Deformation-induced dissolution and growth of precipitates in an Al-Mg-Er alloy during high-cycle fatigue

The dissolution and growth of Al-3(Er,Zr) precipitates during tensile fatigue experiments were investigated by quasi-in situ and postmortem scanning transmission electron microscopy with Z contrast imaging and X-ray energy dispersive spectroscopy. Al-3(Er,Zr) particles were observed with both non-core shell and core shell structures, which were formed during multiple-stage precipitations, in an Al-Mg-Er alloy. After fatigue deformations, the average size of the non-core shell structured precipitates increased significantly. By tracing the same precipitate particles before and after a high-cycle fatigue test, quasi-in situ electron microscopy revealed that the increase of average particle size is associated with the substantial dissolution of small non-core shell structured Al-3(Er,Zr) particles, whose diameters are generally less than 15 nm, and a consequent growth of larger non-core shell Al-3(Er,Zr) precipitates. On the contrary, the core shell structured Al-3(Er,Zr) precipitates remain stable during high-cycle fatigue tests. Possible mechanisms for the dissolution and growth of non-core shell structured Al-3(Er,Zr) precipitates are discussed in terms of particle size, interfacial energy and lattice mismatch, in comparison to the stable core shell structured precipitates. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.