Aluminum transfer buildup on PVD coated work rolls during thermomechanical processing

•Aluminum transfer buildup on PVD coatings during hot rolling was studied.•Cr-coated work rolls displayed the least aluminum transfer and pickup defects.•The uncoated work roll displayed the most aluminum transfer and pickup defects.•TiN and TiCN displayed interchangeable performances depending on the rolling stage.•A two-way material transfer between the work rolls and aluminum piece was noted.

A hot rolling tribo-simulator was used to examine material transfer and adhesion from Al-Mg alloy samples to various PVD coatings deposited on AISI M2 steel rolls. The coatings applied to the work rolls included Cr, TiN and TiCN, which were compared with an uncoated M2 steel work roll after 1, 10 and 20 lubricated hot rolling passes. The average surface roughness (Ra) of the work rolls was 0.17 μm. Material transfer to the work rolls was examined after 1, 10 and 20 passes. Scanning electron microscopy (SEM) and focus ion beam (FIB) microscopy were used to investigate material transfer and adhesion to the surfaces of the work rolls. Aluminum and magnesium transfers were observed on all work rolls' surfaces from the 1st hot rolling pass. Material transfer was most severe on the uncoated M2 steel work roll through the rolling schedule, while the PVD coated work rolls displayed better mitigatigation against aluminum adhesion during both the initial and final stages of the hot rolling schedule. The material transfer on both Cr-coated and uncoated M2 steel rolls contained more magnesium than aluminum after the 1st and but after the 10th rolling pass the trend was the same only for the uncoated M2 steel work rolls. The aluminum transfer covered a larger percentage area than the magnesium transfer on the nitride coatings throughout the rolling schedule.