The dissolution mechanism and kinetics of a number of strontium master alloys in liquid aluminum and A356 alloys have been investigated. The dissolution behaviour of the strontium alloys was found to show marked differences depending on strontium content. Dilute strontium alloys containing less than 63 weight percent Sr were observed to exhibit simple dissolution in both melts. The dissolution rate and the recoveries of these alloys were found to increase with increasing melt temperature. Over the temperature interval of 675-775$ sp circ$C dissolution was determined to be mass-transfer controlled with associated activation energies of 10-20 kcal/mole. Experimental rate constants for dissolution showed good agreement with a mass transfer correlation expressed as k = (0.67(Gr.Sc)$ sp{1/4}$ + 0.58(h/r)) (D/h). The dissolution of high strontium master alloys $(>$63 wt. pct. Sr), unlike the dilute alloys, was accompanied by the formation of various intermetallics. Additions at low melt temperatures yielded the exothermic formation of those intermetallics that have the lowest Sr content as seen in the relevant phase diagram, i.e., SrAl$ sb4$ in liquid Al and SrAl$ sb2$Si$ sb2$ in liquid A356. Due to low reaction rates at these low melt temperatures, these intermetallics formed as dispersed particles that could easily dissolve in the melt yielding high recoveries. At high melt temperatures, the associated chemical reactions yielded, as products, the higher Sr intermetallics which formed with little or no exothermicity. These intermetallics were observed to be scarcely soluble in the melt resulting in low strontium recoveries. The dissolution times of these alloys were found to show good agreement with calculated values based on a two-stage dissolution model comprising an initial exothermic reaction period and a subsequent free dissolution period. The strontium master alloys were classified in two groups; the high Sr alloys that are efficient at low temperatures of 675-7
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.75438 |
| Date | January 1987 |
| Creators | Pekgüleryüz, Mihriban Özden |
| 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: 000550582, proquestno: AAINL44335, Theses scanned by UMI/ProQuest. |
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