Role of secondary phase particles of 2519A aluminium alloy in localised corrosion

The localised corrosion due to the galvanic couples between the precipitated particles and matrix in a new aluminium alloy 2519A was investigated by scanning electronic microscopy, transmission electronic microscopy and scanning Kelvin probe force microscopy. Topography and Volta potential differences relative to the matrix in 3·5%NaCl solution were examined for two kinds of Al2Cu and Al7Cu2Fe particles. Almost the particles showed positive Volta potential difference relative to the matrix. A series of particles nobility was detected with Al7Cu2Fe being less noble than Al2Cu. The potential difference of Al2Cu particles from the matrix was 702 mV in average, while Al7Cu2Fe particles 526 mV. Both of the particles act as cathode and localised corrosion originated mainly from the periphery of coarse ones. The more obvious the particles, the more severe the corrosion pits are.