The study of electroless nickel plating directly on magnesium alloy

• An ideal magnesium alloy electroless nickel plating pretreatment process was gained.
• The ideal pickling formula is H3PO4 25 ml/L, HNO3 25ml/L.
• The ideal activation formula is NH4H2PO4 80 g/L–100 g/L, NH4F 30 g/L–50 g/L.
• Disposed by the process, electroless nickel plating directly can be realized.
• After disposed, corrosion resistance of nickel plating layer was improved greatly.

Magnesium alloy was disposed by three kinds of acid pickling formula and activation formula and the effect of the three kinds of acid activation formula on magnesium alloy was studied by contrast experiment. The experimental results indicated that after disposed by acid pickling formula of HNO3 25 ml/L, H3PO4 25 ml/L, room temperature and activation formula of NH4H2PO4 80–100 g/L, NH4F 30–50 g/L, room temperature, magnesium alloy could realize electroless nickel plating directly. The properties of the nickel plating layer and activation layer were researched by electrochemical polarization curves, X-ray diffraction and scanning electronic microscope and its energy spectrometer. The results showed that the structure of Ni–P coating was amorphous, the Ni–P coating was very meticulous and uniform, the activation coating was mainly MgF2 and Mg2P2O7, and comparing with magnesium substrate, the corrosion potential of magnesium alloys increased by about 1.1 V and the corrosion current density declined obviously. Tested by thermal shock test and file test, the adhesion of magnesium alloy and Ni–P coating was good.