• A novel technology is employed, which enables in-situ evaluation of solidification cracking susceptibility. • Distinct cracking modes associated with the welding velocity were elucidated. • Special inter-dendritic cracking inside single grain is observed at low velocity under high constraint. • Increased susceptibility at high velocities arises from extended mushy zones and elevated strain rates. • Solidification cracking modes are strongly governed by solidification morphology. Solidification cracking originates from strain accumulation in residual liquid films within the mushy zone. However, the influence of welding velocity on complex cracking phenomena remains insufficiently clarified. In this study, a novel system is employed, enabling in-situ characterization of solidification dynamics, cracking behavior, and temperature evolution. Distinct cracking modes associated with the welding velocity and their underlying mechanisms were elucidated. Increasing the welding velocity enhances cracking susceptibility while modifying the solidification dynamics and morphology, which in turn affect the residual liquid and strain distribution. At a low welding velocity of 1.67 mm/s under high constraint, solidification cracking manifests as interdendritic separation inside one grain, contrary to the widely reported behavior that it occurs along grain boundaries. This mode exhibits higher resistance than smooth intergranular separation. At higher welding velocities, the molten pool elongates and grains impinge at the weld center. The resulting increase in cracking susceptibility arises from the longer mushy zone and higher strain rate, rather than from reduction in the high-temperature ductility curve. Supplementary investigation confirms that cracking modes are strongly governed by solidification morphology. These findings advance the understanding of solidification cracking behavior and mechanisms, offering guidance for accurate modeling and the refinement of cracking theory.
Yang et al. (Sun,) studied this question.