Suppression of Samson phase formation in Al-Mg alloys by boron addition

Al-Mg alloys, particularly Al 5083 and Al 5456, are widely used for boat and ship structural applications because of their unique properties such as lightweight, high strength and good weldability. However, structural parts manufactured with these alloys fail catastrophically as a result of the formation of Al3Mg2, known as Samson phase, at grain boundaries. Here we demonstrate that the Samson phase formation is suppressed in Al 5083 by alloying with B, which traps most of Mg in solid solution as AlMgB2 phase. This decreases the supersaturation level of Mg in Al matrix, which is a driving force for the formation of Samson phase in Al 5083. We observe Cu-rich precipitates, instead of the Samson phase, at grain boundaries upon extended annealing at 150 °C. This is a significant finding as it provides new insight as to how to minimize the longstanding problem of sensitization.