Atom-Probe Tomographic Study of Precipitation in an Ultrafine-grained Al-Zn-Mg- Cu Alloy (Al 7075)

Precipitation-hardened alloys can be further strengthened by reducing the grain size down to the ultrafine regime (<1 μm) and thereby incorporating significant grain boundary (GB) strengthening [1, 2]. The ultrafine-grained (UFG) structure is expected to induce an influence on the precipitation behavior, because of the significantly reduced length scale. Nevertheless, there have been very limited studies on the effect of length scale on precipitation [3]. The present study was undertaken to obtain quantitative information on the differences in precipitation behavior between UFG structure and the traditional coarse-grained (CG) counterpart, and to provide fundamental insights into the underlying mechanisms. Al 7075 alloy, with major alloying elements of Zn, Mg and Cu, was selected for study because of its technological importance and the existing extensive studies on precipitation phenomena in CG Al 7075. An UFG Al 7075 alloy was fabricated via powder cryomilling, degassing, hot isostatic pressing and extrusion, followed by solution treatment and artificial aging (T6 temper); a CG counterpart was prepared from unmilled CG powders using the same degassing, consolidation and heat treatment rout