general concept of the grain refinement mechanism in hypoeutectic AlNi alloys has been
adopted from that in wrought alloys without consideration of the influence of the silicon content. In the
present investigation the commerical grain refinement practice in Al-5 foundry alloys has been
experimentally simulated by introducing synthetic TiB2 crystals directly into AlLSi melts. To explore the
possible use of a new generation of Al-Ti-C master alloys in these alloys, the behaviour of synthetic TiC
has also been studied. Experimental findings indicate that in the presence of Si, TIC crystals are highly
unstable in aluminium melts. TiBz crystals alone do not nucleate the cc-phase, whereas in the presence of
dissolved Ti a ternary Al-Ti-Si interfacial layer is formed on the TiB? which subsequently nucleates the
cc-Al, via a peritectic reaction. However, due to a drastic decrease in the peritectic temperature, the
efficiency of grain refinement is greatly reduced. A theoretical analysis indicates that when boron is added
in excess of TiB2 stoichiometry, or simply as AlB2, grain refinement occurs by a eutectic reaction. Copyright