Grain refining of aluminium and its alloys using inoculants

TLDR: Grain structure is an important and readily observable feature in cast aluminium alloys as mentioned in this paper, and three types of grain morphology are possible, namely, columnar, twinned columnar and equiaxed.

Abstract: Grain structure is an important and readily observable feature in cast aluminium alloys. Three different types of grain morphology are possible, namely, columnar, twinned columnar, and equiaxed. Inoculants in the form of master alloys are used to promote the formation of a fully equiaxed grain structure and this is termed grain refinement. Initially, fundamental aspects of solidification are outlined in order that the principles of grain refining using master alloys can be understood. Techniques for the commercial production and testing of common Al–Ti-based master alloys are then discussed briefly. The exact mechanisms by which grain refinement occurs are not yet fully understood and experimental and theoretical studies on the problem are critically reviewed with particular emphasis on (a) the role of solute titanium, (b) the thermodynamics of Al–Ti-based alloy systems, and (c) the nature of heterogeneous nuclei. Finally, current and future trends in the use of grain refining alloys are summarised.