The effect of alloy elements on the corrosion resistance of aluminium the main reason for adding alloy elements into aluminium is to obtain higher mechanical properties, physical properties or better technological properties, the possibility of significantly improving the corrosion resistance of aluminum by alloying is small, and the corrosion resistance of aluminum alloy is rarely better than that of pure aluminum. Cu, MG, Zn, MN, SI, CR, Fe, Ti and B E, Bi, b, PB, Ni, P, Zn, Sn and SB are the main alloying elements which can strengthen al. Their effects on corrosion resistance are as follows: Cu reduces the corrosion resistance of aluminum and increases the tendency of pitting corrosion. Its concrete influence depends on its content existence form and distribution in alloy. Mg has good effect on corrosion resistance of al-Mg alloy to alkaline solution such as lime and sodium carbonate. Al-Mn alloy is also a kind of anti-rust aluminum alloy. Some alloys with a small amount of manganese in place of chromium have good resistance to stress corrosion. Si makes the corrosion resistance of aluminum alloy slightly lower, the specific effect depends on its morphology and distribution. ZN has little effect on the corrosion resistance of aluminum alloy. CR addition amount is only 0.1%-0.3% , which has a good effect on the corrosion resistance and can improve the stress corrosion resistance of some alloys. Fe Reduces the corrosion resistance of aluminum, so the content of iron should be controlled when the corrosion resistance of alloy is high. The corrosion resistance of an alloy in high temperature water at 150-350 °C can be improved by addition of nickel to the alloy. Ni has a tendency to decrease the corrosion resistance, but the effect is less than that of copper. Ti has little effect on the corrosion resistance, and the main reason of adding Ti is to refine the grains. Sn slightly reduces corrosion resistance. Al-Mg, Al-Mn, Al-Mn-mg and Al-Mg-si are the main corrosion resistant aluminum alloys. When MG, Zn, MN, SI and Cu were added to aluminum, the electrode potential of aluminum alloy also changed. The corrosion resistance of aluminum alloy is closely related to the electrode potential of various phases. If the matrix phase is the anode phase and the second phase is the cathode phase, the higher the potential of the second phase and the more the amount, the more serious the corrosion of the alloy. The electrode potentials of common phases in aluminium alloys in NaCl-H2O solution are listed in Table:

As can be seen from the data in the table, compared with pure aluminum, the solid solution containing zinc and magnesium is the anode, the solid solution containing copper is the cathode, Mg5Al8, and MGZN2 are the anode, CuAl2, and FEAL3 are the cathode, MnAl6, and Mg2si have almost the same potential as pure aluminum. Therefore, Al-Mg and Al-Mn alloys have high corrosion resistance, while Al-Cu alloys have poor corrosion resistance. Although the potential of SI and AL is very different, the corrosion resistance of Al 2o 3 + Sio 2 on the surface of the alloy is still very good because of the existence of oxygen or the formation of Protective Al 2O 3 + Sio 2 oxide film on the surface of the alloy in the oxidation medium. 

Source: Web Collation