Effect of long-term natural aging on the tensile and fracture properties of aluminum alloy AA2219-T87 parent and weldments at room and cryogenic temperatures

Abstract

Aluminum alloy (AA2219) is widely used for the fabrication of earth storable and cryogenic propellant tanks. To ensure flight safety, it is important to understand the effect of long-term storage on the mechanical properties, which are dependent on the microstructure. Therefore, the present work is carried out to understand the effect of long term (11 years) ambient storage on the tensile and fracture properties of AA2219-T87 in parent material and weld joint. The tensile test results of naturally aged AA2219-T87 material for 11 years in both parent and weldments indicate an increase in tensile strength at room and cryogenic (77 and 20 K) temperatures. STEM-HAADF and TEM analysis revealed the presence of well-oriented densely populated CuAl2 precipitates (plate-like θ’ and θ” precipitates). The changes in mechanical and fracture properties were understood from the quantification of precipitate distribution, that can be attributed to the natural aging phenomenon taking place at ambient conditions, during the extended period of storage. Here, we report the mechanism towards understanding the increase in strength of AA2219-T87, by the growth of the finer θ” precipitates during natural aging. Since tensile (RT, 77 K, and 20 K) and fracture properties (RT) of welds have improved, with no significant reduction in ductility, long-term naturally aged (up to 11 years) fabricated products of AA2219-T87 are flightworthy.