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

Abstract

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Strengthening mechanisms and deformation behavior of cryomilled Al–Cu–Mg–Ag alloy

“…Note that the significant Al concentration observed in the Mg-O-N dispersoid is actually from the Al 2139 matrix due to ion trajectory aberrations during the APT experiment [54]. In addition, it is worth noting that Cu and [27,53,[55][56][57]. Following the quantitative analysis methods for dispersoids as described in [6], it was found that the average diameter of the Mg-O-N dispersoids was 5.0 ± 3.5 nm, with a number density of 1.4 ± 0.4 x 10 22 m -3 and a volume fraction of 0.268% ± 0.001%.…”

“…Previous research has shown that nanometric grains in combination with elevated content of oxide and nitride dispersoids lead to variations in precipitation kinetics, relative to those in conventionally produced Al alloys [4,24,25,27] Precipitation in the UM material followed the sequence reported for Al-Cu-Mg-Ag alloys with high Cu/Mg ratio, which was first reported by Ringer et al [69], and then confirmed by other groups [37,40,70,71]. It has been shown that there are two precipitation sequences occurring simultaneously (Table 1).…”

“…First, SPD leads to an increase in the density of dislocations and vacancies in metals, as well as a higher volume fraction of grain boundaries. In Al, for example, both of these effects increase solute diffusivity in the matrix which leads to an acceleration in precipitation kinetics [24][25][26][27]. Second, grain boundary strengthening remains a dominant strengthening mechanism in UFG materials [8], and the precipitation strengthening in UFG materials is not as significant in comparison with that in coarse grained (CG) counterparts [4,25].…”

Precipitation in nanostructured alloys: A brief review

“…18,19 Ma et al provided a direct comparison of precipitation phenomena between CG and UFG Al-Mg-Zn-Cu alloys that were fabricated by powder metallurgy. 10,12,20 After T6 temper, the microstructure of the UFG alloy exhibited highly dense nanoscale GP zones and platelet η′ phase precipitates in the grain interiors (Figure 1a). These precipitates were formed via homogeneous nucleation mechanism as most of the dislocations in the grain interiors in the UFG samples were annihilated during the solution heat treatment.…”