Creep behavior in near-nanostructured Al 5083 alloy

Creep tests are being carried out on ultra-fine grained (UFG) Al 5083 alloy processed by consolidating nanocrystalline cryomilled powder particulates in the temperature range of 573-648 K. The creep data show that the apparent stress exponent and the apparent activation energy increase continuously with decreasing stress. Analysis of the data reveals the existence of a threshold stress, τo, whose temperature dependence is much stronger than that attributable to the shear modulus. Incorporation of this threshold stress into a modified creep equation yields a true stress exponent of about 2 and a true activation energy close to that anticipated for boundary diffusion in Al. These values of the true stress exponent and the true activation energy suggest that the rate controlling process is related to boundary sliding.