Gaoyang Mi

Microstructure and mechanical properties of laser-welded joints of Ti-22Al-25Nb/Ti-6Al-4V dissimilar titanium alloys

Laser welding was applied to join 2-mm-thick dissimilar titanium alloys, Ti-22Al-25Nb (at. %) and Ti-6Al-4V (wt. %). Defect-free joints were obtained. The microstructures and mechanical properties of the welded joints were investigated. The results showed that the fusion zone mainly consisted of B2 phase and martensite α′ phase. The heat-affected zone microstructures of Ti-22Al-25Nb and Ti-6Al-4V were different because of the different base metal. The heat-affected zone of Ti-22Al-25Nb mainly consisted of B2 phase, O phase, and α2 phase, whereas the heat-affected zone of Ti-6Al-4V mainly consisted of α phase, β phase, and martensite α′ phase. EDS (Energy Dispersive Spectroscopy) results showed that the element distribution of each titanium alloy heat-affected zone and fusion zone was similar without an obvious change. Due to severe agitation, the element distribution was even. Different microstructures in different heat-affected zones resulted in an unsymmetrical hardness distribution. The hardness of fusion zone was the lowest of around 300 HV when the hardness of Ti-6Al-4V heat-affected zone near fusion zone was the highest of around 400 HV due to the influence of martensite α′ phase. In tensile tests performed at room temperature and 650 °C, the tensile strength of the joint reached 1057 and 363 MPa, respectively. Both these joints fractured at the fusion zone.Laser welding was applied to join 2-mm-thick dissimilar titanium alloys, Ti-22Al-25Nb (at. %) and Ti-6Al-4V (wt. %). Defect-free joints were obtained. The microstructures and mechanical properties of the welded joints were investigated. The results showed that the fusion zone mainly consisted of B2 phase and martensite α′ phase. The heat-affected zone microstructures of Ti-22Al-25Nb and Ti-6Al-4V were different because of the different base metal. The heat-affected zone of Ti-22Al-25Nb mainly consisted of B2 phase, O phase, and α2 phase, whereas the heat-affected zone of Ti-6Al-4V mainly consisted of α phase, β phase, and martensite α′ phase. EDS (Energy Dispersive Spectroscopy) results showed that the element distribution of each titanium alloy heat-affected zone and fusion zone was similar without an obvious change. Due to severe agitation, the element distribution was even. Different microstructures in different heat-affected zones resulted in an unsymmetrical hardness distribution. The hardness of fus...

Study of microstructure and mechanical properties of narrow-gap multi-layer hybrid laser-arc welded 316L austenitic stainless steel

Hybrid laser-arc welding is an emerging welding technology that has a promising prospect in large-scale equipment manufacturing. In this paper, the butt joint of 316L austenitic stainless steel with 40 mm was made by using the multi-layer hybrid laser-arc welding process. On this basis, microstructure and properties of the welded joint were further investigated using an optical microscope, scanning electron microscope, and other methodologies. The results showed that the base materials consist of massive polygonal austenitic with a small amount of ferrites distributed in the grain boundary. What is more, the 316L austenitic stainless steel was heated and solidified in an F-A mode. Thus, ferrites distributed in the grain boundary were coarsened in the heat affected zone and the fusion zone was also composed of massive austenite and ferrites, which were approximately perpendicular to the fusion line. Owing to the different thermal cycles of different layers, the microstructure of the upper layer was coarser than that of the lower layer, and this microstructural inhomogeneity led to the variation of the hardness within the welded joint: hardness value of the upper weld was slightly higher than that of the lower weld. In addition, all tensile specimens were failed at the fusion zone and showed an obvious characteristic of ductile fracture with massive dimples distributing on it. Consequently, this study will broaden the scope of the application for the thick-plate hybrid laser-arc welding technology.Hybrid laser-arc welding is an emerging welding technology that has a promising prospect in large-scale equipment manufacturing. In this paper, the butt joint of 316L austenitic stainless steel with 40 mm was made by using the multi-layer hybrid laser-arc welding process. On this basis, microstructure and properties of the welded joint were further investigated using an optical microscope, scanning electron microscope, and other methodologies. The results showed that the base materials consist of massive polygonal austenitic with a small amount of ferrites distributed in the grain boundary. What is more, the 316L austenitic stainless steel was heated and solidified in an F-A mode. Thus, ferrites distributed in the grain boundary were coarsened in the heat affected zone and the fusion zone was also composed of massive austenite and ferrites, which were approximately perpendicular to the fusion line. Owing to the different thermal cycles of different layers, the microstructure of the upper layer was coarser...

Simulation and Modeling of Shielding Gas on the Welding Defects in the Fiber Laser Keyhole Welding

In this paper, a numerical model is proposed to investigate the keyhole dynamic behaviors and the formation process of hump. Both of the welding processes with and without shielding gas are calculated during the simulation. It is revealed that the hump generated in the weld is caused by the metal flows in the rear part of the keyhole aperture driven by the resultant force of surface tension, recoil pressure and buoyance force. The shielding gas can significantly change the fluid flows in the molten pool and hence suppress the formation of the hump. The proposed method is validated by the confirmation experiments and good agreement between the simulated and experimental results have been found.