Microstructures and precipitation behaviour of cryomilled Al–Zn–Mg–Cu–Mn powders

Abstract

Supersaturated Al-Zn-Mg-Cu-Mn alloy powder was fabricated by rapidly solidification and cryomilling methods. The microstructures and its evolution of the as cryomilled powders during subsequent processing were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that both of diffraction peak shift and broadening are occurred because of dissolution of large numbers of alloying elements into a-Al matrix after cryomilling. The only equilibrium phase precipitated from supersaturated a-Al is g (MgZn 2 ) phase when annealing temperature is below 350uC. No metastable Mn containing precipitate is found when annealing temperature is below 350uC or at 350uC for a short time. When the powder is heated at 350uC for a long time or a high temperature above 350uC, the nano scaled stable Al 6 Mn particles with a uniform distribution precipitates directly from a-Al matrix, however, transition Mn containing phase is not detected by both XRD and SEM methods.