Enhancing thermal stability and strengthening mechanism of Al-Cu alloy via synergistic segregation of Cr, Mn, and Zr at Al/θ′ interface
Gihoon Moon, Eunkyung Lee
Abstract
This study investigated Al–6 wt% Cu alloys containing individual and synergistic additions of Cr, Mn, and Zr to determine the relationships between the mechanical properties, microstructural stability, and strengthening mechanisms after artificial aging and thermal exposure. The separate addition of Cr and Mn plays a significant role in improving the precipitation kinetics and thermal stability of the θ′ precipitates; however, addition of Mn led to a finer θ′ distribution and higher coarsening resistance of θ′ precipitates compared to the addition of Cr. Atom probe tomography demonstrated that addition of Cr or Mn stabilized θ′ precipitates long enough for additional Zr segregation at interfaces, enhancing coarsening resistance up to 350 °C. Interestingly, combined Cr + Zr addition produced an alloy that achieved higher amounts of interfacial Zr segregation and demonstrated better thermal stability compared to Mn + Zr addition after thermal exposure. Finally, the Orowan strengthening mechanisms were insufficient to explain the yield strength of the investigated alloys after artificial aging. The additional strengthening mechanism of θ′ precipitates associated with the transformation strain, which is related to the number density of θ′ precipitates, was confirmed to aid in determining the yield strength of aged alloys.