Abstract:

Electroless NiWP coating with high content of W has been developed on chromiumfree pretreated AZ91D magnesium alloy by using an alkalinecitratebased baths, in which nickel sulphate and sodium tungstate were used as metal ion sources, and sodium hypophosphite was used as a reducing agent. One important modification of the NiWP electroless bath is the addition of sodium carbonate, which works as complexing agent, accelerator and buffer. Codeposition of tungsten resulted in ternary NiWP coating with phosphorus content of 4.84 wt.% and tungsten content of 4.5 wt.%, respectively. Both the electrochemical analysis and the porosity test revealed that the ternary NiWP coating exhibited good corrosion resistance in protecting magnesium alloy.

Key words: materials failure and protection, magnesium alloy, electroless deposition, nickelbased alloy, corrosion resistance