Atom probe microscopy investigation of Mg site occupancy within δ′ precipitates in an Al-Mg-Li alloy

The composition and site occupancy of Mg within ordered delta ' precipitates in a model Al-Mg-Li alloy have been characterized by atom probe microscopy and first-principles simulations. The concentration in the precipitates is found to be almost the same as that of the matrix; however, we show evidence that Mg partitions to the sites normally occupied by Li in the Ll(2) structure. Density functional calculations demonstrate that this partitioning is energetically favorable, in agreement with experimental results. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.