Study On Modification Of Silane Film And Neodymium Concersion Film On Surface Of Magnesium Alloy

Magnesium and magnesium alloy were low density,high specific strength,and abundant resources,they are recognized by the industry as a kind of functional structure integrated materials with the most development potential.However,it was susceptible to corrosion,which largely limit their large-scale application.The silane conversion treatment was simple,safe and environmentally friendly,it has become a major method in the field of magnesium alloy protection.In this paper,the best preparation process of three chemical conversion films(KH550+BTESPT double-layer silane film,KH550+Nd-doped BTESPT double-layer silane film and single neodymium chemical conversion film)in AZ91D magnesium alloy was studied,and compare their protection performance.The results show that the KH550+BTESPT double-layer silane film was uniform and dense,mainly composed of Si-O-Si bonds,the ring-shaped Si-O-Si structure aggregation made the film structure dense and stable on the magnesium alloy surface,forming a good physical barrier can effectively prevent the corrosion of magnesium alloy.After doping with neodymium nitrate,the protection performance was further improved;the optimal concentration of neodymium nitrate was 0.005mol/L.The Nd-doped silane film was composed of ring-shaped Si-O-Si structure and Si-O-Nd bonds.According to the analysis of the film mechanism,a part of neodymium was filled in the siloxane structure in the form of Si-O-Nd,and another part of neodymium was present in the outermost layer of the film layer as inorganic particles.Through in-depth analysis of the corrosion process of the film,the corrosion of the film was roughly divided into three processes.First,Cl-was adsorbed on the surface of the film,and then as the immersion time increased,Cl-penetrated the defect of the film,the magnesium alloy matrix corrosion occured,corrosion products were produced,and finally corrosion products accumulated,and the corrosion resistance of the film will be reduced.After comparison,it was found that the Nd-doped silane film has the best performance.There was ring-shaped Si-O-Si structure in the film,and there were also a large number of Si-O-Nd bonds,so the physical barrier effect was enhanced,resisting corrosion time has increased.