Effect of Oxide Scale on Hot Dip Zn-Al-Mg Alloy Coating Prepared by Reduction Combined with Induction Heating

Abstract

Hot dipping Zn-Al-Mg coatings were prepared by rapid induction heating combined with gas protection. The influence of oxide scale on the structure and surface quality of a hot-dip Zn-6Al-3Mg alloy coating was studied in this paper. The results showed that the reaction of Fe-Al was suppressed by the scale on the surface of the steel plate. When the thickness of scale was 10 μm and the steel entry temperature was 900 °C, the surface quality of the coating was good. The Zn-Al-Mg coatings mainly consisted of the ternary eutectic structure of Zn/Al/MgZn2 and Fe4Al13 at the interface. When the scale thickness was 2–3 μm with the same steel entry temperature, the surface quality of the coating was poor, and serious stripe-like protrusion defects were formed on the surface of the coating, which was mainly caused by the Fe4Al13 phase separating from the substrate / coating interface into the overlay.

Wetting of liquid Zinc-aluminum-magnesium alloy on steel substrate during hot-dipping: Understanding the role of the flux

“…The hot-dipping Zn-Al-Mg alloy required higher surface quality of steel, the surface energy of the oxidized steel matrix is low, which is not conducive to the wetting of the alloy. Further, owing to the presence of oxides [33], the reaction of active Fe atoms in the steel substrate with the liquid Zn-Al-Mg alloy was hindered. Consequently, the wettability between the liquid Zn-Al-Mg alloy and the steel substrate was reduced, and a good quality coating could not be obtained.…”

“…SnCl 2 was added to F4, and the possible reactions that occurred during the wetting process are shown in formulas (29)- (33). SnCl 2 could undergo a substitution reaction with the base iron to form a uniform and dense Sn-containing film on the steel substrate, which reduced the interface energy between the liquid alloy and the steel substrate [38].…”