Quasi-Static and High-Strain-Rate Experimental Microstructural Investigation of a High-Strength Aluminum Alloy
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INTRODUCTION
HIGH-strength 2xxx series aluminum alloys are commonly used for structural components in commercial and military applications. Alloys such as AA2024, 2095, 2219, and 2048 are widely used for applications that require lightweight, high fracture toughness materials, such as automotive and aircraft components, electronic packaging devices, and armored vehicles. AA2219 is a heat-resistant alloy, and it is used in applications that require high specific strength and modulus at relatively high operating temperatures. However, such Al-Cu-Mg alloys have limited fracture toughness and damage tolerance.[1] Al-Cu-Mg-Ag alloys with a high Cu:Mg ratio exhibit improved age hardening as a result of the increased formation of the thermally stable plate-like X (Al2Cu) precipitates on the {111}a habit planes and h’ (Al2Cu) precipitates on the {100}a habit planes within the Al-matrix.[2] In addition, the Ag element addition to the Al-Cu-Mg tertiary alloy system minimizes grain boundary (GB) precipitation, which enhances the toughness of the alloy in the age-hardened condition and decreases the tendency for intergranular failure. AA2139-T8 (Al-Cu-Mg-Ag-Mn) was developed by Cho and Bes,[3] who showed that the addition of Mn produced orthorhombic, rod-like Al20Cu2Mn3 dispersoids elongated in the [010] particle directions,[4] which significantly H.G. SALEM, Professor, is with the Department of Mechanical Engineering, The American University in Cairo, Cairo 11511, Egypt. WILLIAM M. LEE, Research Assistant and M.A. ZIKRY, Professor, are with the Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695-7910. Contact e-mail: [email protected] LAURENCE BODELOT, Research Associate and G. RAVICHANDRAN, Professor, are with the Graduate Aerospace Laboratories, California Institute of Technology, Pasadena, CA 91125. Manuscript submitted July 13, 2011. Article published online January 27, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
improved the fatigue life and fracture toughness of the quaternary alloy system compared with the alloys currently used in the military and aerospace applications, including AA2519.[3] Mn-containing dispersoids were found to provide a fiber-like reinforcement and homogenization of slip through dislocation looping and grain size refinement.[5,6] Walsh et al.[6] reported that Mn-containing dispersoids significantly influence the deformation behavior of the quasi-statically loaded alloy, which is governed by a competition between the dispersed particles homogenizing deformation, which delays void coalescence, and reduced particle spacing, which enhances void coalescence. Coarse microscale Fe-containing inclusions also formed within the Al-matrices of such alloys, which result in degradation of the fracture toughness through the formation of needle-like Al7Cu2Fe inclusions. However, it has been shown that Mn-containing alloys reduce the detrimental effect of these Al7Cu2Fe inclusions.[7] Efforts are currently focused on the understanding of deformation and fracture beh
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