Poor corrosion resistance limits the application of magnesium alloys.Conversion coating is widely used to protect magnesium alloys because of easy operation and low cost.A novel conversion coating on die-cast AZ91D magnesium alloy containing barium salts was studied.The optimum concentrations of Ba(NO_3)_2,Mn(NO_3)_2 and NH_4H_2PO_4 are 25 g/L,15 mL/L and 20 g/L,respectively,based on orthogonal test results.The treating time,solution temperature and pH value are settled to be 5-30 min, 50-70℃and 2.35-3.0,respectively.The corrosion resistance of barium conversion coating is better than that of manganese-based phosphate conversion coating by immersion test.The coating is composed of Ba,P,O,Mg,Zn,Mn and Al by EDX analysis.
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