Evolution of Ω phase in an Al-Cu-Mg Ag alloy a three-dimensional atom probe study

On the origin of the high coarsening resistance of Ω plates in Al–Cu–Mg–Ag Alloys

Effect of rare earth Ce addition on the microstructure and mechanical properties of an Al–Cu–Mg–Ag alloy

Effect of Rare Earth Sc Addition on Microstructure and Mechanical Properties of an Al-Cu-Mg-Ag Alloy

Conventional strain contrast transmission electron microscopy (CTEM) and high-resolution transmission electron microscopy (HRTEM) were performed to establish the nucleation and growth mechanism of Al2CuLi (T1) precipitates in an Al-Li-Cu alloy. It is shown that the growth mechanism ofT
 1 precipitate plates occurs by the diffusional glide of growth ledges composed of b = 1/6〈112〉 partial dislocations on 111 matrix planes and that the growth ledges migrate by the ledge-kink mechanism, as previously suggested by Cassadaet al. 1 for this system.T
 1 plate nucleation is modeled as the dissociation of a perfect b = 1/2〈110〉 matrix dislocation in the vicinity of a dislocation jog. The coordinated dissociation of the dislocation line segments on each side of the sessile jog provides the displacement necessary for the formation of a new hexagonal plate or plate ledge. Strain contrast analysis of the Burgers vector of plate edges and the edges of growth ledges indicates the stacking of partial dislocations is of mixed displacement. Formerly Graduate Student, Department of Materials Science, University of Virginia,

Mechanism of Al 2 CuLi ( T 1 ) nucleation and growth

Adding small amounts (<1wt-%) of both magnesium and silver to an aluminium alloy containing about 4 wt-% Cu causes precipitates with a hexagonal structure (Ω-phase) to form on {111} planes of the aluminium lattice. Precipitation of θ′ on {100} planes may also occur, the relative proportions of the two types of precipitate being dependent on the levels of magnesium and silver, e.g. ~0·7 wt-% of each element almost entirely suppresses θ′ formation. Even when θ′ does form in parallel with Ω-phase, on prolonged aging it tends to dissolve in favour of Ω growth. Using an X-ray technique to establish foil thickness, the relative amounts of Ω and θ′ precipitate have been measured as a function of aging time, analysis of the data showing that growth is diffusion controlled with an activation energy of 136± 15 kJ mol−1.MST/648

V. D. Scott

Papers

Nucleation and growth of precipitates in Al–Cu–Mg–Ag alloys