The composition specification for A3003, a general purpose Al-Mn alloy, allows for Fe contents up to 0.7wt%. However, at higher iron concentrations, an intermetallic phase, ꞵ-Al9Fe2Si2, can precipitate, which has a detrimental effect on the mechanical properties. Thermo-Calc can be used to predict the stability of ꞵ-Al9Fe2Si2 as a function of alloy chemistry and temperature.
The figure shows that ꞵ-Al9Fe2Si2 is stable over a wide temperature range, and three times as much of this phase forms as the iron content increases from 0.2% to 0.7%. If this phase should be avoided for a certain application, then the iron content needs to be strictly controlled in order to suppress the transformation from α to ꞵ-Al9Fe2Si2.