| It is well known that the loss caused by the corrosion of iron and steel is very great.Hot dip galvanizing ofen use to prevent corrosion of steel structure parts at home and abroad, in dry air and clean environment, hot dip galvanized layer of steel structure plays a isolation protection and cathodic protection, protective time can be more than ten years or even decades, is widely used in many fields of the national economy. However, when these steel structures are in the environment of acid rain in a long time, the protective effect of the hot dip galvanized coating occurs electrochemical corrosion, which leads to the protection time of the hot dip galvanized coating on the steel surface is greatly shortened.And traditional technology of hot dip galvanizing is in a relatively low silicon content of rimmed steel, but for the application of the technology to activity of high silicon steel, will often appear Sandelin effect, namely steel of high silicon content will significantly improve the Fe Zn reaction activity. High active silicon steel plating pieces in hot dip, usually the surface of the coating is not bright and clean degree is not high,uneven and large thickness, and poor adhesion, reduce quality of galvanized products, increase the production cost of galvanizing.The corrosion behavior of hot dip galvanizing in acid rain environment and high silicon reactive steel Sandelin effect, this project intends to study of a low melting point Zn-Al-Sn-Bi alloy, and the alloy used for reactive steel surface of hot dip coating, and to explore the alloy and its coating microstructure structure, mechanical properties test, electrochemical corrosion and in simulated acid rain solution corrosion behavior.Through the study on Zn-Al-Sn-Bi alloy and hot dip coating analysis:Add Al, Sn and Bi elements in Zn, the microstructure of Zn-Al-Sn-Bi alloy is obviously refined, the distribution of grain boundary precipitates is more uniform,with the increase of Sn content, the hardness and tensile strength of Zn-Al-Sn-Bi alloy is improved obviously, the average corrosion rate and corrosion current density decreases firstly and then increased. When the content of Al and Bi certain and Sn content is 5%, that microstructure of Zn-15Al-5Sn-0.1Bi alloy with equiaxed fine spherical crystal and bone like or vermicular grain, uniform and fine microstructure of the alloy has a good supporting role to the strength and corrosion resistance, the hardness and tensile strength of the highest, average corrosion rate reached the best state, the self corrosion current density is the smallest, mechanical properties and resistance to corrosion resistance are very well.Hot dip coating after adding Al, Sn, Bi element and alloy coating thickness decreased significantly, coating microstructure has been refined and zeta phase abnormal growth of Sandelin effect suppressed; when the content of Al and Bi must,with the addition of Sn, alloy coating thickness has decreased first and then increased trend, zeta phase of growth showing the first slowed down to accelerate the trend;when the Sn content is 5%, the coating thickness of Zn-15Al-5Sn-0.1Bi alloy reaches the minimum, the smallest for the grain, arranged in a very neat, precipitates along the grain boundary is relatively uniform, no obvious defects, plays a very good protective effect on the matrix. Zn-Al-Sn-Bi alloy coatings in simulated acid rain corrosion behavior and electrochemical corrosion of the alloy are basically the same, as mentioned above, which Sn content is 5% of the Zn-15Al-5Sn-0.1Bi average corrosion rate and corrosion current density minimum, resistance to corrosion performance best, alloy coating corrosion products are uniformly covered on the surface of the coating, no obvious defects, the dense corrosion layer and solid to isolate oxidation, and effectively hinder the corrosive liquid to the substrate to penetrate, retard the corrosion. |
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