Preparation And Corrosion Resistance Study Of Organic-inorganic Composite Chemical Conversion Film On 5052 Aluminum Alloy

Aluminum alloy has the advantages of low density,high specific strength,good electrical and thermal conductivity,good ductility,etc.It is the most widely used class of non-ferrous metal materials.However,it is susceptible to corrosion in harsh environments and requires surface protection.Chemical conversion treatment,as a common surface treatment process,can generate a chemical conversion film on the surface of aluminum alloy,achieving effective protection of the aluminum alloy substrate.Meanwhile,chemical conversion treatment as a pretreatment process for coating can improve the adhesion between the aluminum alloy substrate and the coating.Traditional chromate conversion treatment is gradually abandoned due to the carcinogenic problem of hexavalent chromium,so the development of a new,simple,practical and green chemical conversion treatment process for aluminum alloys has become a current research focus.In this paper,a new chemical conversion treatment process of sodium silicate and acrylamide organic-inorganic composite was developed.The morphology,composition and thickness of the conversion film were characterized by SEM,EDS,FTIR,XPS and AFM.The adhesion with the substrate was tested with the tape test,and the corrosion resistance was tested by EIS test and neutral salt spray test.The results show that the prepared chemical conversion film has excellent corrosion resistance and adhesion with the substrate.The main research results are as follows:First,the optimum process parameters were obtained:the composition of the treatment solution was 1 g L^-1 sodium silicate and 9 g L^-1acrylamide,the temperature was 70℃,and the processing time was 72 h.The conversion film prepared based on the above process parameters was brownish-yellow,uniform and dense,mainly composed of polyacrylamide and silicate,with a thickness of about 50 nm.The charge transfer resistance R_ct of the conversion film was as high as 1.867×10⁸?·cm²,showing better corrosion resistance than the chromate conversion film.In long-term immersion experiments,the conversion film provided effective protection for the substrate for up to 54days,exhibiting excellent long-term corrosion resistance and self-healing properties.The tape test results showed that the conversion film effectively improved the adhesion between the substrate and the organic coating.Second,on the basis of this process,in order to shorten the treatment time and improve the conversion treatment efficiency,the optimal process parameters for adding initiator were determined by single factor experiments:the redox initiation composition was 0.02 g L^-1 potassium persulfate and 0.005g L^-1 ferrous ammonium sulfate,the treatment solution composition was 1 g L^-1 sodium silicate and 9 g L^-1 acrylamide,and the temperature was 80°C.The processing time could be shortened to 12 h.The morphology,composition,substrate adhesion and corrosion resistance of the conversion film prepared by introducing the initiator were comparable to those prepared without the initiator,but the treatment time was effectively shortened.