Study on microstructure and corrosion resistance of high-hardness Zn-1.0Cu-1.0Ti alloy

Abstract

In order to develop a high durability building decoration zinc-based alloy materials, the as-cast Zn-1.0Cu-1.0Ti alloy (ZCT-AC) with homogeneous microstructure and high hardness was successfully prepared by induction melting and rapid solidification. Interestingly, almost all Ti element exists in the as-cast alloy in the form of the homogeneous strip-like TiZn 16 phase, and the Cu element is uniformly dissolved in both the η -Zn and TiZn 16 phase in the form of supersaturated solid solution. The hardness of the ZCT-AC alloy was about 79.3% and 52.7% higher than that of pure Zn and a commercial cold-rolled zinc‑titanium alloy (ZCT-CR), respectively. By potentiodynamic polarization tests in NaCl solution with four different mass fractions (0.1, 1.0, 3.5, and 5.0 wt%) at 25 °C and in 3.5 w.t% NaCl solution at four different temperatures (25, 35, 45, and 55 °C), ZCT-AC alloy showed higher corrosion resistance than the two control samples because of both a high formation efficiency and a high structural stability of passive film. Furthermore, Several plausible corrosion mechanisms of the three samples have been further studied systematically by a long-term immersion tests in 3.5 wt% NaCl solution, the results suggested that the corrosion process of ZCT-AC alloy was dominated by uniform corrosion which led to a higher interface uniformity, the corrosion layer of the alloy had higher uniformity and overall density, and the corrosion rate of both micro-galvanic corrosion and intergranular corrosion were inhibited significantly owing to the uniform distribution of Cu element. This study might provide a theoretical guidance for designing the high durability building decoration materials. • High-hardness as-cast Zn-1.0Cu-1.0Ti alloy shows excellent microstructure homogeneity. • Almost all Ti element exist in the form of strip-like TiZn 16 phases. • Cu element is uniformly dispersed into both of the Zn-rich matrix and the TiZn 16 phase. • The passive film on Zn-1.0Cu-1.0Ti alloy shows high formation efficiency and high structural stability. • Zn-1.0Cu-1.0Ti alloy has higher overall corrosion layer density and interface uniformity.