Magnesium galvanic anodes are commonly used for cathodic protection of underground constructions (tanks, pipelines) and for protection of internal surfaces of tanks containing water (eg. water heaters, hot and cold water tanks, condensers, heat exchangers). Magnesium anodes have a very electronegative potential. For this reason, they are not used in sea water, because in an environment with such a low resistivity, they could excessively polarize the protected structure, which in turn could lead to hydrogen evolution and delamination of the protective coating. Due to the high self-corrosion of magnesium, galvanic anodes have an efficiency of only about 50%. This is an additional factor limiting their use in salt water, because the rate of dissolution of anodes working in this environment would be very high.
Magnesium anodes are made of alloys containing alloy additives, the purpose of which is to improve efficiency and actual current efficiency. The most widespread is the use of alloys of the MgAl6Zn3Mn grade, in which the main alloy additions are aluminum (ca. 6%), zinc (ca. 3%) and manganese (up to 1%).
Actual current efficiency of magnesium anodes is about 1100-1200 Ah/kg, which amounts to consumption of anode material in the amount of up to 8 kg/(A ∙ year).