Characterisation of Oxide Films in Al-Mg Alloy Melts

Abstract:

Oxide films in Al-0.7Mg and Al-9.4Si-2.3Cu-1.0Zn-0.49Mg (in wt%) alloy melts were characterised using advanced analytical electron microscopy. The oxides were collected by pressurised melt filtration for direct examination by SEM and TEM. The results showed that the oxide films consisted of numerous sub-micron sized oxide particles, rather than continuous solid films. The oxide particles formed in the two Mg-containing alloys were identified as MgAl₂O₄ spinel by selected area electron diffraction (SAED) and high resolution TEM combined with EDS analysis. The low level of Mg in the melt resulted in the change of the oxide from alumina to MgAl₂O₄ spinel. The MgAl₂O₄ crystals were typically faceted with their {1 1 1} crystal planes and were about 0.2-1.2 μm in size. High resolution TEM examination of the MgAl₂O₄ / a-Al interfaces revealed that there was a cube-on-cube orientation relationship between the two crystals. The possibility of MgAl₂O₄ particles to act as nucleation sites for α-Al grains during solidification is discussed in terms of the lattice matching at the MgAl₂O₄ / α-Al interfaces along the specific crystallographic orientation relationship.

• Periodical: Materials Science Forum (Volume 765)
• Pages: 220-224
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.765.220
• Online since: July 2013
• Authors: Yun Wang, Hu Tian Li, Zhong Yun Fan, Geoff Scamans
• Keywords: Aluminium Alloy, MgAl₂O₄ Spinel, Oxide Films, TEM

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