Microstructures in the Throat Region of Recovered Aluminum-Alloy Armatures

Previous work investigated macroscopic features of recovered aluminum alloy armatures launched at five different currents. Here, microstructural features of those armatures are explored. Several distinct heat-treatment regimes present near the armature throat surface include grain deformation, melting, and material ejection. Two distinct cracking mechanisms are present. The first-presumably due to liquation cracking-occurs at higher currents, is intergranular, and has cracking directions independent of armature geometry directions. The second-likely due to thermal stresses-is intragranular and has strong dependence on orientation. Detailed photomicrographs of the recovered armatures are presented, along with calculated dimensions of the heat-treatment zones and observed cracks