Plastic anisotropy of ultra-thin rolled phosphor bronze foils and its thickness strain evolution in micro-deep drawing

•Thickness strain distribution in micro-deep drawing of ultra-thin rolled foils are demonstrated (83).•Ultra-thin rolled foil elongates in 90° to RD more than 0° to RD (64).•Strong {111} texture due to high rolling reduction for thin foil makes r-value higher (85).•In spite of high r-value, thickness reduction of foil is more than thicker sheet (80).•Surface roughening is responsible for unstable deformation in micro deep drawing (80).

Metal foils are highly advantageous for producing microcomponents with high-aspect-ratio three-dimensional shapes by miniaturizing the process dimensions in sheet-metal-forming technologies. To characterize existing rolled metal foils at manufacturing sites and to clarify the impact of its strong anisotropic properties on micro-sheet formability, tensile tests and micro-deep drawing tests were performed on phosphor bronze foils with thicknesses of 20–300 μm. Focusing on the Lankford value (r-value) as a useful parameter for conventional sheet-metal-formability, the relation between the r-value of ultra-thin rolled foil and its applicability in micro-deep drawing is investigated. Ultra-thin rolled foil is characterized with a higher r-value due to the strong texture of {1 1 0} and {1 1 1} textures. Although the in-plane tendency of the r-value showed a strong correlation with the thickness distribution of micro-drawn cups, the obtained higher r-value for thinner foils does not correspond to the lower formability of thinner metal foils. As relevant parameter for indicating the forming limit for thin-rolled metal foils, the nonuniformity in thickness due to surface roughening is introduced. The importance of a geometrical anisotropy, such as orientation of surface topography and defects, for the unstable deformation of ultra-thin rolled metal foils is experimentally demonstrated.