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Abstract

The oxidation of molten Al–5 wt-%Mg and Al–5 wt-%Mg–0·5 wt-%cryolite (Na₃AlF₆) has been investigated by carrying out crucible corrosion tests under thermal gradient conditions. Two morphologies of Al₂O₃/Al composite were observed: ‘large balls’ in the absence of cryolite; and small mushrooms in the presence of this salt. Microstructural analysis and thermogravimetric measurements were also carried out to study the effect of cryolite on the oxidation mechanism. The results showed that both composite morphologies are the result of the same directed metal oxidation (DIMOX) process (DIMOX is a trademark of Lanxide Corporation, Newark, DE). Thermogravimetric analysis also confirmed that two morphologies formed under different oxidation kinetic conditions.

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Effect of cryolite on formation of Al 2 O 3 /Al composites produced by oxidation of molten Al–Mg alloy

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