Size Dependence of Age-hardening Revealed

A key question in materials science is how fast properties evolve, which involves the kinetics of phase transformations. In metals, kinetics is primarily connected to diffusion, which for substitutional elements is facilitated by mobile atomic-lattice vacancies. After rapid quenching of various important alloys, such as Al- or Mg-alloys, natural aging can occur, i.e., solute atoms can move slightly and arrange themselves into nanometer-sized clusters. This effect is essential to a variety of high-strength alloys used in electronic devices and in the automotive and aerospace industries.

In a collaborative study conducted by the Nonferrous Metallurgy group at the Montanuniversität Leoben and the ETH Zurich Laboratory of Metal Physics and Technology (LMPT), the authors of the Nature Comm. article investigated the age-hardening of an Al 6016 (Al–Mg–Si) alloy at the atomic level with the help of a new cryo-atom probe tomography method developed at ETH’s “ScopeM” microscopy center. They discovered that cluster formation upon natural aging depends on size, and that diffusion processes stop when the sample size decreases from the micrometer to the nanometer range, independent of the metal used. In addition to the obvious significance of these results for today’s ever-smaller components and modern nanostructured alloys, they are also of great importance for high-resolution microscopy techniques. The sample dimensions used in the latter are generally in the nanometer range, and a size effect has never been taken into account. The researchers thus expect that their discoveries will, ultimately, significantly reduce the inconsistencies encountered over the last two decades regarding early clustering in alloys.