Effect of Microstructure and Bending on the Formation of Cracks in Hot-dip Al-Zn-Si Coating

HUANG Quanxin; Wang Yinjun; ZHANG Jie

doi:10.16490/j.cnki.issn.1001-3660.2025.14.010

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Surface Technology ›› 2025, Vol. 54 ›› Issue (14) : 105-115. DOI: 10.16490/j.cnki.issn.1001-3660.2025.14.010

Corrosion and Protection

Effect of Microstructure and Bending on the Formation of Cracks in Hot-dip Al-Zn-Si Coating

HUANG Quanxin¹, Wang Yinjun^2,*, ZHANG Jie³

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Abstract

The work aims to investigate the effects of microstructure and bending deformation of hot-dip aluminum-zinc- silicon coated steel plate on coating cracks, and then explore the formation mechanism of coating cracks, so as to provide a basis for expanding the application of hot-dip aluminum-zinc-silicon coated steel plate in the field of stamping and forming. The hot-dip Al-Zn-Si coating alloyed samples with holding time of 0.5, 1 and 1.5 min at 600 ℃ were prepared by high-temperature hot stage experiment device, the microstructure of the coating and interface and the microhardness of τ₅ phase were studied. Furthermore, bending tests were carried out to explore the formation of Al-Zn-Si coating cracks. The hot-dip Al-Zn-Si coating consisted of intermetallic alloy layer and solidification layer from inside to outside, the solidification layer consisted of α(Al)-rich phases, α(Al)+β(Zn) zinc-rich phases, a small amount of acicular Si precipitated phases and micro phases of Al-V-Ti, the intermetallic alloy layer mainly consisted of τ₅ phases (Al₈Fe₂Si) and diffusion layer of Fe₃Al. The thickness of the intermetallic alloy layer increased with the increasing holding time at 600 ℃, the multi-layer gradient distribution structure formed and the growth kinetic expression of of τ₅ phases at 600 ℃ was y=8.06x^0.2-8.92, which conformed to the parabolic relationship. The microhardness of Al-Zn-Si alloy, Al-V-Ti phases and τ₅ phases were 85, 390 and 733HV0.2 respectively. The high hardness τ₅ phase in the interface alloy layer of the hot-dip aluminum-zinc-silicon coating was the key factor for the formation of cracks in the coating. The thickness of the interface alloy layer of the hot-dip aluminum-zinc-silicon coated steel plate with the thickness of 1 and 2 mm was about 1-1.5 and 1.5-2 μm respectively. For bending at 1.5a180°, the maximum crack gap width of the coating on the outer surface of the DC51D+AZ coated steel plate with a thickness of 2 mm was about 55 μm. For bending at 0a180°, the crack gap width of the interface alloy layer was about 1-3 μm, and the maximum crack gap width of the outer surface coating was respectively about 75 and 77 μm, respectively. With the increase of the bending angle, the gap of curved steel plate decreased, the bending strain increased, and the width of cracks on the curved outer surface of intermetallic compound alloy layer and coating increased gradually. When the coating was bent and deformed, cracking in the columnar crystals of τ₅ phases occurred firstly at interfacial alloy layer, forming micro-cracks with high density texture characteristics, which was conducive to the adsorption of colloidal corrosion products with better corrosion resistance. Through the microstructure control of the coating, the formability and corrosion resistance of hot-dip aluminum-zinc-silicon coated steel plate would be realized together.

Key words

hot-dip Al-Zn-Si coating / microstructure / τ₅ phase / hardness / bending / crack

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HUANG Quanxin, Wang Yinjun, ZHANG Jie. Effect of Microstructure and Bending on the Formation of Cracks in Hot-dip Al-Zn-Si Coating[J]. Surface Technology. 2025, 54(14): 105-115 https://doi.org/10.16490/j.cnki.issn.1001-3660.2025.14.010

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