**4. Discussion**

The results were intended to discuss the effect of the cooling rate of a Zn-4Al alloy on the corrosion processes at the eutectoid transformation temperature. The main comments are as follows:

1) The microstructure of the material was typical for hypoeutectic cast Zn-Al alloys and was composed of a dendritic η-phase: Zn(Al) solid solution and lamellar (α + η) eutectoid. It contained the products of the eutectoid reaction which transformed the γ phase to (α + η) at

275 ◦C. Increasing the susceptibility to corrosion by increasing the aluminum content in Zn-Al alloys has been reported in the previous literature [5,19] which may be associated with an increased volumetric fraction of the ( α + η) eutectic. Upon progression of the corrosion process, the ( α + η) eutectoid structure in eutectic areas was attacked first and subjected to intense corrosion. Therefore, increasing the eutectic volumetric fraction should deteriorate the corrosion resistance of Zn-Al alloys. The high corrosion tendency of eutectic areas may induce intergranular corrosion [10,22,23]. In the case of two cooperating details, the accompanying pulverisation promotes the penetration of material fragments and the corrosion products into the friction area [22,23].

