| Low carbon steel is widely used in the fields of chemicals, metallurgy, electronicinformation and other fields as an important functional structure material. But becauseof its soft surface and high activity, low carbon steel can hardly meet certain specificrequirements, and therefore an demand to improve their surface properties is neededurgently. A soft magnetic Fe-Si alloy has drawn people’s wide attention, when the Sicontent reaches about6.5%, Optimal magnetic property was achieved with highestmagnetic induction intensity and lowest iron loss. It is difficult to produce6.5%Sisilicon steel with the traditional manufacturing processes due to its poor ductility andprocess ability. Silicon content of silicon steel produced by traditional techniques isgenerally between0.1%and4.0%, so the performance of silicon steel has beenlimited. Therefore, the purpose of this study was to improve the performance oflow-carbon steel by preparing Fe-Si layers on the surface of low-carbon steel. For this，a study has been carried out to prepare Fe-Si alloy layer and Fe-Si composite depositslayer on low carbon steel surface， and the result was further analyzed byelectrochemical research.In this study, two preparation methods have been adopted to prepare two separatetypes of alloy layers. First, after the review of existing solid-phase thermal diffusionmethods and their drawbacks, a new solid-phase thermal diffusion method is proposedin this study to prepare alloy layer on the surface of low-carbon steel. Fe-Si alloycoating was formed after the heat preservation of ultrafine oxide powder applied onthe surface of low carbon steel under hydrogen atmosphere. Secondly, given theunique chemical, physical and mechanical properties of composite deposits layers,composite electro deposition method was adopted to prepare Fe-Si composite depositslayer on low-carbon steel surfaces. Then electrical crystallization nucleation/growthprocess under both a single system and composite system were analyzed throughcyclic voltammetry (C-V), constant potential step technique (i-t) and electro chemicalimpedance spectroscopy (EIS). After the preparation of Fe-Si alloy layer sample，study has been invested in termsof surface morphology, roughness, corrosion resistance, hardness and wear resistanceunder different conditions of holding temperature and penetration composition ratio.The results show that the corrosion current density of the sample is less than the lowcarbon steel substrate. Retaining temperature has the similar impact on corrosioncurrent density and corrosion potential of the samples, corrosion current density of thesamples decreases as the temperature rises when the temperature stays between700℃and1000℃. When the holding temperature stays1000℃, and the mole fraction of Siin the powder was14.3%, the sample owns the lowest corrosion current density, thebest corrosion resistance and strongest ability to protect the substrate; while when themole fraction of Si in the powder under the same temperature arrives16.7%, themagnetic properties of the sample accomplish optimal performance.In the study of Fe-Si composite deposits layer prepared on the low carbon steelsurface，the article started from influence factors of composite electrodeposition，andthen studied the impact of different influence factors，such as particles concentrationin solution and cathode current density have on the content of powder particles. Also,the relevant performances of the Fe-Si composite deposits have been studied.Theresults show that Fe-Si composite deposited layer performs relatively poorly, itscorrosion resistance is slightly better than the substrate, but becomes better after heattreatment. The initial stages of the electrocrystallization of zinc and iron onto glassycarbon electrodes were investigated using cyclic voltammetry and potential stepmethod. The results of cyclic voltammetry show that: In the Fe-Si plating system thestarting deposition potential of iron is-1.00V, which is more positive than-1.05V，thestarting deposition potential of icon in the pure Fe plating system. This proves thatadding nano-silicon can promote electro crystallization nucleation and growth; at thesame time, the basic electrical crystallization process follow Scharifker-Hill model,nearly three-dimensional hemisphere forming the core mode. The measured initialelectric crystal nucleation process (I/Im)2-t/tm dimensionless curves approachingScharifker-Hill model instantaneous nucleation theory curve, the nucleation process is instantaneous nucleation; bath in the Fe-Si in accelerating the introduction ofnano-silica particles of iron electric crystallization process, but does not change themechanism of crystallization electric iron. Electro-crystallization of Fe in Fe solutionand Fe-Si solution follows Scharifker-Hill model, thenon-dimensional ((I/Im)2vs. t/tmplots for electrodeposition was close to the instantaneous nucleation theoretical curveof Scharifker-Hill model, and the process of electrodeposition can be regard asinstantaneous nucleation. The entering of nano silicon powder promoted theelectro-crystallization of Fe, but it doesn’t change the electro-crystallization behaviorof Fe.In Boric acid buffer solution (pH=8.4), Fe-Si alloy layer owns better passivationproperty than the low carbon steel. M-S curves shows all passivation films of preparedsamples demonstrated the characteristics of the n-type semiconductor, with the carrierdensity between1017and1019cm-3. After anode passivation for20min at0.3V with1000℃holding temperature, the majority carriers (holes) density of prepared Fe-Sialloy surface passivation film was significantly lower than the majority carrier(electron) density of low-carbon steel surface passivation film, yet the oppositesituation happened for film resistance. The diffusion coefficient of point defects (metalvacancy) in alloy surface passivation film can be calculated by PDM model. all theother metal vacancy diffusion coefficients of alloy surface passivation film arerelatively small and range from10-14to10-13cm2s-1, except one sample with aholding temperature of800℃and33.3%mole fraction of Si in powder. Through thequantitative analysis of both diffusion coefficient and the carrier density in the film, aconclusion can be drawn that the conductivity of Fe-Si alloy surface passivation film ismainly affected by the carrier density.A visual form operation of artificial neural network software was developed byVisual C#2005computer high-level programming language, the application ofartificial neural network software can establish mapping relation model between Fe-Sicoating technology parameters and its performance. The saturation flux density andcorrosion electricity density closed to actual experimental results, and the relativeerror between the predicted value and the experimental value was less than1.2%. A comprehensive evaluation model was established to evaluate two indicators whichwere saturation flux density and the cathode current efficiency. The model adjustedthe weight value of two indicators respectively and calculated the Fe-Si coatingcomprehensive performance value, in order to get the optimal craft parameters. Thismethod provides reference for practical production and other materials galvanizationcraft design. |
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