Stoichiometric precipitates owe their fixed composition to an ordered crystal structure. Deviations from that nominal value, however, are encountered at times. Here we investigate composition, structure and diffusion phenomena of ordered precipitates that form during heat treatment in an industrially cast Al–Mg–Sc–Zr alloy system. Experimental investigations based on aberration-corrected scanning transmission electron microscopy and analytical tomography reveal the temporal evolution of precipitate ordering and formation of non-equilibrium structures with unprecedented spatial resolution, supported by thermodynamic calculations and diffusion simulations. This detailed view reveals atomic-scale spinodal decomposition to majorly define the ongoing diffusion process. It is illustrated that even small deviations in composition and ordering can have a considerable impact on a system’s evolution, due to the interplay of Gibbs energies, atomic jump activation energies and phase ordering, which may play an important role for multicomponent alloys.

化学计量的沉淀物由于其固定的组成而归因于有序的晶体结构。但是，有时会遇到与该标称值的偏差。在这里，我们研究了在工业铸造的Al-Mg-Sc-Zr合金系统中进行热处理时形成的有序析出物的成分，结构和扩散现象。基于像差校正的扫描透射电子显微镜和分析层析成像的实验研究表明，在热力学计算和扩散模拟的支持下，析出物的时间演变和具有前所未有的空间分辨率的非平衡结构的形成。此详细视图揭示了原子级旋节线分解，主要定义了正在进行的扩散过程。