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

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.

Research on a creep constitutive model of compacted graphite cast iron and its parameter identification method

“…They proposed an improved θ equation to make the prediction results of creep curve more reliable. Ma et al 13 In conclusion, the present study has a relatively high prediction accuracy for the MCR and the degree of correlation curve fitting within a small range of temperature and stress. Nonetheless, the application scope has certain limitations, as it does not fully align with the actual working conditions of CGI cylinder heads, leading to relatively conservative conclusions.…”

“…They proposed an improved equation to make the prediction results of creep curve more reliable. Ma et al 13 conducted creep tensile tests on the Al‐Li‐S4 aluminum alloy at 426.15 K and 200–240 MPa. Their study explored various aspects under creep aging forming conditions.…”

Research on Creep Test of Compacted Graphite Cast Iron and Parameter Identification of Constitutive Model under Wide Range of Temperature and Stress

“…Sci. 2022, 12, 5032 2 of 12 At present, many scholars have carried out much work on the creep behavior of commonly used materials [13][14][15][16][17]. However, most of them have only carried out creep tests under a small temperature and stress range.…”