As part of this master thesis, the process parameters for metallographic preparation, including grinding, polishing and etching, for the magnesium-alloy Mg-Al-Ca-Mn are presented. The grinding, polishing and etching steps are also transferable to other low-alloy magnesium systems. The sample material includes as cast, homogenized, extruded, forged, T5- and T6 heat-treated conditions. The microstructure was first examined in a light microscope (grain size determination) and then in a scanning electron microscope to determine the present phases. Since the grain size in magnesium plays a very important role in terms of strength and ductility, also an analysis of the grain size controlling dispersoids is important. Those particles pin the grain boundaries after recrystallization as a result of warm forming and heat treatment. They appear as intermetallic phases of the composition Al8Mn5, which are rod- or plated-shaped and thermally stable after their formation, but tend to coarsen in the further treatments. Their morphology was also confirmed via transmission electron microscopy. For a prediction of the maximum grain size depending on the phase fraction and morphology of second phases, the Zener equation was applied. The maximum grain size determined by the Zener Drag does not match the measured grain sizes. Therefore, modified Zener formulas were tested for their applicability and possible mechanisms for the interaction of the grain boundaries with the Al-Mn-particles were discussed.