Effect of Cooling Rate at the Eutectoid Transformation Temperature on the Corrosion Resistance of Zn-4Al Alloy.

Marzena M Lachowicz,Robert Jasionowski

doi:10.3390/ma13071703

Abstract

The main purpose of this work was to experimentally determine the effect of the cooling rate during the eutectoid transformation on the corrosion resistance of a hypoeutectic Zn-4Al cast alloy in 5% NaCl solution. This was considered in relation to the alloy microstructure. For this purpose, metallographic and electrochemical studies were performed. It was found that the faster cooling promoted the formation of finer (α + η) eutectoid structures, which translated into a higher hardness and lower corrosion current density. In the initial stage of corrosion processes the eutectoid structure in the eutectic areas were attacked. At the further stages of corrosion development, the phase η was dissolved, and the α phase appears to be protected by the formation of corrosion products.

Highlights

Zinc-based alloys have good tribological properties, relatively high mechanical strength and hardness values, and show good castability due to their low melting points
The hardness increased by more than 20 HV1 for the water-quenched sample compared with the material that was furnace-cooled from the same temperature (300 ◦ C)
The increased hardness due to the increased cooling rate realized from the beginning crystallization temperature and microstructure refinement has been observed by other Authors [27]

Summary

Introduction

Zinc-based alloys have good tribological properties, relatively high mechanical strength and hardness values, and show good castability due to their low melting points. These features make them good candidates for use in automotive and electronics applications, and they have been used in the production of small components and plain bearings. Zn-Al alloys may be used to replace traditional zinc galvanic coatings [11,12,13,14,15,16,17,18] The commercial Galfan alloy has found broad applications in this area [18] but it exhibits several serious drawbacks, including a low creep resistance, low shape stability associated with aging, insufficient corrosion resistance in acidic and alkaline environments, and a low cavitation erosion resistance [5,19,20,21]

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Discussion

Conclusion