| As a matrix material that may replace steel,aluminum alloy and plastic,magnesium alloy has been widely used in industrial production,aerospace,shipbuilding,military and other fields due to its remarkable characteristics,good thermal and electrical conductivity,vibration and shock absorption,castability,weldability,biodegradability and biocompatibility.But because the chemical property of magnesium alloys is more lively and is likely to cause various corrosion in a specific environment,influence its best performance,so the further research on the corrosion resistance of magnesium alloys become one of the metal protection areas to solve the problem,this paper adopts the new type of environmental protection free from contamination of rare earth salt-praseodymium salt and organic molecules phytic acid preparation of composite membrane layer,To explore the best process parameters affecting corrosion resistance.In this paper,two-step film formation method was used.The first step was chemical transformation method.Through single factor experiment and orthogonal experiment,the optimal film formation concentration,transformation time and phytic acid transformation time of praseodymium salt transformation film,temperature,p H and concentration were screened.The second step is to compound praseodymium salt onto phytic acid conversion film and screen out the best post-treatment process of praseodymium salt through single factor test.Through electrochemical performance test,hydrogen evolution and drop test,Mott-Schottky curve to discuss the corrosion resistance of the film layer,through XRD(X-ray diffraction),XPS(X-ray photoelectron spectroscopy),EDS(X-ray energydispersive spectroscopy),FTIR(Fourier transform infrared spectroscopy)and SEM(scanning electron microscopy)to analyze the composition and apparent morphology of the film layer.The quantum properties and adsorption energies of organic phytic acid molecules were analyzed by Gaussian 09 and Material Studiosoftware.The main conclusions are as follows:(1)praseodymium salt transformation film can significantly improve the corrosion resistance of magnesium alloy matrix,and the surface film layer is dense and white sheet.When praseodymium salt concentration is 1.8g/L and film formation time is 30 min,the corrosion resistance of the transformation film is the best,and the corrosion current density decreases by 3-4 orders of magnitude.Under the process parameters of 1.8g/L and 30 min,the hydrogen evolution amount is the smallest and the drip time is the longest,indicating that the corrosion resistance is the best under the parameters.(2)Through orthogonal test and single factor test,the optimal parameter combination of phytic acid transformation membrane was selected as: temperature 40°,p H 4.5,5 g /L and 20 min.After the analysis of drop time and polarization curve,the corrosion resistance is improved by orders of magnitude compared with the matrix.After electrochemical performance test,the best post-treatment parameters of praseodymium salt are p H 4,temperature is 50 °C,and its corrosion resistance is the best.After SEM observation,it was found that thephytic acid conversion film was thin,and the surface was uneven and smooth,with black speckled particles,which affected its densification to a certain extent.The post-treatment of praseodymium salt mainly played the role of sealing holes and strengthening the film layer,and the electrochemical performance verification showed that the corrosion resistance was significantly improved.The results of XRD and XPS showed that the main components of phytic acid-praseodymium salt composite transformation film were praseodymium oxide,some praseodymium hydroxide and some complex formed by phytic acid and magnesium.(3)Mott-Schottky curves are one of the most important methods for analyzing oxide semiconductors.By measuring the N/P state of oxide semiconductors,we can determine the physical properties and corrosion resistance of oxides by obtaining the host concentration and the flat band potential of the conversion film.Gaussian 09 is a quantum analysis of the electron orbital changes in organic phytate conversion films.Material Studio analyzes the changes of adsorption properties of organic phytic acid molecules on the surface of magnesium alloy from the perspective of computational simulation,and the analysis results illustrate that the phytic acid molecules have higher EHOMO orbital energy,which can provide electrons to metal atomic empty orbitals to a greater extent;have lower ELUMO orbital energy,which can accept electrons provided by metal atomic orbitals to a greater extent,combined with the phytic acid in the Mg(0001)surface by molecular dynamics simulation to obtain the results of adsorption energy of phytate on Mg surface,together they indicate that phytate has strong adsorption reactivity and high corrosion inhibition efficiency on the surface of Mg metal substrate. |
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