A critical review: Crystal structure, evolution and interaction mechanism with dislocations of nano precipitates in Al-Li alloys

[Display omitted] •Major nano precipitates and composite precipitates in Al-Li alloys, are surveyed from atomic structure, orientation relationship with matrix and evolution.•Precipitate-dislocation interaction mechanisms of different precipitates in Al-Li alloys are summarized, and the possible main strengthening mechanisms are discussed.•Issues that have hindered the development of nano precipitates in Al-Li alloys and corresponding research directions are proposed. Application aspects in aerospace have led to extensive explores and researches on the Al-Li alloys. Advance of alloy properties and balance of comprehensive performances depend largely on regulation of nano precipitates. However, introduction of further solute elements in Al-Li alloys leads to a greater complexity of precipitation behavior of nano second phase. A pivotal step in understanding the strengthening mechanism is to determine the crystal structure and the evolution pattern of nano precipitate. In this critical review, several major nano precipitates and precursors, as well as composite nano precipitates in Al-Li alloys, are surveyed from composition, atomic structure and orientation relationship with matrix. Nucleation mechanism and evolution process are then discussed. Based on a proper understanding of crystallography, great details are provided on precipitate-dislocation interactions by analyzing the interfacial structure between precipitate and matrix. Finally, the review offers a summary of advances in this field and some inspirations for future research directions.