The effects of different vibration frequencies on the microstructure, residual stress, and fatigue life of welded joints are investigated using laser filler wire welding combined with mechanical vibration. The results show that the vibration frequency of 1055 Hz has a significant effect on the melting width of the laser welding with filler wire joint. The welds have three morphological features of columnar crystals, dendrites, and equiaxed crystals. In addition, the welds with 1055 Hz vibration frequency have the most equiaxed crystals and the highest hardness. The vibration frequency of 524 Hz increases the residual stress of the welded joint by 16%, whereas the vibration frequency of 1055 Hz reduces its residual stress by 8%. It can be shown by tensile experiments that the laser filler wire–welded joints have a higher tensile strength and greater elongation with increase in the vibration frequency. The fracture observation shows that the cleavage step appears in the crack propagation zone. Compared with the vibration frequency of 524 Hz, fatigue fracture at the 1055 Hz vibration has narrower fatigue striation spacing, lower crack growth rate, and higher fatigue life.
Inconel 718 alloy laser-welded joints have poor mechanical properties due to the presence of Laves phases and liquation cracks. This paper intends to solve the above problems by high-frequency micro-vibration-coupled bead-on-plate laser welding. According to the shape of the weld beam, the upper part of the weld is defined as the nail head, and the lower part is the nail body. The results showed that high-frequency micro-vibration can achieve grain refinement. The micro-vibration could break the primary dendrite arm to form secondary dendrite and reduce epitaxial growth of the cellular crystal region. Micro-vibration exacerbated the flow of Niobium (Nb) elements surrounded by dendrites and reduced dendritic segregation, which decreased the formation of Laves phases. The combination of interdendritic Nickel (Ni), Titanium (Ti), and Nb and the precipitation of strengthening phases γ′ and γ″ were promoted. When the vibration acceleration was 50.10 m/s2, it could inhibit the formation of Laves phases among dendrites and the size of the bulk Laves phase was effectively reduced. The cracks generated in the Inconel 718 alloy were distributed at three locations including the nail-head, the nail-body, and the junction of nail-head and nail-body. When the vibration frequency was 919 Hz, the length of the liquation crack reduced from 180 to 110 μm. While under 1331 Hz, the expansion of the liquation crack was extended, with the length of 200 μm.
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