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Forced wetting of steels by liquid Zn-Al alloy J.-S. Diawara*, M.-L. Giorgi*, J.-B. Guillot*, A. Koltsov**, D. Loison** 6th International Congress HTC.

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Presentation on theme: "Forced wetting of steels by liquid Zn-Al alloy J.-S. Diawara*, M.-L. Giorgi*, J.-B. Guillot*, A. Koltsov**, D. Loison** 6th International Congress HTC."— Presentation transcript:

1 Forced wetting of steels by liquid Zn-Al alloy J.-S. Diawara*, M.-L. Giorgi*, J.-B. Guillot*, A. Koltsov**, D. Loison** 6th International Congress HTC 6-9 May 2009 * École Centrale Paris – Laboratoire de Génie des Procédés et Matériaux ** ArcelorMittal Research S.A.

2 Outline Industrial context and objectives Experimental apparatus and protocol Results Conclusion 2

3 Continuous galvanizing process 3 Annealing conditions T800°C N2N2 95 vol.% H2H2 5 vol.% PH2OPH2O 38 Pa

4 Industrial problem FEG-SEM image of IFTi steel surface after annealing Annealing: Aims: Recrystallization of the steel. Protective atmosphere (N 2 -H 2 ) to avoid oxidation of iron. However: Selective oxidation of alloying elements (Mn, Si, Al, Cr, P…) 4

5 Objectives Forced wetting metallic iron partly covered by oxide particles liquid zinc alloy Variation of the kinetic energy of a zinc droplet impacting the steel surface 5 Improvement of the wetting

6 Materials Chemical composition of IFTi steels Polished up to 1 µm Chemical composition of the zinc alloy Zinc droplet mass: 80 ± 0.5 mg CMnSiPAlCrTiBNiN Average composition of the IFTi steel studied (x wt.%) AlFe 0.18 ± ± Average composition (4 trials) of Zn-Al-Fe alloy in weight% measured by Atomic Absorption Spectroscopy (SpectraAA, Varian) 6

7 Experimental apparatus and protocol 1 Gas atmosphere: N 2 -H 2, frost point -60°C (1 Pa H 2 O) Annealing Melting and spreading of the droplet Excess pressure from 15 to 50 mbar to release the liquid metal droplet 7

8 8 Spreading sequence of the Zn-Al droplet on the steel surface Excess pressure P= 15 mbar, V 0 = 0.8 m/s, KE = 2.8 x10 -5 J, t = 15 s The flight and the impact of the droplet on the surface was followed by a high-speed camera (CMOS, pco. 1200hs) at a rate of frames/s. Capillary Steel surface

9 Measurements 9 *Drop Snake method programmed as a plug-in for ImageJ * A. F. Stalder, G. Kulik, D. Sage, L. Barbieri, Hoffmann P., (2006) Colloids Surf, A Physicochem. Eng. Asp. 286:92. Mean contact angle is determined by averaging left contact angle and right contact angle

10 Sequence of droplet falling onto the substrate between t = 0 to 6 ms before the contact 10 Measurement of the impact velocities

11 Kinetic energy and We number Excess pressure (mbar) V 0 (m/s) 0.8 ± ± ± ± 0.3 Kinetic energy (x J) 2.8 ± 0.36 ± 38 ± 29 ± 3 We Impact velocities and kinetic energies during the droplet fall calculated from the images depending on the excess pressure 11 We > 1, Spreading is mainly controlled by kinetic energy

12 Characterization of the surface after annealing EDS analysis of the oxide particles FEG-SEM image of IFTi steel surface after annealing Roughness of The IFTi steel surface after annealing (Interferometric Microscopy) R a (nm)R t (nm) 9 ± 231 ± 7 Average roughness (5 points) 12 Mn, Si, Al…

13 Dimensionless diameter Increase of the spreading diameter when increasing the kinetic energy 13

14 14 Contact angle Decrease of contact angle when increasing the kinetic energy Fe/Zn Popel et al Tarasova et al Increase KE

15 Reactive wetting Interfacial layer formation pinned the triple line. Prevent the receding of the droplet. 15 SEM image of the interface Zn/Steel Concentration profile of Fe, Zn and Al. SEM image of the triple line

16 Summary of the wetting experiments Kinetic energy (x10 -5 J)2.8 ± 0.36 ± 38 ± 29 ± 3 Static contact angle (deg)35 ± 520 ± 415 ± 414 ± 3 D/D ± ± ± ± 0.10 D/D 0 _max0.62 ± ± ± ± 0.14 Average contact angle (left and right) for 3 series of trials measured when the droplet reached an equilibrium state after 1000 ms of contact 16

17 Conclusion Forced wetting of steel substrates by a liquid zinc alloy (0.18 wt% Al wt% Fe). Sequences of falling and spreading of the droplet onto the surface by varying the impact velocity. Evolution of the contact angle and the dimensionless diameter with spreading time. Increasing the impact velocity of the droplet causes an increase of the final and maximum spreading diameter and a decrease of the final contact angle. 17

18 Thank you for your attention 18


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