Research On Cerium Conversion Coating Process And Properties Of Mg₂Ni Alloy

Because Mg₂Ni hydrogen storage alloy has a higher hydrogen storage capacity,alower production cost,a richer resources and so on,it has become one of the mostpromising hydrogen storage materials now.However,its lower corrosion resistance andcycle stability will hinder the practical application of this alloy.In this article,the processof cerium conversion coating on the cast-state Mg₂Ni alloy is stydied by using theorthogonal layout. The surface morphology and composition of the cerium conversioncoating is analysised by using the ways of SEM and EDS. And the performance ofcerium conversion coating is also tested by using the analytical methods, such as, Tafelpolarization curve, EIS and so on. While the concentration of Ce（NO₃）₃is0.05mol· L^-1,the pH is4, the treatment time is10min and the addition of film-acceleration agent is2ml· L^-1, the best coating will be formed at room temperature（25±5℃）. And on thesebasis, the single factor affecting of the concentration of Ce（NO₃）₃, pH and the additionof film-acceleration on cerium conversion coating of cast-state Mg₂Ni alloy is alsostudied. At the same time，the impact of corrosion resistance about the ball millingtechnology and the replacement of La element on the cast-state Mg₂Ni alloy ispreliminary researched, too. And under the best filming condition of the cast-stateMg₂Ni alloy，the cerium conversion treatment about these two different kinds of alloysis carried out. The results show that a layer of light yellow conversion coating can beformed while the cast-state Mg₂Ni alloy, the ball milling state Mg₂Ni alloy and the cast-state La0.1Mg1.9Ni alloy are put in the acidic solution respectively. The acidic solutionmainly contains Ce（NO₃）₃. The coating elements mainly are O and Ce. After treated bythe coat-forming solutiao, both the corrosion potential and the surface charge transferresistance of the matrix alloy are improved.So the corrosion resistance and the cyclestability can be improved，too.The corrosion resistance and the cycle stability can beimproved along with increasing of the concentration of Ce（NO₃）₃, the addition of HNO3and the addition of accelerant H₂O₂.However, the thicker layer on the surface of thematrix alloy will affect the conductivity of alloys. And the addition of HNO3and the addition of accelerant H₂O₂will promote the filming formation. The film surface willbecome more dense and uniform. Meanwhile, the fewer cracks will appear on the alloysurface.But after ball milling treatment，the Mg₂Ni alloy will appear a significantphenomenon of reunion.And the amaller the particle size is, the bigger the alloy specificsurface area will be. The corrosion resistance and the cycle stability will go down.However, the alloy discharge capacity will be increased. And the corrosion resistanceand the cycle stability can be improved by the replacement of La element on the cast-state Mg₂Ni alloy itself. After dealing with the film-forming solution, the corrosionresistance and the cycle stability will be further improved.