Fatigue strength and microstructure evaluation of Al 7050 alloy wires recycled by spray forming,extrusion and rotary swaging |
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| Affiliation: | 1. Programa de Pós-graduação em Ciência e Engenharia de Materiais (PPG-CEM), Universidade Federal de São Carlos (UFSCar), Rod. Washington Luiz, Km 235, 13565-905 São Carlos - SP, Brazil;2. Divisão de Materiais, Instituto de Aeronáutica e Espaço, CTA, Praça Marechal Eduardo Gomes, 50, 12228-904 São José dos Campos - SP, Brazil;3. Departamento de Engenharia de Materiais (DEMa), Universidade Federal de São Carlos (USFCar), Rod. Washington Luiz, Km 235, 13565-905 São Carlos - SP, Brazil;1. School of Materials, Beijing Institute of Technology, Beijing 100081, China;2. School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China;3. Advanced Research Institute of Multidisciplinary Science, Beijing Institute of Technology, Beijing 100081, China;1. College of Energy Engineering, Yulin University, Yulin 719000, China;2. Yulin Key Laboratory of Metal Matrix Composites and Remanufacturing Technology, Yulin University, Yulin 719000, China;1. School of Materials Science and Engineering, Central South University, Changsha, China;2. Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education, Central South University, Changsha, China;3. School of Civil Engineering, Harbin Institute of Technology, Harbin, China;1. National Key Laboratory for Precision Hot Processing of Metal, Harbin Institute of Technology, Harbin 150001, China;2. KaShui Technology (Huizhou) Co., Ltd., Huizhou 516000, China;1. Institute for Space Systems, German Aerospace Center (DLR), Robert-Hooke-Str. 7, 28359 Bremen, Germany;2. Jet Propulsion Laboratory (JPL), California Institute of Technology, 4800 Oak Grove Drive, Pasadena CA91109, USA |
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| Abstract: | Recycled high-strength aluminum alloys have limited use as structural materials due to poor mechanical properties. Spray forming remelting followed by hot extrusion is a promising route for reprocessing 7xxx alloys. The 7050 alloy machining chips were spray formed, hot extruded, rotary swaged and heat-treated in order to improve mechanical properties. Microstructures, tensile properties and fatigue strength results for a 2.7 mm-diameter recycled wire are presented. Secondary phases and precipitates were investigated by XRD, SEM, EBSD, TEM and DSC. As-swaged and heat-treated (solution and aging) conditions were evaluated. Mechanical properties of both conditions outperformed AA7050 aerospace specification. Substantial grain refinement resulted from the extensive plastic deformation imposed by rotary swaging. Refined micrometric and sub-micrometric Al grains, as well as coarse and fine intermetallic precipitates were observed. Subsequent solution treatment resulted in a homogeneous, recrystallized and equiaxed microstructure with grain size of 9 μm. Nanoscale GP(I) zones and η′ phase precipitates formed after aging at 120 °C, imparting higher tensile (586 MPa) and fatigue (198 MPa) strengths. |
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| Keywords: | Al−Zn−Mg−Cu alloy spray forming thermomechanical processing microstructure fatigue |
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