Microsegregation Elimination and Nanoscale Dispersoid Control in Al-Cu-Li Alloy via Optimized Double-Step Homogenization
摘要
The distribution uniformity of alloying elements critically affects the workability and mechanical performance of Al-Cu-Li alloys. Homogenization treatment is an effective method to reduce elemental segregation. This work focuses on double-step homogenization with a fixed first step of 400 °C for 16 h and evaluates second-step temperatures of 470, 480, and 490 °C for 24 h. Compared with 470 and 480 °C, the 490 °C/24 h second step achieves more complete dissolution of Cu-Mg-rich constituents and lower residual interdendritic segregation while maintaining a uniform Al3Zr dispersoid population, thereby identifying 400 °C/16 h + 490 °C/24 h as the optimal schedule. Under the optimal DH schedule, the unstable Al2CuLi phase redissolves and fine Al3Zr dispersoids precipitate uniformly; at 490 °C, Cu-Mg-rich constituents dissolve within ~ 24 h, whereas Fe-rich intermetallics remain undissolved. The optimized double-step homogenization eliminates dendritic segregation, homogenizes solute distribution, and promotes uniform L12-structured Al3Zr formation. These changes enhance strength and ductility via dispersion strengthening and reduced stress concentration. Consequently, the ultimate tensile strength increases to 196.0 MPa from 113.7 MPa (as-cast) and 121.2 MPa (400 °C/16 h), while total elongation rises to 0.82% from 0.16 and 0.22% (i.e., + 72% UTS and + 413% ductility versus as-cast; + 62% UTS and + 273% versus 400 °C/16 h). These quantitative gains highlight the value of double-step homogenization for microstructural refinement and mechanical improvement, providing a strong basis for industrial processing of Al-Cu-Li alloys for advanced structural applications.