Next-generation composite Al-Mg-Zr fuels for bio/chem-agent defeat applications rely on intermetallic formation reactions to reduce ignition temperatures below melting point of Al. Scaling-up the ball-milling synthesis of these powders will require a detailed understanding of how milling parameters and powder composition impact the evolution of powder microstructure. In the present work, we explore the effect of milling duration on the size, microstructure, and properties of (Al-8Mg):3Zr, (Al-8Mg):Zr, 3(Al-8Mg):Zr and 4(Al-8Mg):Zr composite powders. We report compositionally dependent refinement of Zr inclusions in the Al-8Mg matrix that impacts ignition temperatures (T-ig). For (Al-8Mg):3Zr and (Al-8Mg):Zr composite powders, T-ig initially drops as milling time increases to 60 min and then either plateaus or rises at longer milling times. In contrast, T-ig generally decreases over the full 90 min milling duration for the two Al-8Mg-rich compositions. Reductions in heterogeneity and average Zr inclusion size dominate the ignition behavior and lead to steady decreases in T-ig. (C) 2020 Published by Elsevier B.V.