Strengthening of Aluminum Powder Pellets under High-Velocity Impact

Aluminum powder (3-4.5 micron-particle diameter) was consolidated into pellets and used as projectiles in high-velocity impact experiments with a modified .410 caliber powder gun. Typically, the forces induced on the pellet after gun-powder ignition will fragment the pellet such that structural integrity is compromised and the pellet fractures before entering the explosion chamber. A metallurgical treatment was developed to alter the material properties of the Al pellets, such that they retain their structural form throughout flight in the explosion chamber. A treatment of annealing and quenching was applied to the pellet in such a way as to reorder the Al particle microstructure, which was observed by SEM imaging. Untreated consolidated pellets were used as a control sample and compared with treated pellets that were shot via a powder gun at 1300m/s into an explosion chamber where pressure and high-speed video data were collected. For untreated projectiles, pressure generation was very inconsistent, as the pellets normally failed before reaching the explosion chamber. The treated pellets maintained their structural integrity throughout flight in the chamber, observed by video, and resulted in consistently high-pressure generation. This study provides a qualitative and quantitative understanding of how the preparation technique for consolidated powder projectiles can influence their mechanical properties and resulting reactivity upon impact. Results provide a fundamental perspective for the mechanisms that improve the mechanical integrity of consolidated powder projectiles.