Morphologies and corrosion properties of PVD Zn-Al coatings

Physical vapour deposition (PVD) Zn alloy coatings are being considered as possible alternatives to conventional hot dip and electrochemically deposit ed coatings on steel substrates. Variation of the deposition temperature le ads to very different microstructures being observed by SEM, primarily due to the low melting point of zinc. In the present study this phenomenon has been investigated in more detail. Zn+5 at.% Al coatings were deposited by m agnetron sputtering using a homogeneously alloyed Zn-Al target. As the subs trate temperature is increased, the coating morphology changed from a compa ct to an open sponge/woollen-like microstructure and the coating thickness increased by up to a factor of 10. The Zn-Al coatings displayed a hexagonal structure corresponding to that of Zn. The corrosion properties were inves tigated by potential-time and salt bath immersion tests. Interestingly, bot h the barrier and sacrificial protection afforded by the coating were indep endent of the microstructure. (C) 2000 Published by Elsevier Science S.A. A ll rights reserved.