| Based on previous research on hard anodic oxidation preparation technology, the work ofrare earth salt ceric sulfate and mixed with organic acid to ceramic oxide film hardness andgrowth rate and wear resistance are analyzed in the topic to further explore the newtechnology of preparation of high hardness alloy Al2O3ceramic membrane.6061aluminum alloy best oxidation process parameters were adopted, with hardness,film growth rate as the main evaluation,with microhardness meter (MVC-1000-JMT1) anddigital coating thickness gauge (TT230) to determine the hardness and thickness of oxidefilm,index to optimize the ceric sulfate concentration was0.8m/L for best.Sulfuric acidconcentration and oxidation temperature act as variables,the best sulfuric acid containing cericsulfate electrolyte mass fraction was14%and oxidation temperature was-2S℃aredetermined. Computer microscopic image analyzer (XJP-6A) was used to analysis themicrostructure, the friction testing machine (MM-200) was used to measure frictioncoefficient of oxide films,results show that when ceric sulfate was contained in theelectrolyte，finish and density degree were better than ordinary oxide film in the same oxidetemperature, and when the temperature rises to more than0℃, no corrosion pit of ordinaryhard anodized, and the trend of decline in the coating appearance quality is decreasedinfluenced by the temperature rising，this may be based on the special electronic structure ofCe4+which play a catalytic effect on oxide film transformation,and can hinder the solution ofoxide film in the sulfuric acid electrolyte.The organic acids:5-sulfo salicylic acid, citric acid and oxalic acid were added into theelectrolyte respectively， and the microhardness and film-forming rate in differentconcentration were compared.The citric acid was selected as the best organic acid in cericsulfate process and the appropriate concentration was set to0.18mol/L. In this study,oxidation time and current density were set as the important variable parameters that had animpact on the oxide film’s properties. Then, the microhardness and film-forming rate werecompared in different parameters,the results showed that the microhardness for520HV couldbe got within process conditions containing compound additives, current density for4.5A/dm2, oxide film for50~70min.The microscopic morphology of oxide film was analyzedby SEM. The result showed that the film’s microhardness with ceric sulfate process weremore dense and smooth compared with ordinary acid hard anodic oxidation film. Under theeffect of compound additives containing citric acid, the density and finish degrees wereimproved greatly.Through the EDS spectrum analysis,the result showed that Ce4+didn’t becontained in oxide film.Organic acid radical ion and Ce4+conducted complexing reactions that produced complexation ion to handling H+from the oxidation surface, then made the filmgrowth speed up,and the acid radical ion can conduct complexing reaction with Al3+whichdissolved out from the oxide film,so it also attended handling H+.The above reactions leadedto oxide film grow rapidly and the unit cells arrange closely and regularly,so oxide filmperformance is improved.Citric acid contains three hydrogen bonds why may make it betterthan other organic acids containing two hydrogen bonds.In addition,this work analyzed the film-forming situation and hardness and thickness ofthe6061aluminum alloy’ hard anodic oxidation films in the same oxidation condition butdifferent substrate thickness,it is concluded that the larger substrate thickness is, the lessinternal temperature increase by the oxide heat influencing, which brought less negativeinfluence on the growth of oxidation film, so the film-forming rate is higher and the corrosionact on porous layer is less, the hardness and thickness of oxidation film would be higher. |
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