INFLUENCE OF TITANIUM TO BORON RATIO ON THE ABILITY TO GRAIN REFINE ALUMINUM-SILICON ALLOYS

Grain refinement is achieved in aluminium alloys by inoculating the mo lten metal with small amounts of titanium and boron. Grain refiners co ntaining high concentrations of titanium and boron are available comme rcially for this purpose. However, these grain refiners come in differ ent chemical compositions giving rise to a variety of Ti/B ratios. Alt hough it is accepted that increasing the amount of boron in the grain refiner gives beneficial effects on its performance, evidence for this is available principally in wrought aluminium alloys or in pure alumi nium. Foundry alloys which contain high concentrations of silicon did not appear to respond in a manner similar to the other aluminium alloy s. Hence, this work was undertaken to investigate the effects of vario us grain refiners on Al-Si alloys. One Al-Si alloy of a hypo-eutectic composition and another of eutectic composition were chosen for the st udy. The performances of three Tibor alloys Al-6%Ti, Al-5%Ti-1%B and A l-2.5%Ti-2.5%B were assessed on the two Al-Si alloys. The results show that the grain refiner Al-2.5%Ti-2.5%B is the most potent in both Al- Si alloys while the Al-6%Ti gave the worst performance. The refined gr ain size depends on the Ti content, Ti/B ratio and the matrix alloy co mposition. A logarithmic dependence of grain size on Ti level was noti ced in some cases while a power law dependence was appropriate for som e others.