Visco-Plastic Flow of Metal in Dynamic Conditions of Complex Strain Scheme

Abstract

The article applies to a piece of research inspired by the new technology of plastic metal forming called the KOBO method, which uses the mechanical and structural effects of cyclic changes of deformation path. Its commercial usage in the field of large plastic deformations, especially for the production of extruded elements made of hardly deformable metal alloys, naturally generated a question about the optimal conditions for carrying out the process and the criteria for their establishment, i.e., constitutive description. In this context, the work provides data on the force and energy consumption of aluminum and 7075 aluminum alloy extrusion processes, carried out using the KOBO method, and their dependence on the strain rate and temperature. The mechanism of deformation occurring during extrusion by the KOBO method was identified as visco-plastic flow. Characteristic parameters of the process, such as viscosity coefficiency, activation energy, activated volume, and the concentration of point defects generated during the process were evaluated.

Metal Forming of Lightweight Magnesium Alloys for Aviation Applications

“…Being induced this way super plastic mode of deformation makes possible to deform metals with very high deformation (SPD process) at low temperature (room temperature) [17,18]. Hence, despite of very low load capacity of the press the methods allows for the variety of metallic product to be extruded at room temperature from the billet, which size and dimensions are shown in Fig.…”

Microstructure of Commercial Purity Titanium Subjected to Complex Loading by the Kobo Method

“…High plastic strain is enabled through decrease of deformation force by destabilization of dislocation structure and activation of heterogeneous visco-plastic flow [11] [12]. Destabilization of structure is caused by changes of deformation path during the process which results from cyclic changes in loading scheme.…”

Strain rate sensitivity of Al-based composites reinforced with MnO2 additions

“…As compressed bars, 60 mm in length and 40 mm in diameter were extruded using a KOBO press. Details of the KOBO method's processing are presented elsewhere [29,30]. The charge was not preheated before processing to avoid chemical reaction between MnO 2 and the matrix.…”