The Influence of Boron on the Mechanism of Grain Refinement in Dilute Aluminium-Titanium Alloys

AbstractThe phases separating from melts treated with titanium and boron were identified, crystallization nuclei were analysed, and the significance of the initial Ti/B ratio of the melt in relation to grain refinement was demonstrated. Special attention was given to establishing the true relationship between the boron content and the position of the Al–Ti liquid us under both equilibrium and non-equilibrium conditions. The evidence is consistent with TiAl3 precipitation on boride particles during cooling from the melt holding temperature; the particle complexes so formed then nucleate the aluminium solid solution. The presence of a solid-solution phase of the (Al,Ti)B2 type was confirmed, but Its mode of formation does not play a major role in the grain-refining mechanism.