| Magnesium alloy has higher specific strength than aluminium alloy and steel.It has good shock absorption performance, can bear the weight of biggish concussion quiver burthen. It has excellent performance for cutting process and polishing, and easy to be founded. It can resists aging and has perfect electric conduction and heat conduction performance.It has wider application in the electron equipment, voiture and war industry things. Magnesium will be corrupted by oxidation because of its low electrode potential.The special character has restricted the application of magnesium alloy.Make some proper disposal on magnesium alloy surface to enhance its corrosion resisting capability. It is a hotspot in magnesium alloy corrosion resisting study. The Ce conversion coating has been gotten on AZ91 magnesium alloy surface by chemical translation. The translation technics has been ascertained and optimized in the paper. The influence of test factor on conversion coating surface morphology and performance has been stuied.The corrosion resisting of conversion coating has been mensurated by point- corrosion method and 3.5%NaCl liquor. The electrode potential- time curve has been determined by electrochemistry method. The chemical mechanism of forming conversion coating has been discussed. The surface morphology and major element have been studied by SEM and EDS.Magnesium alloy sample has been pretreated with two different methods. The best disposal technics is hydrochloric acid concentration 0.15mol/L, disposal time 30s, and hydrofluoric acid concentration 350mL/L, activation time 2min. Both test process at room temperature.The influence on conversion coating morphology surface and performance has been studied. Surface of the sample pretreated with hydrochloric acid is looser than the surface without pretreatment, and the crystal phase is clear. The sample lightens after pretreated,and the surface colour from silvery white change to silver gray. The sample is activated by hydrofluoric acid after hydrochloric acid pretreatment. It is analyzed by EDS. The result shows that the fluorin element consists in crystal phase and intergranular. The film composed by fluorin element on the sample surface enhances the corrosion resisting of the sample.The samples have been treated with translation solution. The conversion coating was observed by SEM. The conversion coating of hydrochloric acid pretreatment sample has wider and deeper crackle than hydrofluoric acid pretreatment sample.The translation technics has been ascertained and optimized by proper orthogonal test method. The result is that strong oxidant H2O2 has great influence to the surface morphology and performance of conversion coating. The appropriate quantity accede to the solution can enhance conversion coating corrosion resisting commendably. The increase weight of the film increases with test temperature. The corrosion resisting reduces with the test temperature when the temperature exceeds the optimal temperature. The reason is that the high temperature causes translation rate elevatory. The higher test temperature leads conversion coating loose. The translation solution consistence has conformed influence as test temperature on conversion coating. Test time has influence on the conversion coating. Too lack test time only get half-baked film. But the corrosion resisting performance will descend if test time too long. The reason is that the translation solution destroys the conversion coating.The best technics is Ce(NO3)3 0.02 mol/L, H2O2 2.0mL/L, test temperature 35℃, time 30min.The Ce conversion coating has been treated by Na2MoO4 and Na3PO4 to improve its corrosion resisting performance. The influence on conversion coating surface morphology and performance has been studied. The reaction mechanism of Na2MoO4 treatment has been discussed. And the Na2MoO4 treatment technics is Na2MoO4 15g/L, temperature 50℃, time 30 min.The conversion coating colour will be shoaled after being treated by Na2MoO4 solution. The crackle becomes narrow. The conversion coating is covered with molybdenum. The corrosion resisting performance has been measured by dip it in the 3.5%NaCl solution. |
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