• Dendritic thermomechanical deformation-induced dendrite bending is not random but concentrates on the casting surface, providing a new understanding of solidification defects.
• Thermal stress in dendrites increases with growth and accumulates after dendrite bridging, with axial contraction exceeding transverse contraction.
• High-stress regions in primary dendrite trunks are located below dendrite bridging near the solidified part, with maximum transverse stress on the casting surface.
• Surface stress concentration is attributed to transverse temperature gradients from lateral mold wall heat dissipation and inconsistent mold constraints, guiding process optimization.