Gamma phase precipitation processes in quenched beta phase Cu–Zn–Al alloys at an electron concentration of 1.53

The precipitation of the γ phase in quenched β Cu–Zn–Al alloys at an electron concentration (e/a) of 1.53 was studied in detail by optical, scanning and transmission electron microscopy. Two precipitation processes were found: (i) a dendritic precipitation in cuboidal regions of 10–40 μm was found at low quenching velocities, below about 500 K s−1, but was suppressed by increasing the quenching rate to 1150 K s−1; (ii) small spheroidal precipitates with γ-brass structure, typically 10 nm in size, were observed even after quenching at the highest velocities. They formed on first- and second-neighbour antiphase boundaries. The latter process was found to occur more readily than in Cu–Zn–Al alloys at e/a=1.48. The hysteresis of the spontaneous martensitic transformation was not appreciably affected by the presence of the latter precipitates.