Correlation of Electrochemical, ASTM Test and Metallographic Annalyses in the Corrosion Behavior of 5XXX Aluminum Alloys

Aluminum 5000 series (5xxx) alloys are commonly used for ship structures. The alloys with > 3% Mg have problems with sensitization, collection of the b-phase (Mg₂Al₃) at grain boundaries when exposed to elevated temperatures. The corrosion mode of many sensitized alloys is exfoliation, while non-sensitized alloys tend to pit. This study was conducted to find correlation of corrosion mode to electrochemical cyclic polarization data by comparison with ASTM G66 and ASTM G67 accelerated tests data.
Electrochemical and ASTM G66, G67 results are correlated with the metallographic analyses to assess b-phase presence and impact on corrosion mode and extent and to develop a quantitative expression for the degree of sensitization (DOS).  Welded material presents greatest challenge to this endeavor as chemical composition varies across the fusion region and the base metal temper is disrupted in the heat affected zone.