Effect of Changes in Plastic Flow During Non-Steady State Deformation on Force Behavior in Micro-Extrusion of Pure Copper

In recent years, copper-based conductive and heat dissipation components have required fine structures for miniaturization and enhanced functionality. Micro-forming is an excellent processing method characterized by high productivity and suitability for mass production. Since small workpieces can be formed within a short stroke in micro-extrusion, it is important to understand the deformation behavior immediately after the start of extrusion. However, before steady state is attained, the evolution of microstructure and plastic flow with stroke progression during non-steady-state deformation has not yet been sufficiently clarified. In this study, to investigate the effect of changes in plastic flow on force behavior, micro-extrusion tests were conducted using pure copper. The geometric and crystallographic characteristics of the deformation structure were then analyzed. The extrusion force behavior exhibited three distinct stages, including a peak of the force. The force peak was attributed to changes in plastic flow associated with the deformation structure formed at the sample tip immediately after the start of extrusion. This change leads to the evolution of the effective extrusion ratio, which significantly influences the force response during non-steady-state deformation.