The β phase Mg₁₇Al₁₂ influences the high-temperature strength as well as the corrosion properties of Mg-Al-Zn alloys. The morphology and distribution of β Mg₁₇Al₁₂ are normally determined by standard metallographic methods, which result in only a two-dimensional picture. Synchrotron-radiation-based microtomography can give a three-dimensional image of the microstructure and was used to characterize the distribution of Mg₁₇Al₁₂ and Al₈Mn₅ in as-cast and extruded Mg-Al-Zn alloys.