PSI - Issue 3

4

Vittorio Di Cocco et al. / Procedia Structural Integrity 3 (2017) 231–236 Author name / StructuralIntegrity Procedia 00 (2017) 000–000

234

250

50 Phases thickness [  m] 100 150 200

 +   +  + 

0

0

200

400

600

800 1000

Dipping time [s]

Fig.4. Dipping time influence on intermetallic phases thickness (on the left); Coating metallography, on the right (dipping time equal to 180 s; Nital 2 for 5 s).

25000

20000

15000

0 sec 15 sec 60 sec 180 sec 360 sec 900 sec

10000

5000

Bending Moment [N • mm]

0

0

10

20

30

40

Bending angle [°]

Fig.5. Influence of the dipping time on the bending tests results (on the right). Influence of the dipping duration on cracks development (on the left; bending angle equal to 30°). The LOM analysis of the longitudinal sections of the bended specimens allows to show the presence of cracks in some intermetallic phases. Cracks initiate in the most brittle intermetallic phases (in the  phase and, probably, in the not visible  ) and propagate in the  phase. Cracks do not propagate in the most ductile phase that corresponds to the external pure Zn layer (  phase; figure 5, on the left). As a consequence, the presence of the  phase layer does not allow the contact between the substrate (the steel to be protected) and the environment. This phenomenon can be observed considering the steel galvanized with a dipping time of 15 seconds, where no  phase is measured.