Study On The Technology Of Zn-Ni/Nano-Al₂O₃ Alloy Coating Electrodeposition

The corrosion of metal has caused great harm and economic loss to the human society.The traditional galvanized coating is the most extensive used and economical measures to prevent corrosion.With the rapid development of modern industry and science technology,the traditional galvanized coating can't meet the requirements any more.Therefore,technology workers have taken a series of measures and Zn-based alloy plating is one of the most effective methods.This subject independently developed the preparation technology of zinc-nickel/nano-Al₂O₃ composite coatings that can be more excellent corrosion resistance coating without passivation under the background. Not only simplified the process to reduce costs,and reduce environmental pollution.This experiment has optimizated single factor,and studied the influence of every factor on the ingredients of the composite plating.Consequently,the general rules of the ucomposition of the composite plating were found.On this basis,using the instrument of CHI832 electrochemical analyzer made by Shanghai Chenhua,D/Max-2400 X-ray diffraction made by Japanese Natural science company and QUANTA200 scanning electrical microscope made by Holland FEI company,etc,to analyze and research the cathodic polarization,composition,structure,microstructure and corrosion product of the zinc-nickel/nano-Al₂O₃ composite coatings.The corrosion resistance of the zinc-nickel/nano-Al₂O₃ composite coatings has been studied by acid corroding method and neutral salt spray test.The result has shown that:(1) The best solution for the formula and process:ZnO 20g·L^-1;NH4Cl 200·gL^-1;NiCl₂·6H₂O 40g·L^-1;H₃BO₃ 20g·L^-1;nano A1₂O₃ 25g·L^-1; saccharin 1.5g·L^-1;sodium dodecyl sulfate 1.5g·L^-1;appropriate additives;pH 6.0; plating time 120min;D_K 4A·dm^-2;temperature 50℃;stirring speed 200rpm.(2) zinc-nickel/nano-Al₂O₃ composite coatings made from this bath composition and technological condition,which contained Ni 13%and Al₂O₃ 0.4%-0.6%,showed a good appearance and corrosion resistance.(3) When the corrodibility of the medium was stronger,the metal component in the plating influenced more to the speed of corrosion. When the corrodibility of the medium was weaker,the effect of Al₂O₃ particle in the plating to reduce the speed of corrosion was more obvious.(4) The galvanization inlayed the Al₂O₃ particle into the clad layer mechanically.Due to the inactive chemical property of Al₂O₃ particle,the mechanical shielding effect reduced the actual surface area of the metal.Thereby the non-oxidizability of the clad layer was improved. But when the zinc-nickel/nano-Al₂O₃ composite coatings which contained Ni 13%in the composite coatings was composed by singleyphase,there is no corrosive microbattery.(5) When the plating corrosion happened in salt water,Al₂O₃ particle formed complex salt with zinc and nickel respectively.The surface of the plating will be covered by these corrosion products which can play a part of reducing corrosion.(6) As a result of the addition of Al₂O₃ particles into the plating,the plating crystallizations were more micromesh.The assignment of crystal grain was much more even and orderly.Because of the decrease of the porosity factor,the possibility of chemical and electrochemical corrosion directly happened in substrate was reduced enormously.