Poster Presentation 24th Australian Conference on Microscopy and Microanalysis 2016

‘Golden’ effect on precipitate nucleation and growth in an Al-Cu-Au alloy     (#206)

Yiqiang Chen 1 2 , Zezhong Zhang 1 2 , Zhen Chen 1 2 , Amalia Tsalanidis 2 , Matthew Weyland 1 , Scott Findlay 1 2 , Leslie J Allen 3 , Jiehua Li 4 , Nikhil Medhekar 2 , Laure Bourgeois 1 2
  1. Monash Centre for Electron Microscopy, Monash Univesity, Clayton, VIC 3800, Australia
  2. The Department of Materials Science and Engineering, Monash University, Clayton, VIC 3800, Australia
  3. School of Physics, University of Melbourne, VIC 3010, Australia
  4. Chair of Casting Research, The University of Leoben, Leoben A-8700, Austria

We have used high angle annular dark-field (HAADF) in the scanning transmission electron microscope (STEM) to investigate the Au distribution within Guinier-Preston (GP) zones and θ’ (Al2Cu) precipitates in an Al-Cu-Au alloy. We have experimentally observed denser and narrower precipitate size distributions with the trace addition (200ppm) of Au. Atomic-resolution HAADF imaging was obtained as a function of ageing temperature and time. The measured Au distributions have been compared to complementary first principle calculations and thermodynamic predictions. We have therefore demonstrated that due to the strong negative formation enthalpy in precipitates Au could lower the energy barrier to nucleation at the early stage of phase separation so as to accelerate the nucleation and refine the GP zones. We also showed that subsequent θ’ precipitate growth was accelerated by both the strong negative formation enthalpy of Au in θ’ and the refined GP zones whilst at the later stage Au atoms are most likely to cluster in θ’ precipitates. Our findings confirmed the role of Au on accelerating the phase separation in this Al-Cu-Au alloy, therefore providing a potential way to refine alloys’ microstructure for improving the mechanical performance of these high-strength light alloys.