Microsegregation-induced corrosion fatigue behavior of a cast Mn-Cu alloy in 3.5 wt% NaCl solution

초록

Manganese-copper (Mn-Cu) alloys are promising high-damping materials for marine and vibration-sensitive applications, where resistance to corrosion fatigue is critical for long-term reliability. However, their corrosion fatigue behavior under the combined action of chloride exposure and cyclic loading remains insufficiently understood, particularly in large-scale cast alloys containing pronounced compositional heterogeneity. Here, the corrosion fatigue behavior of a sand-cast Mn-Cu alloy was investigated in a 3.5 wt% NaCl solution by separately evaluating the effects of pre-corrosion damage and continuous chloride exposure during fatigue testing. High-cycle fatigue tests were conducted under three conditions: in air, in air after pre-corrosion, and in a 3.5 wt% NaCl solution after pre-corrosion. Pre-corrosion in 3.5 wt% NaCl solution led to selective corrosion of Mn-rich dendritic regions arising from casting-induced microsegregation. Subsequent fatigue testing revealed a stepwise reduction in fatigue resistance, with the highest resistance observed in air, followed by pre-corroded specimens tested in air and pre-corroded specimens tested in NaCl solution. This trend demonstrates the combined detrimental effects of corrosion damage and cyclic loading. Cross-sectional analysis further showed that fatigue cracks propagated predominantly along Cu-rich interdendritic channels in air, whereas continuous chloride exposure promoted transgranular crack propagation through the dendrite core regions. These observations indicate that selective Mn dissolution and cyclic loading act synergistically to accelerate crack initiation and modify crack propagation paths, resulting in decreased fatigue resistance. This study provides insight into the corrosion fatigue behavior of cast Mn-Cu alloys and highlights the critical role of casting-induced microsegregation in governing corrosion-assisted crack initiation and propagation. © 2026 The Authors.

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