Initiation and evolution of the aluminium-alloy transfer on hot-work tool steel at temperatures from 20 °C to 500 °C

During the forming of aluminium alloys there are several difficulties associated with controlling the process parameters and the product quality due to the severity of the contact. Adhesion and, in particular, the formation of transfer films of aluminium alloys on the surfaces of hot-work tool steels are very negative phenomena in this process and require a better understanding. The present work is focused on the initiation and evolution of the transfer of the aluminium alloy EN AW-6060 to the nitrided hot-work tool steel AISI H13 in the temperature range from 20 degrees C to 500 degrees C. All the tests were performed under cross cylinder single-pass, dry-sliding-contact conditions over different sliding distances. The contact was investigated in terms of the surface area and the volume of the transferred aluminium alloy to the surface of the tool steel, the topography of the wear trace and the corresponding coefficient of friction. The results show the strong dependence of the tribological properties in the contacts of the nitrided hot-work tool steel and the aluminium alloy on the temperature. However, it was found that the whole tribological behaviour is largely already defined during the very early stages of sliding, i.e., at the initiation of sliding, after which it becomes even more pronounced as the temperature increases. At low temperatures (20-200 degrees C) the surface roughness of the tool steel was found to be the key initial cause of the aluminium alloy's transfer, while at higher temperatures (300-500 degrees C) this transfer occurred predominantly due to strong adhesion. (C) 2014 Elsevier B.V. All rights reserved.