A method for the refining and structural modification of Al—Mg—Si alloys for permanent-mold casting or sandcasting, which Al—Mg—Si alloys have the general composition of 5.0-10.0 weight % Mg; 1.0-5.0 weight % Si; 0.001-1.0 weight % Mn, 0.01-0.2 weight % Ti, less than 0.001 weight % Ca, less than 0.001 weight % Na, and less than 0.001 weight % Sr, and as the remainder, Al, and wherein phosphorus is added to the alloy melt in a quantitative range of from 0.01 to 0.06 weight %, referred to the total mass of the alloy.