Preparation Technology And Performance Study On Ti-6A1-4V Alloy Surface Using Micro-arc Oxidation

As a novel technology of surface modification, Microarc Oxidation(MAO) has great potential and abroad application prospect. It has important application background and value in aerospace and aviation fields.In order to obtain a good oxidation coating on surface of Ti-6A1-4V alloy,NaOH,Na2SiO3 and Na2HPO4 coatings were Prepared in the corresponding electrolyte system by micro-arc oxidation (MAO) method,and the optimal MAO parameters were obtained by using direct current constant voltage electrical source. Microstructure of the coatings was characterized using XRD, SEM and EDS techniques. The formation mechanism of MAO coating was investigated. The thickness, rigidity and anti-causticity of coatings were tested. The influence of electrolyte concentration and temperature was discussed to the variational disciplinarian of sparking voltage. As the result of research as follows:When Na2HPO4 and Na2SiO3 solution were choosed as electrolytic solution, the magnitude of sparking voltage minish linearly with the hoist of electrolytic solution and initial temperature. when the concentration was very small, the adust phenomenon took place easily on the edge of nodic titanium alloy board; by contraries, sparking was found difficultly.When Na2HPO4 and Na2SiO3 solution were choosed as electrolytic solution, micro-arc oxidation coatings had the porous structure in different disposal time,electrolytic solution concentration and voltage. The rigidity,thickness,surface roughness and size of tiny hole augment of coating increased gradually, growth velocity and corrosion resistance increased primitively and then minish, but density of tiny hole decreased gradually. The results show that anatase and rutile titania on the titanium surface mostly. Anatase titania droped off and rutile titania increased gradually, which will play a leading role.The quality of oxidation film became more velveter with increase of NaF concentration. Thickness of film and rigidity increased gradually with increase of NaF concentration. Although pore size increased and the number of microporous decreased gradually, corrosion resistance increased gradually, the performance of oxidation film mentioned above two kinds of electrolyte was not the same, so the corrosion resistance of oxidation film was more better to a certain degree in NaOH solution Containing additive NaF.Through the test, the optimized working conditions are determined: electrolyte concentration is 3g/L NaOH +0.4mol/LNaF, micro-arc voltage is 280V, oxidation time is 10min in NaOH solution Containing additive NaF; electrolyte concentration is 0.3mol?L, micro-arc voltage is 180V, oxidation time is 300s, initial temperature of electrolyte is 10℃in Na₂HPO₄ solution; electrolyte concentration is 50g?L, micro-arc voltage is 280V, oxidation time is 50-150s, initial temperature of electrolyte is 20℃in Na₂SiO₃ solution; Like this, oxidation film of homogeneous pore size and good compactness can be obtained.In a word, to prepare perfect micro-arc oxidation film, interreaction of various factors must been taken into account.