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Accelerated growth of oxide film on aluminium alloys under steam: Part I: Effects of alloy chemistry and steam vapour pressure on microstructure

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Publication Date
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Online Research Database In Technology
Keywords
  • Steam
  • Vapour Pressure
  • Aluminium Alloys
  • Oxide Growth
  • Boehmite
  • Intermetallic Particles
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Abstract

Aluminium alloys were treated with steam of varying vapour pressures which resulted in the growth of aluminium oxyhydroxide layers of an average thickness of ~450–825 nm. The microstructure and composition of the generated layers were characterised by GD-OES, FEG-SEM, GI-XRD and TEM. The thickness of the oxide layeras well as the compactness increased with steam vapour pressure. The increase in vapour pressure also resulted in a better coverage over the intermetallic particles. Oxide layer showed a layered structure with more compact layer at the Al interface and a nano-scale needle like structure at the top. The kinetics of formation of film understeamwas rapid; approx. 350nm thick layers were generated within 5 s of steam treatment, however increase in thickness of the oxide retarded further growth. The enrichment or depletion of different alloying elements at the surface of aluminium as a result of alkaline etching pre-treatment influenced the thickness and growth of theoxide. Moreover the steam treatment resulted in the partial oxidation of second phase intermetallic particles present in the aluminium alloy microstructure.

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