| Magnesium(Mg)and its alloys have broad application prospects in the field of structural materials and medical implant materials.However,the poor corrosion resistance of Mg alloys easily leads to the loss of mechanical properties and pre-failure during service,which cannot meet the needs of practical applications.In this paper,organic corrosion inhibitors were mixed with conversion treatment solution,and the conversion coating was modified by its adsorption or complexation with metal ions.The Mg(OH)2 coating with hexagonal nano-sheet structure was prepared using one-step hydrothermal method with LiOH solution as a mineralizer and modified by adding EDTA-2Na,in order to reduce the corrosion rate of AZ31 Mg alloy.The thickness of the EDTA-Mg(OH)2 coating is approximately twice that of the Mg(OH)2 coating.Nano-scratch test shows a strong adhesion between EDTA-Mg(OH)2 coating and its substrate.Electrochemical results exhibit that the corrosion current density(icorr)of EDTA-Mg(OH)2 coating is two orders of magnitude lower than that of AZ31 substrate,which indicates an obvious improvement in the corrosion resistance.The formation process and corrosion mechanism of the coating demonstrates that AIMn phase plays a critical role in the growth process of the coating.The Ca-PL-Cys coating with a radial structure on the surface of the Mg alloy was prepared in the traditional calcium-phosphorus treatment solution containing an appropriate amount of L-cysteine in water bath at 60?.The microstructure of Ca-PL-Cys coating was more regular and uniform.The surface roughness of the Ca-PL-Cys coating was significantly reduced to 2.41±0.23?m,and the coating thickness was almost doubled compared to the traditional calcium-phosphorus coating.Electrochemical tests also show that the icorr of the Ca-PL-Cys coating was about two orders of magnitude lower than that of the AZ31 substrate.The presence of L-cysteine promoted the nucleation and growth process of the coatings;and the grain size was significantly reduced,which could effectively increase the corrosion resistance of the coating.Amino acid Schiff base was prepared from L-cysteine and glucose in alkaline environment.The Ca-PSchiff base coating was prepared in the traditional calcium-phosphorus treatment solution containing an appropriate amount of amino acid Schiff base in water bath at a temperature of 60?.The microstructure of the Ca-PSchiff base coating was more uniform;and the roughness was obviously reduced.Electrochemical results showed that the icorr of the Ca-PSchiff base coating was two orders of magnitude lower than that of the AZ31 substrate,and the corrosion resistance was significantly improved.XRD test demonstrated that the amino acid Schiff Base could induce the formation of hydroxyapatite.Theoretically,it could improve the osteoinductive and osteocompatible of the coating. |
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