In this paper computer simulation of small-angle X-ray scattering (SAXS) curves was applied to determine the size, shape, and distribution of secondary phases formed in the aluminum matrix during dynamic ageing. SAXS patterns were registered in transmission mode for Al-Mg-Si alloys foils. For the first time the spatial distribution of dispersed phase particles was accounted during the simulation of scattering curves. Scattering curves were simulated in the large angular range to improve the accuracy of the results. The method of SAXS was preliminarily tested on similar samples after artificial ageing to validate the used approach.