APFIM/TEM observations of a high strength - creep resistant Al-Cu-Mg-Si-Ge alloy

Atom probe field ion microscopy (APFIM) in conjunction with transmission electron microscopy (TEM) were used to study the clustering and precipitation processes in an experimental Al alloy designated ALMAGEM, having composition Al-2.41Cu-0.34Mg-0.1Si-0.04Ge (at. %). Independent clusters of Cu, Mg, Si and Ge were detected in the as-quenched condition. At 170 °C, age hardening proceeds through a single stage, however, several precipitation processes were detected. During the early stages of ageing, the microstructure contained a fine and uniform dispersion of GP zones. Atom probe analysis also detected evidence of a preferred Mg-Ge interaction in samples aged for 5 min. Further ageing resulted in partial reversion of the GP zones and a co-precipitation reaction involving the formation of θ', rod-shaped Cu-Mg rich GPB-like zones and Mg-Ge precipitates or zones. Moreover, Si was usually detected in all phases, but levels varied. Furthermore, Mg was detected in association with θ'. Peak hardness at 170 °C was associated with the presence of the Cu-Mg rich GPB-like zones.