Effect of Second Phase on the Pitting Corrosion of ZL101A Aluminum Alloy in Thin Electrolyte Layer Environment Containing Cl

The pitting corrosion of ZL101A aluminum alloy in the thin electrolyte layer containing Cl⁻ was studied through the salt spray test. The pitting corrosion behavior was mainly characterized by scanning electron microscopy, electrochemical measurements and in-situ scanning Kelvin probe force microscopy. The results indicated that the second phases in ZL101A aluminum alloy had significant effects on the pitting corrosion behavior. The Al–Si phase acted as an anode phase induced the initiation of corrosion pits, which leaded to the decrease of polarization resistance (R) and the propagation of corrosion pits along the depth direction. Act as cathodic phase, Mg–Si–Fe phase and Si-rich/Al-poor phase have an 800 mV and 660 mV lower Volta potential than the matrix, respectively. The Volta potential difference between Mg–Si–Fe phase and matrix decreased more significantly than that between Si-rich/Al-poor phase and matrix which remained intact with the duration of corrosion. This verified the higher electrochemical stability of Si-rich/Al-poor phase than Mg–Si–Fe phase, which should be related to the presence of Mg and Fe in Mg–Si–Fe phase.