Effect of molten pool flow on microstructure in 2195 Al-Li alloy joint fabricated by heterogeneous-wavelength hybrid laser welding

The heterogeneous-wavelength hybrid laser welding (HW-HLW) technology effectively integrates the advantages of different laser beams as independent welding heat sources. This hybrid laser source exhibits considerable potential for application in laser processing, particularly in the joining of metals that are inherently challenging to weld. In this paper, The HW-HLW experiment was carried out for 2195 Al-Li alloy. The microstructure distribution characteristics of welded joints under different laser heat sources were investigated. The thermal-flow coupling model during welding was established to elucidate the effect of molten pool flow behavior on the microstructure. The results indicated that, in comparison to the single fiber laser welding, the ability of cold mixed liquid containing crystal nuclei to enter the molten pool was increased under the improving molten flow behavior during HW-HLW. Consequently, a larger EQZ region is formed in the waist region of the weld, as well as the grain size of EQZ is significantly increased. Besides, the growth direction of columnar dendrites is roughly perpendicular to the EQZ boundary.