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

The dissolution and growth of Al₃(Er, Zr) precipitates during tensile fatigue experiments were investigated by quasi-in situ and post-mortem scanning transmission electron microscopy with Z contrast imaging and X-ray energy dispersive spectroscopy. Al₃(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 Al₃(Er, Zr) particles, whose diameters are generally less than 15 nm, and a consequent growth of larger non-core–shell Al₃(Er, Zr) precipitates. On the contrary, the core–shell structured Al₃(Er, Zr) precipitates remain stable during high-cycle fatigue tests. Possible mechanisms for the dissolution and growth of non-core–shell structured Al₃(Er, Zr) precipitates are discussed in terms of particle size, interfacial energy and lattice mismatch, in comparison to the stable core–shell structured precipitates