Zinc-magnesium-pigment rich coatings for corrosion protection of aluminum alloys

Chromate (Cr(VI))-based pigments have been widely used for corrosion protective coatings because of their outstanding protection efficiency especially for aluminum alloy products. However, due to environmental issues associated with Cr VI, more and more requests are being made for alternative solutions. In the presented work zinc was modified by alloying with magnesium to achieve a combination of properties cathodic protection and less reactivity during production, storage and application of the pigments. The magnesium content leads to a lowering of the electrochemical potential which allows the cathodic protection of aluminum alloys, zinc magnesium pigments were prepared in different compositions with special attention to the intermetallic phases MgZn, Mg2Zn3, and MgZn2. Pigments were produced and a zinc magnesium rich coating was formulated and compounded. Pickled samples of M 2024 unclad were coated and the corrosion behavior investigated. A durability of more than 10,000 h in salt spray test could be achieved. (C) 2013 Elsevier B.V. All rights reserved.