The exclusive effects of gas induced semi-solid parameters such as rheocasting temperature, agitation intensity and flow rate of gas injection into the melt on the average size and shape factor of primary α-Al particles and subsequently tensile properties of 319 aluminum alloy have been studied. Applying vigorous agitation and rapid heat extraction simultaneously in the early stages of solidification in order to achieve a slurry with fine and dispersed primary α-Al particles is essential. Hence, in order to investigate these two factors separately, three different types of graphite diffusion in three proportional gas flow rates have been used. It was found that a reduction in rheocasting temperature leads to a decrease in the average size of the primary α-Al particles and an increase in their sphericity and improvement of tensile properties as well. The average size of primary particles slightly decreases as the agitation intensity …