Corrosion behaviour of Al-Zn coatings in 5%wt NaCl solution

Several aluminium-based coatings deposited by Physical Vapour Deposition are tested as an alternative solution to chromium, nickel and zinc-based coatings in order to protect efficiently steel from corrosion.

The objective of this study is to define the corrosion parameters of different Al-Zn compositions with a zinc content varying from 3%at. to 19%at. The samples were tested in saline solution. Results show that the corrosion behaviour depends on the zinc content. Below a specified value included between 10%at. and 16%at., the alloys suffer from pitting corrosion. Above 16%at. Zn, the corrosion is generalized. Besides, the reactivity increases with zinc content while the open circuit potential shifts toward more negative values and gets closer to the pure zinc open circuit potential in this medium.

These alloys present very interesting properties for steel protection, for zinc content high enough to have generalized corrosion. Nevertheless, zinc content has to be well defined in order to avoid a high dissolution of the coating. Keywords : Corrosion, Al-Zn, PVD, sacrificial coatings