Abstract
Nanostructured Al powder produced by cryomilling showed good microstructural stability against thermal exposure. However, the grain growth behavior in a stress/strain field during thermomechanical processing is less understood. In this work, the microstructure evolution in an Al-7.5Mg alloy was studied via direct ECAP consolidating the cryomilled powder with an average grain size of 25 nm. The ECAP was conducted at 200 and 325 degree C and after 4 passes, the samples showed averaged grain sizes of 170 and 450 nm, respectively. However, the bulk sample by HIP consolidating the annealed (24 hrs at 400 degree C) cryomilled powder at 400 degree C only showed an average grain size of 100 nm, indicating that plastic strain introduced during ECAP may have played a role in grain growth. TEM examination revealed that grain rotation and coalescence contributed to the observed grain growth. Finally, the mechanical behavior of the ultrafine-grained Al-7.5 Mg alloys was discussed.