Issue 22

V. Di Cocco, Frattura ed Integrità Strutturale, 22 (2012) 31-38 ; DOI: 10.3221/IGF-ESIS.22.05 34 surfaces as traditional coatings, while coatings obtained by Zn-Ti bath are characterized by high values of roughness, because they are not optimized galvanizing conditions. Presence of Sn improves bath fluidity and leads to better surface aspect, being better the wetability of melted Zn-Sn alloy. Furthermore the presence of Ti increases bath reactivity, leading to a not well homogeneous surface. Behaviors of Zn-Sn and Zn-Ti baths influence kinetics of coatings formations both in terms of coatings thicknesses and of typology of intermetallic phases. Coatings obtained from Zn-Sn bath are characterized by the traditional phases as shown in Fig. 1b, whereas presence of Ti leads to coatings constituted by a  phase in the inner layers, and by an outer layer made of three phases. In Fig. 3 kinetics of whole coatings and intermetallic phases thicknesses are shown. 0 100 200 300 400 500 600 0 200 400 600 800 1000 Thicknesses [  m] Dipping time [s] delta zeta eta TOT. ( a) 0 100 200 300 400 500 600 0 200 400 600 800 1000 Thicknesses [  m] Dipping time [s] delta Tri‐Phasic TOT. ( b) Figure 3 : Coatings and their intermetallic phases thicknesses: a) coatings from Zn-Sn bath, b) coatings from Zn-Ti baths. Presence of 3%Sn in the bath covers a linear increase of whole coating thicknesses in the dipping time, while intermetallic  ,  and  phases are characterized by a diffusion phenomenon of growth . High reactivity of Zn-Ti bath provides to enlarge the thicknesses of whole coatings, as shown in Fig. 3b, where a sharply increase at 360s is followed to a weak increase at 900s. Main parts of coatings are represented by tri-phase zone for all investigated dipping time, whereas  phase is characterized by a decrease of thickness from 60 to 180s, due to interdiffusion between inner and outer zones. Specimens thickness influences its bending behavior as shown in Fig. 4 where both Zn-Sn and Zn-Ti coatings bending resistance increases with the increasing of dipping time and therefore of its thickness. 0 5000 10000 15000 20000 25000 30000 35000 0 10 20 30 40 Bending moment [N · mm] Bending Half‐angle [°] Sn 3% ‐ 15 sec ‐ 30° Sn 3% ‐ 60 sec ‐ 30° Sn 3% ‐ 180 sec ‐ 30° Sn 3% ‐ 360 sec ‐ 30° Sn 3% ‐ 900 sec ‐ 30° ( a) 0 5000 10000 15000 20000 25000 30000 35000 0 10 20 30 40 Bending moment [N · mm] Bending Half‐angle [°] Ti 0.5% ‐ 15 sec ‐ 30° Ti 0.5% ‐ 60 sec ‐ 30° Ti 0.5% ‐ 180 sec ‐ 30° Ti 0.5% ‐ 360 sec ‐ 30° Ti 0.5% ‐ 900 sec ‐ 30° ( b) Figure 4 : Bending behavior of galvanized specimens: a) galvanized in Zn-Sn bath, b) galvanized in Zn-Ti bath. At high values of deformation Zn-Sn coatings show an increase of strength, whereas coatings from Zn-Ti bath show a slight decrease (Fig. 4a and Fig. 4b). Highest values of strength are observed in Zn-Sn coatings. In terms of elastic recovery, coatings from Zn-Sn are characterized by a fully recover at investigated deformation, but Zn-Ti coatings show a loss of recover property as shown in Fig. 4b.