De-alloying corrosion in the heat-affected zone in Mn-Al bronze weld

This study reports on de-alloying corrosion in a heat-affected zone (HAZ) of marine propeller Mn-Al bronze. The HAZ consisted of α, β∗ phases and a 2-5 μm thick α/β∗ interface layer. The β∗ phase having high aluminium content was expected to corrode first, it found that the de-alloying initiated from the α/β∗ interface layer. TEM diffraction patterns and images showed Cu3Mn2Al and orthorhombic L-J precipitates in Cu2MnAl matrix plus numerous dislocations and strain fields, which caused the layer to be corroded first. This study suggests that microstructure is a critical factor for corrosion more than the highly reactive aluminium content.