Grain refinement of Al-Si casting alloys is commonly assessed by the presence of Ti and B in the melt, but in the last decade, thermal analysis has become an alternative control tool for the determination of the degree of refinement in the melt prior to casting. The objective of this work is to determine the best optimum method to predict the grain size in 319 and 356 Al-Si casting alloys by the use of the thermal analysis technique. Different time and temperature parameters from the cooling curve and its derivatives have been analyzed for a variety of grain refined samples. Four different master alloys (Al-6%Ti, Al-5%Ti-1%B, Al-2.5%Ti-2.5%B and Al-5%B) and two salt fluxes (AlTab-75%Ti and TiLite75BC-75%Ti-l.5%B) were used as grain refiners and samples were frozen at two different cooling rates (1.0 and 0.1°C/s). The effect of type of refiner and cooling rate on the thermal analysis parameters has been analyzed. / A time parameter, t1, which is the duration of the recalescence period, and the maximum undercooling and recalescence temperatures, TU and TR respectively, yield the best correlation with grain size. These results are consistent irrespective of the type of grain refiner, for both 319 and 356 alloys, but only when the alloy solidifies at a cooling rate of 1.0°C/s). Lower cooling rates produce scattering in the results. / Grain growth velocity, as calculated from the dendrite coherency point, correlates well with grain size for both alloys. A grain growth model is proposed to explain the effectiveness of these thermal parameters, where the duration of the recalescence period is related to a free growth period of the grains. Thermal analysis parameters related to the nucleation period seem to be sensitive to the type of grain refiner used and do not show good correlation with grain size.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.36015 |
| Date | January 1999 |
| Creators | Gloria Ibarra, David. |
| Contributors | Gruzleski, John E. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Mining and Metallurgical Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001737898, proquestno: NQ55334, Theses scanned by UMI/ProQuest. |
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