Described here is a method for pretreating the surfaces of weld parts of aluminum or alloys thereof, and weld parts produced with said method. Prior to welding, the weld parts are subjected to a treatment (17) in an acidic, aqueous solution, wherein the acidic, aqueous solution contains ions of the elements boron and/or silicon and/or titanium and/or zirconium and/or hafnium. The invention consists in that a polishing step (9) is carried out prior to the treatment in the acidic, aqueous solution to make for better sliding in a feed apparatus during the welding process.