Abstract
The article presents the results of studies on the influence of Mg on the formation of the periodic layered structure of the Zn-AlMg coatings. These coatings were produced by the double batch hot dip method in a Zn bath and then in a Zn-Al(Mg) bath with a content of 15, 23, 31 wt.% Al and 3, 6 wt.% Mg. The microstructure of the coatings (OM, SEM) was revealed and the phase composition (XRD) obtained in two-component Zn-Al baths and Zn-AlMg baths were determined. The periodic layered structure was found to consist of alternating FeAl3 phase layers and a bath alloy (Zn + Al + Mg). Moreover, it was observed that the addition of 3 wt.% Mg reduces the thickness of the coating in baths containing 23 and 31 wt.% Al. However, the addition of 6 wt.% Mg causes complete disappearance of periodic layered structure in a bath with 23 wt.% Al. In a bath with a content of 31 wt.% Al the addition of 6 wt.% Mg creates a compact layer consisting of the FeAl3 phase containing the precipitation of the MgZn2 phase and Fe2Al5 phase. Such a structure of the coating transition layer limits the growth of the periodic layered structure in the coating.
Highlights
The hot dip galvanizing process is an efficient and economical way to protect steel structures against corrosion
Wang [9] claims that the presence of a periodic layered structure has a positive effect on the corrosion resistance of coatings
After removal from the Zn bath, the samples were immersed in the Zn-Al or Zn-AlMg bath for 30, 60, 120 and 240 s
Summary
The hot dip galvanizing process is an efficient and economical way to protect steel structures against corrosion. In batch hot dip methods, there is a need for fluxing and a much longer bath time and higher temperature. Under such conditions, the reactions between the iron and the bath are very violent, leading to the formation of complex coatings. The use of the double batch hot dip method for the production of coatings allows us to lower the bath temperature while ensuring the processability and continuity of the obtained coatings. Mg addition to the Zn-Al baths on the formation of periodic layered structure in coatings obtained by double batch hot dip methods
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