The use of gas-generating mold coatings for the grain refinement of aluminum

Experiments are described in which an effervescent mold coating containing hexachloroethane has been used to promote the dynamic grain refinement of commercial purity aluminum ingots. The influence of the amount of hexa chloroethane in the mold coating, the degree of superheat of the cast metal and the nature of the mold material was assessed. Comparison has been made with unrefined ingots and with ingots grain refined using conventional inoculation procedures. It is concluded that low levels of hexa chloroethane (10 to 20 wt pct in the mold coating) can produce effective refinement provided conditions exist favorable for the survival of dendrite fragments or nucleating particles generated by the remelting associated with turbulence in the liquid or chemical and/or mechanical interactions between the effervescing gas and the mold coating. The effectiveness of refinement is enhanced by high rates of heat transfer and low pouring superheats. Visiting Professor in the Department of Mechanical Engineering, State University of Campinas.