Crack Paths 2012

In presence of dispersed phase grains at interface, cracks propagate in dispersed

phases and if grains of dispersed phases are in chain shape from to outer surface, it is

possible to propagates through the whole coating. Furthermore presence of dispersed

phases cover to a brittle behaviour of outer zone and it performs as preferential ways to

crack propagation as showed in Fig. 5b.

Radial crack damage, evaluated in terms of number of cracks per millimetre of

deformed arc, are evaluated in phases of Zn-Sn and Zn-Ti coatings, and in phase in

Zn-Sn coatings.

205

/m m ]

/m m ]

aeg [ C r a c k s

[C r a c k s

15

aeg

D a m

D a m

12050505 5

15

25

35

5

15

25

35

Bending halfangle [°]

Bending halfangle [°]

1050

a)

b)

Figure 6: Intermetallic phases damage: a) Zn-Sn3%coating bath, b) Zn-Ti0.5% coating

bath.

At low bending angles no cracks are present in phase in Zn-Sn coating, but damage

increases at higher angles. In phase damage are present al low angles and increase

than a plateau at higher deformation angle (Fig. 6a).

But higher damage are present in phase of Zn-Ti coatings, where at high

deformation angle damage is twice that Zn-Sn coatings.

C O N C L U S I O N

In this work bending cracks in two Zn-based coatings are investigated in order to

evaluate mechanical properties, cracks paths and damage of intermetallic phases.

Presence of Sn do not changes intermetallic phases characteristic in traditional Zn

coatings, but presence of Ti leads to a presence of an outer zone, formed by a double

phases ductile matrix and a brittle dispessed phase.

Zn-Sn coatings are characterized by high bending strength and good elastic recovery

properties than Zn-Ti coatings, probably due to high values of damage.

333