Investigation of the size effect on flow stress and deformation mechanism in Cu-Zn thin sheets

Understanding and regulating flow stress is crucial for producing high-performance metal thin sheets. Uniaxial tensile tests on Cu-Zn thin sheet metal reveal that the grain size at the inflection point of the size effect on flow stress (SEFS) increases with higher Zn content. This study investigates the intrinsic mechanisms affecting the SEFS, with a focus on how Zn content, grain size, and free surface influence deformation mechanism transitions in face-centered cubic metal thin sheets. Increasing Zn content reduces stacking fault energy, promotes the transition from dislocation wavy slip to planar slip and deformation twinning, increases geometrically necessary dislocation density, and mitigates SEFS. The relationship between the critical stress and strain for the onset of planar slip and deformation twinning and the square root of the grain size deviates from linearity, highlighting the size effect on the deformation mechanisms transition in metal thin sheets. This study identifies the size effects on deformation mechanisms and elucidates their underlying mechanisms. It provides new insights into controlling SEFS in metal thin sheets and lays a foundation for the design of high-performance metal thin sheets.