The nano-structural characterization of Ω and S phases in Al-5.1Cu-1.0 Mg-(0.4Ag) AA2024 aluminum alloys

Cheng Ling Tai, Mien Chung Chen, Tsai Fu Chung, Yo Lun Yang, Sheng Long Lee, Tzu Ching Tsao, Zhusheng Shi, Jianguo Lin, Te Cheng Su, Hsueh Ren Chen, Jer Ren Yang

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Abstract

The effects of a minor addition (0.4 wt%) of Ag to Al-5.1Cu-1.0 Mg aluminum alloy on the microstructural evolution and mechanical properties have been investigated. The under-ageing, peak ageing, over-ageing, and prolonged ageing at 185 °C were studied for the alloys with and without Ag additions to further correlate the microstructure with mechanical properties. The faster increment of hardness during the early stage (1–5 h) and much higher ultimate tensile strength (530 Mpa) at peak ageing condition in Ag-containing specimen were attributed to the formation of the Ω phase triggered by the Ag addition. In over-aged specimens, the S phase in the Ag-free specimen coarsened significantly, whereas the S phase in the Ag-containing specimen remained nearly the same size as that in its peak-ageing treated specimen. The formation of the Ω phase in the Ag-containing specimen presumably consumed the same solute atoms as the S phase, i.e., Cu and Mg, leading to the depleted zones of Cu–Mg in the aluminum matrix and thus suppressing the coarsening of the S phase during the ageing time from 11 h (peak ageing) to 18 h (over ageing). After ageing for 100 h (prolonged ageing), the S phase coalesced in both alloys. However, the Ω phase in the Ag-containing specimen still maintained a thickness of ∼3 nm with a high level of volume percent (2.74 vol %), which contributed significantly to the UTS (449 MPa).

Original languageEnglish
Article number145361
JournalMaterials Science and Engineering A
Volume881
DOIs
StatePublished - 10 Aug 2023

Keywords

  • AA2024 aluminum alloys
  • High resolution transmission electron microscopy
  • Minor Ag addition
  • Suppression of S phase
  • Thermally stable Ω phase

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