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Substrate Surface alloying coating microstructure and properties of hot dip galvanized sheet

Author: LiYaDong
Tutor: WangShengMin；JiangSheMing
School: Kunming University of Science and Technology
Course: Materials Processing Engineering
Keywords: Galvannealed Surface roughness Zn-Fe alloy phase Nick Chalking
CLC: TG174.44
Type: Master's thesis
Year: 2010
Downloads: 96
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Abstract


In recent years, with high-grade hot dip galvanized and galvannealed steel sheets widely used in the automotive and home appliance, the people more and more attention to the surface quality of the galvanized sheet. The high surface quality galvanized sheet generally refers to the strict control of surface roughness and surface state, which called for the formation of plate-shaped, high dimensional accuracy, tolerances, no surface defects after order processing. Study found that the formation of surface defects of hot dip galvanized steel sheet for two main reasons, one due to the of hot galvanized cold rolled substrate surface defects of genetic make follow-up galvanized sheet surface quality can not meet the requirements; the other hand, due to hot-dip zinc production process, the formation of surface defects. And the changes of surface roughness and surface scratch is common to both the surface defects of the cold-rolled substrate. The topics to a different surface roughness and different types of scratches, the cold rolled substrate for the study, and its alloying galvanizing treatment. Experimental methods, the use of metallurgical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and glow spectrum (GDOES) observational studies with different roughness and different types of scratches substrate by the hot-dip galvanizing and alloying process Zn-Fe alloy coating morphology and growth process; study of surface roughness and scratches on the alloying coating performance. 60 ° V test, the neutral salt spray test and electrochemical corrosion experiments on different state of the surface of the substrate alloy plating the anti chalking performance and the evaluation of corrosion resistance. The results show that the same alloying with the substrate surface roughness increases, the specific surface area of ??the reaction between the substrate and the liquid zinc increases, the reaction rate of a Zn-Fe coating layer; alloying of the plating layer. Zinc process - iron diffusion speed and the degree of alloying of the coating increased. Coating Fe content increased to improve the weldability and corrosion resistance of the coating, but it reduces the anti-chalking performance of the coating. It was found, 510 ℃, insulation 15s alloying process, the substrate roughness 0.6 lt; Ra ≤ 0.8 μm, the the alloying coating has the best overall performance. The presence of substrate scratches undermine the continuity and smoothness of the surface, in the hot-dip galvanizing process hinder the substrate surface flow of liquid zinc galvanized coating surface to form a small bump. Alloying process, scratch intense than normal interface interface alloy reaction, leading to scratch parts of zinc - iron alloy phase abnormal growth of the coating surface to form raised, raised the height of the scratch depth and the degree of alloying. Plating raised produce to reduce the the coating anti chalking performance of, and had a negative impact on the corrosion resistance of the coating.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology > Metal complex layer of protection
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