Effects of pretreatments of magnesium alloys on direct electroless nickel plating

Abstract

The effects of two different pretreatments on direct electroless nickel plating of magnesium alloys have been studied in order to obtain an environmentally friendly process of pretreatment. The surface morphology, chemical composition and corrosion resistance were characterised using SEM, energy dispersive X-ray and polarisation curves. An environmentally friendly pretreatment has been finally established by the procedure of pickling with nitric acid plus phosphoric acid, twice activating with K₄P₂O₇ and NH₄HF₂. It is found that a coarse surface was produced on the Mg substrate via the researched pretreatment. The adherence between the coating and the substrate was improved. A compact Ni–P alloy coating with better adhesion and corrosion resistance was fabricated. The phosphorus content in the coating was ∼11·24%.

Keywords:

• Magnesium
• Plating
• Pickling
• Activations
• K₄P₂O₇
• NH₄HF₂

This study is jointly funded by the National Natural Science Foundation (grant no. 21176061), by the Development Program of Key Disciplines and Key Natural Science Foundation (12JJ2006) in Hunan Province.