Grain refinement and mechanical properties improvement of Al-Cu-Li Alloy cylindrical shell through multi-step pre-recovery annealing

Abstract

Grain refinement is a critical approach for enhancing the properties of Al-Li alloy components. However, deformed grains frequently undergo abnormal growth during solid solution treatment due to recrystallization. This study systematically evaluates the effects of pre-recovery (PR) treatments—including single-step PR (SSPR), and multi-step PR (MSPR) on the microstructure and mechanical properties of Al-Cu-Li alloy cylindrical shells. Compared to SSPR, MSPR significantly improves fine grain retention by facilitating dislocation annihilation and rearrangement during static recrystallization. The pre-recovery-E (PR-E) treatment, specifically designed to optimize energy release, effectively reduces stored energy in most grains. This leads to suppressed grain growth during recrystallization (average grain size ~ 28.4 μm) due to diminished driving forces. In addition, grains oriented <001>∥ND and their grain boundaries with a 30°<111> orientation exhibit high migration mobility during solid solution treatment because the stored energy gradient distribution facilitates the grain growth. However, after the MSPR treatment, the growth of these grains was effectively inhibited. Meanwhile, the higher T₁ phase density endows it with excellent performance. Consequently, ultimate tensile strength and yield strength increase by 24 MPa and 32 MPa, respectively. This study provides valuable insights into improving the extreme mechanical properties of Al-Cu-Li alloy components.