CONCURRENT SIZE AND SHAPE COARSENING OF GAMMA' IN AL-AG

The coarsening of γ′ precipitates in aluminum-silver has been investigated. Thesplate-shaped precipitates have coherent broad faces, and a hexagonal close packed crystal structure and develop on ∝111∝ planes of the aluminum matrix. During growth, a dispersion of nonequilibrium shaped γ′ precipitates develops. To understand the subsequent size and shape coarsening of these γ′ precipitates, several microstructural parameters have been experimentally determined as a function of aging time through quantitative electron microscopy. The measured thickening rate and nterledge spacing confirm that precipitate thickening takes place by a ledge mechanism and that the overall coarsening process of these precipitates is related to the average interledge spacing which remains relatively constant throughout the coarsening stage. The change in precipitate diameter does not appear to obey any temporal law and most likely accomodates the precipitate thickening and local supersaturation. © 1990.