Mechanical milling (alloying) is one of the non-equilibrium techniques used to prepare alloys with exceptional properties. This technique was employed in this research to develop a new class of Al- and Mg-based nanocomposite alloys using SPEX high energy milling. These nanocomposites are characterized by the dispersion of nanocrystals in an amorphous matrix. Zirconium was added to the Al-Mg alloys for the purpose of promoting glass formability. As-milled samples were annealed at 400°C for 1 hour to investigate the thermal stability of the nanostructure. The phase evolution of the resulting alloys was studied using XRD and TEM/EDS, which showed a strong dependence of the resulting metastable phases on the starting alloys compositions. / The nanocomposite structure was developed at Zr concentrations of 20 and 35 at.% regardless of the Al/Mg ratio and with some traces of oxidation. However, the amount of amorphous phase was varied in each case depending on the Al concentration into the alloy, since in low Al-containing alloys the amount of amorphous phase was less pronounced. It was found that higher Zr concentrations will lead to greater refinement of the nanostructure. These nanocomposites showed improved mechanical properties, in terms of higher hardness values, in addition to improved thermal stability. The improvement in thermal stability was attributed to the presence of Al3Zr which proved to contribute significantly to retarding grain growth via grain boundary pinning. / Additionally, the employment of mechanical alloying was beneficial in producing Al3Zr in the cubic L12 ordered structure which improves the ductility of the alloy. Moreover, the homogeneity ranges of gamma-Al 12Mg17 and Al3Zr were extended significantly due to the nature of the non-equilibrium processing. In this research, the alloy with the maximum hardness was Al40Mg25Zr35, which has an average hardness value close to 780 HV and average crystallite size of about 10 nm. A common observation in the alloys that showed a higher hardness values combined with improved thermal stability, is that they contain higher Al and Zr concentrations. / Le broyage mécanique est une technique hors équilibre qui permet la fabricationde nouveaux alliages avec des propriétés exceptionnelles. Lors de cette recherche, unbroyeur SPEX 8000 a été utilisé pour développer une nouvelle classe denanocomposites à base d'aluminium et de magnésium. Ces nanocomposites tirent leurspécificité de leur dispersion de nanocrystaux dans une matrice amorphe. Duzirconium a été ajouté aux alliages d'aluminium et de magnésium pour promouvoirl'amorphisation. Les échantillons de poudres broyées ont été recuits à 400°C pour 1heure pour évaluer la stabilité thermique des différentes phases. Leur évolution a étécaractérisée par diffraction par rayon-X et par MEBIEDS. TI fut démontré que lesphases métastables obtenues dépendent fortement de la composition des alliages dedépart.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.102948 |
| Date | January 2007 |
| Creators | Al-Aqeeli, Naser. |
| 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, Metals and Materials Engineering.) |
| Rights | © Naser Al-Aqeeli, 2007 |
| Relation | alephsysno: 002612169, proquestno: AAINR32129, Theses scanned by UMI/ProQuest. |
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