Study of β precipitation and layer structure formation in Al 5083: The role of dispersoids and grain boundaries

Abstract

Beta (β) phase precipitation and subsequent intergranular corrosion and cracking present some of the main concerns for the usage of Al 5xxx series alloys. In this manuscript, β phase precipitation and changes in grain boundary interfacial structures are presented for Al 5083 samples sensitized at 100 °C for 6 months. It was observed that β phase precipitates are formed on/near different type of dispersoids and at high angle grain boundaries. Some precipitates formed directly on the surface of Al6Mn dispersoids, while some precipitates were detected near Al6(Mn,Fe) dispersoids and were connected to the β phase precipitate by dislocation bands. This may suggest that dislocation bands existing between the dispersoid and β phase precipitates can act as fast paths for atom diffusion and assist the growth of the β phase. The precipitation of β phase on/near preexisting dispersoids or at boundaries is ascribed to the decrease in nucleation energy needed for heterogeneous nucleation. After sensitization, layer structures containing a high density of dislocations and distortion regions were found at the grain boundaries. The thickness of the grain boundary layer increases at grain boundaries with higher misorientation angles.