Bimodal microstructures in nanocrystalline Al and Al-Mg alloy powders prepared by cryogenic ball milling

Abstract

The microstructures of nanocrystalline Al and Al-7.6 at% Mg alloy powders processed by cryogenic ball milling (i.e., cryomilling) and subsequent thermal annealing were characterized using transmission electron microscopy. The as-milled samples primarily consisted of equiaxed grains with average sizes of similar to 26 nm. The annealing treatments at elevated temperatures resulted in bimodal grain-size distributions, with sub-micrometer-sized grains embedded in a matrix of nanocrystalline (<50 nm) grains. The bimodal microstructures were formed during the processes of recovery and recrystallization.