Microstructure and Mechanical Properties of Cryorolled Aluminum Alloy AA2219 in Different Thermomechanical Processing Conditions

Abstract

In the present study, aluminum alloy AA2219-T87 bars were cryorolled to various amounts of deformation in two pre-deformation conditions: (1) without solution treatment i.e., as-received T87 (WST-CR) and (2) with solution treatment (ST + CR). The solution treated and cryorolled bars were further annealed leading to a third condition: (3) solution treated, cryorolled, and annealed (CR + Annealed). Room-temperature mechanical properties have been evaluated for all three cryorolled conditions. Significant improvement in the 0.2 pct YS and UTS values was obtained for bars cryorolled to cross-sectional area reduction of more than 50 pct in the solution-treated condition (ST + CR), whereas for bars cryorolled in the without solution-treated condition (WST-CR), only an improvement in the 0.2 pct YS was observed. Cryorolling did not enhance the precipitation kinetics nor did it increase the response of the alloy to aging. The mechanical properties were correlated to the microstructures obtained by optical and transmission electron microscopy. Microstructural evolution in the ST + CR condition indicated gradual progression of the principal restoration mechanism from dynamic recovery (DRV) to dynamic recrystallization with an increasing amount of plastic deformation. Transmission electron microscopy of WST-CR and ST + CR specimens showed an increase in dislocation density as a function of the amount of deformation indicating suppression of DRV at cryogenic temperatures. Cryorolling in the solution-treated condition to cross-sectional area reduction of more than 50 pct (ST + 70 pct CR) was found to impart an optimum combination of strength and percent elongation in the present study.