Studies Of Nickel Plating On Mg-RE Alloy

Firstly,the work studied the effects of acid pickling activation time,NH₄HF₂,RE on corrosion resistance of acid pickling activation layer in H₃BO₃+H₃PO₄+NH₄HF₂ acid pickling activation process.Secondly,the work studied the effects of acid pickling activation time,RE,Gd（NO₃）₃ and Nd（NO₃）₃ on corrosion resistance of acid pickling activation layer in H₃BO₃+H₃PO₄ acid pickling activation process.The acid pickling activation layer obtained by treating 40s with solution（H₃BO₃ 30g/L、H₃PO₄ 60m L/L、Gd（NO₃）₃ 10mmol/L）has better corrosion resistance.Thirdly,the work studied the effect of pretreatments on the potentiodynamic polarization curve of electroless nickel coating.The results show that the pretreatment process without acid pickling activation process can be used to directly electroless nickel plating.The E_CORR of electroless nickel coating is-0.700V.The pretreatment process without acid pickling and activation not only simplifies the process,but also avoids the use of NH₄HF₂,which is more efficient and environmentally.Fourthly,the work studied the effect of pH,Temperature and electroless plating time on the mass and thickness of electroless nickel coating,as the pretreatment without acid pickling activation.The electroless nickel coating are 0.4196 g and 38.7（?）m under the optimum conditions of pH7,T=80℃,t=240 min.Fifthly,the work studied the effects of electroless plating time,pH and J on the mass of coating.The optimum conditions were that electroless plating time was40 min,pH=5.5,J=3.12 A/dm²,and the mass of electroplating nickel coating was 0.0999g.The results of potentiodynamic polarization curves show that the electroless nickel coating prepared at pH 7.5 and T=80℃has the best corrosion resistance(E_CORR=-0.101 V).The electroplating nickel coating prepared by electroless plating for 40 min and J=2.34 A/dm²has better corrosion resistance(E_CORR=-0.150V).EDX shows that the electroless nickel coating is Ni-P layer（P=21.63wt%）,the thickness is about 30（?）m.The electroplated nickel coating is Ni.SEM shows that Gd（NO₃）₃ can significantly improve the surface morphology of acid pickling activation layer.Electroless nickel coating has obvious nodules.Ni-P have cellular nickel-phosphorus morphology.The pretreatment has little effect on the surface of electroplating nickel coating.XRD shows that the alkali layer,acid pickling activation layer and electroless nickel coating are amorphous,while the nickel coating is crystalline.The innovation is that the electroless nickel plating could process on magnesium alloys without acid pickling activation.