To provide a method for refining Al alloy molten metal by which the yield of Al molten metal is improved by the suppression of the slagging in the surface of the Al molten metal to the utmost while maintaining the high reduction levels of dehydrogenation and the removal of inclusions in alum flux, and further, the removability of slag is improved, and to provide flux for refining Al alloy molten metal.

Aluminum alloy molten metal for malleable aluminum material is subjected to molten metal refining of reducing hydrogen in the molten metal with alum powder as flux for refining, and jointly, slag floated up on the surface of the molten metal is removed. In this case, the content of moisture including crystallization water in the alum powder is controlled to 0.7 to 4.0% by a measuring method by a heating drying mass system, and the amount of the slag to be generated on the molten metal refining is suppressed to ≤3 mass%.