Self-formation of MgO or Al₂O₃ surface layer by annealing of CuMg or CuAl dilute alloys

Self-formation of MgO or Al₂O₃ surface layer on CuMg or CuAl alloys by annealing in H₂ gas was investigated theoretically and experimentally. Theoretical consideration shows that Mg or Al can segregate to the surface of Cu during the annealing, while the enrichment ability is much stronger for Mg. Meanwhile, the MgO or Al₂O₃ surface layer is self-formed by the preferential reaction of Mg or Al with O₂ remnant in H₂ atmosphere. The Al₂O₃ surface layer is expected to play a role in passivating the surface of Cu. However, the MgO layer would suffer failure in passivating the surface due to incorporation of Cu and fissures formed in MgO during the annealing process. Our theoretical predictions are in agreement with experimental observations.