Aluminum magnesium alloys comprise an important class of alloys often used in the automotive, aerospace, and marine industry because of their low density and good corrosion resistance. These parts are often produced by a casting processing; creating microstructures, most commonly dendrites, that can affect the properties of the material. Critical experiments have been carried out on the Al-Mg system in order to understand how dendrite growth direction varies with composition. Through experimental studies under steady state growth, critical compositions at which the transition in preferred growth direction occurs were examined. The orientations of the resulting dendrites were measured using orientation imaging microscopy (OIM). OIM data showed the primary dendrite trunk was not affect by the change in magnesium composition keeping a (100) orientation throughout. However, there was transition in the secondary dendrite arm orientation from (100) to a (110) that occurred around 15 - 20 wt. % Mg. Though the OIM data suggests only a (100) primary dendrite trunk orientation, at some compositions a 60y angle between the dendrite trunk and side arms was also observed indicating a (110) primary dendrite trunk and (110) secondary arms.