below 3 at%. Because grain size is Limited by dynamic recrystallization during extrusion, any improvement in the tensile properties would need a thorough study of the effect of the critical densification parameters (eg ram speed and temperature).