An experimental study on optimum lubrication for large-scale severe plastic deformation of aluminum-based alloys

Reducing friction plays a key role in the technological application of severe plastic deformation (SPD) techniques like equal-channel angular pressing (ECAP). In this paper, we report on an experimental study that investigates the suitability of various commercially available lubricants for SPD processing. We consider a custom-built friction test that allows the evaluation of the potential of different lubricants under typical SPD processing conditions. In order to determine an optimum lubrication system for the ECAP process, the friction test is specifically adapted with respect to the specific characteristics occurring during ECAP, such as large sliding distances and high pressure between the ECAP die and the processed material. We discuss how different lubricants influence the processing of the material with a focus on the pressing forces (during ECAP, and during an alternative SPD process, transverse impact extrusion) and the resulting surface quality of the processed ECAP billets. A wax-based lubricant is identified as an environmentally friendly and clean lubricant that provides excellent properties. With this lubricant, even for large sliding distances, low friction values are recorded and this results in low pressing forces and an excellent surface quality. Since lubricants play an important role in further developing SPD processes, the results presented here may help to optimize existing SPD processes and to scale up processes for future industrial applications.