Galvanic corrosion properties of differently PVD-treated magnesium die cast alloy AZ91

Different types of PVD coatings and plasma treatments were applied for the surface treatment of magnesium die cast alloy AZ91 specimens. The different types of surface treatment were all developed by the authors and the fundamental properties are described elsewhere. The coating systems were: 9 mu m CrN hard coating 3 mu m TiN coating 0.5 mu m plasma anodisation layer and 3 mu m Al2O3 coating The wear and corrosion properties of the differently surface-treated AZ91 samples show crucial influence on the coating characteristics. While the well known metalloid CrN coatings show good wear properties due to high hardness and high coating thickness (9 mu m), their corrosion properties are very poor due to crucial micro galvanic corrosion at coating defects. The plasma anodised and additionally Al2O3-coated specimens show good corrosion properties and are also prospective for tribological applications although their wear characteristics yet cannot reach the values for CrN-coated specimens. The publication shows the results of a novel immersion technique to determine the time dependent corrosion behaviour of coated magnesium alloys [B.L. Tiwari, J.J. Bommarito, Magnesium Technology 2 (2002) 269.]. Furthermore, the galvanic corrosion properties of differently coated AZ91 samples in contact with untreated AZ91, different aluminium alloys, roller bearing steel 100Cr6 and a titanium alloy TiAl6V4 were determined. The galvanic corrosion properties were tested according to DIN 50019. (c) 2004 Elsevier B.V. All rights reserved.