| Zn-Al coating is a new type metal protective technology which has manyadvantages such as high corrosion resistance and no hydrogen embrittlement, and ithas been widely used in cars and marine steel structures. This coating has thefunctions of physical shielding, passivation protection and sacrificial anode protection,which can provide effective protection for steel fasteners. In marine environment,Zn-Al coating is often combined with other corrosion protective technology such aszinc impregnation and organic coating, which can greatly improve the protectiveproperties of the-metal.The research purpose of this paper is to optimize the factors which affect thecoating through the evaluation of physical properties of the liquid and coating, thenwe can get a new type of Zn-Al coating. It simplifies the procedure of coatingtechnology and reduces the production cost of the coating liquid. Then, the researchachieved good protective effect comparing with dacromet coating.The research content of this paper include the optimization of Zn-Al coating fluidformulation and the coating preparation process. Liquid coating formulationoptimization include the ratio of zinc and aluminum components,zinc powdertreatment，passivation agent content, the types and content of the thickener, thecontent of wetting agent etc. Passivation agent content was used from little to more,then the ratio of zinc and aluminum component was gradually increased. Wettingagent content was related to the stability of the coating liquid. The thickener waschosen methyl cellulose, ethyl cellulose, polyvinyl alcohol amide, and polyethyleneamide, respectively. We can select the best formula through the evaluation of thephysical properties and corrosion resistance of liquid and coating. The results showedthat Zn Al (7:1)，zinc powder after surface treatment,passivation agent（4%），thickener cellulose class (methyl or ethyl) effective component from0.3g/100ml to0.5g/100ml，wetting agent25%with water45%. We could achieve the bestperformance of the coating under this formulation.The technology optimization of the coating preparation mainly includes sinteringtemperature, time, and depositing process. The metal samples were treated by oil removal,sand blasting and depositing, then burnt into membrane. Sinteringtemperature is a key factor of film forming. In this paper, sintering temperature wascontrolled by275℃,300℃,325℃, and350℃, respectively. After that, thedroping sulfonated experiments were tested to determine the sintering qualified, andwe can preliminary confirm a large temperature scope. In this obtained temperaturescope, we can select an accurate temperature from the low temperature point to thehigh temperature point. After ammonium nitrate fast evaluation tests, we candetermine the optimized sintered temperature. Depositing ways mainly have twoways,dumping for fasteners and brushing for flat surface. The results showed that themetal samples under the condition of the sintering temperature (330℃), the sinteringtime (25min) has the best corrosion resistance. And the preparation of rotation speed(40r/s), forward-rotating (15s), counter-rotating (15s), coating thickness ismoderate.We can use time interval test to obtain the failure time of the liquid coating.Wehave designed two method to solve this problem, one is to store liquid coating; thesecond is to separate the passivation solution from metal slurry, when we use we mix.Through infrared testing,heat comprehensive analysis and other methods, test twokinds of liquid in spacing interval. Results showed that if we separate A from B, wecan save more than20d; if we blend, it can only be saved7d. The failure reasonmainly was the reduction of hexavalent chromium which was the failure of thepassivation mechanism, therefore we compared with the chromium-free Zn-Alcoating. After calculation, we found that it was cheaper than other similar liquidcoating in country and abroad.In summary, those experiments optimize the formula of coating liquid, and thecoating has certain corrosion resistance. The study in this paper provides a newmethod of preparing Zn-Al dope liquid, and has a reference value of researching andimproving Zn-Al dope liquid. |
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