Ａｌ‐Ｃｕ‐Ｓｃ合金中のθ′‐Ａｌ２ＣｕとＡｌ３Ｓｃの成長および不均一析出における相互作用

Abstract

An Al–2.5 mass%Cu–0.23 mass%Sc alloy is strengthened by fine and uniform distribution of coherent spherical L12–Al3Sc phase and semicoherent plate-like θ′–Al2Cu phase, which precipitate during aging. These precipitates interact on growth and heterogeneous precipitation each other. In the present work, mechanisms of growth and heterogeneous precipitation between the two phases in the Al–2.5 mass%Cu–0.23 mass%Sc alloy aged at 623 K were investigated on the basis of TEM observation. On aging at 623 K, growth rate of θ′–Al2Cu phase in the Al–Cu–Sc alloy is much larger than that in the Al–Cu alloy. Growth rate of Al3Sc is almost same and very small in both of Al–Cu–Sc alloy and Al–Sc alloy and this is much smaller than that of θ′–Al2Cu phase. This is considered to be closely related to the high binding energy between scandium atoms and vacancies. Coarsening process of Al3SC and θ′–Al2 Cu phases obey the LSW theory of diffusion controlled particle coarsening. The migration of scandium or copper atoms to the strain fields of the interface dislocations formed at θ′–Al2Cu/matrix or Al3Sc/matrix interface have a significant effect on the heterogeneous precipitation of Al3Sc phase on θ′–Al2Cu phase or θ′–Al2Cu phase on Al3Sc phase.