The Galling Behavior of Advanced Coating Contacts with Aluminium Alloy during Sliding Wear

This paper investigates the galling behaviour of a range of hard coatings applied to tooling surfaces during the sheet forming of an aluminium alloy workpiece. A total of three types of tooling materials were investigated, two of which were subject to PVD deposited coatings of AlCrN, CrN and DLC applied to the working surface. The third tooling material had undergone induction heating, plasma-nitriding and polishing. To evaluate the galling behaviour of the applied coatings, a tribological evaluation was conducted using a pin-on-disc test set-up at a constant load and varying temperature. The coated discs, replicating the tooling material, were tested against aluminium alloy pins AA6082 and AA7075 representing the workpiece material. This investigation indicated that the friction and galling behaviour of aluminium is highly dependent on temperature, and the use of two different aluminium pins had no significant effect. At room temperature, it was found that carbon-based coatings provide the lowest friction and the best protection against galling, whilst nitride-based treatments exhibit better performance at high temperature. Moreover, at elevated temperatures, coated tools exhibit superior anti-galling properties compared to uncoated tools.