Effect of Mg on Microstructure and Growth Kinetics of Zn-22.3Al-1.1Si Coating

Abstract

The effects of Mg on the microstructure and growth kinetics of the hot-dip Zn-22.3Al-1.1Si-x Mg (x = 0, 0.2, 0.4, and 0.6) coatings were investigated in detail. Scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction studies revealed the presence of η-Zn, α-Al, Zn/Al eutectoid, (Si), Al/Si eutectic, and Zn/Al/Mg2Zn11 ternary eutectic on the top surface of these Mg-containing coatings. Especially, a small amount of MgZn2 phase appears in top surface of Zn-22.3Al-1.1Si-0.6Mg coating. Five phases are found in the alloy layers, i e, Fe2Al5, FeAl3, τ5C, τ5H, and τ1. The addition of 0.2% Mg can delay the emergence of FeAl3 phase. When the Mg content is more than 0.2%, the outer layers of coating change from τ5C to τ5H phase. The growth of the inhibition layer is diffusion controlled for various Mg content baths. Mg improves the corrosion resistance of the Mg-containing coatings, and the Zn-22.3Al-1.1Si-0.6Mg coating possesses the highest protective properties.