Investigation On Silanization Surface Treatment Technology Of Mg-Gd-Y Rare Earth Magnesium Alloy

In recent years,the development and application of magnesium alloy components have experienced rapid growth,effectively supporting the realization of lightweight and high-strength design targets for aerospace components.At present,Mg-Gd-Y rare earth magnesium alloys are widely used in aerospace equipment components such as cabin sections and frame beams due to their high strength and heat resistance.Considering the disadvantage of magnesium alloys in terms of corrosion resistance,the development of environmentally friendly surface treatment technologies has become the key foundation for the stable and reliable service of magnesium alloy components.This paper focuses on the storage and in-process corrosion problems of Mg-Gd-Y rare earth magnesium alloys and develops silane surface treatment technology to improve the corrosion resistance of magnesium alloys.First,the silane treatment process is optimized under alkaline and acidic silane hydrolysis systems,and suitable doping modifiers are selected to improve the corrosion resistance of the silane film.On this basis,composite silane treatment technology and double-layer silane film technology are used to further improve the corrosion resistance of magnesium alloys.Finally,a micro-arc oxidation/silane composite film layer is prepared to explore the feasibility of sealing defects in magnesium alloy micro-arc oxidation films through silane treatment,fully utilizing the advantages of both micro-arc oxidation and silane surface treatment technologies.KH560 silane coupling agent is used to treat Mg-Gd-Y rare earth magnesium alloy.The pre-treatment process,hydrolysis process,and curing process are optimized under alkaline hydrolysis system,and a complete and dense silane film is prepared on the magnesium alloy surface using the optimal process parameters.The results show that after KH560 silane treatment,the corrosion process of Mg-Gd-Y rare earth magnesium alloy changes from an active dissolution state to a passivation tendency,and its self-corrosion current density decreases from 6.91×10^-5A·cm^-2to 1.18×10^-7A·cm^-2,significantly improving corrosion resistance.Doping modifiers for silane hydrolysis solutions are screened under both alkaline and acidic hydrolysis systems.The research results show that under the alkaline hydrolysis system,the use of sodium silicate doping modification of the silane hydrolysis solution can further improve the corrosion resistance of the silane film,and the corrosion current density can be reduced to 2.21×10^-8A·cm^-2,with the anodic polarization curve showing a significant passivation tendency.Under the acidic hydrolysis system,the addition of an appropriate amount of phytic acid can improve the corrosion resistance of the silane film.Overall,the corrosion resistance of silane films prepared under alkaline hydrolysis system is better.In order to utilize the advantages of different types of silane coupling agents and further improve the corrosion resistance of silane films,this paper explores the composite silane treatment technology for the magnesium alloy surface and successfully prepares a BTSE-KH560-OTES（BKO）multi-silane film layer.Compared with the aforementioned KH560 single-silane film,the multi-silane film has significantly improved corrosion resistance,and the time it takes for corrosion to occur in a 3.5%Na Cl solution increases from72 hours to 168 hours.Based on the research of single-silane and composite silane treatment technology,a double-layer film technology is further explored to combine the two and improve the corrosion resistance of the silane film.A double-layer silane film with KH560single-silane film as the bottom layer and BKO multi-silane film as the top layer is prepared through a two-step method,and the protection time for Mg-Gd-Y magnesium alloy in Na Cl solution is increased to 288 hours.In order to improve the long-term corrosion resistance of Mg-Gd-Y rare earth magnesium alloys,a micro-arc oxidation/silane composite film layer with a micro-arc oxidation film as the bottom layer and BKO multi-silane film as the top layer is prepared.The results show that silane treatment has an excellent sealing effect on defects such as micropores and micro-cracks in magnesium alloy micro-arc oxidation films,and the protection time of the composite film layer for magnesium alloys in Na Cl solution is increased to 360 hours.Electrochemical Impedance Spectroscopy（EIS）analysis shows that after the silane sealing treatment,the resistance of the porous layer,dense layer,and charge transfer resistance of the micro-arc oxidation film all significantly increase,with the resistance of the porous layer showing the most significant improvement.