Direct nickel electrodeposition on magnesium alloy in pyrophosphate electrolyte

Direct nickel electrodeposition on a Mg alloy, AZ31B, was conducted in an electrolyte containing potassium pyrophosphate, nickel sulfate, potassium fluoride and ammonium hydroxide. The effect of potassium fluoride on the Mg alloy in a pyrophosphate nickel electrolyte was investigated using polarization and EIS methods. The chemical state of the Mg alloy was also analyzed by XPS. The effect of added ammonium hydroxide on electroplated nickel layer was observed by FE–SEM. A magnesium fluoride film, which was formed by added potassium fluoride, inhibits the dissolution of the Mg alloy in the electrolyte. The current efficiency was increased and surface cracks on the nickel layer were also eliminated by adding ammonium hydroxide to the electrolyte. The direct nickel electrodeposited Mg alloy showed significantly improved corrosion resistance compared to the uncoated Mg alloy. A successful and protective electrodeposited nickel layer was formed on the Mg alloy in pyrophosphate nickel electrolyte due to the addition of potassium fluoride and ammonium hydroxide.

Research highlights
► Direct nickel electrodeposition on a Mg alloy in pyrophosphate nickel electrolyte.
► Inhibition of the dissolution of the Mg alloy by added KF.
► Increased current efficiency and eliminated surface cracks were obtained by NH3·H2O.
► Nickel electrodeposited Mg alloy showed significantly improved corrosion resistance.