Revisiting the crystal structure of the equilibrium S (Al2CuMg) phase in Al–Cu–Mg alloys using X-ray absorption spectroscopy (XAFS)

Abstract

Even though, the crystal structure of the intermediate (S’) and the equilibrium S (Al2CuMg) phase were subject of many investigations using mostly imaging or diffraction techniques, the results remain still controversial. Several reports indicate that the metastable S’ phase differentiates from the stable S phase only by their level of coherence and orientation relationship with the aluminum matrix while their crystal structures seem to be identical.In this study, for the first time X-ray absorption spectroscopy (XAFS) was used to verify the correct crystal structure for the S (S’) phase considering the well-known models reported by Perlitz and Westgren, Mondolfo, Kilaas and Radmilovic, Radmilovic et al. and Yan et al.. The crystal structure was confirmed by direct comparison to simulated XAFS spectra using the simulation tool FDMNES. The results support the widely accepted model proposed by Perlitz and Westgren in 1943 as the correct crystal structure.