Quantitative evaluation of the effect of Ag-addition on the concurrently-existing precipitation kinetics in the aged Al-Cu-Mg(-Ag) alloys

Mien Chung Chen, Tsai Fu Chung, Cheng Ling Tai, Yu Hsuan Chen, Jer Ren Yang, Sheng Long Lee, Chien Nan Hsiao, Cheng Si Tsao, Che Min Chou

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Abstract

Two Al-Cu-Mg(-Ag) aluminium alloys, having the same base composition of Al-5.11Cu-0.96 Mg-0.58Mn-0.12Zr (wt.%) but different Ag contents, 0 and 0.7 Ag (wt.%), and accordingly denoted 0A and 7A samples, were aged at 185 °C. In early-ageing, the formation of disk-like Mg-Cu and Mg-Ag nano(co–)clusters can be quantitatively examined by Small angle X-ray scattering (SAXS), respectively. In the prolonged ageing of the 0A samples, the thickening in the disk-like θ-precipitates leads to a lower aspect ratio. For S-precipitates, the change in the total surface area and the single-particle surface area indicates that the coalescence mechanism is prevalent from peak-ageing to over-ageing, and then after over-ageing, the precipitate coarsening dominates. The coarsening in S and θ precipitates presumably leads to a lower mechanical strength. Alternatively, in the aged 7A sample, the SAXS technique in conjunction with transmission electron microscopy (TEM) quantitatively reveals Ω-precipitates possessing a nearly constant thickness but an increase in diameter with ageing time. Additionally, the stable behaviors of the total surface and size of S-precipitates illuminate that the coalescence/coarsening mechanisms are significantly slowed down. The concurrently-existing precipitation kinetics of Ω and S have provided an in-depth understanding of the higher strength of the aged 7A sample.

Original languageEnglish
Article number111766
JournalMaterials and Design
Volume227
DOIs
StatePublished - Mar 2023

Keywords

  • Ag addition
  • Aged Al-Cu-Mg(-Ag) aluminium alloys
  • Multiple precipitate evolutions
  • Small angle X-ray scattering
  • Transmission electron microscopy

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