The Effect of Aging Time on Spallation of 2024-T6 Aluminum

Incipient spall thresholds have been measured and spall fracture surfaces and internal structure examined for 2024 aluminum subjected to impulsive loading by a capacitance discharge flyer plate technique. The incipient spall threshold was found to be 10 to 14 higher in under peak hardness material compared to that aged to peak hardness or overaged. The spall fracture surfaces in the underaged specimens also showed the greatest effect of the high strain rate loading. In that condition, the very ductile fracture mode, observed at low rates, was changed to a less ductile appearing fracture mode dominated by the presence of inclusions. The work hardening ability of the various aged conditions, as determined from low rate tensile tests, was found to correlate with the ability of those conditions to show shock hardening and with the retention of dislocations in the structure following the high rate loading.