The A356 alloy, which consists of 100-200 ppm modifier, namely strontium was examined. The samples were solidified unidirectionally, and each sample had a pair which was solidified in a rotating magnetic field. The microstructure of the samples: morphology and the fraction of eutectic silicon was studied. The morphology of eutectic Si was very different in the samples - the samples solidified at different movement velocities – so it was necessary to determine the quantity of strontium. Magnetic stirring changes both the strontium content and the extent of modification. This paper describes the investigation methods and the effects of strontium modification.