Thermodynamic evidence for a poisoning mechanism in the Al–Si–Ti system

Abstract

The poisoning of grain refinement in aluminium alloys owing to the presence of silicon is investigated using CALPHAD based thermodynamic modelling software. The existence of primary phases other than α-aluminium, namely TiSi₂ and TiSi, which are stable at typical melt holding temperatures, is consistent with microstructural observations of other researchers. The compositional and temperature range of these phases are calculated. The software is also used to determine the effect of silicon and titanium additions on the growth rates of α-aluminium grains via the growth restriction parameter Q. These results are used to explain poisoning in silicon containing foundry alloys via a thorough review and discussion of the relevant literature.

Keywords:

• POISONING
• SOLIDIFICATION MICROSTRUCTURE
• ALUMINIUM ALLOYS
• CALPHAD
• GROWTH RESTRICTION