Mechanism and Analysis of Orange Peel Formation on Bent Thin-Walled Copper Tubes

Thin-walled pure copper tubes, extensively used in high-heat-flux electronic devices due to their excellent thermal conductivity, often develop orange peel defects during bending processes. This study compares tube samples with and without orange peel defects by analyzing their macro-surface morphology and microstructural evolution before and after bending. The crystal plasticity finite element model (CPFEM) was developed to explore the correlation between crystallographic orientation and surface defects. Finally, a multi-scale model of the tube bending process was developed by integrating the macroscopic finite element method (FEM) with the visco-plastic self-consistent (VPSC) approach to simulate and analyze the formation of orange peel defects on the outer wall of the tube at the bending site. The results indicate that high-temperature sintering causes significant grain coarsening and pronounced recrystallization textures in the matrix. Samples exhibiting orange peel defects contain banded annealing twins with textures distinct from the matrix, characterized by low Schmid factors and poor plastic deformation compatibility. CPFEM simulations demonstrate that during uniaxial stretching, "soft-oriented" matrix grains experience negative displacement along the surface normal, forming depressions, whereas "hard-oriented" grains undergo positive displacement, generating protrusions. This mismatch in localized deformation results in the formation of the macroscopic orange peel morphology. Simultaneously, the VPSC simulation results reveal that the number of activated slip variants differs between tubes with and without orange peel defects. Tubes with defects exhibit fewer activated slip variants and experience greater resistance to deformation.