Abstract: This invention relates to a process and apparatus for treating molten aluminum prior to casting by adding a hydrogen-containing treating gas to the atmosphere over the molten aluminum during melting. A preferred treating gas is finely-atomized water vapor which is added to the fuel-air mixture to be delivered to burners to obtain a disassociation of water vapor into hydrogen and oxygen. The added hydrogen satisfies the affinity of molten aluminum for hydrogen, the addition being controlled to near the saturation point temperature of hydrogen within the molten aluminum. Improved casting properties are obtained in the molded parts which have smaller grain refinement and greater dispersion of shrinkage on cooling to solidification. The treating gas may also consist of hydrogen gas or ammonia gas, the hydrogen being supplied over the molter aluminum when heated to a temperature ranging from about 1200.degree. F. to 1480.degree. F.