Distribution and evolution of aging precipitates in Al-Cu-Li alloy with high Li concentration
(1. School of Materials Science and Engineering, Central South University, Changsha 410083, China;
2. Key Laboratory of Nonferrous Materials Science and Engineering of Ministry of Education, Central South University, Changsha 410083, China;
3. Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Center, Central South University, Changsha 410083, China
4. Aerospace Research Institute of Materials and Processing Technology, Beijing 100076, China)
2. Key Laboratory of Nonferrous Materials Science and Engineering of Ministry of Education, Central South University, Changsha 410083, China;
3. Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Center, Central South University, Changsha 410083, China
4. Aerospace Research Institute of Materials and Processing Technology, Beijing 100076, China)
Abstract: The evolution and distribution of the aging precipitates in 1460 Al-Li alloy with high Li concentration (2.14%, mass fraction) during T6 aging and two-step T8 (4% predeformation) aging were investigated through TEM. The aging precipitates include d? (Al3Li) and T1 (Al2CuLi) phases, of which the d? phases are formed first in grain interiors. A lot of d?/GPI/d? composite precipitates in which GPI zones are flanked with a pair of d? phases, are formed at 145 °C of T6 aging, which are thermally stable. At 160 °C and 175 °C of T6 aging, many T1 phases nucleate first at subgrain boundaries and grain boundaries, and then form and grow within grains. As to the T8 aging, the d?/GPI/d? composite precipitates are formed during the first-step aging at 130 °C for 20 h, which are thermally stable during the second-step aging at 160 °C. The plastic predeformation accelerates T1 nucleation within grains during the second-step aging at 160 °C.
Key words: Al-Li alloy; precipitate; T6 aging; T8 aging; aging temperature