Behavior of an aluminum 2024 alloy produced by powder metallurgy

Creep tests were conducted over a range of temperatures from 523 to 603 K on an unreinforced 2024 Al alloy fabricated by powder metallurgy processing. The creep curves under ail testing conditions exhibit a brief quasi-steady-state condition and then a very extended tertiary stage leading to Failure. A logarithmic plot of the minimum creep rate against the applied stress leads to a high and variable stress exponent and a high apparent activation energy. Prior to creep testing, the specimens contained large particles identified as Al2Cu and Al2CuMg. A precipitation of fine particles occurred during testing; this was especially evident in the long-term tests at the highest testing temperature. An analysis of the creep data is developed based on incorporating a threshold stress into the creep equation and using measurements of particle densities in order to include the influence of continuous precipitation during testing. The significance of the threshold stress is examined, and it is shown that the analysis leads to a stress exponent of 5 and an activation energy approximately equal to the value for lattice self-diffusion in pure aluminum. Copyright (C) 1997 Acta Metallurgica Inc.