Weld appearance and microstructure of Invar alloys hybrid multi-layer welded joints using laser-MIG

Invar alloy plates with thickness of 19.05 mm were welded with Invar M93 filler wire by laser-MIG hybrid welding. The effects of welding parameters on weld appearance including beam penetration, weld witch and depth-to-witch ratio were analyzed. The features and the forming mechanism of the microstructure on different regions of the weld were investigated. The results show that the weld depth-to-witch ratio gradually decreases from 2.6 to 0.86 in average and the witch of HAZ obviously increases from back weld to cover weld, leading to the weld appearance changing from nail-head shape to goblet shape. Narrow Austentic columnar dendrite crystals in longitudinal direction and oblique diagonal cellular dendrite crystal are formed in weld center and off-centered area, respectively. The grain size in different regions of the weld increases layer-by-layer. In addition, HAZ is also found at the boundary of adjacent weld layers, where appears epitaxial solidification. © 2016, Central South University of Technology. All right reserved.