Dissertation
Dissertation > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology

Effect of Intermetallics Phase on Electrochemical Performance of Al-Mg Alloys for Sacrificial Anode

Author WuTong
Tutor LiuChangRui
School Xi'an University of Architecture and Technology
Course Materials Processing Engineering
Keywords Al-Mg alloy Intermetallic Sacrificial anode Alloying Electrochemical performance
CLC TG174.4
Type Master's thesis
Year 2010
Downloads 36
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Cathodic protection by sacrificial anodes is one of the important methods for protecting metal materials. The common anode materials include zinc anodes, magnesium anodes and aluminum anodes. Because of Aluminum alloys’ superiority, such as high-energy capability (3.6 times of zinc,1.35 times of magnesium), light weight, long life, and low cost compared with magnesium and zinc alloys. Aluminum alloys have become popular as galvanic anodes for cathodic protection. But commercially pure aluminum exhibits a relatively noble potential in corrosive environment due to an impervious Al2O3 film on the surface. It is not suitable for sacrificial anode. Magnesium alloys have high potential applied to iron and steel. But it is not suitable for sacrificial anode too, because of the low current efficiency and high corrosion rate. The way to improve the performance of the anodes is alloyed with other elements.To base on the alloy phase electrochemistry theorem, this paper investigated the influence of magnesium contents on microstructure and electrochemistry properties of alloy anodes. With the magnesium contents improve, there are large area intermetallic in alloy structure. In order to improve the performance of alloy anodes, experiment alloyed with Zn, Mn, and Rare Earth Element Ce. The open potential, self-corrosion rate, polarization rate, electrochemical property and corrosion morphology were studied. The main conclusions were as following:When the content of magnesium increased to 10 percent, large area intermetallic phase Mg5Al8 were be formed in alloy’s microstructure. Experimental results indicated that it had an activated effect on aluminum alloy anodes. With the increase of magnesium quantities, the open potential was reduce, and the polarization rate was decreased also. When the content of magnesium was increased to 30%, the open potential of Al-Mg anodes was reduced to-1.132V in 3.5% NaCl solution. However, the dissolution of alloyed anodes with more than 20% quantities of magnesium was unsymmetrical.When the content of magnesium increased to 60 percent, the intermetallic phase Mg17Al12 were be formed in alloy’s microstructure. Its potential is high than magnesium. Low content of the intermetallic phase Mg17Al12 could promote alloy’s corrosion. With the content increased, intermetallic phase Mg17Al12 was continuous distribution around substrate. Then it could reduce alloy’s self-corrosion rate.alloyed with Rare Earth Element Ce in Al-25Mg. The content was from 0.3 percent to 1 percent. Experimental results indicated that it had an activated effect on aluminum alloy anodes. The open potential was reduce after alloyed with rare earth element Ce. When alloyed with Eare Earth Element Ce, the corrosion rates of magnesium anodes were reduced. Rare Earth Element Ce on Al-Mg alloys also has the role of grain refinement.Alloyed with the contents of 1 percent of Zn on the magnesium alloy had the role of grain refinement. It could make the corrosion uniform, and reduced the corrosion rate of magnesium alloys. When alloyed with the content of Zn over 9%, due to the role of the middle phase, alloy anode material properties would have a negative impact.

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