Microstructural control of al alloys using intrinsic oxides

Thesis

Currently, there is not enough information available on the effect of inclusions on extrusion alloys. Theoretical calculations in the past demonstrated the probable role of oxides in Fe-intermetallic phase selection (Cao et al., 03). However, no concrete evidence can be found in the literature to support this argument. This study investigates the role of in-situ oxides in intermetallic phase selection. Various Mg oxides (spinel and MgO) were formed in-situ by adding different levels of Mg. A special intermetallic extraction process was used for 3D analysis. SEM, EDS and XRD analysis were used for qualitative and quantitative analysis. Dry and wet surfaces of the oxide bi-films were observed with the wet surfaces highly associated with MgO and spinel particles. MgO particles had spherical morphology and there average diameter was observed to be in the range 200nm-400nm, whereas spinel particles had octahedral morphology with average length of the side in the range 1-2μm. MgO was found in locations which appear to be the most probable nucleation points of α-AlFeSi intermetallics and Mg₂Si. These results provide a new and more distinctive perspective on the actual morphology of Fe-rich intermetallics and Mg oxides than the ones that exist in the literature. It also provides direct evidence of the role of inclusions (oxides) in intermetallic phase nucleation. This information can be utilised to improve the surface properties in 6xxx extrusion alloys.

Authors: Verma, A

• Publication date: 2015
• DOI: 10.5287/ora-a4mpbpze8
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Intermetallics; Solidification; TP1; Aluminium
• Subjects: Materials Sciences; Physical metallurgy; Materials processing; Architecture; Alloys