Microstructural and damp-heat corrosion characteristics of Zn-2 wt%Al solder alloys containing trace Ag

Abstract

Zn-2 wt%Al alloy with micro-addition of Ag (0–1.5 wt%) was fabricated into as-cast and wire-shaped. The effect of Ag addition on alloy microstructures was investigated through SEM/EDS, XRD and DSC technology. Then the damp-heat corrosion experiment was carried out on wire-shaped alloy. And the influence of Ag on the corrosion characteristics was further studied through SEM/EDS, XRD, hardness test and weighting method. The results showed that the addition of Ag coarsened both primary η-Zn dendrites and eutectic lamellar β-ZnAl in as-cast alloy. Furthermore, during the plastic deformation process to obtain wire-shaped alloy, the increasing Ag content could facilitate the intermetallic compounds formation (AgZn3, AlAg3) and the oxidational pitting of primary η-Zn. Whether Ag was added or not, Zn-2 wt%Al alloy underwent oxidation and stress corrosion during the damp-heat corrosion experiment, which resulted in the oxidational weight gain and the corrosion layer forming. The addition of Ag tended to facilitate the oxidation of alloy during the corrosion to induce more significant micro-cracks in corrosion layer. Nevertheless, because the increasing Ag content reduced the corrosion-prone Al-rich phases and was favored to produce corrosion-resistance phases (oxides, intermetallic compounds) hindering the diffusion of corrosion medium along micro-cracks, the stress corrosion progress from the surface to the centre of wire-shaped alloy was suppressed. And correspondingly, the oxidational weight gain amount and the corrosion layer depth were all reduced with the increasing Ag content.