PRETREATMENT OF ALUMINUM SURFACES WITH CHROME-FREE SOLUTIONS

摘要

The invention relates to a method for pretreating workpieces having an aluminum or aluminum alloy surface. With the purpose of forming and/or joining by welding or gluing said workpieces to workpieces similarly pretreated or optionally workpieces precoated in a different manner or optionally precoated parts made of steel and/or zinc coated and/or alloy coated steel and with the aim of performing a subsequent permanent corrosion-protective treatment, the workpieces undergo the following three-step treatment: a) rinsing with an aqueous acid solution containing a mineral acid; b) rinsing with water, c) contacting the workpieces with an aqueous, acid solution that is chrome and polymer-free and that contains Ti and Zr as complex fluorides in a weight ratio of Ti:Zr ranging from 2:1 to 1:2, in such a way that after subsequent drying a layer weight of 2 to 15 mg/m<2> (calculated as Ti/Zr metal) is obtained, wherein solutions having different concentrations and pH values are used depending on the application form.