Understanding corrosion mechanism of Sn–Zn alloys in NaCl solution via corrosion products characterization

Abstract

The corrosion products formed on Sn-Zn solder alloys were systematically studied to elucidate the corrosion mechanism of Sn-Zn alloys in chloridecontaining solution. Sn-Zn alloys were subjected to immersion and polarization treatment in a 0.5 M NaCl solution. Ex situ analysis, including surface and crosssection, of the corrosion products was carried out by scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDX). The corrosion products presented porous microstructure formed by a fine interlinked network. An increase of zinc content resulted in more pores and cracks of the corrosion products, indicating degradation of corrosion resistance. Intriguing is the finding that a gradient of chlorine concentration from the outer layer inwards the alloys through the Zn-rich precipitates is observed, which demonstrates the migration of chloride ions inwards the alloys. Based on the results, a corrosion mechanism was proposed and discussed that explains the observations. Particular attention was paid to the anodic dissolution of Zn-rich precipitates.

Electrochemical corrosion behaviour of Sn-Zn-xBi alloys used for miniature detonating cords

“…Furthermore, the corrosion product exhibiting a ball-shaped morphology was observed, which was found the aggregate of the ZnO plates (EDS analysis on S3). These ball-like ZnO products have been previously reported by other researchers on the study of Sn-Zn alloys after immersion corrosion [8]. Figure 8a and 8b presents the SEM micrograph of the surface of the Bi-containing Sn-3Zn-1Bi and Sn-3Zn-5Bi alloys after polarization measurements in 0.5 M NaCl solution, respectively.…”

“…Interestingly, the pitting product, Zn5(OH)8Cl2·H2O, exhibited a porous interlinked network structure. A similar porous network-structured corrosion product was also reported on the study of Sn-Zn [8]. The pores could provide ease of transport of Cland OHfrom solution inwards the interior of the alloys.…”

“…Sn (OH)2 → SnO + H2O (8) 3SnO + 2Cl -+ 2H2O → Sn3O(OH)2Cl2 +2OH - (9) In this way, the additional galvanic effect could have a negative effect on the corrosion resistance of Sn-Zn alloys. However, it worthy noted that the detrimental galvanic effect caused by β-Sn/Bi microgalvanic couple was believed to be minimal because the corrosion potential difference between Bi and Sn is small [26].…”

“…Liu et al [7] investigated the pitting phenomenon of Sn-xZn (x=6.5, 9.0, 12.0 wt.%) binary alloys in aerated and quiescent 0.5 M NaCl solution, demonstrating that the pitting susceptibility increases with increasing the Zn contents, which is ascribed to the defects along the intergranular boundaries between Zn-rich phase and Sn matrix. It has been pointed out that the poor corrosion resistance of Sn-Zn alloys is due to the preferential dissolution of Zn-rich phase, which exist in both primary and eutectic phase [8].…”

Corrosion characterization of Sn-Zn solder: a review

“…Also, sample geometry plays an important role in determining current transients. In the investigation of corrosion properties of solders, most of the studies have focused on bulk solder (Liu et al , 2015b, 2015c, 2016). As for Sn-Zn solder, a constant potential of −400 or −500 mV Ag/AgCl was mostly applied especially in NaCl (Liu et al , 2015b, 2015c, 2015d, 2016).…”