BEHAVIOR OF AN ALUMINUM-2024 ALLOY PRODUCED BY POWDER-METALLURGY

Creep tests were conducted over a range of temperatures from 523 to 60 3 K on an unreinforced 2024 Al alloy fabricated by powder metallurgy p rocessing. The creep curves under ail testing conditions exhibit a bri ef quasi-steady-state condition and then a very extended tertiary stag e leading to Failure. A logarithmic plot of the minimum creep rate aga inst the applied stress leads to a high and variable stress exponent a nd a high apparent activation energy. Prior to creep testing, the spec imens contained large particles identified as Al2Cu and Al2CuMg. A pre cipitation of fine particles occurred during testing; this was especia lly evident in the long-term tests at the highest testing temperature. An analysis of the creep data is developed based on incorporating a t hreshold stress into the creep equation and using measurements of part icle densities in order to include the influence of continuous precipi tation during testing. The significance of the threshold stress is exa mined, and it is shown that the analysis leads to a stress exponent of 5 and an activation energy approximately equal to the value for latti ce self-diffusion in pure aluminum. Copyright (C) 1997 Acta Metallurgi ca Inc.