The Effects of Precipitates and Mn-bearing Particles on the High Strain-Rate Compression of High Strength Aluminum
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1225-HH04-08
The Effects of Precipitates and Mn-bearing Particles on the High Strain-Rate Compression of High Strength Aluminum K. ELKHODARY(a), W. LEE(a), B. CHEESEMAN(b), L. SUN(c), D. BRENNER(c), M. ZIKRY(a) (a) Dept. of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695-7910 (b) Army Research Laboratory, Aberdeen, MD, Aberdeen Proving Ground, MD 21005-5069 (c) Dept. of Materials Engineering, North Carolina State University, Raleigh, NC 27695-7907
ABSTRACT Transmission electron microscopy (TEM) and specialized dislocation-density based crystalplasticity formulations and finite-element schemes were used to investigate the effects of nanosized precipitates and micro-sized Mn-bearing particles on the behavior of Al-Cu-Mg-Ag alloys. By accurately representing crystallography and the morphology of the different precipitates, accurate predictions can be obtained that indicate that the nano-sized and ’ precipitates promote ductility and toughness by inhibiting shear-strain localization; whereas the micro-sized dispersed particles intensify localization. Collectively, the precipitates and dispersed particles, however, promote the strengthening of the alloy. INTRODUCTION Al-Cu-Mg-Ag alloys can have relatively high strength, temperature resistance, toughness, and damage tolerance. However, the underlying microstructural mechanisms operative under dynamic loading have not been well understood or quantified. The objective of this study is to delineate between the role of micro-sized Mn-bearing particles and nano-sized precipitates in 2139-Al [1] under high rates of dynamic loading. TEM imaging was used to identify the precipitates and dispersed particles in a representative 2139-Al plate. Specialized microstructurally based finite element simulations, which explicitly account for precipitates and their rational orientations, were then conducted to investigate the behavior of these phases for different alloy deformation and failure modes. The paper is organized as follows: A characterization of the microstructure of 2139-Al is presented in Section 1, an outline of the finite-element approach is given in Section 2, the finite element results are discussed in Section 3, and a summary of the salient conclusions is given in Section 4. 1. 2139-AL MICROSTRUCTURE Transmission electron microscopy (TEM) was used to characterize the precipitates and Mnbearing dispersed particles in a 1.5” thick 2139-Al plate. A JEOL JEM-2000FX Electron Microscope was used for imaging at 200 kV. Samples for TEM observation were prepared using electrochemical polishing. Samples were cut from the plate to approximately 0.125 mm foils using a diamond saw. Disks of 3 mm were punched from the foil and mechanically polished. Samples were then electrochemically polished down to an electron transparent thickness using a Fischione Twin-Jet Polishing Apparatus with a 20% Nitric Acid and 80% Methanol mixture at 15V and 160 mA at 243K. It was observed that precipitates are 44 nm in length, and less than 3nm in thickness.
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