The microstructure and resultant mechanical properties of the MM55 manganese brass applied to ship sand - cast propeller were investigated in relation to the propeller blade section thickness. It was stated that the increase of blade section thickness from 15 mm to 45 mm resulted in the increase of the volume fraction of α-phase by 5.3% and that of κ-phase by 23.7%, the decrease of the volume fraction of α-phase by 2.9%, the 0.2% proof stress R0.2 by 11.3%, the ultimate tensile strength Rm by 5.5% and the 5.65 √Soelongation A5 by 16.8%.
