CORRELATION BETWEEN CREEP-BEHAVIOR IN AL-BASED SOLID-SOLUTION ALLOYS AND POWDER-METALLURGY AL-ALLOYS

The creep characteristics of Al-based solid solution alloys and powder metallurgy (PM) Al alloys are reviewed. Consideration of available in formation shows that the creep behavior of Phl Al alloys is different from that of Al-bnsed solid solution alloys with regard to the stress dependence of creep rate as inferred from the value of the stress expo nent, n, and the temperature dependence of creep rare as measured by t he value of the activation energy? P. For example, according to well-d ocumented experimental evidence. the activation energies for creep in Al-based solid solution alloys, whether they behave as class I (alloy class, n = 3) or class II (metal class, n = 5), are close to that for self-diffusion in Al. By contrast, the apparent activation energies fo r creep in PM Al alloys are not only much higher than those reported f or Al-based solid solution alloys but also variable. It is suggested t hat the aforementioned differences arise from the presence of a thresh old stress for creep in PM Al alloys; that the origin of such a thresh old stress is related to the interaction between moving dislocations a nd oxides particles which are present as a result of processing these alloys by powder metallurgy; and that by incorporating the threshold s tress and its temperature dependence in the analysis, the true creep c haracteristics of PM Al alloys become similar to those of Al-based sol id solution alloys. The consistency between this suggestion and experi mental trends for two Phl Al alloys, PM 6061 Al and Phl 2124 Al, is ex amined. (C) 1998 Elsevier Science S.A. All rights reserved.