The Study of a Phosphate Conversion Coating on Magnesium Alloy AZ91D: II. Effects of Components and their Content in Phosphating Bath

摘要

This paper involved a phosphate conversion coating on magnesium alloy AZ91D. The effects ofcomponents and their content in phosphating bath on the phosphate conversion coatings were studied.The optimum content for each component in phosphating bath was zinc oxide (ZnO) 2.0 g/L,phosphoric acid (H3PO4) 12.0 g/L, sodium fluoride (NaF) 1.0 g/L, sodium tartrate (C4H4O6Na2) 4.0g/L, sodium nitrate (NaNO3) 6.0 g/L and sodium pyrophosphate (Na4P2O7) 0.5 g/L. The presence ofNa4P2O7 in phosphating bath refined the microstructure of the crystal layer and made the phosphateconversion coatings more fine and smooth. The phosphate conversion coating formed at the optimumcondition was composed of Zn3(PO4)2, Zn2Mg(PO4)2 and Zn.