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6672473 
Journal Article 
Pretreatment for chemical conversion of ADC12 aluminum alloy in cobalt salt-based solution 
Li, Hf; Ren Yi, j 
2018 
37 
7 
312-316 
INSPEC:18559707 
The pretreatment processes including alkaline etching and pickling were optimized through orthogonal tests to improve the performance of cobalt-based chemical conversion coating on a high-silicon die-cast aluminum alloy ADC 12. The optimal process conditions are NaOH 50g/L, EDTA 1.5 g/L, temperature 30 degC, and time 180 s for alkaline etching, and nitric acid 400 mL/L, hydrofluoric acid 150 mL/L, temperature 40 degC, and time 20 s for pickling. The conversion coating obtained thereunder is continuous, complete, mainly composed of Al2O3 phase, and able to endure the potassium dichromate dropping corrosion for 348 s.