Microstructural and strain rate effects on plastic deformation in aluminum 2219-T87

Carlos D Rincon, University of Texas at El Paso

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

Engineering, Metallurgy|Engineering, Materials Science

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.
http://digitalcommons.utep.edu/dissertations/AAI9832821

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