The Role of Mn in the Corrosion Behavior of Al-Mn Alloys

The role of manganese in the corrosion behavior of commercial Al-Mn alloys has been examined by means of corrosion tests and metallographic techniques. Alloys containing 0.4-1.2% Mn, 0.4-0.8% Fe, 0.15% Si and some with small amounts of magnesium have been fabricated and evaluated. Results have shown that corrosion resistance increases with an increase in the Mn/Fe ratio in the alloy, but remains unaffected by the magnesium addition. The beneficial role of manganese is interpreted as reducing the difference in potential between the matrix and the intermetallics because of the supersaturation of manganese in the aluminum matrix and the manganese enrichment of the intermetallics. This reduction in the potential difference between the matrix and the intermetallics decreases the extent of overall corrosion.