The invention relates to a flux for application to and the reduction of oxide layers on a metallic solid or molten surface that is composed at least of potassium, fluoride, and moieties of water. The flux is formed from a reactant containing moieties of zirconium fluoride and/or lithium fluoride and/or sodium silicon fluoride and/or potassium cryolite and/or potassium aluminum fluoride (KaAIF4) as well as moieties of salts based on zirconium and/or lithium and/or potassium and/or sodium and/or bismuth and/or boron and/or titanium. The invention further relates to a method for casting basic aluminum alloys as well as the use of the disclosed flux for reducing oxide layers on molten basic aluminum alloys.