Sliding behaviour of hard and self-lubricating PVD coatings against a Mg-alloy

In the present work, the friction and wear behaviour of the AM60 Mg-alloy (nominal chemical composition: Mg–6% Al–0.3% Mn; hardness: 52 HV) dry sliding against coated AISI M2 high-speed steel has been investigated. Different coatings were deposited on the high-speed steel by means of the PVD technique: three hard coatings (TiN, CrN and ZrN) and two self-lubricating coatings (MoS2 and WC/C).The sliding tests were carried out using a block on disc testing rig. The testing conditions were selected with the aim of simulating the tribological loading present during dry drilling of Mg-alloys. The tests were carried out at a load of 200 N and a sliding speed of 0.8 m/s. In the second part of the work, tests at lower loads (150, 100 and 50 N) were also conducted.The analysis of the wear behaviour (in particular the formation of a Mg transfer layer on the coatings), along with the continuous monitoring of friction coefficient and contact temperature, allowed us to understand the acting wear mechanisms and therefore to propose specific guidelines for the selection of the drilling parameters.