High-resolution transmission electron microscopy study on reversion of Al2CuMg precipitates in Al–Cu–Mg alloys under irradiation

•Quantitative HRTEM revealed reversed transformations of precipitates in an Al alloy.•Besides S-Al10Cu3Mg3, two new intermediate structures, Al3CuMg and Al18Cu5Mg5, were determined.•The reversed transition was due to irradiation-induced atom displacement.

Image deconvolution analyses showed that reversion of S-Al2CuMg precipitates occurred in an Al–Cu–Mg alloy during high-resolution transmission electron microscopy observations. A fraction of Mg and Cu atoms in the precipitates diffused into Al matrix due to electron beam irradiation at 300 kV, resulting in structural/chemical reversion of the precipitates. The structural reversion of the S-Al2CuMg precipitates is closely related with irradiation-induced displacement of atoms. The strong attraction between Cu and Mg atoms might assist the sub-threshold displacement of Cu atoms. One transitional structure is determined to be S′′-Al10Cu3Mg3, a precursor of S-Al2CuMg. Two other transitional structures, Al3CuMg and Al18Cu5Mg5 which have the same lattice parameters of a = c = 0.405 nm as that of S′′-Al10Cu3Mg3, but different b values, are suggested.