Abstract: A method for treating or pre-treating parts, profiles, strips, or wires comprising surfaces of aluminum, or other metal surfaces with an acidic, aqueous solution containing fluoride and phosphate.

Abstract: The invention relates to a method for treating or pre-treating parts, profiles, strips, or wires comprising surfaces of aluminium, or alloys containing aluminium optionally in the presence of surfaces consisting of other metals or alloys with an acidic, aqueous solution containing fluoride and phosphate. Said method is characterised in that the fluoride is present at least partially as a free fluoride in the solution and that in the bath of phosphating solution, the content of free fluoride is maintained within a concentration range of between 5 and 500 mg/l Ffree and that of aluminium is maintained within a concentration range that is less than or equal to 100 mg/l Al ions (including complexed Al). To achieve this, increases in the aluminium content are reduced to contents of less than or equal to 100 mg/l Al ions in the bath, using a precipitation container outside the phosphating bath by circulating the phosphating solution from the phosphating bath to the precipitation container and vice versa.