For more than 50 years grain refinement of aluminium and its alloys is common industrial practice. Several theories have been developed to understand the different mechanism of this technique. Common grain refiners for Al alloys are Ti and B. But up to now there is no consensus on the mechanism of grain refinement in aluminum alloys. One important aspect of grain refinement is the thermodynamics of the phases involved.
In this work the different theories of grain refinement of Al-Si alloys are presented. A thermodynamic data set for the quaternary Al-Si-Ti-B system were developed. Thermodynamic calculations were shown for the ternary Al-Ti-B, Al-Si-B, Al-Si-Ti and the quaternary Al-Si-Ti-B system. The relevance for problems in grain refinement is discussed on several calculated sections.