Research On Process And Properties Of Magnesium Alloy Anodic Oxidation

In this paper,anodizing technology was used to surface treatment of Mg₉₇Y₂Zn₁-0.5Al alloys under different technological conditions.The effects of current density,oxidation time and electrolyte composition on the anodic oxidation process and the morphology and properties of the oxide film were respectively studied.The appearance of the oxide membrane was observed by scanning electron microscope and optical microscope,X-ray diffractometer analyzed the composition of oxide film,and the properties of the membrane layer were tested by dynamic potential polarization,rockwell hardometer and so on.To determine the optimum anodization current density,optimum anodization time.By using single factor method,anodic oxidation was made under different current density?5,10,15,20mA/cm²?and different reaction time?10,20,30,40min?.The effects of current density and time on the oxide film were studied.The results show that with the increase of current density,the holes in the film gradually decrease and the pore size increases slowly,the corrosion resistance of oxide film first increases and then decreases.Current density is15mA/cm²,there are few pores on the oxide film,the pore size is smaller,the film is thicker,the corrosion loss is the smallest,corrosion resistance is the best.After gradually increasing the reaction time,the aperture size on the membrane first decreases and then increases,the corrosion resistance increases first and then decreases.When the oxidation time is 20min,the oxide film is thicker and has smaller pore size and higher corrosion resistance.To optimize the electrolyte concentration,orthogonal experiment,range analysis and other methods are used to optimize it.Finally,the best electrolyte composition is sodium hydroxide 40g/L,sodium silicate 85g/L,sodium carbonate 40g/L and sodium citrate 50g/L.Under the formula,the film is thicker,smaller pores,higher film forming voltage and higher corrosion resistance.According to XRD analysis,the optimized oxide film is mainly composed of MgO,MgSiO₃ and Mg₂SiO₄.To improve the smoothness of the oxide film,urea,ethylenediamine tetraacetic acid and so on are respectively added to the best electrolyte.The effects of additives on the oxide film were explored.The study show that when the amount of additive is 5g/L,the film smoothness is improved,the corrosion resistance is improved,and hardness is slightly lower.In three kinds of additives?urea,ethylenediamine tetraacetic acid,three hydroxymethyl methylamino methane?,the three hydroxymethyl methylamino methane is the best additive to improve the corrosion resistance of film.To reduce the adverse influence of small holes,improve the appearance of the film,respectively,the sealing of the film hole sealing?including hot water sealing,sodium silicate seal,silica sol seal?,influence of sealing hole on the microscopic appearance and performance of oxide membrane was studied.Results shows that,through hot water sealing the gully on the film layer becomes less and holes are few.Silicate sealing,the gully on the film is not changed,and the holes are reduced.After the silica sol sealing,the gully on the film disappeared,microporous rarely.After three ways hole sealing,the corrosion resistance of the film is enhanced,the hardness value decreases slightly except for boiling water sealing.Among them,the silica gel sealing hole on the corrosion resistance of the film to improve the best.