Size-dependent diffusion controls natural aging in aluminium alloys

Abstract

A key question in materials science is how fast properties evolve, which relates to the kinetics of phase transformations. In metals, kinetics is primarily connected to diffusion, which for substitutional elements is enabled via mobile atomic-lattice vacancies. In fact, non-equilibrium vacancies are often required for structural changes. Rapid quenching of various important alloys, such as Al- or Mg-alloys, results for example in natural aging, i.e. slight movements of solute atoms in the material, which significantly alter the material properties. In this study we demonstrate a size effect of natural aging in an AlMgSi alloy via atom probe tomography with near-atomic image resolution. We show that non-equilibrium vacancy diffusional processes are generally stopped when the sample size reaches the nanometer scale. This precludes clustering and natural aging in samples below a certain size and has implications towards the study of non-equilibrium diffusion and microstructural changes via microscopy techniques.

Study of natural aging on nanoparticles and their strengthening effect in Al-Mg-Si alloy

“…The APT samples of NA were prepared by electrolytic polishing and were completed within 10-15min. NA will not occur again in the APT sample after the preparation is completed which was proved by [12]. The APT experiments were carried out on LEAP 5000 XR with laser mode at a temperature of 25 K and a laser pulse frequency of 200 kHz.…”

Precipitation kinetics in metallic alloys: Experiments and modeling

“…In metals, most solutes forming precipitates are substitutional and thus the diffusion mechanisms involve mainly the movement of vacancies. Therefore, the precipitation kinetics is directly controlled by the concentration of vacancies by their diffusion rate within the material and by their interaction with solutes [96][97][98]36,99,100]. An important exception is the precipitation of cementite in steels during martensite tempering, where carbon diffuses interstitially.…”

New frontiers in atom probe tomography: a review of research enabled by cryo and/or vacuum transfer systems

“…As a result, they were able to experimentally verify that clusters of Si are the first to form during the natural aging process. In a later study, the same team also used the same approach to demonstrate that specimen size–dependent diffusion in atom probe tips affect the aging and clustering processes, an important consideration for the study of microstructural changes via microscopy techniques [ 82 ].…”