Particle evolution in Mg-Zn-Zr alloy processed by integrated extrusion and equal channel angular pressing: Evaluation by electron microscopy and synchrotron small-angle X-ray scattering

The evolution of intermetallic precipitate particles in Mg-Zn-Zr alloy ZK60 during thermomechanical processing by integrated extrusion and equal channel angular pressing was investigated in detail. Electron microscopy was employed to analyse individual particles and their orientation within the Mg matrix, while small-angle X-ray scattering (SAXS) was used for an assessment of global particle behaviour and statistical significance of their volume in the microstructure. A significant redistribution of prismatic rod-type and basal platelet-type precipitates, as well as their resolutioning followed by the formation of prismatic platelets, was found. The platelet-type precipitates lying on prismatic planes were hitherto unknown for the Mg-Zn-Zr system. These precipitates were present in a statistically significant amount detectable by SAXS. Such precipitates should favour an increase of critical resolved shear stress for basal slip in the Mg matrix, thus contributing to an improved performance of the Mg-Zn-Zr alloy. The possibility of formation of prismatic platelet-type precipitates in Mg alloys proven in this paper opens up a new avenue for the design of relatively inexpensive high-performance magnesium alloys.