Effect of temperature on galvanic corrosion of Al 6061-SS 304 in nitric acid

Abstract

Nitrogen tetroxide (N2O4) is commonly used as an oxidizer for bipropellant liquid, and galvanic corrosion of its storage tanks was a serious problem. The immersion and electrochemical experiments of Al 6061-SS 304 galvanic pair were carried out in 30% nitric acid at different temperatures. The accelerated galvanic corrosion of Al 6061 and the effect of different temperatures on its corrosion behavior were studied. The surface morphology, number of corrosion pits and electrochemical parameters of Al 6061 before and after corrosion were measured and analyzed by means of SEM, EDS and electrochemical methods. The results show that when Al 6061 was coupled with SS 304 at 10 °C, the driving potential difference between them reached 366 mVSCE, and Al 6061 was used as the corrosion anode. In the SEM images, three kinds of galvanic corrosion phenomena can be seen obviously after coupling. When the temperature is between 10 °C and 30 °C, the corrosion pits are mainly composed of aluminum matrix coupled with second phase particles with positive or negative volt potential relative to it. When the temperature was between 40 °C and 50 °C, the corrosion pits showed mainly intergranular corrosion at the interface of different grains. At the same time, the increase in temperature led to the decrease in galvanic potential and the change in corrosion current. There was no simple linear relationship between galvanic current and temperature, but it satisfied a certain quantitative relationship, and the theoretical ratio was highly consistent with the actual ratio by the K–S test.

Keywords

• N2O4 propellant
• Galvanic corrosion
• Al 6061
• K–S test