Grain refinement by Al-Ti-B alloys in aluminium melts: a study of the mechanisms of poisoning by zirconium

Conventional grain refining tests confirm that the presence of zirconium in commercial purity aluminium melts dramatically reduces the effectiveness o f Al-Ti-B grain refiners. Quantitative comparisons suggest that this poison ing action cannot be attributed solely to reduction in growth restriction a rising from changed solute contents in the melt. Microscopic analysis of Ti B2 particles in an aluminium based zirconium containing metallic glass show s the potential for substitution of zirconium for titanium. Analysis of a c onventional Al-5 wt-%Ti-1 wt-%B refiner doped with zirconium shows the pote ntial for similar modification of Al-3 Ti. Thus zirconium can affect the nu cleation stage of grain refinement by substituting for titanium in the alum inide and/or the boride phase, consistent with earlier work suggesting that the key to the nucleation potency is the existence of a layer of Al-3 Ti o n TiB2 particles. MST/4298.