Transmission Electron Microscopic Investigations of Grain Boundary Beta Phase Precipitation in Al 5083 Aged at 373 K (100 °C)

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 44; no. 3; pp. 1279 - 1289
• Main Authors: Goswami, Ramasis, Holtz, Ronald L.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Boston Springer US 01.03.2013; Springer; Springer Nature B.V
• Subjects: Aluminum alloys; Applied sciences; Characterization and Evaluation of Materials; Chemistry and Materials Science; Exact sciences and technology; Grain boundaries; Materials Science; Metallic Materials; Metallurgy; Metals. Metallurgy; Microstructure; Nanotechnology; Structural Materials; Surfaces and Interfaces; Symposium: Environmental Damage in Structural Materials under Static/Dynamic Loads at Ambient Temperature; Thin Films; Transmission electron microscopy; Dislocation Cell Structure; Bulk Diffusion; Intergranular Corrosion; HAADF Image; Transmission Electron Microscopy Observation; Beta phase; Grain boundary precipitation; Microstructure; Grain boundary
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-012-1166-9

The fine-scale microstructure of an Al 5083 alloy sensitized at 373 K (100 °C) for 3, 7, 14, 30, 45, and 90 days has been investigated using transmission electron microscopy (TEM) to study the evolution of the β phase (Al 3 Mg 2 ) at grain boundaries. In fully sensitized Al 5083, the β phase (Al 3 Mg 2 ) mostly forms heterogeneously at grain boundaries. TEM observations showed that the grain boundary precipitation of β phase was discrete up to 14 days of aging, and grain boundaries were fully covered by the β phase after 30 to 45 days of aging. The early stages of β growth on the grain boundaries are consistent with the collector-plate mechanism. We find no evidence of either Mg depletion or segregation at the grain boundaries. The initial growth rates as well as the thicknesses after long aging times are greater than can be accounted for by bulk diffusion of Mg to the grain boundaries. We suggest that dislocation pipe diffusion is necessary to account for the β growth rates.