Evolution of precipitates during two-stage stress-aging of an Al-Zn-Mg-Cu alloy

• Published in: Journal of alloys and compounds Vol. 684; pp. 177 - 187
• Main Authors: Lin, Y.C., Zhang, Jin-Long, Chen, Ming-Song
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.11.2016
• Subjects: AGING MECHANISMS; Aluminum alloy; BOUNDARIES; DIFFUSION; Evolution; Forming; Grain boundaries; Microstructure evolution; NUCLEI; PHASES; PRECIPITATES; Precipitation; Stress-aging; TEM; Stress-aging; Precipitation; TEM; Microstructure evolution; Aluminum alloy
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2016.05.161

Two-stage stress-aging behaviors of an Al-Zn-Mg-Cu alloy are studied. The precipitates evolution during two-stage stress-aging is analyzed. It is found that the formation of precipitate nuclei mainly occurs in the first stage stress-aging. With increasing the first stage stress-aging temperature, the nuclei gradually grow up and partly transform from GP zones to η′ phases. Meanwhile, continuously-distributed aging precipitates appear along grain boundaries, and no obvious precipitate free zone can be detected. In the second stage stress-aging, aging precipitates (η′ and η phases) easily coarsen, but the density of intragranular aging precipitates highly depends on the first stage stress-aging temperature. Furthermore, discontinuously-distributed η phases appear along grain boundaries with a broadened precipitate free zone. Two-stage stress-aging processing can optimize the distribution of aging precipitates within grains and at grain boundaries. Additionally, when the external stress is enhanced, the diffusion kinetics of solute atoms could be accelerated through the interaction between dislocations and aging precipitates. Therefore, the formation and growth of stable aging precipitates are greatly promoted under large external stress. These important conclusions can be used for fabricating the complex shaped aluminum sheet components by combining both the mechanical forming process and aging treatment, such as creep-aging forming technology. [Display omitted] •Two-stage stress-aging behaviors of an Al-Zn-Mg-Cu alloy are studied.•The formation of precipitate nuclei mainly occurs in the first stage stress-aging.•In the first stress-aging stage, no obvious precipitate free zone can be detected.•In the second stress-aging stage, aging precipitates (η′ and η phases) easily coarsen.•The external stress accelerates interactions between dislocations and aging precipitates.