| In recent years,with the development of technology and the enhancement of environment protection consciousness, the nonpolluting and nontoxic chemical conversion coating of magnesium alloy has become the hotspot of researchers' study. But the existing research of chemical conversion coating is mainly occur in an aqueous environment, it's inevitable to react so violently between magnesium alloys and water in acidic water solution system that the consistency of conversion coating is influenced seriously by a large number of hydrogen precipitation, which reduces the protection of conversion coatings. Therefore, the research of anhydrous conversion coating makes more sense.This article is based on the phytic acid which richs in organic functional groups (such as hydroxyl) and the Nd salt which tends to dissolve in organic solvents as main ingredients to explore the new anhydrous chemical conversion coating in the carrier of anhydrous ethanol.The surface morphology, section morphology, organizational structure, performance and the difference of aqueous and anhydrous with Nd salt conversion coating were studied by the SEM,EDS,XRD,XPS,FTIR and electrochemical workstation,ect. According to the results of this research,analyzed the formation mechanism of anhydrous phytic acid conversion coatings and anhydrous Nd salt conversion coatings. At the same time,simulated the stress field variation of conversion coating surface crack initiation under different influencing factors by computer.The results of conversion coating preparation are: The citric acid pretreatment process of anhydrous phytic acid conversion coating and the addition of tartaric acid of the conversion process by anhydrous Nd salt are all improve the quality of conversion coating film and corrosion resistance effectively; Determined the film forming technology of anhydrous phytic acid conversion coating: pretreatment of 45 s, concentration of 15 g/L, time of 240 min,temperature of 25 ?.The comparison results between aqueous and anhydrous with Nd salt conversion coating are: compared with aqueous Nd salt conversion coating, anhydrous Nd salt conversion coating is more compact, its adhesion to the magnesium alloy substrate is better, but its corrosion resistant performance is only slightly better than the latter.The exploration results of the conversion coating formation mechanism are: it is similar to the aqueous phytic acid conversion coating, the formation of anhydrous phytic acid conversion coating is cooperated with the dissolution of substrate and the deposition of the chelate product of Mg2+ and phytic acid; Anhydrous Nd salt conversion coating is mainly composed of Mg, Nd and A1 oxides and hydroxides and other inclusions of the solute.The results of computer simulation are: the water evaporation rate, chemical composition,the thickness of conversion coating and other factors are all have an effect on surface morphology and the change of internal stresses with the conversion coating during the cracking,and the simulation results reflect the the micro conclusion which cannot be given in the process of the experiment,it also provides a theory basis for cracking and controlling of flaws of conversion coating, Thun, the computer simulations development to the application and the optimization of conversion coatings has very important significance. |
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