Issue 22

V. Di Cocco, Frattura ed Integrità Strutturale, 22 (2012) 31-38 ; DOI: 10.3221/IGF-ESIS.22.05 32 temperature, immersion time, pre-galvanizing surface temperature, etc.) and chemical parameters (bath and steel chemical compositions, flux chemical composition, etc.). Processes are very important also on typologies of coatings; eg. in the galvanized steel strip, produced through a continuous hot-dip galvanizing process, the thickness of the adhered zinc film must be controlled by impinging a thin plane nitrogen gas jet [2]. Zn [%wt] Temperature [°C] Phase  [99.94% Zn] ( a)  phase  phase  phase  phase ( b) Figure 1 : Intermetallic phases in a traditional hot dip galvanizing coating: a) Zn-Fe status diagram portion [1], b) Morphological aspects of intermetallic phases. Presence of silicon in the material is very important for coatings formation and its properties. Because of the limited solubility of silicon in the  layer, an excessive content of silicon in steels accumulates on the surface of substrate. The Fe/Zn reaction determines movement of the  - Fe/  interface towards the steel substrate. The  - Fe phase, rich in silicon and slightly soluble in  layer, breaks and the particles enters in to  layer through the  layer. Then silicon-rich  - Fe, dissolving in the  layer, accelerates the growth of the  layer to steel substrate, and the coating becomes loose [3]. When coated steel sheets are subjected to corrosive environments, their corrosion behavior is affected by changes of the coating texture and also by the microstructure. Basal plane texture coefficient increases with the increasing of lead zinc bath content of zinc bath, as well as increases the texture coefficient of high angle pyramidal, low angle pyramidal and prism planes.  layer thickness is increased by increasing the lead content of the zinc bath. Coatings having a better corrosion resistance are characterized by greater basal texture coefficient and smaller  layer thickness [4]. To prevent the penetration of the aggressive ion Cl - in outdoor exposition, the presence of oxide under coating is accepted. Moreover the galvanic performance of the coating improves with the presence of ZnO-rich inner alloy layers as also evidenced when polarization studies were conducted with a different approach [3]. In the last years, there has been an increase in zinc coatings research, focusing both on coating procedures and on mechanical behavior characterization, in order to optimize Zn layer thickness and mechanical performances [5]. In this work a traditional ZnSn bath and an innovative ZnTi bath were considered to obtain coatings on iper Sandelin steel plate specimens. Bending tests [6-10] were performed to investigate damaging micromechanisms in intermetallic phases. M ATERIAL AND METHODS wo kinds of Zn-based baths were used in order to generate coatings characterized by different intermetallic phases. It were used a Zn-Sn (3.0 wt %) bath and a Zn-Ti (0.5 wt %) bath at 460± 2 °C. For all the investigated Zn-based baths, 3 mm thick of commercial carbon steel plates were considered. Steel chemical composition is T