2023 年 64 巻 2 号 p. 458-466
This study investigated the cluster formation process in the early stages of 353 K aging in Al–1.04 mass%Si–0.55 mass%Mg alloys by means of soft X-ray absorption fine structure (XAFS) measurements and first-principles calculations. XAFS at the Si-K and Mg-K edges was carried out at the BL27SU beamline at SPring-8. To observe the structural changes in detail, an XAFS apparatus able to hold the sample at 353 K in a vacuum chamber and cool it rapidly to suppress the progress of clustering was developed. Density functional theory (DFT) calculations were used to simulate the Si-K and Mg-K edge spectra for various cluster models. Based on the results, the cluster formation process in the early stages of aging at 353 K was qualitatively clarified. Initially, Mg–Va (Va: vacancy) pairs and Si–Va pairs were formed, then 2-MgVa clusters formed by bonding between Mg–Va pairs along (100); subsequently, L10 clusters were formed by Mg atoms ordered along (100), and then SiVa-py clusters with Va adjacent to the first-nearest-neighbor atom of Si atoms and Si-py without adjacent Va were formed, in which Mg–Va pairs and Si–Va pairs were individually united, respectively. Monolayer and multilayer structures then developed as aging proceeded, involving Mg and Si atoms ordered along (100), in which Mg and Si atoms were bonded.