Synergistic effects of Cd, Si and Cr additions on precipitation strengthening and thermal stability of dispersoids in AA3003 alloy

The thermally stable Mn-rich dispersoids in Al alloys were recently reported to have a significant dispersion strengthening effect. Further improvements in the dispersion strengthening and thermal stability of Mn-rich dispersoids are required to achieve satisfactory mechanical properties for elevated temperature applications. This study reports that, with minor additions of Cd, Cr and increased Si content, the yield strength of the modified AA3003 alloy is increased by 39% compared to the base alloy subjected to the same heat treatment. Moreover, the thermal stability of the modified alloy when exposed to a long-term thermal holding up to 1000 h at 400 °C is greatly improved. Microstructural characterizations reveal that the dispersoids in the modified alloy are greatly refined, and their distribution is more homogeneous compared to the base alloy. It is observed that the Cd-rich clusters/nanoparticles formed in the initial stage of heat treatment, can effectively “attract” dispersoid-forming atoms (e.g. Mn, Si and Cr) and subsequently lead to a heterogeneous nucleation of dispersoids on them, which is responsible for the enhanced dispersoid precipitation and dispersion strengthening in the modified alloy. The partitioning of the low-diffusivity peritectic element Cr into dispersoids can improve the thermal stability and increase the number density of dispersoids in the centre of dendrite arms, which also contributes to the promising mechanical properties of the modified alloy.