Comprehensive study of the effect of hot-dipping process parameters on Sn-Sb coating properties for α-brass substrate

Abstract

This study's main purpose is to achieve an optimal hot-dip coating condition of Sn-Sb for an α-brass alloy. Therefore, the hot-dipping parameters, including pre-flux lubricants, immersion temperature, time, and withdrawal speed were investigated. ZnCl₂ and SnCl₂ were used as pre-flux bath additives. The temperature of the immersion bath was selected to be in the range of 250-300 °C. Also, the exposing time and withdrawal speed of the specimens during the hot-dipping process were in the range of 10-60 sec and 254-1524 mm/min, respectively. Visual inspection of the coating revealed that by using SnCl₂ as a pre-flux additive, high-quality smooth coating is achieved. According to the AFM result, the initial roughness value of the substrate was 450 nm. The coating's roughness value with SnCl₂ and SnCl₂+ZnCl₂ pre-fluxes were in the range of 300-500 and 700-900 nm, respectively. Therefore, ZnCl₂ pre-flux is associated with a rougher surface. Corrosion test analysis revealed that both coating condition with different pre-fluxes leads to increasing corrosion resistance however better improvement in corrosion behavior is accomplished by smooth coating surface. The quantitative analysis of the polarization curve revealed that the corrosion rate of the smooth coating is decreased 7-12.5 times in comparison with the substrate. According to the SEM analysis, the predominant phases which were appeared at the interface of the coating and substrate were Cu₃Sn and Cu₆Sn₅. SEM analysis revealed that the Cu₃Sn intermetallic compound was this first phase, which was promoted near to the substrate vicinity during the hot-dipping process.