Issue 48

C. Bellini et alii, Frattura ed Integrità Strutturale, 48 (2019) 740-747; DOI: 10.3221/IGF-ESIS.48.67 742 350 550 750 950 1150 1350 65 75 85 95 Temperature [°C] Zn [wt%]  →      L+   L ←(  ) Figure 1 : Section of phase diagram of zinc-iron [4]. In the past, the additions of Pb were used to fluidify the zinc bath, increasing also the Γ layer thickness and improving the corrosion resistance [13]. Many processes were optimized for the Pb additions, but today the presence of Pb cannot be accepted due to recent laws. The main element that is usually considered as Pb substitute is the Sn, but other metallic elements can be used leading to different intermetallic phases formations and different corrosion and mechanical performances. More studies, oriented to the intermetallic phases damage, have been carried out [15-18] in order to better understand the behaviour of the intermetallic phases in tensile and in compression loads. In the last years a new cheap class of cast irons, the Ductile Cast Irons (DCIs) became more and more interested in galvanizing protection [19]. This is due to the performances of DCIs which are characterized by mechanical properties similar to the medium and low carbon steels [20-24]. In this work, a commercial Ductile Cast Iron, the GS500, characterized by a ferritic-pearlitic matrix is investigated in order to evaluate the coating formation during different dipping time. The kinetic of coating formation and the role of graphite nodules have been analysed by means of Light Optical Microscope (LOM) and Scanning Electron Microscope (SEM) observations. Presence of thermal cracks has been investigated too. M ATERIAL AND METHODS n this work a commercial GS500 ductile cast iron, characterized by a ferritic-pearlitic matrix is investigated in order to observe the kinetics of coating formations, taking into account the role of the graphite nodules. Then, galvanized specimens are used to perform bending tests in order to evaluate the damage of different intermetallic phases. The chemical composition of the GS500 used in the galvanizing operation is shown in Table 1. C Si Mn P S Cr Sn Fe 3.65 2.72 0.18 0.03 0.010 0.05 0.035 Bal. Table 1: Chemical composition investigated DCI (wt%) [19]. Rectangular flat specimens 80x25x3mm are machined from a rolled bar of GS500 in order to obtain samples to be galvanized and immediately protected by using a wetting oil. In this case, no pickling operation is needed and the surfaces of specimens are not etched by any acid. Before galvanizing, the oil layer is removed by using soap solutions and rinsed with alcohol. Subsequently, the specimens are fluxed in an aqueous solution containing 280 g/l ZnCl2 and 220 g/l NH4Cl I