Achieving high strength and good laser welding performance by adding Sc to T8-aged Al-Cu-Li alloys with different Cu/Li ratios

Abstract

In this work, the effects of Sc addition and variations in the Cu/Li ratio on the microstructure, precipitation behavior, laser welding performance, and mechanical properties of Al-Cu-Li alloys were systematically investigated. The results show that the addition of Sc refines as-cast grains, transforming coarse columnar grains into fine equiaxed grains. In high Cu/Li ratio alloys, the addition of Sc leads to the formation of the W (AlCuSc) phase. Reducing the Cu/Li ratio alters the solidification sequence, favoring early precipitation of the Al₂CuLi phase and inhibiting W phase formation. The addition of the Sc significantly increases the elongation, while the introduced W phase does not cause a significant decrease in the strength of the T8-aged alloy. A lower Cu/Li ratio reduces the T₁ phase volume fraction, but the high density of δ′/GPI/δ′ composite phases compensates for the strength loss from T₁ phase. The addition of the Sc element significantly refines the grain size of the welded joints and suppresses solidification and liquation cracks. Simultaneously, a large number of Al₃(Sc, Zr) particles precipitate in the HAZ, enhancing the strength of the joints and reducing softening in this zone. The medium Cu/Li ratio alloy exhibits excellent overall mechanical properties and welding performance.