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Study on Multi-Step Creep Aging Behavior of Al-Li-S4 Alloy

1,2,3, 1,3, 1,3,* and 1,3,*
1
School of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China
2
Beijing Institute of Aerospace Systems Engineering, Beijing 100076, China
3
State Key Laboratory of High-performance Complex Manufacturing, Central South University, Changsha 410083, China
*
Authors to whom correspondence should be addressed.
Metals 2019, 9(7), 807; https://doi.org/10.3390/met9070807
Received: 10 July 2019 / Revised: 18 July 2019 / Accepted: 19 July 2019 / Published: 22 July 2019
(This article belongs to the Special Issue Analysis and Design of Metal-Forming Processes)
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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. View Full-Text
Keywords: Al-Li-S4 alloy; creep aging; multi-step phenomenon; mechanical properties; distribution characteristics Al-Li-S4 alloy; creep aging; multi-step phenomenon; mechanical properties; distribution characteristics
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Ma, Y.; Xia, F.; Zhan, L.; Xu, Y. Study on Multi-Step Creep Aging Behavior of Al-Li-S4 Alloy. Metals 2019, 9, 807.

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