《Al-Cu-Sn》.pdf

The Effect of Trace Additions of Sn on Precipitation in Al-Cu Alloys: An Atom Probe Field Ion Microscopy Study S.P. RINGER, K. HONO, and T. SAKURAI We have studied the early stages of 0 precipitation in an A1-Cu-Sn alloy by atom probe field ion microscopy (APFIM) and transmission electron microscopy (TEM). Clusters of Sn atoms were ob- served in as-quenched samples, and their formation clearly precedes the formation of the 0 phase. Transmission electron microscopy also revealed that elevated temperature aging leads to the for- mation of spherical particles. Atom probe analysis and microbeam electron diffraction suggested that these particles were /3-Sn (I4Jamd, a = 0.583 nrn, and c = 0.318 nm). The TEM observations showed that 0 nucleated heterogeneously on these particles. We have also examined the O/a interface following further precipitate growth to check for possible Sn segregation. Atom probe analysis of both the broad face and the narrow rim of the platelike 0 precipitates has shown no evidence of Sn segregation at ff/a interfaces. It was also found that cold work prior to aging inhibits the formation of Sn particles resulting in a lower number of these types of nucleation sites for the 0 phase. Atom probe analysis has also revealed solute depletion at grain boundaries during the early stages of aging in the A1-Cu-Sn alloy, and this, in conjunction with vacancy depletion, explains the formation of