| The corrosion phenomenon of materials is widespread in all aspects of life,from daily life to industrial production,from small steel structure to large steel structure,material corrosion phenomenon exists all the time,so the problem of material protection has become a topic of widespread concern of the people.Mechanical plating technology is widely used because of its advantages such as no hydrogen embrittlement,low cost,simple operation,but with the passage of time,the corrosion resistance of a single galvanized layer has been unable to meet people’s requirements on the corrosion resistance of materials.The chemical properties of aluminum are active,and it is easy to be oxidized in the natural environment.The surface is wrapped by dense alumina and presents a blunt state,and the corrosion resistance is good.How aluminum affects the anticorrosive properties of Zinc-aluminum alloy coatings has become a problem concerned by researchers in the field of material protection.In view of this,in this paper,by adding strong acids and fluorinated acids to the plating solution,zinc aluminum alloy coating was prepared on the surface of steel substrate,and the corrosion resistance of zinc aluminum alloy coating was studied.In this paper,metallographic microscope,stereopicroscope and scanning electron microscope were used to analyze the microstructure of Zinc-aluminum alloy coating.Salt spray test and electrochemical test were used to study the influence of aluminum element and aluminum content on its corrosion resistance.The results showed that:（1）Compared with pure zinc coating,the self-corrosion potential of zinc-aluminum alloy coating has a positive shift of 158m V.The corrosion current density of zinc-aluminum alloy coating is much less than that of pure zinc coating.The fitting circuit Rcoat value of zinc-aluminum alloy coating is 3.5 times that of pure zinc coating,and the arc radius of zinc-aluminum alloy coating is significantly larger than that of pure zinc layer.The time of red rust in the neutral salt spray test is 120 h longer than that in the pure zinc coating.The corrosion rate of Zn-Al alloy coating in total immersion test is lower than that of pure zinc coating.Neither of the two coatings was corroded through the test of wet heat and salt spray,and the two coatings showed good resistance to wet heat environment.（2）With the increase of aluminum content in the coating,the corrosion current density of Zinc-aluminum alloy coating is1.664×10-3,1.001×10-3,9.025×10-4A·cm-2,respectively.The change of self-corrosion potential of zinc-aluminum alloy coating is not large,and the arc radius of AC impedance spectrum of the sample increases significantly with the increase of aluminum content.The time of red rust in neutral salt spray test samples was 360,432,480 h,respectively.The corrosion rates of total immersion coatings were0.0706,0.0623,0.0435 g·m-2·h-1with the increase of aluminum content.No obvious red rust was found in three kinds of Zn-Al coatings after salt spray and heat alternating test.It shows that the corrosion resistance of the coating increases with the increase of aluminum content in the coating.（3）Compared with the non-superheated Zinc-aluminum alloy coating after heat treatment,there is a thermal diffusion layer inside the zinc-aluminum alloy coating after heat treatment,the self-corrosion current density of the coating decreases,the Rpvalue is little different,and the impedance arc radius is significantly smaller than that of the non-heat treated sample.The average corrosion rates of total immersion are0.0697 and 0.0879g·m-2·h-1,respectively,which decrease by 20%,indicating that the thermal diffusion layer in the coating can further resist the corrosion of the corrosive medium.（4）After heat treatment,the corrosion current density of Zn-Al alloy coating（5%,10%,20%）was 4.583×10-4,2.704×10-4,4.596×10-4A·cm-2with the increase of aluminum content,and the impedance arc radius of Zn-Al-10%coating was the largest.The Rcoat value of the fitting circuit is 855,5279,2945Ω·cm2.The corrosion current density of the total immersion test is 0.0604,0.0525 and 0.0546 g·m-2·h-1,respectively.When the content of aluminum in the Zn-Al alloy coating exceeds 10%,the loose Fe-Al3 phase in the thermal diffusion layer of the coating increases,and the corrosion resistance of the alloy coating decreases.Therefore,the corrosion resistance of the three Zn-Al-10%Zn-Al alloy coatings is the strongest.（5）The corrosion resistance mechanism of Zinc-aluminum alloy coating can be divided into four aspects:physical shielding of coating tissue,cathodic protection of sacrificial anode,self-healing and passivation of alloy coating. |
PDF Full Text Request