Modelling of inoculation of metallic melts : Application to grain refinement of aluminium by Al-Ti-B

Grain refinement of aluminium and its alloys is common industrial practice. The field has been extensively investigated by many workers over the past 50 years, not only to develop efficient grain refiners for different aluminium alloys, but also to achieve an understanding of the mechanism of grain refinement. The present review confines itself to the literature on grain refinement by heterogeneous nucleation and alloying. Initially, the fundamentals of grain refinement by inoculants are outlined. The types of grain refiner, Al-Ti-B master alloys in particular, and their methods of manufacture are next discussed. The grain refining tests to assess the efficiency of the grain refiners and the grain refining behaviour of aluminium alloys are also discussed in brief. The performance of a grain refiner, as well as the response of an aluminium alloy to grain refinement, is influenced by the microstructure of the grain refiner as controlled by the process parameters involved in its preparation and the alloying elements present in the aluminium alloy. The roles of these factors, and particularly the roles of poisoning elements such as Si, Cr, Zr, Li, are reviewed. The paper also reviews the mechanisms of grain refinement, the fading and poisoning phenomena, and the trends in the development of new grain refiners for aluminium alloys containing poisoning elements.

Grain refinement of aluminium and its alloys by heterogeneous nucleation and alloying

Solidification microstructures: recent developments, future directions

A model of grain refinement incorporating alloy constitution and potency of heterogeneous nucleant particles

Grain Refining Mechanism in the Al/Al-Ti-B System

Grain refinement in commercial aluminium alloys can be achieved by addition of Al–Ti–B master alloys, containing α aluminium, TiB2, and Al3 Ti. The final grain size depends on the kinetics of both ...

New studies of nucleation mechanisms in aluminium alloys: implications for grain refinement practice

Conventional grain refining tests confirm that the presence of zirconium in commercial purity aluminium melts dramatically reduces the effectiveness of Al–Ti–B grain refiners. Quantitative comparisons suggest that this poisoning action cannot be attributed solely to reduction in growth restriction arising from changed solute contents in the melt. Microscopic analysis of TiB2 particles in an aluminium based, zirconium containing metallic glass shows the potential for substitution of zirconium for titanium. Analysis of a conventional Al–5 wt-%Ti–1 wt-%B refiner doped with zirconium shows the potential for similar modification of Al3 Ti. Thus zirconium can affect the nucleation stage of grain refinement by substituting for titanium in the aluminide and/or the boride phase, consistent with earlier work suggesting that the key to the nucleation potency is the existence of a layer of Al3 Ti on TiB2 particles.

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M. A. Kearns

Papers

New studies of nucleation mechanisms in aluminium alloys: implications for grain refinement practice

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