Preparation Of Sol-gel Anticorrosive Coatings On Aluminum Alloy And Their Properties

Aluminum alloys are widely used in aerospace,automotive chemical and other manufacturing industries due to their low density,good ductility,high plasticity and so on.However,their unstable chemical properties and poor corrosion resistance make aluminum alloy parts easy to be corroded.Therefore,the surface treatment and anti-corrosion of aluminum alloy have been the concern of materials researchers at home and abroad.In this paper,TiO₂ and SiO₂inorganic coatings,MTMS(Trimethoxymethylsilane)modified silicone coatings and MTMS-DMDPS(Trimethoxymethylsilane-Dimethoxydiphenylsilane)modified silicone resin coatings were prepared on aluminum alloy substrate by sol-gel technology.The preparation methods,difference of corrosion resistances and corrosion resistance mechanism of TiO₂,SiO₂ and two organic-inorganic composite coatings were comparatively studued.The results showed that MTMS-DMDPS modified silicone resin coating possessed the best corrosion resistance.Furthermore,the MTMS-DMDPS modified silicone resin coating was coated on micro-arc oxidation(MAO)layers of aluminum alloys by spray method.Their sealing effect was studied by electrochemical test,salt spray test,etc.The conclusions were as follows:(1)TiO₂ and SiO₂inorganic anticorrosive coatings were prepared on aluminium alloy by sol-gel technology and their anticorrosion properties were studied.The results indicated that their precursor sols can not coated on the surface of the aluminium substrate by spraying,because of lower viscosity and severe sagging of sols.Nano-scale inorganic coating can be achieved on aluminum substrate with spin method to improve corrosion resistance,however,it is easy to crack in the process of heat treatment,the salt spray test of these coating showed that severe pitting corrosion occurred in the salt spray for 168 h hours.(2)A single-component MTMS modified silica sol was synthesized and an anticorrosive coating was prepared on 6061 aluminum alloy.The best stoichiometry of MTMS modified silica sol was:n_(MTMS):n_(TEOS)=1:3,V_H2O:V_Si=2:1,and V_acid:V_Si=1:80.Nevertheless,the sol can not uniformly coated on the surface of alumimum alloy by spraying due to their low viscosity.The sol can be used to prepare a great corrosion resistant coating on aluminum alloy by spin method,and they can endure 168 h salt spray test and show 6H hardness,and first-level adhesion.(3)A two-component modified silica sol was developed,which was organic-inorganic silica sol was obtanined by using MTMS and DMDPS as the raw materials of organosiloxane to modify silica sol.The best stoichiometry of MTMS-DMDPS modified silica sol was as follow:the p H of alkaline silica sol was adjusted to 3-4,mixed solution of MTMS and DMDPS siloxane was added,its weight ratio to silica sol was 6:5.Then,solvent diethylene glycol butyl also was added.The sol was reliuxed and stirred for 2 h,then dehydrated at 95?for 2 h.The viscosity of the obtained sol was 176 m Pa·s,so it was suitable to be prepared by spraying and spinning method on aluminum substrate.A 13?m thick coating was prepared on the aluminum alloy by spraying method,with 6 H hardness,second-level adhesion.And there was no macroscopical changes on the coating surface after 720 h of salt spray.(4)The micro-arcoxidation(MAO)film on aluminum alloy was sealed with the MTMS-DMDPS modified silicone resin,and the anti-corrosion effect of the sealing layer was studied.The result demonstrated that constructing a two-component MTMS-DMDPS modified sealing layer on the MAO layer can effectively improve the corrosion resistance of MAO sample.The salt spray resistance time of micro-arc oxidation casting aluminum workpiece can be increased from 72 h to 480 h.