THE MATERIAL PHYSICS OF DEFORMATION OF AA5182 UNDER HOT ROLLING CONDITIONS

The forming process of hot rolling not only has obvious commercial importance but also is scientificzdlychallenging to understand. Accurate charactmization is difficult as material physics affecting plastic deformation change on the same time scale as that of the process itself. Recovery and recrystallization provide examples: the development of an annealed state may occur between rolling passes, with subsequent impact on upcoming rolling passes. We have used the constitutive response of the metal in interrupted loading experiments to ascertain whether recrystallization or recovery is an active mechanism as a function of deformation history, complimenting a study of Wells et al.[1998]. INTRODUCTION: We found that loading aAA5182 compression specimen to a given state, pausing for a particular time, and reloading the specimen gave not only constitutive information, but it allowed us to ascertain whetier or not the specimen had recrystallized during the pause. The key to this understanding was plotting the materials constitutive response as hardening (@), that is ddd~ versus stress (c). Common to all tests, @versus CTplotsshow an initial transient followed by a linear decrease in hardening rate with stress (VOC6behavior). The stress level at which individual curves join the common curve gives indication of the restorative mechanism: recrystallized samples join at stresses less than or equal to, and recovered samples stresses greater than that observed for the initial curve. By varying the lengths of the pause in the loading history we were able to determine the time required for recrystallization as a function of strain rate and temperature. This procedure was inspired by the technique of “metallography by Instron” used by McQueen and Jonas[1975]. PROCEDURES, RESULTS AND DISCUSSION: The deformation of the AA5182 at a strain rate of 3.0s-1to 0.25 compressive strain at 475°C provides a specific example of this technique. These results are shown in Fig. 1. One can seetheclosematch between theinitial hardening response and that from reloading after hold times of 20 and 25s. The reload hardening after a 10s hold is simikw to these data, perhaps just a bit higher. The hardening curves after holds of 4,2, and 1s are distinctly higher than the Ioading data. We have taken x-ray inverse pole figures of two compression specimens that were quenched after deformation to 0.25 strain at 475°C and 2=3s-1. In the first case the specimen was immediately quenched and secondly the sample was held for 3s at 475°C