Improved Multi-Directional Forging Process and Its Effect on Microstructure and Three-Directional Mechanical Properties of 2195 Al-Li Alloy

Abstract

Reticular crystal phases and abnormally coarse grains are key problems that restrict the improvement of the mechanical properties and uniformity of Al-Li alloys. The effects of the multidirectional forging (MDF) process on the microstructure at the edge and center and the three-directional mechanical properties of the 2195 Al-Li alloy were investigated. The results show that the strong deformation resistance produced by one heat forging at 400 ℃ with seven upsetting and six stretching (400-7U6S-1) fully broke the reticular crystal phases at the grain boundaries and obtained the dispersed phase structure. The high density of dislocations accumulated by strong deformation promoted the dissolution of the dispersed secondary phases, and the area fraction of the secondary phase particles at the edge and center decreased from 3.88% and 1.97–0.75% and 0.61%, respectively, which prevented the occurrence of intergranular fractures and dramatically improved the ductility. Meanwhile, the dissolution of the second phases enhanced the precipitation force of the T1 phases and inhibited the precipitation of δ’ phases. Furthermore, the higher density of dislocations significantly increased the nucleation rate of dynamic recrystallization and eliminated the abnormally coarse grains, and thus acquired a uniform ultra-fined grain structure and the average grain diameter was reduced from 159 μm to 17 μm. The tensile strength, yield strength and elongation in the width direction increased to 592 MPa, 545 MPa and 8.0%, respectively, and increased by 7.2%, 7.2% and 90.5%, respectively. In particular, the maximum difference in the elongation of the forgings in the width direction decreased from 83.3 to 11.1%.

Graphical Abstract