Study On The Environment-friendly Anodization Of Magnesium Alloy And Properties Of The Film

As the lightest metal structural material,magnesium alloys are applied to automotive,electronic and aeronautical industries increasingly because of a number of desirable features, including high specific strength,high specific rigidity,damping performance and recycled easily.However, their applications are limited severely for their low corrosionr esistance.For the moment,it is quite urgent and significant to find an environment-friendly anodizing process of magnesium alloy, and develop a encapsulation process to increase the corrosion resistance of the anodized coating in the industrial application of magnesium alloy.The anodizing electrolyte which is not contain Cr and environment-friendly of AZ31 magnesium alloys and prcess has been studied in this paper. In the experiment,orthogonal layout was applied and the dropping testing time,average erodent speed,the grade of salt spray test were selected as the appraisal parameters.According to the results of the orthogonal layout experiment,we found the best content of the components for the electrolyte. In rder to improve the electrolyte composition,we added new ingredients into the above-mentioned electrolyte,finally we found the optimum electrolyte and process.The voltage-time curve,coating thickness-time and micro-appearance examination were employed to study the coating-forming dynamics of the anodized coating on magnesium alloy.The results indicated that,the anodized film formed shorted after electrifying the anode.As the anodized time prolonging and the final voltage hoist,the thickness of the film increased,but not increased as linearity.Initally,the thickness of the film increased fast,as the time prolonged ,it increased slowly until it didn't increase. XRD,SEM,EDS were employed to study and analyse the ingredients,morphologied and structures of anodized coating.It indicated that, the anodized film formed on the substrate of AZ31 was even and compact, but there were some holes in it, the film was mainly composed of MgAl₂O₄(sspinel) and MgO(periclase,syn).The surface appearance and corrosion resistance of the anodic films at different technical parameters were studied,they have the similar surface appearance, anode.As the anodized time prolonging and the final voltage hoist,the thickness of the film increased and the film becomed coarse,the holes in the film becomed bigger,but the number of the holes becomed smaller,the corrosion resistance of the film improved.Compared the corrosion resistance of the films which were formed at different technical parameters,we found that the film which formed at the 80v final voltage and 20min anodized time had the best corrosion resistance. Exorbitant voltage and longer anodized time were not propitious to improve the corrosion resistance of the film.The corrosion resistance of anodized coating of magnesium alloy was evaluated through different methods such as dropping test,total immersion test,neutral salt spray test,polarization curves,and the same conclusion was acquired.It revealed that the corrosion resistance of magnesium alloy was to a corking extent improved through the new anodizing treatment.Compared with bth DOW17 and HAE,the the classical anodizing processes for magnesium and its alloy,the above-mentioned new process could imrove the corrosion protection of die-cast magnesium alloy AZ31 significantly.Cohesion test indicated that the anodic film produced by the new process was testified to have firm adhesion with substrate.The corrosion resistance of the film was further enhanced after encapsulation.