Microstructures And Mechanical Properties Of Laser Beam Welded 2198 Aluminum Lithium Alloy

Lightweight, high performance, high reliability and low cost are the eternal theme about structural design and manufacturing of modern flight. Selecting advanced lightweight structural materials, and using the advanced processing technology are the main ways to realize lightweight design.Advanced aluminum-lithium(Al-Li) alloy, with lightweight and high strength, has a promising application prospect in aerospace due to their excellent properties of anti-fatigue crack growth and corrosion resistance. 2198 Al-Li alloy is a structural material of our large passenger aircraft and belongs to the third generation of Al-Cu-Li alloy. Laser beam welding is an advanced joining technology with many advantages, like highly centralized heat energy, small amount of heat input, high welding speed, small deformation and so on. Therefore, laser beam welding of 2198 Al-Li alloy has an important research significance and market prospects.Laser beam welding of 2198 Al-Li alloy, with filler wire, is the study subject. The influences of welding parameters on weld forming and hot crack susceptibility, the relationship between the microstructure and mechanical properties of welded joint, the influence of heat treatment on microstructure and mechanical properties of the welded joint were investigated. The research results as follows:The excellent and hot crack free welded joint was obtained by filling Al-Cu 2319 wire and optimizing welding parameters. The optimal welding parameters for laser power is 3 kW, welding speed is 3 m/min, and wire feeding rate is 2 m/min. Equiaxed dendrites are obtained in as welded weld, equiaxed fine grain zone(EQZ) is located at the edge of the weld, that EQZ is 40-50 ?m wide and its grain is 5-10 ?m in size. Precipitates, distributed in grain boundary, are small spherical theta’(Al2Cu) phase and some needle-like T1(Al2CuLi) phase. Tensile strength of the welded joint is 272 MPa and the microhardness is 72.9 HV0.1.The coarsening grain and boundary are obtained after PWHT. It indicates that the spherical theta’(Al2Cu) phase, needle-like T1(Al2Cu Li) phase and a small amount of short rod-like phase existes in weld zone. Meanwhile, a large number of non-continuous short rod-like precipitates are on grain boundary and the obvious precipitate free zone are around the grain boundary. The PWHT joint was fractured in weld zone. The tensile fracture demonstrates an intergranular and transgranular fracture. Tensile strength of PWHT joint is up to 393 MPa and microhardness improves to 130.1 HV0.1, meanwhile, the fluctuation range of microhardness is small; Therefore, the mechanical properties of welded joints improves obviously due to these precipitated phase in weld.