3DAP measurements of Al content in different types of precipitates in aluminium alloys

Three-dimensional atom probe and field ion microscopy have been used to determine the composition of precipitates formed in several types of aluminium-based alloys. Special attention has been paid to local magnification artefacts, which are often suspected to strongly disrupt the precipitates' apparent composition. The charge state of Al ions has been used to identify the nature of precipitates (lower or higher evaporation field than the matrix) and also to determine the origin of Al ions observed in 3D reconstructions. The use of a cluster identification method, which allows erosion concentration profiles to be drawn, has revealed the importance of trajectory overlaps in the measurement of the precipitates' composition. By applying this method to low-evaporation-field precipitates in a 7XXX alloy, good agreement was found between atom probe measurements and observations in transmission electron microscopy and small angles X-ray scattering. Copyright (C) 2007 John Wiley & Sons, Ltd.