Microstructural evolution after creep in aluminum alloy 2618

Abstract

The microstructural evolution of Al–2.24 Cu–1.42 Mg–0.9 Fe–0.9 Ni (AA2618) alloy after 195 °C/18 h aging, as well as after 180 and 240 °C/100 h creep, has been studied by transmission electron microscopy and high resolution electron microscopy (HREM). The Guinier–Preston–Bagaryatsky (GPB) zones/co-clusters, S″, S, and Al9FeNi phases co-exist in the alloys after the 195 °C/18 h aging. After creep, precipitates become coarser and the transformation of GPB zones/co-clusters and S″ to S phase take place. A large number of GPB zones/co-clusters as those in aging state exist after 180 °C/100 h creep which possibly dynamically precipitates during the creep process. After the 240 °C/100 h creep, most of the precipitates are S variants with a few GPB zones and S″ phase. More dislocations appear upon which precipitate colonies form after creep. HREM images show that most of the early precipitates less than about 5 nm cannot exhibit perfect lattice image for the existence of stress. However, certain GPB/co-clusters possessing coherent relationship with the matrix can also be observed. HREM demonstrates that certain S particles viewed along [100]S and [013]S have classic orientation relationship with the matrix, and that those upon the dislocations depart from the standard orientation.