Three ladder Mg-Mn sacrificial anodes with different chemical compositions were poured by permanent mold.The corrosion behavior was investigated by galvanostatic corrosion test in saturated calcium sulfate-magnesium hydroxide solution.The results indicate that:the impurity elements are severe due to the solute segregation

and the grain sizes distributed heterogeneously result in the un-evern current efficiency at different distance to the surface of the metal mold.The impurity elements are formed into the intermetallic phases locally distributed at the grain boundaries

resulting in the intergranular corrosion of magnesium sacrificial anode.Furthermore

with the increase of heterogeneous degree of secondary phase size

the mechanical spalling at un-corrosion position is promoted

resulting in the increase of weight loss of the anode and decreasing the electric current efficiency.The corrosion morphology observation reveals that the more localized strip-shaped etch pits are formed on the surface of the magnesium anode with more serious mechanically spalling and heterogeneous corrosion

resulting in the lowest current efficiency of 41%.With the decrease of diameter of corrosion hole on surface of magnesium anode and the increase of distribution uniformity

the current efficiency is improved increasingly.