Role of Al2Cu and Al3Fe in pit initiation of aluminum: insights from coarse single- and multi-particle electrodes

Abstract

Abstract Al specimens containing coarse Al 2 Cu or Al 3 Fe particles were fabricated by spark plasma sintering through mixing pure Al powder with Cu or Fe powder, followed by hot forging and heat treatment to form intermetallic particles with diameters primarily in the range of 50–100 μm. Corrosion behavior was investigated using two electrode types: a small electrode (25 × 25 μm) containing a single particle and a large electrode (5 × 5 mm) containing multiple particles. Pitting did not occur in the small electrodes, whereas it initiated in the large electrodes. The entire surface of the small electrodes was considered to become alkalized; therefore, the pitting potential increased, preventing pitting initiation. In the large electrodes, particles were sparsely dispersed, leaving regions unaffected by alkalization; therefore, pitting was considered to initiate in these regions. Pit initiation was governed by the presence of Al-matrix regions that remained non-alkalized and by the condition in which the corrosion potential exceeded the pitting potential. Even in the large electrodes, particle discoloration (dealloying) and trenching were absent in pH‑buffered NaCl solution, demonstrating that these phenomena required local alkalization on the particles. However, pitting occurred in the Al 3 Fe specimen under naturally aerated conditions, even though no trenching was observed, indicating that trenching was not a prerequisite for pitting. In alkaline solutions, Al 2 Cu and Al 3 Fe particles discolored through the formation of surface layers: Al 2 Cu formed a substantially thicker layer, whereas Al 3 Fe formed a thinner layer.

The authors' abstract, as published at the source. npj Materials Degradation, 2026 · DOI ↗