Promoting single-step shearing to improve the strength-ductility synergy in an Al-Cu-Li alloy

Abstract

This study investigates the correlation between strength-ductility synergy and precipitate-dislocation interactions during tensile deformation in a peak-aged Al-Cu-Li alloy, with and without pre-deformation. The solution-treated and peak-aged (ST-PA, T6 temper) specimen exhibits a yield strength of 554 MPa but limited ductility (3.1 % elongation to failure). Pre-deformation (2–8 %) doubles elongation while modestly enhancing strength. Although pre-deformation negligibly alters grain structure, it narrows precipitate-free zones (PFZs). Microstructural analysis reveals that plate-like T₁ precipitates with high aspect ratios dominate strengthening. Pre-deformation effectively refines these precipitates, reducing the proportion of multilayer T₁ precipitates (2–3 unit-cell thickness) from 46 % to < 20 %. During tensile straining, multilayer T₁ precipitates undergo either large-displacement shearing or rotation by bypassing dislocations, inducing matrix distortion and significant local dislocation accumulation. In contrast, monolayer T₁ precipitates with a thickness of one unit-cell facilitate single-step shearing with a displacement of only one atomic layer, promoting uniform dislocation slip and suppressing Orowan loop formation. Additional shearing of δ′/θ′/δ′ precipitates in pre-deformed alloys further mitigates local stress concentration. These findings provide mechanistic insights for enhancing uniform deformation capacity and offer guidelines for optimizing precipitation to achieve optimized strength-ductility balance in Al-Cu-Li alloys.