Abstract:The metallographic microscope, scanning electron microscope, energy dispersive spectrometer, scanning Kelvin probe force microscope were used to observe and characterize the secondary phases of 7A52 aluminum alloy, and the volta potential of micron dimension secondary phases was tested. The results indicate that the h phase in long strip shape is incoherent with the matrix, whose strengthening effect is relatively weak. The η' phase in disk shape semi coherent with the matrix is the most important ageing strengthening phase. The Al₆Mn precipitates in approximate square block shape distribute in the grains and grain boundaries. The Al₃Zr precipitates in ball shape are very small and their density is very high, forming a strong pinning effect on the dislocations. The irregularly shaped intermetallics AlMnFe and Mg₂Si disperse along the rolling direction in the matrix, and their volta potentials are lower than those of the matrix. Hereby, they are easy to be dissolved and corroded in erosive environments, thus becoming the stress corrosion cracking initiation sites. The same second phase with different sizes show different relative volta potentials to the matrix. The volta potential of AlMnFe is lower than that of Mg₂Si intermetallics, which means that AlMnFe intermetallics are easier to be corroded in erosive environments. These measurement results will help in the crack initiation analysis in stress corrosion cracking.

Key words: 7A52 aluminum alloy; second phases; microstructure; volta potential