Process of Chrome-free Chemical Conversion Film on Aluminum Alloy

Take the weight of phosphate conversion coating and the rate of weight loss in 3.5% NaCl solution as evaluation indexes, orthogonal experiment was used to determine the optimal formula and technological parameters of phosphate conversion processing solution with Y2O3 as additive. The parameters are as follows: ZnO 8 g/L， H2PO3 20 mL/L， NaF 0.8 g/L， Y2O3 0.02 g/L， temperature = (40±2) ℃, time=8-10 min, pH = (3.0±2). The phosphate conversion films formed under the technological conditions has good corrosion resistance. The binding force between the conversion films which were differently processed on aluminum alloy samples after painting and the organic coating was studied by simulated atmospheric corrosion and full immersion test. The results show that under the same experimental conditions, the bonding force between the phosphate conversion film generated with Y2O3 as additive and the organic coating is superior to that of phosphate-chromate conversion film.