Study On Micro - Arc Oxidation - Electrophoresis Composite Films Of Cast Rare Earth Magnesium Alloy

Although there has rich reserves in magnesium alloys and its excellent structuralproperties, it has many difficulties to be widely used because of its poor corrosion resistance.As a means to strengthen the material properties, the micro-arc oxidation process has played akey role in more and more occasions. Thus, micro-arc oxidation on magnesium alloyprocessing technology to improve its overall performance has very important significance.(1) By studying the influence of Gd content in the cast high rare earth magnesium alloyson microstructure and corrosion properties, This article explains the relationship betweenmicrostructure and corrosion resistance;Choosing the optimal containing of Gd and analyzingthe corrosion mechanism of magnesium alloy, we get the following conclusions:With Gd content increasing to9%, the second phase distribute on the alloy grainboundaries and the diffusion phase uniformly distributed in-Mg is also increasing. in thiscase, the grain size is minimized, and the rate of corrosion-resistant measured in neutral saltspray test is minimum which is0.396mg·cm-2·h-1,while corrosion potential is to maximumand corrosion current density to minimum.(2) This paper complex a large of domestic as well as international documents and makehigh-magnesium alloy micro-arc oxide in silicate system electrolyte. After extensive tests, weadjust the voltage parameters to three stages. By orthogonal experiments, we optimize theprocess parameters in silicate electrolyte system: voltage of each stage are550V、500V、450V；Duty cycle is20%; Plus number is15and the oxidation time is50min. Under theoptimal process parameters, the electrolyte formulation are optimized by orthogonal test:sodium silicate20g/L, sodium tetraborate40g/L, NaOH20g/L, triethanolamine15ml/L,nickel acetate0.12g/L, a complexing agent (sodium citrate)15g/L; Had the film analyzed onXRDand EDS,we get following: the film is mainly composed of the spinel phase Mg2SiO4，cubic structure of MgO, of MgSiO3, of MgCO3and of Ni2O3which also contains a smallamount of Na, Gd and other elements.(3) This article also describes a micro-arc oxidation process electrophoresis plugged. By discussing a series of experimental parameters(voltage, electrophoresis time and curingtemperature), and the neutral salt spray corrosion, acid corrosion thickness and appearancewhich are indicator to evaluate, we focus on the voltage parameters to discuss variousproperties and have a optimal parameter as follows: under the DC power supply, the voltageof150V, electrophoresis normal temperature, curing conditions of at175~185℃30min andthe curing time is30h.The final process for magnesium alloy micro-arc oxidation is that voltage of each phaseparameter is550V,500V,450V; duty cycle is20%; the pulse number is15; the oxidationtime is50min; sodium silicate is20g/L and sodium tetraborate is40g/L.