Effect of instability of TiC particles ongrain refinement of Al and Al–Mg alloysby addition of Al–Ti–C inoculants

Abstract

Thermodynamic modelling shows that while TiC is a stable phase in Al–Ti–C grain refiners, it should decompose on addition of the refiners to typical Al alloys. The present work assesses the impact of melt composition on TiC stability and on grain refiner performance, which has been tested at various addition levels in Al and Al–Mg alloys. In melts with compositions that stabilise TiC, there is effective grain refinement with little fading of performance on holding the refiner in the melt. In melts with compositions in which TiC is not stable, grain refinement is impaired even at short holding times, and becomes markedly worse at longer holding times. It is concluded that in typical cases progressive decomposition of TiC does occur, and that this can have a significant effect on grain refinement by inoculation with Al–Ti–C master alloys.