Grain-size affected mechanical response and deformation behavior in microscale reverse extrusion

Abstract

The continuing demand on device miniaturization has motivated the interest in micro metal forming technologies for manufacturing metal parts with sub-mm characteristic dimensions. In this work, axisymmetric reverse extrusion experiments were conducted on Cu 110 and Al 1100 alloy rod specimens with widely varying initial grain sizes, achieved through equal channel angular pressing (ECAP) and post annealing. Accompanying crystal plasticity finite element (CPFE) simulations were carried out. At a characteristic extrusion dimension (CED) of ∼100 µm, defined by the sidewall thickness of the extruded cup-shaped structures, the deformation characteristics of the reverse extrusion process were investigated. Specifically, the characteristic plastic strain for extrusion and the influence of initial grain size on the extrusion mechanical response and shape of extruded parts were examined in detail through scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), in combination with CPFE simulations. The mechanical response of extrusion showed deviations from continuum scaling behavior as the CED became small as compared to the initial grain size. The present study serves as a baseline for further studies of metal forming at the meso to micro scales.