Role of Fe/Mn Ratio and Cooling Rate on Precipitation of Iron Intermetallics α-AlFeMnSi and β-AlFeSi in a 356 Alloy

The effect of Fe/Mn ratio and cooling rate on the proficiency formation of iron intermetallics α-AlFeMnSi and β-AlFeSi was studied. Low Fe/Mn ratio promotes the formation and growth of α-AlFeMnSi and hinders the formation of β-AlFeSi. Increasing the cooling rate decreases the formation temperature of β-AlFeSi below the silicon-aluminum eutectic temperature. This effect is attributed to reduction of the β-AlFeSi particles in the microstructure. The combination of Fe/Mn = 1.5 ratio and cooling rate of 1 °C/s suppresses almost completely the β-AlFeSi particles and promotes the formation of α-AlFeMnSi. A general conclusion is: the α-AlFeMnSi phase is promoted at low Fe/Mn ratios and at high cooling rates, while the condition is opposite for β-AlFeSi phase.