SIGNIFICANCE OF CONTINUOUS PRECIPITATION DURING CREEP OF A POWDER-METALLURGY ALUMINUM-ALLOY

Experiments were conducted to evaluate the creep properties of a 2024 aluminum alloy fabricated by powder metallurgy processing. The creep c urves exhibit a minimum creep rate followed by an extended tertiary st age prior to failure. Using the values of the minimum creep rates, the apparent stress exponents are high and variable suggesting the presen ce of a threshold stress. Observations using transmission electron mic roscopy (TEM) reveal the occurrence of a continuous precipitation of f ine particles during the tests. Although the density of these particle s is dependent upon the testing conditions, quantitative measurements show that their average size is of the order of similar to 60 nm under all conditions. A temperature compensated time is introduced to descr ibe the evolution of fine particles during testing, and this permits t he development of a relationship which can be used to estimate the den sity of fine particles under any selected conditions.