Date Added: Jul 2009
Aluminum alloys with magnesium content greater than three weight percent, such as the 5xxx alloy family, are susceptible to a process called sensitization when exposed to temperatures in excess of 150?F for extended periods of time. ?-phase precipitates, which are rich in magnesium, tend to migrate to the grain boundaries when enough thermal energy is available. As a continuous network of ?-phase precipitates at the grain boundaries is formed the material becomes sensitized. ?-phase precipitates are anodic to the aluminum-based matrix material; therefore sensitization can lead to increased susceptibility to stress corrosion cracking, intergranular corrosion, exfoliation, and reduced useable life. Several ships with aluminum deckhouse structures have exhibited sensitization and subsequent stress corrosion cracking on aluminum deck plates.