| The use of aluminum alloy parts with low density and high specific strength is one of the main ways to reduce the weight of agricultural equipment.However,aluminum alloy has low hardness,poor wear resistance,and easy corrosion.In a complicated agricultural production environment,it is easy to cause corrosion failure or wear failure of parts due to surface damage.Therefore,constructing a reasonable surface coating has become a key link for aluminum alloys to be used in the lightweighting of agricultural equipment.Micro-arc oxidation(MAO)is a new technology for surface modification of valve type metals such as aluminum,magnesium,and titanium.Using this technology,a layer of ceramic phase oxide protective film can be grown in situ on the metal surface.The film has high hardness,high wear resistance and high corrosion resistance.At the same time,thanks to the film formation mechanism of the MAO process,there are a large number of uniformly distributed micropores(discharge channels)in the film layer.These micropores can be used as microcontainers supporting repair agents and corrosion inhibitors for the modification of the film layer,and providing a good structural foundation.Therefore,this paper intends to use 6061 aluminum alloy as the research object,using the MAO process to prepare the basic film,using the micropores in the film layer as the container,supporting the layered double hydroxides(LDHs)and8-hydroxyquinoline(8-HQ)corrosion inhibitor,construct a MAO-LDHs/HQ-composite film with high hardness,high wear resistance,strong corrosion resistance,hydrophobicity and certain self-healing function.To achieve this research goal,the main research content and conclusions are as follows:(1)The optimized combination of electrical parameters of micro-arc oxidation.Through the orthogonal test,the optimal combination of power supply parameters under this experimental condition was obtained,namely:The power parameter was set to current density 6A/dm2,oxidation time 45min,and duty cycle 30%.The thickness of the dense layer of the MAO film obtained under this condition is about about 15?m.The polarization resistance RP of the MAO film reaches 4.8×105?·cm2,which is 2 orders of magnitude higher than that of the aluminum substrate.(2)Preparation and performance study of MAO-LDHs composite membrane.In this part of the study,MAO-LDHs composite membrane was first prepared by hydrothermal method.Then,using SEM,EDS,XRD and FT-IR methods to characterize the film,the results show that after 24 hours of crystallization and deposition,LDHs crystals grow in situ on the surface of the MAO film to form a composite film.The obtained LDHs crystals are large Part of the sheet-like structure is not only widely distributed on the surface of the MAO film layer,but also distributed in large numbers inside the micropores and cracks.The performance test of the obtained composite membrane was further conducted and compared with the MAO membrane.The results are as follows:Wettability tests showed that the contact angle of the composite membrane increased from 44.7°to 57.1°,indicating an increase in hydrophobicity.Electrochemical tests showed that the self-corrosion potential of the composite film Ecorrincreased to-0.19 V,and the corrosion current density icorr decreased to 2.4×10-6 A/cm2,indicating that the corrosion resistance of the composite film was improved.Friction and wear tests showed that under 3N load,the composite film and the real-time friction coefficient are lower and more stable.Hardness tests results showed that as the crystallization time increases,the hardness of the composite film shows a downward trend.(3)Analysis of morphology and film formation mechanism of MAO-LDHs composite film under different process parameters.Comparing the micromorphology and performance of the composite membranes obtained under different crystallization times and ion concentrations,it was found that LDHs crystals will agglomerate more and more as the cation concentration in the reaction system rises.It was found that LDHs crystals will reunite with the increase of cation concentration in the reaction system.A small amount of crystal reunion can improve the corrosion resistance and density of the sample,but a large number of crystal reunion reduce the corrosion resistance and density,that is,the growth of LDHs It is a"Dissolve-Redeposit"process.Based on the morphology and performance of the composite film under different process parameters,the optimal process parameters of the composite film prepared under this experimental system:The crystallization time is 36h,and the molar concentrations of Mg(NO3)2 and Al(NO3)3 are 0.05mol/L and 0.0167mol/L,respectively.Under this parameter,the effective porosity Pv and corrosion current density icorr of the composite membrane are the lowest,and the corrosion resistance and compactness of the membrane layer are the best.(4)MAO-LDHs/NO3-composite membrane loaded with 8-HQ modification test.The 8-HQ modification test of the composite membrane was carried out by the water bath method,and the temperature was set to 35?.The analysis was carried out by means of EDS,XRD and FT-IR.After the 8-HQ corrosion inhibitor was loaded,the intercalated NO3-ions of the MAO-LDHs/NO3-composite membrane after being successfully replaced by HQ-group,the hydrophobicity of the film layer was significantly improved,and its contact angle increased from 71.7°to 95.4°,reaching the standard of hydrophobic surface(CA>90°).After the modified composite membrane was scratched with a scratcher,it was immersed in 3.5wt%Na Cl solution for self-repair study.The results showed that after 48 hours of immersion,a large amount of C and N elements from the HQ-group appeared in the scratches of the MAO-LDHs/HQ-composite membrane,accompanied by petal-like particles.After analysis,the petal-like particles are chelated products of HQ-group and Al3+ions,namely Al(HQ)3.It is proved that the MAO-LDHs/HQ-composite film can suppress the active site at the scratch through three steps of"Corrosion induction-Release corrosion inhibitor-Inhibit corrosion",and has a certain physical self-healing function.In summary,the basic film was prepared by the micro-arc oxidation process,using the micropores in the film layer as the container to load LDHs,and further modified by8-HQ.The MAO-LDHs/HQ-composite film was successfully constructed on the 6061Al substrate.The film layer not only has the characteristics of high hardness,high wear resistance and strong corrosion resistance,but also has hydrophobic properties and certain self-repairing functions. |
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