Microstructure and Mechanical Properties of Sc/Zr Modified 1460 Al-Li Alloy Fabricated by Laser Powder Bed Fusion

Abstract

The preparation of Al-Li alloy by laser powder bed fusion (LPBF) technology, especially Al-Li alloy with high Li content, is of great significance for lightweight of aerospace equipment. However, the significant susceptibility of Al-Li alloys to hot cracking during the process limits their advancement. This study starts from the two aspects of process control and composition modification, to achieve the production of crack-free and high-quality 1460 Al-Li alloys. Crack-free 1460 specimens can only be prepared at extremely low scanning velocity. The process window is markedly expanded by Sc/Zr modification. The heterogeneous nucleation of Al3(Li,Sc,Zr) results in significant grain refinement and effectively suppresses crack initiation and propagation. The unique bimodal heterogeneous microstructure endows the alloy with notable mechanical properties. After the addition of 0.6Sc-0.3Zr, the ultimate tensile strength (UTS), yield strength (YS), and elongation (δ) of 1460 alloy are increased by 104%, 158%, and 43.9%, respectively. The strength-plasticity synergism is primarily attributed to grain refinement strengthening, precipitation strengthening, and hetero-deformation induced strain hardening resulting from its unique bimodal heterogeneous microstructure. The UTS and YS of 1.2Sc-0.6Zr modified 1460 alloy increased by 156% and 279%, respectively. However, this further increase in the Sc/Zr content significantly deteriorates the plasticity of the alloy. This work establishes a foundation for advancing the use of Al-Li alloys in high-performance, lightweight, and complex aerospace structures.

Keywords: Laser powder bed fusion, Al-Li alloy, Microstructure, Crack, Mechanical property