Precipitation Process in a High Mg to Cu Ratio Al-Mg-Cu-Ge Alloy

Abstract

Precipitation process of Al-4.0Mg-1.5Cu-0.25Ge (wt.%) alloy ageing at 200 degrees C was investigated using conventional and high-resolution transmission electron microscopy techniques. For the peak-aged condition at 25 hours, the strengthening mainly derived from homogeneously formed GPB zones (2-4 nm in size) and fine S-phase precipitates (similar to 10 nm in size). Simultaneously, small amount of coarse S-phase precipitates and cube-shaped Z'-phase precipitates were also formed. Z-phase was transformed into more stable Z-phase with prolonged ageing. The microstructural evolution among those precipitates was preliminarily discussed.