Entmischungs- und Rückbildungskinetik von silber- und kupferhaltigen Aluminium-Legierungen

Precipitate assemblies formed on dislocation loops in aluminium-silver-copper alloys

“…Considerable differences in the precipitation of the γ ′ phase in the ternary alloys. have been reported [11,23,19,24]. The γ ′ plates in ternary alloys were found to be finer in scale and were formed in greater number densities than in binary Al-Ag [11].…”

“…The Al-Ag-Cu phase diagram contains only binary phases in the aluminium-rich region [16] and the equilibrium phases identified are those found in the Al-Ag and Al-Cu binary systems. The γ ′ phase has also been reported in Al-Ag-Cu alloys [17,18], along with copper-containing θ ′′ (Al 3 Cu) and θ ′ (Al 2 Cu) intermediate phases [17,19,11,20,21]. The equilibrium γ (AlAg 2 ) and θ (Al 2 Cu) phase were also found after high temperature ageing [17].…”

“…have been reported [11,23,19,24]. The γ ′ plates in ternary alloys were found to be finer in scale and were formed in greater number densities than in binary Al-Ag [11]. Recent quantitative measurements found γ ′ number density were an order of magnitude greater in the ternary alloy compared to binary alloys aged under identical conditions [24].…”

“…The nucleation of the γ ′ (AlAg 2 ) phase is considered difficult despite the coherent precipitate-matrix interface, low interfacial energy [10] and the minimal volumetric strain [9] associated with the phase transformation. Silver-rich Guinier-Preston (GP) zones, whose formation precedes that of γ ′ , have been observed after 200 h ageing at 175 • C [11], indicating that significant amounts of silver remained partitioned to the GP zones, rather than precipitating as the γ ′ intermetallic phase. Precipitation of γ ′ precipitates generally requires the existence of suitable heterogeneous sites such as grain boundaries [12], dislocations [13,14,1] or dislocation loops [13] to assist in nucleation.…”

Nucleation and growth of the γ′(AlAg2) precipitate in Al–Ag(–Cu) alloys

“…There is exceptionally good 1:2 matching between the interplanar spacing of Al {111} planes (0.23 nm) and the γ ′ basal plane (c = 0.4607 nm [2]). This permits the formation of high-aspect ratio plates in Al-Ag [5,6,7] and Al-Ag-Cu alloys [8,9,10], in which the basal plane retains coherence with the {111} Al habit plane.…”