TiAIN superlattice structured PVD coatings: a new alternative in the machining of aluminium alloys for aerospace and automotive components

A 3 μm thick superlattice structured TiAlN/VN coating has been deposited by the steered cathodic arc/unbalanced magnetron sputtering technique. The coating has been tested in dry high-speed milling of aluminium alloys Al7010-T7651 and AlSi9Cu1 and the performance compared to that of the diamond-like carbon (DLC) coated, TiAlCrYN coated and uncoated tools. In milling the Al7010-T7651 alloy, TiAlN/VN and DLC coated tools showed comparable performance, outperforming TiAlCrYN coated and uncoated tools by a factor of 2.3 and 3.5, respectively. In the case of milling AlSi9Cu1, the DLC coatings failed to produce any lifetime improvement, TiAlCrYN showed 65% longer lifetime thus rendering TiAlN/VN as the best performing coating with 100% longer lifetime compared to that of the uncoated tools. The tests further showed that TiAlN/VN reduces the cutting forces and improves the surface finish. Scanning electron microscopy of the cutting edge carried out after the cutting tests showed that the TiAlN/VN coating significantly reduces metal transfer and built-up edge formation.