Micro-Electrochemical I n Situ Observation of Pit Initiation at Precipitates in AA5182 Al-Mg Alloy in 0.1 M NaCl

Abstract

Pit initiation at intermetallic particles in an Al-Mn alloy (AA5182-O) was investigated. Al-Fe-Mn, Al-Fe-Mn-Si, and Mg2Si intermetallic particles were detected in this alloy. In situ observation of a small electrode area was performed during potentiodynamic anodic polarization in naturally aerated 0.1 M NaCl at 298 K. For the Al-Fe-Mn particle, a trench was generated around the particle, and the trench increased as the electrode potential increased. However, no increase in size was observed at higher potentials. Then, a pit was initiated inside the trench. The same behavior was observed for the Al-Fe-Mn-Si particle. However, the trench growth stopped at a relatively low potential, and no pit was generated in the trench. There was no trench generated around Mg2Si. It appears that Si in the particles suppresses the trench formation and growth, which improves the pitting corrosion resistance of aluminum alloys.