Previous work showed that particles of mechanically alloyed Al · Mg powders burn faster than aluminum. However, such powders were coarser than fine aluminum commonly used in energetic formulations. This work addresses preparation of mechanically alloyed Al · Mg powders in which both internal structures and particle size distributions are adjusted. Powders with 50-90 at.% Al were prepared and characterized. Milling protocol was optimized to prepare equiaxial, micron-scale particles. Ignition temperatures measured using an electrically heated filament were much lower than those of pure Al powders and are close to those of Mg. Powders were aerosolized and ignited in air; the maximum pressure was higher, rates of pressure rise were greater, and ignition delays were shorter for the mechanically alloyed powders than for pure Al with directly comparable particle size distributions. Individual particle combustion experiments used laser ignition and showed that the alloyed particles burn in two stages, with the first stage gradually disappearing with an increased Al concentration. The effect of particle size d on its burn time t for the prepared alloys is relatively well described by a t ∼ d n law, where n is varying in the range of 1.1-1.5 for different compositions.

Adding aluminum to propellants, pyrotechnics, and explosives is a common way to boost their energy density. A number of approaches have been investigated that shorten aluminum ignition delay, increase combustion rate, and decrease the tendency of aluminum droplets to agglomerate. Previous work showed that particles of mechanically alloyed Al-Mg powders burn faster than similarly sized particles of pure aluminum. However, preparation of mechanically alloyed powders with particle sizes matching those of fine aluminum used in energetic formulations was not achieved. This work is focused on preparation of mechanically alloyed, composite Al-Mg powders in which both internal structures and particle size distributions are adjusted. Binary powders with compositions in the range of 50 - 90 at. % Al were prepared and characterized. Milling protocol is optimized to prepare equiaxial, micron-scale particles suitable for laboratory evaluations of their oxidation, ignition, and combustion characteristics. Quantitative particle size analyses are done using low-angle laser light scattering. Electron microscopy and x-ray diffraction are used to examine particle morphology and phase makeup, respectively. Combustion of aerosolized powder clouds is studied using a constant volume explosion setup. For all materials, ignition and combustion characteristics are compared to each other and to those of pure Al. Compositions with improved performance (i.e., shorter ignition delay and faster pressurization rate) compared to pure Al are identified.