Effect of Aging Treatment on Fatigue Behavior of an Al-Cu-Mg-Ag Alloy
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for lightweight materials with excellent mechanical properties at elevated temperatures spurs the development of new compositions based on existing alloys. Titanium alloys have historically been used in many elevated temperature aerospace applications: however, the use of this class of materials results in drastically higher cost and weight, relative to aluminum alternatives. One idea that has been explored is to design new alloys based on the current aluminum alloys to push the limits of elevated temperature structural capability. For instance, Al 2024 is a well-known aerospace alloy selected for structural applications in aircraft due to its high specific strength. However, with the increasing speed of modern aircraft, the fuselage material needs to withstand higher temperatures beyond the capability of the currently used aluminum alloys. M.E. BURBA, Graduate Student Researcher, is with the Materials Engineering Department, University of Dayton, Dayton, OH 45469, and also with the US Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/RXCM, Wright-Patterson Air Force Base, Dayton, OH 45433. Contact e-mail: micheal.burba.ctr@ wpafb.af.mil M.J. CATON, Senior Research Engineer, and C.J. SZCZEPANSKI, Research Engineer, are with the US Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/RXCM, Wright-Patterson Air Force Base. S.K. JHA, Research Engineer, is with the Universal Technology Corporation, Dayton, OH 45432, and also with the US Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/ RXCM, Wright-Patterson Air Force Base. Manuscript submitted March 28, 2013. Article published online September 6, 2013 4954—VOLUME 44A, NOVEMBER 2013
The alloy discussed in this article is a developmental alloy that was considered for a next-generation supersonic civil transport vehicle capable of speeds up to Mach 2.0, which causes the leading edges of the aircraft to reach 403 K (130 C).[1] Al 2024 does not meet the mechanical property requirements at this temperature. Therefore, the developmental alloy, which has a baseline composition similar to that of Al 2024 with a few minor alloying modifications, was designed to achieve higher creep strength than commercial Al 2024, as reported in the literature.[2] This experimental alloy will be referred to as Al-Cu-Mg-Ag alloy in this article. The strength and hardness of aluminum alloys are increased via heat treatment as opposed to work hardening. Conventionally, aluminum alloys are used in the peak aged condition since the highest strength levels are achieved through this heat treatment. The peak aged temper (T6) process for Al 2024 based alloys involves a solution treatment at 793 K (520 C) for 5.5 hours with a rapid quench to 293 K (20 C) in cold water, and then soaking at 458 K (185 C) for 10 hours in silicone oil followed by rapid quenching to room temperature in petroleum oil.[2] Lumley et al.[3] have shown that cast and wrought aluminum alloys actually achieve similar high strengths as seen in T6 when th
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