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The Al-Cu-Li-(Mg) alloy is a high-performance lightweight material strengthened by complex coexisting precipitates that form in the alloy upon thermal ageing.Using high-resolution(scanning) transmission electron microscopy in association with first-principles energy calculations,we systematically studied the complex coexisting precipitates in the alloys and correlated their precipitation sequences with thermal ageing processes applied.The principal results are the following:(1) eight types of precipitates can be observed in the alloy;(2) of these precipitates,the T_1-phase is most stable.The S-phase precipitates with segregated Li atoms at their interfacial edges are unexpectedly more stable than the σ-phase;(3) the T1-phase has a characteristic precursor that plays the key role in its nucleation and growth.
The Al-Cu-Li- (Mg) alloy is a high-performance lightweight material was strengthened by complex coexisting precipitates that form in the alloy upon thermal aging. Using High-resolution (scanning) transmission electron microscopy in association with first-principles energy calculations , we systematically studied the complex coexisting precipitates in the alloys and correlated their precipitation sequences with thermal aging processes applied.The principal results are the following: (1) eight types of precipitates can be observed in the alloy; (2) of these precipitates, the T_1-phase is most stable. The S-phase precipitates with segregated Li atoms at their interfacial edges are unexpectedly more stable than the σ-phase; (3) the T1-phase has a characteristic precursor that plays the key role in its nucleation and growth.