Breakdown of passivity of aluminium alloys by intermetallic phases in neutral chloride solution

Aluminium alloys are successfully used in several technological applications. Aluminium itself has weak mechanical properties, hence it is alloyed with other elements and thermally treated to improve and tailor its characteristics. These processes remarkably change the original structure of Al from a homogeneous solid solution to a complex polyphase structure. The growth of intermetallics in the Al matrix allows the hardening process to take place but a modification of the chemical resistance of the alloy can occur. In this paper the influence of intermetallics, formed in some binary and ternary alloys (Al–Cu, Al–Cu–Be, Al–Mg–Zn), on the passivity breakdown and corrosion properties of aluminium is investigated and discussed with the aid of electrochemical measurements (anodic polarisation, electrochemical impedance spectroscopy EIS) and surface analysis (SEM, TEM, AES).