The behavior of lead during the solidification of Zn-0.1Al-0.1Pb coating on batch hot-dipped steel

The typical spangle on batch hot-dipped Zn-0.1Al-0.1Pb alloy coating was investigated. The morphology, distribution, chemical composition and identification of the phases on coating surface were examined by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), respectively. It is found that most of spangles usually exhibit three distinct regions: smooth, feathery and coarse regions, of which lead surface segregation across the coating surface was detected increasingly more significant. Furthermore, lead micro-segregation with the form of tiny orthohexagonal particulates (<0.5 μm), mainly happens in the interdendritic spacing instead of the grain boundary probably owing to no sufficient diffusion. Based on the experimental results and compared to CGL, the solidification sequence of the Zn-0.1Al-0.1Pb coating was analyzed assisted with Zn-Pb phase diagram; the morphology of the spangle is modeled on consideration with the interaction of the thermal condition and the crystallization orientation; the profile of precipitated lead particulates is well explained in the view of crystallography.