Microstructure and Corrosion Behavior of Sn-Zn Alloys

In the present work, the microstructure, phase constitution, and corrosion behavior of binary Sn-xZn alloys (x = 5, 9 and 15 wt.%) were investigated. The alloys were prepared by induction melting of Sn and Zn lumps in argon. After melting, the alloys were solidified to form cast cylinders. The Sn-9Zn alloy had a eutectic microstructure. The Sn-5Zn and Sn-15Zn alloys were composed of dendritic (Sn) or (Zn) and eutectic. The corrosion behavior of the Sn-Zn alloys was studied in aqueous HCl (1 wt.%) and NaCl (3.5 wt.%) solutions at room temperature. Corrosion potentials and corrosion rates in HCl were significantly higher compared to NaCl. The corrosion of the binary Sn-Zn alloys was found to take place by a galvanic mechanism. The chemical composition of the corrosion products formed on the Sn-Zn alloys changed with the Zn weight fraction. Alloys with a higher concentration of Zn (Sn-9Zn, Sn-15Zn) formed corrosion products rich in Zn. The Zn-rich corrosion products were prone to spallation. The corrosion rate in the HCl solution decreased with decreasing weight fraction of Zn. The Sn-5Zn alloy had the lowest corrosion rate. The corrosion resistance in HCl could be considerably improved by reducing the proportion of zinc in Sn-Zn alloys.