Phase transformation and microstructural changes during aging process in Ag-Pd-Cu-Pt-Zn alloy

The Ag-Pd-Cu-Pt-Zn alloy was studied in order to elucidate the age hardening behaviour, phase transformation and changes in microstructure and element distribution during the aging process. The grain interior precipitation of the Cu rich phase from the Ag rich alpha(1) matrix caused an apparent increase in hardness, and the formation and expansion of the Cu rich entanglement structures decreased the hardness. The phase transformation of the Cu-Pd rich alpha(2) phase occurred during softening in the later stage of the aging process, which resulted in the retardation of further softening. Pt was concentrated in the Cu-Pd-rich alpha(2) particle-like structures, and Zn was exclusively concentrated in the CuPd beta particle-like structures at approximately four times its concentration in the original alloy composition. The Cu-Pd rich alpha(2) and CuPd beta phases, which contained large amounts of Cu, constituted the particle-like structures of various sizes without an apparent contribution to the age hardenability.