Barium phosphate conversion coating on die-cast AZ91D magnesium alloy

摘要

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.