Tools for machining are made of hard steels and cemented carbide (WC-Co). For specialized applications, such as aluminium machining, diamond or polycrystalline cubic boron nitride are also used. The main problem with steel, isthat itexhibits a relatively low hardness (below 10 GPa) which strongly decreases upon annealing above about 600 K.Thus, the majority of modern tools are nowadays coated with hard coatings that increase the hardness, decrease the coefficient of friction and protect the tools against oxidation. A similar approach has been recently used to obtain a longer duration of the dies for aluminium die-casting.

In the present experimental work, a WC/C coated 7075-T6 aluminum alloy was considered from the corrosion point of view. The coating was deposited by PVD technique with a final thickness of about 2.5μm. In order to study the influence of the coating on the corrosion behavior of the aluminum alloy, the samples surfaces were partially coated and the interface among the metal and the coating was analyzed after the corrosion tests described into the ASTM G110 standard. Such experimental plan was decided in order to simulate the possible in-service local removal of the thin and hard coating. This kind of damage, due for example to a foreign object impact, can occur because of the great hardness difference between the coating and the substrate. The experimental tests were carried out on samples with different surface finishing, ranging from about 0.02μm Ra (mirror-polished surface) to about 0.8μm Ra (320 grit paper). The aim of such choice was to investigate the effect of a surface roughness different from the optimal one (mirror polished) on the coating deposition. Moreover a different corrosion resistance is expected.