The deformation process and the underlying deformation mechanisms both at the external surface and in the internal area of AA6061-T6 under compression were investigated using digital image correlation, electron backscatter diffraction (EBSD), and transmission electron microscopy. The results reveal an inhomogeneous distribution of macroscopic strain across the specimen surface. Moreover, EBSD observations indicate that the external area of specimen experiences significantly different loading conditions compared to the internal area. Additionally, the grains of external area predominantly oriented along \(\left\langle {110} \right\rangle\) ||RD, \(\left\langle {001} \right\rangle\) ||RD, and \(\left\langle {111} \right\rangle\) ||RD. The grains of internal area exhibit oriented along \(\left\langle {110} \right\rangle\) ||RD, \(\left\langle {001} \right\rangle\) ||RD, and \(\left\langle {011} \right\rangle\) ||TD. Furthermore, the subgrain, dislocation walls, dislocation pile-up, dislocation cells and precipitated phases can be observed for the grains at internal area of compressed specimen. Such superior plastic deformation capability of specimen stems from these underlying mechanisms, which arise primarily from friction-induced disparities in stress states between the external and internal regions of the specimen. Numerical simulations confirm that both the friction coefficient and the deformation level jointly govern the stress distribution. Specifically, the internal area experiences a confined, quasi-hydrostatic stress state, whereas the external area approaches a condition closer to ideal uniaxial compression for the free surfaces.
