Uncovering Ce-rich clusters and their role in precipitation strengthening of an AE44 alloy

The peak-aged (250 degrees C for 4 h) magnesium-aluminum-rare earth (Mg-Al-RE) alloy AE44-2 produced using high-pressure die casting, exhibits a 10 % increase in yield strength attributed to the formation of nanoscale AlMn precipitates. Here, in the as cast state, we show by atom probe tomography Ce-rich clusters in the dendritic and not in the inter-dendritic alpha-Mg, despite a higher RE concentration. Their formation hence depends mainly on solidification kinetics and not on the concentration. The Ce-rich clusters within the dendritic region, act as heterogeneous nucleation sites for the formation of Al10Mn7RE2 nanoscale precipitates during the T5 heat treatment. No changes in the Al11RE3 lamella phase were observed, including to the concentration of segregated Si at the Al11RE3/alpha-Mg interface. Understanding the precipitate formation pathways, specifically the influence of low concentrations of Ce in the dendritic matrix, provides a pathway for tailoring mechanical properties by manipulating these clusters and consequently precipitation.