Effect of Mg on the Microstructure and Corrosion Resistance of the Continuously Hot-Dip Galvanizing Zn-Mg Coating

Anping Dong; Baoping Li; Yanling Lu; Guoliang Zhu; Hui Xing; Da Shu; Baode Sun; Jun Wang

doi:10.3390/ma10080980

Effect of Mg on the Microstructure and Corrosion Resistance of the Continuously Hot-Dip Galvanizing Zn-Mg Coating

Materials (Basel). 2017 Aug 22;10(8):980. doi: 10.3390/ma10080980.

Authors

Anping Dong^{1

2}, Baoping Li³, Yanling Lu⁴, Guoliang Zhu^{5

6}, Hui Xing^{7

8}, Da Shu^{9

10}, Baode Sun^{11

12

13}, Jun Wang^{14

15

16}

Affiliations

¹ School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. apdong@sjtu.edu.cn.
² Shanghai Key Lab of Advanced High-temperature Materials and Precision Forming, Shanghai 200240, China. apdong@sjtu.edu.cn.
³ Hechi Industry and Information Committee, Hechi 547000, China. libaoping987654@163.com.
⁴ Department of Nuclear Materials Science and Engineering, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China. luyanling@sinap.ac.cn.
⁵ School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. glzhu@sjtu.edu.cn.
⁶ Shanghai Key Lab of Advanced High-temperature Materials and Precision Forming, Shanghai 200240, China. glzhu@sjtu.edu.cn.
⁷ School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. xinghui@sjtu.edu.cn.
⁸ Shanghai Key Lab of Advanced High-temperature Materials and Precision Forming, Shanghai 200240, China. xinghui@sjtu.edu.cn.
⁹ School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. dshu@sjtu.edu.cn.
¹⁰ Shanghai Key Lab of Advanced High-temperature Materials and Precision Forming, Shanghai 200240, China. dshu@sjtu.edu.cn.
¹¹ School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. bdsun@sjtu.edu.cn.
¹² Shanghai Key Lab of Advanced High-temperature Materials and Precision Forming, Shanghai 200240, China. bdsun@sjtu.edu.cn.
¹³ State Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China. bdsun@sjtu.edu.cn.
¹⁴ School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. junwang@sjtu.edu.cn.
¹⁵ Shanghai Key Lab of Advanced High-temperature Materials and Precision Forming, Shanghai 200240, China. junwang@sjtu.edu.cn.
¹⁶ State Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China. junwang@sjtu.edu.cn.

Abstract

The microstructure of continuously hot-dip galvanizing Zn-Mg coating was investigated in order to obtain the mechanism of the effects of Mg on the corrosion resistance. In this paper, the vertical section of the Zn-0.20 wt % Al-Mg ternary phase diagram near the Al-low corner was calculated. The results indicates that the phase composition of the Zn-0.20 wt % Al-Mg ternary phase diagram near the Al-low corner is the same as Zn-Mg binary phase diagram, suggesting Al in the Zn-Mg (ZM) coatings mainly concentrates on the interfacial layer between the coating and steel substrate. The microstructure of continuously hot-dip galvanizing ZM coatings with 0.20 wt % Al containing 1.0-3.0 wt % Mg was investigated using tunneling electron microscopy (TEM). The morphology of Zn in the coating changes from bulk to strip and finally to mesh-like, and the MgZn₂ changes from rod-like to mesh-like with the Mg content increasing. Al in the ZM coatings mainly segregates at the Fe₂Al₅ inhibition layer and the Mg added to the Zn bath makes this inhibition layer thinner and uneven. Compared to GI coating, the time of the first red rust appears increases by more than two-fold and expansion rate of red rust reduces by more than four-fold in terms of salt spray experiment. The ZM coating containing 2.0 wt % Mg has the best corrosion resistance. The enhanced corrosion resistance of ZM coatings mainly depends on different corrosion products.

Keywords: TEM; Zn-Mg coating; continuously hot-dip galvanizing; corrosion resistance.