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Dynamic interplay between dislocations and precipitates in creep aging of an Al-Zn-Mg-Cu alloy

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Abstract

Creep age forming (CAF) is an advanced forming technology used for manufacturing large complex integrated panel components. However, in creep aging (CA), unlike in sole creep or aging procedure, the dislocation movement and the precipitation process occur simultaneously, leading to difficulty in understanding of the dynamic interplay between these two phenomena. In this work, taking 7050 Al alloy, a typical Al-Zn-Mg-Cu alloy, as the test material, an experimental scheme combining pre-deformation, artificial aging (AA), and tensile/compressive CA is designed to decouple and reveal the dynamic interaction mechanism of both phenomena. From AA experiments, the static interaction between dislocations and precipitates is studied, and then their dynamic interactions in CA and each evolution are comparatively investigated. The research shows that both total strain and strain rate increase with the increase in pre-deformation in tensile and compressive CA. However, the total creep strain in compressive CA is larger than that in tensile CA. In additional, the more the dislocations are induced, the sparser and more heterogeneous the overall distribution of precipitates becomes. For dynamic interplay, in the first stage of CA (I), under thermal-mechanical loading, the GP zones and η′ phases gradually nucleate and grow, while the effect of dislocation multiplication is dominant compared with dislocation annihilation, leading to an increase in total dislocation density. Soon, the dislocation movement is gradually hindered by tangling, pile-up, and the precipitates that have grown on the dislocation lines, this decreases the mobile dislocation density and results in a significant decrease in creep rate. In the second stage (II), the precipitates grow further, especially those lying on the dislocation lines; the effects of pinning and hindrance are enhanced until the dislocation multiplication and annihilation reach a dynamic equilibrium, and the total and mobile dislocation densities tend to be roughly unchanged, thus, the creep rate remains relatively constant in this stage.

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Acknowledgements

The research is supported by the National Natural Science Foundation of China for Key Program (Grant No. 51235010), the National Science Fund for Excellent Young Scholars (Grant No. 51522509), and the Marie Curie International Research Staff Exchange Scheme (IRSES, MatProFuture, Grant No. 318968) within the EC 7th Framework Programme (FP7). Meanwhile, we would like to thank the Analytical & Testing Center of Northwestern Polytechnical University for assistance in transmission electron microscope imaging.

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Authors and Affiliations

  1. State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an, 710072, People’s Republic of China

    Heng Li, Tian-Jun Bian, Chao Lei, Gao-Wei Zheng & Yu-Fei Wang

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  1. Heng Li
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  2. Tian-Jun Bian
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  3. Chao Lei
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Correspondence to Heng Li.

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Li, H., Bian, TJ., Lei, C. et al. Dynamic interplay between dislocations and precipitates in creep aging of an Al-Zn-Mg-Cu alloy. Adv. Manuf. 7, 15–29 (2019). https://doi.org/10.1007/s40436-018-0240-y

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  • DOI: https://doi.org/10.1007/s40436-018-0240-y

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