Journal
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
Volume 759, Issue -, Pages 465-478Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.msea.2019.05.066
Keywords
Al-Mg-Zn alloy; T-phase; Solute clustering; Precipitation; Atom probe tomography
Categories
Funding
- Major State Research and Development Program of China [2016YFB0300801]
- National Natural Science Foundation of China [51571013, 51301017]
- Beijing Laboratory of Metallic Materials and Processing for Modern Transportation, China
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The AlMgZn phase (T-phase)-an interesting strengthening phase in precipitation-hardened aluminum alloys has not received sufficient attention and is very different from the commonly studied eta-MgZn2 phase. This study focuses on Al-5.1Mg-0.15Cu-xZn alloys with a Zn/Mg ratio below 1.0. This is different from commonly known 7xxx series alloys whose Zn/Mg ratios are above 2.0. The relations among the age-hardening response behavior, clustering of Mg-Zn or Mg-Cu atoms, and precipitation of different hardening phases in Al-5.1Mg-0.15Cu-xZn alloys are investigated via atom probe tomography and transmission electron microscopy. According to the results, the Zn addition stimulates the precipitation of coherent T '' precipitates, but suppresses S-Al2CuMg and beta-Al3Mg2 phases. This results in an enhanced and accelerated age-hardening response in alloys with high Zn contents. The 3.0Zn (wt.%) alloy with finer T '' precipitates exhibits the best age-hardening response, followed by the 2.0Zn (wt.%) alloy with T' precipitates and the 1.0Zn (wt.%) alloy with T precipitates. Clusters with high Mg/(Al + Zn + Cu) ratios cannot act as effective precursors for the transformation of Mg-Zn clusters into T '' precipitates, thereby resulting in a weaker age-hardening response and lower hardness in the 1.0Zn (wt.%) alloy. Furthermore, although T-phases originate from different alloys, their Mg/(Al + Zn + Cu) ratios reach the constant value 3/7 for larger particle sizes. This challenges the chemical composition of traditional equilibrium T precipitates.
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