| 5A90 aluminum-lithium alloy is an Al-Li-Mg series alloy with high specific strength,rigidity,corrosion resistance and welding performance.However,as a kind of anti-rust light alloy,the anodic characteristics of its intermediate phase still get it corroded in severe corrosive environment,which makes this kind of aluminum alloy workpieces fail.This paper uses the micro-arc oxidation process to modify the surface of the 5A90 aluminum-lithium alloy sheet,and prepares the micro-arc oxidation film under different oxidation time and electrical parameters(voltage,pulse frequency and duty cycle).Adding nano-TiO2 additives with different particle diameters to the electrolyte,its influence on the corrosion resistance of the micro-arc oxide film is explored.The experimental results are as follows:Under the conditions of a pulse voltage of 450 V,a frequency of 250 Hz,and a duty cycle of 40%,the film thickness is positively correlated with the oxidation time at 10 min?50 min,and the film thickness of oxidation for 50 min is the largest at 24.04 ?m.The number of microholes is the least.The self-corrosion current density is the smallest and the corrosion resistance is the best.The phase composition of the prepared micro-arc oxide film is ?-Al2O3 phase(corundum),?-Al2O3 phase,LiAl5O8 phase and MgSiO4 phase;under the conditions of pulse voltage of 450 V,duty ratio of 40%,and oxidation time of 30 min,the thickness of the oxide film at frequencies of 250,400,550,700,and 850 Hz is negatively correlated with the frequency.The film thickness at 250 Hz is the largest,reaching 20.24 ?m.The increase in frequency will reduce the corrosion resistance of the micro-arc oxide film firstly and then increase it.The film prepared at 850 Hz has the best corrosion resistance;under the conditions of a pulse voltage of 450 V,a frequency of 250 Hz,and an oxidation time of 30 min,the film thickness of the oxide film with duty ratios of 20%,25%,30%,35%,and 40%is positively correlated with the duty ratio,and the film thickness is the largest under 40%duty ratio,which can reach 22.40 ?m.The increase of the duty cycle will reduce the corrosion resistance of the micro-arc oxide film firstly and then increase,and the film has the best corrosion resistance performance at 40%duty cycle.Oxidation time,pulse frequency and duty cycle can not change the corrosion mechanism of alloy micro-arc oxide film in 3.5 wt%NaCl aqueous solution.The EIS of micro-arc oxide films has two time constants,which are composed of high and medium frequency capacitive reactance arc and low frequency capacitive reactance arc.Under the conditions of a forward voltage of 350 V,a reverse voltage of 150 V,a pulse frequency of 250 Hz,and a duty ratio of 40%,TiO2 particles with sizes of 25,40,60 and 100 nm were added to the electrolyte,and the reaction was performed for 15 minutes.The effects of different particle sizes of TiO2 additives on the performance of micro-arc oxidation film is compared.The particle size of the TiO2 additive is negatively related to the thickness of the oxide film.The thickness of the oxide film is the largest when TiO2 with a size of 25 nm,which can reach 29.97 ?m;the increase in the size of the nano-TiO2 particles will increase the corrosion resistance of the micro-arc oxide film.The arc oxidation film has the best corrosion resistance;the particle size of TiO2 does not have a great influence on the Ti content in the micro arc oxidation film;the EIS of the alloy micro-arc oxidation film prepared with all sizes of nano additives has three times constant,composed of high-frequency capacitive reactance arc and two low-frequency capacitive reactance arcs,the corrosion mechanism remains unchanged. |
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