| Hot dipped aluminized steels possess favorable hot resistance, corrosion resistance and wear resistance characteristic in easily oxidized and corrosion medium. At the same time it maintains the mechanical properties of matrix material. Therefore, they are widely applied in metallurgy, electric power, petro, chemical industry, etc. The property of hot dip aluminized steel mainly depends on two factors:one is the continuous integrity of coating; the other one is the composition of coating. Process of hot dip aluminized method has a significant effect on the property of coating, and dual bath method is the best one. This experiment used dual bath method for hot dip aluminized coating to eliminate the influence of process method on the continuous of coating. By adding different contents of rare earth, manganese alloy elements to liquid aluminum, so as to further improve hot dip aluminized steel corrosion resistance. The tests are used to determine the most suitable alloying element content. By adding alloying elements, the pinhole leakage plating coating and the effect of harmful impurities is reduced and decreased, which makes coating corrosion resistance more superior.Using Q235steel sheet as samples, the dual bath method hot dip aluminized process parameters is set. Hot dip aluminized technological parameters include hot-dip temperature, hot-dip time and ascension speed, and hot-dip temperature has a more remarkable impact on the coating thickness and leakage plating. Therefore, this experiment mainly researches the hot-dip temperature. With macroscopic observing, the dual hot dip aluminized temperature is suitable from700-720℃, at which the coating gets has a continuous and smooth exterior, so this experiment selects715℃as the hot dip aluminized temperature.Then by using different content of rare-earth aluminium alloy manganese and aluminum alloy, manganese aluminum alloy, the influence of manganese and rare earth on the hot dip aluminized steel corrosion resistance has been studied. With optical microscope and scanning electron microscope, the microstructure of hot dip aluminized was analyzed, and its formation mechanism is discussed. Through rare nitric acid soaking experiment, weight loss on unit area and unit time to describe the content of needle in the coating is analyzed, then the density of coating can be judged. The coating corrosion resistance is tested by soaking the coating with the5%NaCl solution. Corrosion resistance of coating in acid is also tested. The experiment indicated that0.2～0.3%of rare earth can maximize improve the the corrosion resistance of hot dip aluminized coating. Coating with0.1～0.3%of rare earth has effectively reduced pinhole and leakage plating, Coating with0.3%rare earth has the best corrosion resistance of sea water. Excess adding of rare earth elements will reduce the corrosion resistance of coating. When the content of manganese is about1.1～1.3%, corrosion resistance of hot dip aluminized specimens is the most obvious. However, adding excess manganese will not improve the corrosion resistance effects. The sample with1.2%Mn and no more than0.3%of rare earth has the best coating corrosion resistance. Adequate re and manganese can effectively improve the corrosion resistance of hot dip aluminized coating. |
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