Abstract
Creep age forming (CAF) is a new technology developed for manufacturing large aluminum components in the aerospace industry. Aluminum–lithium alloys may be used in aerospace components because of their high modulus, specific strength and specific stiffness. Therefore, the creep deformation, mechanical properties and aging precipitation of Al-Li-S4 alloy under CAF conditions were studied. It was found that the creep behavior presents double steady state creep stages during the creep aging process. With the increase of stress level, the first steady creep rate increased, but the second steady creep rate was slightly reduced. Coincidentally, in the first steady state creep stage, the yield strength of the studied alloy also showed a slow increase stage. TEM observation showed that Al-Li-S4 alloy mainly contains two precipitation phases, T1 phase and θ’ phase. A few precipitates form during the first steady creep stage. Then, a lot of nucleation and growth of T1 phase resulted in rapid increase of yield strength. At the same time, the increase of stress level effectively inhibited the growth of T1 phase, which resulted in these strengthening phases being more uniform, and thus improved the mechanical properties of materials. On this basis, the relationship between the multi-step behaviors of creep, mechanical properties and aging precipitates are discussed. It is considered that the main reasons for the multi-step phenomenon of creep and mechanical properties are strongly related to the nucleation, growth and distribution of T1 phase.
Highlights
Creep Ageing Forming (CAF) is a metal forming technology developed for manufacturing large aluminum components in the aerospace industry [1]
Hu et al [6,7] studied the effects of creep aging and single stress-free aging on the mechanical properties and micro-precipitates of Al-Li-S4 alloy, and studied the effects of pre-deformation on creep aging and related mechanical properties of Al-Li-S4 alloy
The micro-structure of Al-Li-S4 alloy during creep aging process is analyzed by using Titan G2 60-300 spherical aberration correction projection electron microscopy(FEI Company, Hillsboro, OR, USA) to photograph the high-angle annular dark field (HAADF) inside the alloy and energy spectrum analysis (EDS), as well as the tensile tests of creep specimens were carried out on CMT-5105 electronic universal testing machine to analyze(SUST Company, Zhuhai, China) the microstructural evolution and mechanical properties of the alloy during creep aging
Summary
Creep Ageing Forming (CAF) is a metal forming technology developed for manufacturing large aluminum components in the aerospace industry [1]. For creep aging forming process, many scholars have developed a special unified field constitutive model for CAF process. The creep aging process of aircraft panel was simulated by the finite element method. Through ABAQUS finite element analysis software, Li et al [13] analyzed the influence of temperature and other parameters on the resilience of stress relaxation of a panel. A constitutive model for 7050 aluminum alloy in pre-aging state and for finite element analysis was established. Lam et al [14] Zhan’s constitutive model was applied to the finite element analysis of creep aging of AA 2219 alloy, and the springback of CA 2219 alloy in CAF process was successfully predicted. The creep aging behavior of Al-Li-S4 aluminum alloy under different applied stress conditions and its macroscopic model are studied in this paper. The micro-structure of Al-Li-S4 alloy during creep aging process is analyzed by using Titan G2 60-300 spherical aberration correction projection electron microscopy(FEI Company, Hillsboro, OR, USA) to photograph the high-angle annular dark field (HAADF) inside the alloy and energy spectrum analysis (EDS), as well as the tensile tests of creep specimens were carried out on CMT-5105 electronic universal testing machine to analyze(SUST Company, Zhuhai, China) the microstructural evolution and mechanical properties of the alloy during creep aging
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