Transformation of iron containing constituent intermetallic particles during hydrothermal treatment

Aluminium alloys AA3102 and AA9108 were treated with high temperature steam, which resulted in the formation of an oxide layer of average thickness of 300-400 nm. Hydrothermal steam treatment resulted in the removal or oxidation of Al (Fe) Mn and Al (Fe-Si) Mn type intermetallic particles present in the alloys. Furthermore, electron energy loss spectroscopy analysis revealed that the during the steam treatment, the Fe enriched areas of the Al (Fe-Si) Mn type intermetallic particles were transformed into Fe2O3 and Fe3O4 phases, while energy-dispersive X-ray spectroscopy line profile measurements by scanning transmission electron microscope showed that Mn and Si were leached out and incorporated into the surrounding oxide layer. Further, the part of intermetallic phase was transformed into polycrystalline material.