Skip to content
Licensed Unlicensed Requires Authentication Published by De Gruyter April 18, 2013

The Mechanism of Dross Formation during Hot-dip Al-Zn Alloy Coating Process

Qun Luo, Feng Jin, Qian Li, Jie-Yu Zhang and Kuo-Chih Chou


The dross formation is closely related with the solubility of Fe in the molten bath. When the Fe level exceeds the saturation solubility of liquid, the dross precipitates in the form of intermetallic compounds. Inductively coupled plasma atomic emission spectrometry (ICP) was used to determine the content of Fe in molten bath. The morphology of the bottom dross was observed by scanning electron microscopy (SEM). Based on the experimental results and the calculated phase diagram of the Al-Zn-Si-Fe system, the effects of bath temperature and Si content in the molten bath on the Fe solubility were analyzed, and then the mechanism of dross formation was investigated. The results showed that when the bath temperature decreased from 630 °C to 590 °C, the solubility of Fe in liquid reduced from 0.12 wt.% to 0.06 wt.% and 0.17 wt.% FeAl3 would precipitate from the liquid. Compared with the Fe dissolution lines at different Si content, it can be seen that the solubility of Fe in Al-Zn melt increased with the increasing of Si content from 0.5 wt.% to 1.5 wt.%. However, the amount of precipitated FeAl3 in 55wt.%Al-Zn-1.5Si molten alloy (0.17 wt.%) was greater than that in 55wt.%Al-Zn-0.5Si molten alloy (0.14 wt.%) in the same temperature range. It means that the more the Si contents in the liquid, the greater the amount of dross formation.

Shanghai Key Laboratory of Modern Metallurgy & Materials Processing, Shanghai University, Shanghai 200072, China

Received: 2012-08-01
Accepted: 2012-12-23
Published Online: 2013-04-18
Published in Print: 2013-04-17

©[2013] by Walter de Gruyter Berlin Boston

Scroll Up Arrow