On the size effects in micro/meso semisolid extrusion–forging of A356 aluminum alloy

Abstract

Micro/meso forming is an economically competitive process for the fabrication of miniature metallic parts. Scaling conventional metal forming down to micro/meso scale leads to the so-called size effects. In this study, the size effects in micro/meso semisolid extrusion–forging (MSEF) of A356 aluminum alloy were numerically and experimentally investigated. An experimental setup for MSEF was developed, and the mechanical performance of A356 aluminum alloy in the semisolid state was tested. Then, the MSEF with various die-hole diameters and various friction coefficients were numerically investigated to examine the size effects in the processes. With certain punch displacements, it was found that the aspect ratio of the extruded pin decreased and the forging load increased during the miniaturization of the die-hole. In addition, the contact condition and the lubrication became increasing critical when the die-hole got smaller. Furthermore, various experiments were performed using A356 aluminum alloy. When the die-hole shrunk in the experiments, the changes of the pin aspect ratio and the forging load followed similar trends with the numerically simulated results. The size effects in the MSEF experiments mainly belong to the first-order size effect. In addition, no significant defect was found in the formed specimens with a die-hole diameter down to 0.55 mm, indicating great formability of the MSEF. The size effects identified in the MSEF process in this study assist in understanding the material flow and the cavity filling in the micro/meso semisolid forming with complicated geometrical shapes.