Dynamic Precipitation Behavior Of 2297 Al-Li Alloy During Multi-axial Compression

2297 alloy has received great attention in the aerospace field due to its low density and high specific strength.Multi-axial compression（MAC）is an efficient method which can produce ultrafine grained microstructures with high dislocation densities,and significantly enhance the material properties.The influence of MAC on the second phases in alloys is very complex.In-depth study of the evolution behavior of the precipitates in aging-strengthened alloy during deformation is very important to control the alloy structure and optimize the material properties.In this paper,2297 alloy was used as the research object,the ultra-fine grain structure was obtained by the multi-axial compression.The microstructure evolution of 2297 alloy in the process of MAC deformation was systematically studied,and the effect of subsequent heat treatment on the precipitation behavior and mechanical properties of MAC-ed alloy was discussed.The precipitates was characterized by transmission electron microscope（TEM）.And the mechanical properties were investigated by hardness test and room temperature tensile test.The main research conclusions are as follows:（1）The strong deformation of MAC introduced a large number of defects such as dislocations and subgrain boundaries,which significantly increases the precipitation rate of the second phase of 2297 alloy.The precipitation behavior of the strengthening phase is affected by both stress and temperature.The precipitation of theθ’phase was significantly suppressed during the strong deformation process.At 120°C,the matrix first precipitated theδ’/β’phase,and then the T₁ phase precipitated;while at 160°C and 200°C,the T₁ phase first precipitated from the matrix,and then theδ′/β′phase precipitated.（2）In the process of multi-axial compression at 160℃and 200℃,the T₁ precipitates in the matrix was kinked and broken by strong shearing action,and the obtained T₁ precipitates is smaller in size,about 20～40nm.While theδ′/β′precipitates was relatively stable.（3）The strong deformation of MAC combined with aging treatment resulted in a high-strength and high-plastic Al-Li alloy with ultrafine grain structure.The 2297 alloy suffuered 6 passes of MAC processing at 200°C,and then aged at 120°C for 40 h.The yield strength of the alloy can reach518 MPa,and the elongation was about 10%.