Giant segregation effect and surface mechanical modification of aluminum alloys by oxygen plasma source ion implantation

Implantation of 30 keV oxygen ions in some magnesium containing aluminum alloys was performed using an ECR plasma source ("OPSII" process). The mechanical implantation effects were studied by AFM-nanoindentation, and the chemical effects by high resolution XPS and SIMS depth profiling. Surface hardening is obtained, consistent with the formation of very fine oxide precipitates. Since the temperature rises to similar to 400 degreesC during oxygen plasma source ion implantation (OPSII), Mg surface segregation is observed as expected. However, O and Mg are also found at the similar to 10 at.% level as far as 0.5 mum below the surface, ten times deeper than the O-ion range. The possibility of an artefact has been eliminated by various tests. XPS indicates that MgO dominates while Al remains mostly metallic. (C) 2001 Elsevier Science B.V. All rights reserved.