Direct electroless Ni-P plating on AZ91D magnesium alloy
(1.山西省太原市太原理工大学表面工程研究所
2.Research Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan 030024; China
3.Shanxi Seikou Institute of Magnesium Technology, Taiyuan 030002, China)
2.Research Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan 030024; China
3.Shanxi Seikou Institute of Magnesium Technology, Taiyuan 030002, China)
Abstract: An electroless Ni-P plating treatment was applied on AZ91D magnesium alloy to improve its corrosion resistance. Optimum pretreatment conditions and optimum bath of electroless nickel plating for magnesium alloy were found through many experiments. In order to avoid bother of pre-plating medium layer, a set of procedure of direct electroless Ni-P under the acid condition was investigated. The properties of the coating with 10% phosphorus were investigated. The results show that a coating with high hardness, low porosity and good adhesive strength is obtained. X-ray diffraction patterns show that the structure of the coating is an amorphous phase. After annealing at 400 ℃, the amorphous phase of Ni-P is transformed to crystalline phases，and some intermetallics as Ni3P and Ni5P2 are deposited from Ni –P solid solution along with an enhancing hardness from Hv 450 to Hv 910.
Key words: magnesium alloy; direct electroless Ni-P plating; amorphous; adhesive strength