Effects of heat input on microstructures and mechanical properties of LAZ931 magnesium-lithium alloy in High-Speed TIG welding

• Published in: Materials letters Vol. 378; p. 137483
• Main Authors: Jin, Jiangshan, Li, Yuntao, Zhao, Xianwei, Huang, Yiming, Yue, Chenyang, Yang, Lijun
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2025
• Subjects: Heat input; High-Speed TIG Welding; LAZ931 magnesium-lithium alloy; Mechanical properties; Precipitate phase; Heat input; Mechanical properties; LAZ931 magnesium-lithium alloy; High-Speed TIG Welding; Precipitate phase
• ISSN: 0167-577X
• DOI: 10.1016/j.matlet.2024.137483

[Display omitted] •Obtain the first TIG welded joints of LAZ931 magnesium-lithium alloy.•High-speed TIG welding of Mg-Li alloys achieved joints with very narrow melt widths and exceptional performance.•Investigate the effect of varying heat input on the microstructure.•Establish a connection between the mechanical properties of welded joints and their microstructure. LAZ931 magnesium-lithium (Mg-Li) alloy is a novel ultra-light alloy material. This research investigates the Tungsten Inert Gas (TIG) welding process of a 2.15 mm thick LAZ931 magnesium-lithium alloy thin plate without wire filling. The objectives are to determine the appropriate heat input range, achieve welded joints with good forming quality, and examine the effect of heat input on the microstructure and mechanical properties of the welded joints. The results show that post-TIG welding at high welding speed, the melt width of the entire welded joints is very narrow only about 9 mm, and a small amount of MgLiAl2 (θ) phase and AlLi (γ) phase precipitate in the weld seam zone(WSZ), while a significant amount of θ phase precipitates in the heat-affected zone (HAZ), making the HAZ the highest in strength due to precipitation strengthening. With increasing heat input, the quantity of θ phase decreases, resulting in reduced strength and hardness but increased plasticity in the HAZ. The highest hardness in the HAZ was measured at 87.6 HV, with the base material (BM) exhibiting the lowest hardness. The tensile strength of the joint reaches 163.2 MPa, with an elongation of 23.9 %, and the fracture mode is a mixed ductile–brittle fracture.