Architecturally Arranged Precipitates Yield a New High Strength Al-Cu-Sc-Zr-Mn Alloy with Exceptional Thermal Stability

Abstract

The refinement and thermal stability of intermediate theta-prime ( θ' ) precipitates are critical in the development of new high strength 2xxx series aluminium-copper (Al-Cu) alloys for high temperature applications. In this work, we use trace additions of Sc, Zr and Mn in an Al-6.5wt.%Cu alloy to refine and stabilise the θ' precipitates. The Al 3 (Sc, Zr) core/shell dispersoids significantly refine the θ' precipitates by acting as preferential nucleation sites during artificial ageing. Adding Mn results in a significant increase of hardness during ageing at 190 °C. Furthermore, hardness is maintained for up to 24 h of thermal exposure at 280 °C. Transmission electron microscopy (TEM) reveals that the addition of Mn leads to a finer and denser distribution of θ' precipitates, and greatly slows the growth and coarsening of the θ' precipitates at elevated temperatures. Differential scanning calorimetry (DSC) shows that this can be attributed to an enhanced nucleation and improved coarsening resistance of the θ' precipitates in the presence of Mn. A combination of energy dispersive spectroscopy (EDS) and atom probe tomography (APT) reveals that Mn, Zr and Sc segregate at the Al/ θ' semi-coherent interfaces. This segregation lowers the interfacial energy of the θ' precipitates and provides a barrier for solute drag, thus lowering the nucleation energy and enhancing their thermal stability. A final benchmark reveals that the Al-Cu-Sc-Zr-Mn alloy surpasses other common elevated temperature high strength Al alloys.