Nucleation of Ω phase in an Al-Cu-Mg-Mn-Ag alloy aged at temperatures below 200°C

In an Al-Cu-Mg-Mn alloys containing 0.4 wt% Ag, the nucleation of ω phase occurs readily even aging at 160°C. The nucleation of ω phase occurs predominantly upon the Mn bearing dispersoids. The presence of Si in Al-Cu-Mg-Mn alloys with relatively high Mg:Si ratios does not inhibit the formation of the ω phase. The presence of excess amounts of Si in the alloy does, however, give rise to the formation of an additional precipitate, σ, and such an observation is consistent with the known role of Si in stabilizing the σ phase in Ag and Mn free Al-Cu-Mg alloys.