Tribological Performance of AlCrN, TiAlN, and Arc-DLC Coatings in Hot Forming of Aluminum Alloy

This study aims to evaluate the tribological performance of commercial PVD coatings in alleviating material transfer under unlubricated contact in the hot forming of aluminum alloy. The commercial PVD coatings included AlCrN, TiAlN, and Arc-DLC coatings, deposited on the forming tool surface. The warm and hot upsetting sliding test (WHUST) was used as a friction test in this study to reproduce the severe contact conditions from the hot forming process of AA6082-T6 aluminum alloy. The WHUST was performed at 300 °C, 400 °C, and 500 °C to investigate the effect of temperature on the tribological performance of each coating. The results found that the AlCrN and TiAlN coatings exhibited similar performance. They dominated the initial aluminum transfer by adhesive bonding. In contrast, the Arc-DLC coating mainly caused the initial aluminum transfer by mechanical plowing due to its lower chemical affinity to the aluminum alloy. In addition, the tribological performance of each coating highly depended on the temperature. Higher temperatures resulted in both stronger intermetallic bonding at the interface and lower yield strength of the aluminum alloy. These behaviors led to the variations in the coefficient of friction, the 3D topography and the SEM morphology along the wear track of the specimen, and the thickness of the adhered aluminum layer on the coating surface. In comparison, the Arc-DLC coating provided better tribological performance in mitigating the aluminum transfer than the others.