Isothermal decomposition of some β Cu-Zn-Al alloys with e/a=1.48

The isothermal aging effects in some beta Cu-Zn-Al alloys containing between 9.98 and 16.33 at.% Al and a constant electron per atom ratio, e/a, of 1.48, were studied by optical and electron microscopy and time dependence of microhardness and electrical resistivity in the temperature range of 473 and 773 K. On aging, for all compositions, the beta phase decomposes into a mixture of (alpha + gamma) phases, with an earlier formation of gamma phase in alloys with higher Al content. The hardness and the electrical resistivity increase with aging time at each temperature, but the causes of these changes are not the same: the hardness variations are associated mainly with the gamma precipitation while the resistivity changes are related to the eutectoid decomposition. (C) 1999 Published by Elsevier Science S.A. All rights reserved.