Effect of grain size on springback and system energy in micro V-bending with phosphor bronze foil

In this paper, the effect of grain size on springback in the micro V-bending process of phosphor bronze foil (face-centered cubic structure) is investigated. Grain size effect is expressed by the ratio of material thickness (T) to average grain size (D), and these T/D values are divided into three groups: larger than 1, less than 1, and approximately equal to 1. It has been found that springback angles were the lowest when T/D ≈ 1. Electron backscattering diffraction (EBSD) measurement results show that the twinning boundaries change with the ratios of T/D before and after bending. When T/D > 1, the high relative frequency of Σ3 implies that the specimen has a high system energy, which can result in large springback behavior. The equal relative frequencies of Σ3 for specimens with three ratios also prove that twinning boundaries can be regarded as an indicator of system energy. The effect of grain size on grain reorientation during bending is also discussed, and it was found that the least quantities of high surface energy {110} planes in the T/D ≈ 1 material could contribute to the least springback angles.