The tensile response and fracture behavior of an Al-Zn-Mg-Cu alloy: Influence of temperature
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The Tensile Response and Fracture Behavior of an AI-Zn-Mg-Cu Alloy: Influence of Temperature T.S. Srivatsan, S. Anand, D. Veeraghavan, and V.K. Vasudevan A high-performance, high-strength, and novel AI-Zn-Mg-Cu alloy in the T7751 condition was deformed to failure in laboratory air environment at ambient and elevated temperatures. Temperature influenced the tensile response of the alloy for both the longitudinal and transverse orientations. Strength decreased with an increase in test temperature, with a concomitant improvement in ductility. Test results indicate the alloy response to be the same for both the longitudinal and transverse orientations. No major change in the macroscopic fracture mode was observed with the direction of testing. Tensile fracture, on a microscopic scale, revealed features reminiscent of both ductile and brittle mechanisms. The microscopic fracture behavior was a function of test temperature. The mechanisms and intrinsic micromechanisms governing the tensile fracture process are discussed in terms of mutually interactive influences of microstructural effects, matrix deformation characteristics, test temperature, and grain boundary failure.
Keywords aluminum alloy, deformation, fracture, microstructure
1. Introduction THE SUSTAINED requirement for new and improved materials for a spectrum of high-performance applications in the aerospace and ground transportation industries is driven by a fascinating mix of scientific, economical, and even military motivations. These materials, while offering considerable savings in weight, must concurrently be durable and damage tolerant for a wide variety of applications ranging from airframe structures for aircraft to space vehicles, including lightweight armored carders. In fact, the sustained success achieved with high-strength aluminum alloys coupled with the tried and true design concept, aided by a consistent record of continuous improvement in alloy development efforts and cost effectiveness, has provided resistance to the adoption of alternative materials. The stringent demands placed on the newer generation of military and civilian aircraft has engendered considerable scientific and technological interest in the development, emergence, and use of new and improved aluminum alloys as attractive and viable alternatives to the existing high-strength commercial alloys belonging to the 2xxx and 7xxx series. However, extensive use of age-hardenable 2xxx-series and 7xxx-series alloys, at high strength levels, was hampered by their poor secondary properties of toughness, stress corrosion cracking, and cyclic fatigue resistance, particularly in the short transverse direction. The intrinsic ability to predict and control microstructures was established as the most viable and attractive technique to achieve notable improvements in toughness, stress corrosion resistance, cyclic fatigue resistance, and fracture properties (Ref 1). Microstructural control can be systematically achieved through changes in alloy chemistry (Ref 2-5), the use of
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