Microstructural and strain rate effects on plastic deformation in aluminum 2219-T87
Abstract
A fundamental investigation has been conducted on the effects of microstructure and strain rate on the plastic deformation of theta-prime-strengthened 2219 aluminum. The motivation for this work is based upon a previous study which showed inhomogeneous and locally extreme work hardening in the HAZ regions in VPPA 2219-T87 butt welds. This strongly suggests that the HAZ microstructure plays a major role in the deformation and fracture process in precipitation hardened aluminum alloy 2219. Tensile specimens of the weld joint exhibited more rapid work hardening in the heat-affected-zone (HAZ) at higher strain levels. Microhardness contour maps for these welds illustrated that late stage deformation was concentrated in two crossing bands at about 45$\sp\circ$ to the tensile axis. The width of the deformation bands and the ultimate tensile strength seemed to be dictated by the amount of work hardening in the HAZ. In this study, three different heat treatments were used to produce samples with different particle sizes and particle spacings, but all hardened by copper aluminide precipitates of the $\theta\sp\prime$ structure. The heat treatments were categorized as being (A) as-received T87 condition, (B) T87 condition aged at approximately 204$\sp\circ$C for 3 hours and (C) T87 over-aged at 204$\sp\circ$C for 7 days. Uniaxial tensile tests consisted of two sets of experiments: (1) three heat treatments (A, B, and C) at two strain rates (0.02 min$\sp{-1}$ and 0.2 min$\sp{-1})$ and (2) three heat treatments that were interrupted at select stress-strain levels (0.8% and 2% total strain) during the tensile tests at strain rate equal to 0.02 min$\sp{-1}$ at room temperature. Furthermore, a detailed transmission electron microscopy (TEM) study demonstrates the microstructural development during tensile deformation. The Voce equation of strain-hardening provides a slightly better fit to the tensile curves than the Ludwik-Hollomon equation. At higher strains, localized areas showed strain fields around $\theta\sp\prime$ platelets had diminished. Lastly, in every treatment, both the yield and tensile strength were slightly higher for the higher strain rate, but only by 0.5 to 2.0 ksi.
Subject Area
Materials science|Metallurgy
Recommended Citation
Rincon, Carlos D, "Microstructural and strain rate effects on plastic deformation in aluminum 2219-T87" (1998). ETD Collection for University of Texas, El Paso. AAI9832821.
https://scholarworks.utep.edu/dissertations/AAI9832821