Wettability of Mn x Si y O z by Liquid Zn-Al Alloys
- PDF / 253,071 Bytes
- 4 Pages / 593.972 x 792 pts Page_size
- 106 Downloads / 189 Views
I.
INTRODUCTION
TO reduce environmental problems such as global warming, many efforts have been made to develop lightweight high-strength steels. Subsequently, the galvanizing process has been applied widely to protect highstrength steels from corrosion.[1] Generally, manganese and silicon are added to the steel to enhance its strength by using the solid-solution-strengthening mechanism. However, during the annealing process, manganese and silicon segregate on the steel surface to form nanometersized oxides on or near the surface. As revealed in the phase diagram, stable oxides at the annealing temperature of around 1073 K (800 C) are MnO, MnSiO3, Mn2SiO4, and SiO2 (Figure 1). Recently, Lee et al. reported that during the annealing process of the highstrength interstitial free (IF) steel containing Si and Mn nanometer-sized oxides were formed easily on the steel surface.[2] Because these oxides show poor wettability when immersed in liquid zinc and zinc alloys, uncoated (bare) spots are found on the surface of high-strength steels after the hot-dip galvanizing process.[3–6] Kato et al.[7] and Nomura et al.[8] reported that the oxide type might affect the zinc-coating performance. On the other hand, Lee et al. asserted that the morphology of surface oxides rather than the oxide type might affect the wettability of high-strength steels.[2,9] To clarify the dominant factor determining the wettability, we need the basic information of the wettability of each oxide by liquid zinc alloy. However, to the best of the authors’ knowledge, the wettability of each oxide by liquid zinc alloys has not yet been reported. In the present study, therefore, the wetting YUNKYUM KIM and MINSOO SHIN, Graduate Students, and JOONHO LEE, Associate Professor, are with the Department of Materials Science and Engineering, Korea University, Seoul 136-713, Korea. Contact e-mail: [email protected] CHENGYING TANG, formerly Postdoctoral Researcher with the Department of Materials Science and Engineering, Korea University, is now Professor with the Department of Materials Science and Engineering, Guilin University of Electronic Technology, Guangxi 541004, P.R. China. Manuscript submitted March 3, 2010. Article published online April 6, 2010. 872—VOLUME 41B, AUGUST 2010
behavior of MnO, MnSiO3, Mn2SiO4, and SiO2 by two liquid zinc alloys (Zn-0.12 wt pct Al and Zn-0.23 wt pct Al) was investigated with the dispensed drop method.
II.
EXPERIMENTAL
For the wetting experiments, a lab-made dispensed drop test machine was used. Details are described in reference 2. Here, we simply describe the general experimental procedure. In a cross-shaped quartz reaction tube, the liquid drop dispenser was placed 4 mm above the sample oxide substrate. The furnace was made up of Kanthal heating elements, which were capable of increasing the temperature up to 1273 K (1000 C). The furnace temperature was measured with two K-type thermocouples. The wetting experiments were conducted at 723 K (450 C) by dropping a drop of liquid zinc alloy (~0.1 g) onto the oxide sub
Data Loading...
