Strong stress-level dependence of creep-ageing behavior in Al–Cu–Li alloy

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 802; p. 140381
• Main Authors: Ma, Peipei, Zhan, Lihua, Liu, Chunhui, Yang, Jianshi, Chen, Kailiang, Huang, Zhibin
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 20.01.2021; Elsevier BV
• Subjects: Aging (metallurgy); Alloys; Aluminum base alloys; Al–Cu–Li alloys; Copper; Creep age forming; Creep strength; Creep tests; Dislocation mobility; Heat treating; Mechanical properties; Microstructure; Precipitates; Precipitation; Precipitation hardening; Reversion; Scanning transmission electron microscopy; Softening; Strain; Tensile tests; Yield strength; Yield stress; Al–Cu–Li alloys; Precipitation; Microstructure; Creep age forming
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2020.140381

The creep responses, mechanical properties and microstructure evolution in an Al–Cu–Li alloy creep-aged under different stress levels have been systematically investigated by creep test, tensile test and high-angle annular dark-field scanning transmission electron microscopy. When the applied stress is lower than the yield strength, the creep deformation exhibits a four-stage behavior with double primary creep. For high-stress-aged samples, the alloys experience an unusual rapid strain increase at the initial holding stage and then exhibit a normal two-stage creep behavior. The stress-exponent analysis indicates the creep mechanism changes from diffusion creep to dislocation climbing with the stress exceeding the yield strength. The apparent preferential alignment of δ′/θ'/δ′ composite precipitates (stress-orienting effect) can be frequently observed in the low-stress-aged samples and is demonstrated to be responsible for the reduced precipitation strengthening potential compared to the stress-free-aged sample. The high-stress-loading induced dislocations result in a considerable increase of both the creep response and mechanical strength. The unusual strain increase is ascribed to the inelastic deformation caused by softening (material strength lower than the holding stress) due to dislocation recovery and solute clusters reversion within a short-time interval. The dislocation hardening compensates the softening induced by the stress-orienting effect of both T1 and δ′/θ'/δ′ composite precipitates in the high-stress-aged samples. Our results reveal the microstructural factors sensitive to the stress-level during both the stress-loading and holding stages determine the stress-level dependent creep-ageing response in Al–Cu–Li alloy.