Characterization of Zr-Containing Dispersoids in Al–Zn–Mg–Cu Alloys by Small-Angle Scattering

Abstract

The characterization of Zr-containing dispersoids in aluminum alloys is challenging due to their broad size distribution, low volume fraction, and heterogeneous distribution within the grains. In this work, small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) were compared to scanning electron microscopy (SEM) and transmission electron microscopy (TEM) regarding their capability to characterize Zr-containing dispersoids in aluminum alloys. It was demonstrated that both scattering techniques are suitable tools to characterize dispersoids in a multi-phase industrial 7xxx series aluminum alloy. While SAXS is more sensitive than SANS due to the high electron density of Zr-containing dispersoids, SANS has the advantage of being able to probe a much larger sample volume. The combination of both scattering techniques allows for the verification that the contribution from dispersoids can be separated from that of other precipitate phases such as the S-phase or GP-zones. The size distributions obtained from SAXS, SANS and TEM showed good agreement. The SEM-derived size distributions were, however, found to significantly deviate from those of the other techniques, which can be explained by considering the resolution-limited restrictions of the different techniques.

The Effects of Double-Step Homogenization on Precipitation Behavior of Al3Zr Dispersoids and Microstructural Evolution in 2196 Aluminum Alloy

“…However, the homogenization process faces two major challenges: (1) Conventional single-step homogenization cannot fully dissolve all the coarse constituents with different melting points, resulting in an inadequate strengthening potential. (2) Due to the low diffusion rate and solubility of Zr in the Al matrix, Zr is prone to segregation at the dendrite center during solidification, resulting in low Zr concentration between dendrite arms and grain boundaries [11][12][13][14]. The uneven distribution of the Al 3 Zr dispersoids is unfavorable for the recrystallization resistance of the alloy [13][14][15][16].…”

“…(2) Due to the low diffusion rate and solubility of Zr in the Al matrix, Zr is prone to segregation at the dendrite center during solidification, resulting in low Zr concentration between dendrite arms and grain boundaries [11][12][13][14]. The uneven distribution of the Al 3 Zr dispersoids is unfavorable for the recrystallization resistance of the alloy [13][14][15][16]. Additionally, the presence of coarse primary Al 3 Zr constituent can even promote recrystallization [8,17,18].…”