Presentation on theme: "Forced wetting of steels by liquid Zn-Al alloy"— 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 HTC6-9 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 protocolResultsConclusion
3 Continuous galvanizing process Annealing conditionsT800°CN295 vol.%H25 vol.%PH2O38 Pa
4 Industrial problem Annealing: Aims: Recrystallization of the steel. Protective atmosphere(N2-H2) to avoid oxidation of iron.However:Selective oxidation of alloying elements (Mn, Si, Al, Cr, P…)FEG-SEM image of IFTi steel surface after annealing
5 Objectives Forced wetting Improvement of the wettingForced wettingmetallic iron partly covered by oxide particlesliquid zinc alloyVariation of the kinetic energy of a zinc droplet impacting the steel surface
6 Materials Chemical composition of IFTi steels Polished up to 1 µmChemical composition of the zinc alloyZinc droplet mass: 80 ± 0.5 mgCMnSiPAlCrTiBNiN21179132717740.185.2Average composition of the IFTi steel studied (x 10-3 wt.%)AlFe0.18 ± 0.050.010 ± 0.001Average composition (4 trials) of Zn-Al-Fe alloy in weight% measured by Atomic Absorption Spectroscopy (SpectraAA, Varian)
7 Experimental apparatus and protocol 1Gas atmosphere: N2-H2, frost point -60°C (1 Pa H2O)AnnealingMelting and spreading of the dropletExcess pressure from 15 to 50 mbar to release the liquid metal droplet
8 Spreading sequence of the Zn-Al droplet on the steel surface CapillarySteel surfaceExcess pressure P= 15 mbar, V0 = 0.8 m/s, KE = 2.8 x10-5 J, t = 15 sThe 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.
9 MeasurementsMean contact angle is determined by averaging left contact angle and right contact angle*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.
10 Measurement of the impact velocities Sequence of droplet falling onto the substrate between t = 0 to 6 ms before the contact
11 Kinetic energy and We number Excess pressure (mbar)15273750V0 (m/s)0.8 ± 0.11.2 ± 0.61.4 ± 0.21.5 ± 0.3Kinetic energy (x 10-5J)2.8 ± 0.36 ± 38 ± 29 ± 3We354852Impact velocities and kinetic energies during the droplet fall calculated from the images depending on the excess pressureWe > 1 , Spreading is mainly controlled by kinetic energy
12 Characterization of the surface after annealing FEG-SEM image of IFTi steel surface after annealingRoughness of The IFTi steel surface after annealing (Interferometric Microscopy)EDS analysis of the oxide particlesRa (nm)Rt (nm)9 ± 231 ± 7Mn, Si, Al…Average roughness (5 points)
13 Dimensionless diameter KE = 2.8 x10-5 JIncrease of the spreading diameter when increasing the kinetic energy
14 Contact angleFe/ZnPopel et al. 1975Tarasova et al. 1976Increase KEDecrease of contact angle when increasing the kinetic energy
15 Reactive wetting SEM image of the interface Zn/Steel SEM image of the triple lineInterfacial layer formation pinned the triple line.Prevent the receding of the droplet.Concentration profile of Fe, Zn and Al.
16 Summary of the wetting experiments Kinetic energy (x10-5 J)2.8 ± 0.36 ± 38 ± 29 ± 3Static contact angle (deg)35 ± 520 ± 415 ± 414 ± 3D/D00.59 ± 0.040.70 ± 0.030.86 ± 0.140.94 ± 0.10D/D0_max0.62 ± 0.040.74 ± 0.050.91 ± 0.131 ± 0.14Average contact angle (left and right) for 3 series of trials measured when the droplet reached an equilibrium state after 1000 ms of contact
17 ConclusionForced 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.