Galvanic dissolution behavior of magnesium-1 mass%manganese-0.5 mass% calcium alloy anode for cathodic protection in fresh water

Abstract

Magnesium-1 mass%manganese-0.5 mass%calcium (Mg-1 mass%Mn-0.5 mass%Ca) alloy was used as sacrificial anode. This work was performed to investigate the galvanic dissolution behavior of the alloy anode for cathodic protection in fresh water. The microstructure and dissolved surface of the alloy anode were analyzed with an electron probe micro analyzer, a scanning electron microscope with energy dispersive X-ray spectrometer and a microscope. The current efficiency of the anode has been measured by laboratory test method of galvanic anodes for cathodic protection. It was found that calcium is present uniformly at the grain boundaries as Mg2Ca or Mg-Ca-Si compounds. Calcium compounds dissolve preferentially compared to the matrix of magnesium, as a result the anode uniformly dissolve compared to Mg-1 mass%Mn alloy anode. The current efficiency of the anode for the dissolution was higher than that of Mg-1 mass%Mn anode. On the other hand, manganese is added in order to decrease the local cathode to magnesium alloys, however the part of manganese compounds act as the local cathode in the alloys.