Heterogeneous precipitation of intermediate phases on Al3Zr particles in Al-Cu-Zr and Al-Li-Cu-Zr alloys

Abstract

Heterogeneous precipitation of intermediate phases on dispersoid particles of Al3Zr was examined in both Al-4%Cu-0.18%Zr and Al-2%Li-3%Cu-0.15%Zr alloys with special attention to the coherency state of the particles which might change during solution treatment through recrystallization. Specimens were solution-treated and directly aged at 473 K without quenching to prevent the formation of dislocation loops which can act as the heterogeneous nucleation sites for intermediate phases. In the Al-Cu-Zr alloy, the dispersoid particles are coherent with matrix in a recovered (unrecrystallized) region and they act as heterogeneous nucleation sites for the θ’ phase in such a way that the particles are in contact with broad coherent planes of θ′ precipitates. On the other hand, the particles become incoherent in a recrystallized region and they are in contact with narrow incoherent planes of the precipitates. In the Al-Cu-Li-Zr alloy, however, the particles are coherent both in recovered and recrystallized region and they are in contact with coherent planes of T1 precipitates. This nucleation behavior of intermediate phases is explained in terms of the reduction in the interfacial energies during nucleation. © 1990, The Japan Institute of Light Metals. All rights reserved.