Optimizing the composition of master alloys for grain refining aluminium
- Nanyang Technological Univ., Singapore (Singapore)
Aluminium alloys are grain refined by inoculating the melt with specially prepared master alloys, called Tibor alloys, which contain high levels of Ti and B. Such Tibor grain refiners are commercially available in various chemical compositions and are widely used by aluminium smelters, alloy makers and even foundries. Systematic studies have been done to evaluate the grain refining potency of several of these commercial Tibor alloys. The general finding had been that the inoculation level, i.e., content of Ti and B in the matrix alloy after inoculation, has a marked effect on the resulting grain size. Ti and B in solution will readily combine to form TiB{sub 2} under these conditions and hence, the presence of free Ti and B simultaneously in solution is an unlikely prospect. Depending on the prevailing B/Ti ratio, either free Ti, or free B, is likely to occur except when the ratio is the ideal stoichiometric atom ratio of 2/1 for TiB{sub 2}. Commercial grain refiners have B/Ti atom ratios lower than 2/1, i.e., they contain an excess of Ti. Evaluations of grain refiners have shown that an excess of Ti is essential for efficient grain refinement. On the other hand, eliminating B totally from the grain refiner also diminishes its potency. Therefore, B plays an important role in improving the grain refinement potency of Tibor alloys but, too much of it may lessen the effect. An optimum B/Ti ratio may then exist. This study was undertaken to determine this optimum value.
- OSTI ID:
- 409678
- Journal Information:
- Scripta Materialia, Journal Name: Scripta Materialia Journal Issue: 9 Vol. 35; ISSN 1359-6462; ISSN SCMAF7
- Country of Publication:
- United States
- Language:
- English
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