To improve the mechanical properties of the most widely used Al-Si foundry alloys, small amounts of magnesium are often introduced. However, the effect of magnesium on the eutectic microstructure is unclear. The aim of the present work is to investigate the effect of magnesium on the eutectic microstructure and to clarify its role in the silicon solidification. / Experiments were performed on hypoeutectic and eutectic alloys (Al-7%Si, Al-11%Si, Al-13%Si and 413.2 alloys). Assessment of the eutectic microstructure was done using thermal analysis and metallography. The silicon phase was quantified by image analysis in terms of its perimeter, shape factor and aspect ratio. The results reveal that in hypoeutectic and eutectic synthetic alloys magnesium decreases the homogeneity of the microstructure. At about 1%Wt Mg, however, magnesium refines slightly the silicon phase. It was found that magnesium has a negative effect on strontium modification, that is, it changes the microstructure from well modified to partially modified. This is believed due to the presence of a complex intermetallic compound $ rm(Mg sb2SrAl sb4Si sb3)$ formed prior to the eutectic transformation. It is suggested that magnesium not be added in excess of 0.6 Wt% in strontium modified Al-Si alloys.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.60473 |
| Date | January 1991 |
| Creators | Joenoes, Ahmad T. (Ahmad Taufik) |
| 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 | Master of Engineering (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: 001287950, proquestno: AAIMM72026, Theses scanned by UMI/ProQuest. |
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