In the present study, the corrosion behavior of an as-cast magnesium alloy was studies focusing on the galvanic corrosion between a precipitate and Mg-rich matrix. Through immersion and electrochemical tests, the variation of the corrosion behavior with the alloy composition and alloy system was discussed in detail. The corrosion rate of an as-cast alloy increased abruptly to 9 wt.% A1 in both alloys, but in the composition range of over 12 wt.% A1, the corrosion rate reveals a different tendency than the alloy system. The [~-phase that is a typical precipitate in an Mg-xA1 alloy is a more potent cathodic phase than is the ternary precipitate in a Mg-xAl1Zn alloy. In the case of the Mg-xA1 alloy, the formation of a galvanic cell between the precipitate and matrix promotes the preferred dissolution of the matrix, but the precipitate in the Mg-xAl-lZn alloy has a minor effect on the corrosion behavior of the Mg-rich matrix. However, the corrosion rate of as-cast MgxA1 and Mg-xAl-lZn alloys which contain precipitate, depends mainly upon the corrosion behavior of the Mg-rich matrix, which is influenced by the A1 content. It depends additionally upon the variation of the Anode-Cathode Area Ratio (ACAR) and the chunk breakage of precipitate during corrosion.

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