INFLUENCE OF GRAIN REFINER ADDITION ON THE PRECIPITATION OF Fe-RICH PHASES IN SECONDARY AlSi7Cu3Mg ALLOYS

摘要

The effect of grain refiner addition on the precipitation of Fe-rich compounds in secondary AlSi7Cu3Mg has been studied. Thermal and metallographic analysis techniques have been used to examine the formation of Fe-bearing intermetallics. The results show that grain refinement with AlTi5B1 can alter the precipitation sequence of Fe-rich phases. In non-grain refined alloy and grain-refined alloy with AlTi10, two different Fe-rich phases, alpha-Al-15(Fe, Mn)(3)Si-2 and pi-Al8Mg3FeSi6, form, whereas, with AlTi5B1 addition, the beta-Al5FeSi phase also tends to crystallize, nucleating on TiB2 particles. It has also been demonstrated how at high cooling rates, the b-Al5FeSiinvolved reactions occur more preferentially, when compared to alpha-Al-15(Fe,Mn)(3)Si-2 phase. This crystallization behaviour is explained in terms of phase diagram relationship and the nucleation kinetics of competing beta-Al-15(Fe, Mn) Si-3(2) and b-Al5FeSi phases.