Enhanced dispersoid precipitation and dispersion strengthening in an Al alloy by microalloying with Cd

The dispersion hardening effect of Mn(Fe)-containing dispersoids in aluminium alloys has long been ignored since it is difficult to achieve a high number density of fine dispersoids with conventional alloying compositions. This work demonstrates a minor addition of Cd (0.05 at.%) can dramatically enhance the precipitation of alpha-Al(Mn,Fe)Si dispersoids and therefore the dispersion strengthening of AA3003 alloy. Similar to the 3003 base alloy, a peak hardness in the Cd-containing alloy was obtained after continuous heating to 450 degrees C. However, an improvement in yield strength by 25% was achieved by the Cd addition. Detailed transmission electron microscopy (TEM) and atom probe tomography (APT) investigations show that the Cd addition has changed the nucleation behaviour of a-Al(Mn,Fe)Si dispersoids from the conventional heterogeneous nucleation on dislocations to a more homogeneous manner. It is found that a high number density of Al-Cd nanoprecipitates formed during heating between 150 and 250 degrees C. These Al-Cd precipitates attracted Mn and Si atoms to form Mn,Si-rich clusters in/around them, which acted as the precursors for the later nucleation of alpha-Al(Mn,Fe)Si dispersoids at similar to 300 degrees C. As a result, the number density of dispersoids formed in the Cd-containing alloy after heating to 350-450 degrees C is about twice as that in the base alloy subjected to the same heat treatment. This work proposes a new approach to enhance the nucleation of alpha-Al(Mn,Fe)Si dispersoids, which can help to further develop cheap Mn(Fe)-containing dispersoid-strengthened aluminium alloys for high-temperature applications. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.