Alloy development for the enhanced stability of Ω precipitates in Al-Cu-Mg-Ag alloys

Abstract

The coarsening resistance and thermal stability of several V plate-dominated microstructures were controlled through altering the chemistry and thermomechanical processing of various Al-Cu-Mg-Ag alloys. Quantitative comparisons of V nucleation density, particle size, and thermal stability were used to illustrate the effects of alloy composition and processing conditions. The long-term stability of V plates was found to coincide with relatively high levels of silver and moderate magnesium additions, with the latter limiting the competition for solute with S-phase precipitation. This analysis revealed that certain microstructures initially dominated by V precipitation were found to remain stable through long-term isothermal and double-aging heat treatments, which represents significant improvement over the previous generation of Al-Cu-Mg-Ag alloys, in which V plates dissolved sacrificially after long aging times. The quantitative precipitate data, in conjunction with a thermodynamic database for the aluminum-rich corner of the Al-Cu-Mg-Ag quaternary system, were used to estimate the chemistry of the a/V-interphase boundary. These calculations suggest that silver is the limiting species at the a/V interfacial layer and that V plates form with varying interfacial chemistries during the early stages of artificial aging, which is directly related to the overall stability of certain plates.

Precipitation in a Ag-Containing Mg-Y-Zn Alloy

“…The segregation of Mg and Ag to the habit plane of the X plates leads to enhanced nucleation rates and thermal stability of the X plates. [50,54] C. Distribution of c¢¢ Precipitates…”

Impact of Cu/Mg Ratio on Thermal Stability of Hot Extrusion of Al-4.6 Pct Cu-Mg-Ag Alloys

“…The S phase is formed by dissolution of the X and h¢ phases. Recently, Gable et al [18] reported that the high level of Mg addition to Al-Cu-Mg-Ag alloy led to the precipitation of the S phase, which phase hindered the thermal stability of the X phase for long-term exposure above a temperature of 200°C. The T phase is generated by dissolution of the h¢ phase during extended exposure of the alloy over 150°C.…”

Statistical Model for the Mechanical Properties of Al-Cu-Mg-Ag Alloys at High Temperatures

“…Lumley and Polmear [10] mentioned that the composition of Ω was close to that of Al 2 Cu with Mg and Ag detected at /Ω interfaces. Gable et al [11] studied the stability of Ω phase at different aging temperatures of 200 and 250 ∘ C. It was shown that the density of Ω phase plates decreases intensely if the alloy is aged at a temperature at 250 ∘ C or higher for 30 minutes or longer. Also, Gable et al [11] showed that the thickness of Ω phase increases significantly if the alloy is aged at 250 ∘ C. Xiao et al [12] confirmed this observation where the Ω phases are thermally stable at temperatures below 200 ∘ C.…”

“…However, Ω phases in Al-Cu-Mg-Ag were finer compared with Al-Cu-Mg free of Ag. Gable et al [11] showed that the content of Ω phase is related to the content of Mg. Ω phase works with the other well-known precipitates and to enhance the mechanical properties significantly. The habit planes of phases are {001} and have a composition of Al 2 Cu and tetragonal plate-like shape [9,13].…”