Regulating the microstructure and mechanical properties of Al-Cu-Li alloys via optimizing Cu/Li ratio and homogenization

The effect of homogenization process on the microstructure evolution and mechanical properties of Al-Cu-Li alloys with various Cu/Li ratios (ranging from 2.4 to 3.7) are studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and synchrotron radiation X-ray computed tomography (SR-CT) analysis. The results show that with the increase in the Cu/Li ratio, the volume fraction of the secondary phase (fv) f v ) in the as-cast alloys gradually increases, and the morphology of the secondary phases transforms from spherical-like to chain-like. For the single-step homogenization (SSH), the fv v decreases with increasing homogenization temperature and time. The 510 degrees C /24 h is identified as the optimal SSH regime due to the alloys exhibiting a lower fv v and a shorter SSH time than other SSH regimes. Interestingly, the alloys processed by double-step homogenization (DSH) exhibit a lower fv v compared with the SSH process. The residual secondary phases consist of a small number of regular block-Al2Cu, 2 Cu, dispersed Al20Cu2Mn3 20 Cu 2 Mn 3 phase and spherical-like Zr-rich phase after SSH and DSH. Furthermore, according to the results of diffusion kinetics analysis, the secondary phases can be dissolved completely into the matrix after homogenization treatment at 510 degrees C for 22.9 h. Therefore, the 450 degrees C / 12 h+510 degrees C / 24 h (DSH-24) is determined as the optimal homogenization regime. After DSH, a large number of spherical-like GP-Li and Al3Li 3 Li nanoparticles are precipitated during natural aging. The critical resolved shear stress calculation model suggests that the Al-4.1Cu-1.3Li alloy with a Cu/Li ratio as 3.2 possess high yield strength. The Al-4.1Cu-1.3Li alloy processed by DSH-24 exhibits excellent mechanical properties, with yield strength of 299 MPa, ultimate tensile strength of 449 MPa, and elongation of 18.8 %. This study provides a foundation for the development of high-performance Al-Li alloys.