Effect of CoCrMo Die and Tool Surface Nano-Texture on Micro Backward Extrusion Formability of AA6063-T6

Abstract

To manufacture micro parts used in medical and electronic devices, the machining scale must be reduced to the microscale. However, when applying existing plastic forming processes to the machining of microscale parts, the size effect caused by material properties and friction results in variations in product accuracy. To suppress the size effect, appropriate tool materials and tool surface treatments suitable for micro-scale machining must be considered. This study investigated the effects of tool surface properties such as die surface nano-texture on microextrudability such as extrusion load, product shape, and crystal structure of the product using AA6063-T6 billets as test specimens. A CoCrMO die was used as a new die material suitable for microextrusion. The extrusion load increased rapidly with the progression of the stroke for both dies. In the case of the CoCrMo die with nano-texture applied, the extrusion load was considerably lower than that of the AISI H13 die. Moreover, the extrusion length of the CoCrMo die with nano-texture applied was longer than that of the AISI H13 die. In addition, the nano-textured CoCrMo die exhibited less adhesion on the die surface. The results of material analysis using electron backscatter diffraction indicated that the nano-textured CoCrMo die improved material flowability and facilitated the application of greater strain. However, the AISI H13 die exhibited lower material flowability and non-uniform strain. Therefore, the tribology between the tool and the material was controlled by changing the surface properties of the die to improve the formability.