Strength Degradation in AA5083 Armor Plate after Exposure to Elevated Temperatures

The thermally-driven evolution of β-phase (Al3Mg2) and its impact on strength is explored for three different producers of aluminum alloy 5083-H131 used in armor applications. Specimens were exposed to 100°C air for periods of up to 30 days. Through a combination of optical microscopy and computational image analysis, the extent of matrix β and grain boundary β in the microstructure was assessed. Quasi-static tensile testing was also used to measure strength as a function of exposure time. It was found that a degradation in yield strength strongly correlates with the rapid emergence of matrix β-phase and not slowly evolving grain boundary β networks typical of a sensitized microstructure. The decrease in yield strength is attributed to the loss of the solid solution strengthening via matrix β-phase precipitation. This suggests that field exposure to solar radiation, ambient air, or engine/exhaust heat could lead to a loss in the level of ballistic protection afforded by the alloy even without a sensitized condition.