Effect of Grain Size on Formability in Micro-extrusion

－Research on Forward-Backward Micro-extrusion of Aluminum Alloy 1^st Report－

Abstract

When scaling down a conventional forming process to the microscale, the influence of the size effect must to be considered. This effect comes from the material properties and frictional behavior at the microscale. We investigate the effect of grain size on the forward-backward micro-extrusion behavior of an aluminum alloy using a desktop experimental setup. The extrusion force increases with decreasing grain size, which agrees with the Hall-Petch effect. The backward extrusion length increases with decreasing grain size because of the tendency of small grains to flow into the small backward extrusion gap. A micro-Vickers hardness test shows that a smaller billet grain size leads to more significant work hardening upon plastic deformation. We focus on the simulation of micro-extrusion for a 6063 aluminum alloy billet by the ALE-based finite-element method. In this process, the material is extruded both forward and backward with dependences on the grain size and friction conditions. The metal flow separation caused by an increasing friction coefficient indicates that the friction at the die-billet interface affects the complicated metal flow in forward-backward extrusion.