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The effect of adding trace elements in hot galvanizing liquid of electric heating zinc boiler

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The effect of adding trace elements in hot galvanizing liquid of electric heating zinc boiler

Published: 2018-05-30 Author: Click:

The effect of adding trace elements in hot galvanizing liquid of electric heating zinc boiler

Zinc pot abstract: the introduction of all kinds of alloy elements in hot galvanizing liquid will have an important impact on the performance, structure and appearance of zinc coating.This paper mainly introduces the influence of the lining corrosion performance of the broken layer when 11 kinds of common elements such as aluminum, silicon, magnesium and rare earth are added into the hot quilt zinc liquid, and introduces the latest theoretical research results at home and abroad, which has certain guiding significance for the research of hot quilt zinc alloy.

The introduction

With the rapid development of China's automobile, construction and household appliances industries, the demand for highly corrosion resistant materials is increasing year by year.Hot dip galvanizing as a coating technology with excellent corrosion resistance, has been widely used in various industries.The addition of trace elements in hot dip galvanizing solution can effectively improve the corrosion resistance and coating quality of steel materials.

The effect of every element turbulence in hot galvanizing liquid

1.1 rare earth elements

After mixing rare earth elements with natural dielans in hot dip galvanizing liquid, not only can improve the coating surface luster, improve the coating corrosion resistance and machining performance, prolong the service life, but also can reduce the thin coating thickness and obviously reduce the temperature of hot dip galvanizing liquid.It is generally believed that the addition of thin elements will not change the structure of hot dip galvanized layer, the role of rare earth elements on the coating mainly has two aspects: l) under certain cooling conditions the presence of thin elements can make the coating surface organization finer;2) rare earth can improve the compactness of the coating surface film, form a dense and uniform oxide layer on the coating surface, and thus improve its high temperature oxidation resistance.

Recent studies have suggested that the diffusion of rare earth elements in metal compounds is uneven, and segregation occurs at the phase interface where steel base and zinc liquid contact, which inhibits the mutual diffusion of matrix and coating alloy elements and delays the growth of intermetallic compounds.And studies suggest that rare earth elements can on metal impurities, especially the high electronegativity of S, O, S, 0 impurities such as higher electronegativity will accelerate the grain boundary corrosion, is an important factor of accelerated corrosion) yuan home removal effect, as the enrichment of surface active elements in the coating surface, forming dense homogeneous oxidation film that limit blocked outside atoms to zinc coating internal diffusion, slow down the corrosion process, improve the corrosion resistance.

Rare earth elements in hot dip galvanizing solution have a certain impact on the coating thickness, adding the appropriate amount of rare earth elements can significantly reduce the thickness of the alloy layer, when the rare earth is 0.03%~0.10%, zinc alloy layer thinning degree is the most obvious;However, when the rare earth is more than 0.20%, RE - Zn compounds appear in the coating, affecting the properties of the coating.

1.2 silicon

When the iron content in hot dip galvanizing liquid is high, the silicon can react with the iron to form the iron-silicon compound to remove the iron.In addition to removing iron, silicon can inhibit the growth of zinc alloy layer, but the coating containing silicon often shows brittleness.Because silicon is almost insoluble in zinc alloy coating and distributed on the substrate in the form of bulk silicon single particle size, and silicon gu grain hardness is much higher than the substrate, in zinc alloy coating silicon particles play a role of hard point, so silicon containing zinc alloy coating has a higher wear resistance.The presence of silicon can also improve the high temperature and corrosion resistance of zinc alloy coating.

Adding proper amount of silicon in hot dip galvanizing solution can inhibit the growth of Fe - Zn or Fe - Al alloy phase and enhance the adhesion of coating.The addition of silicon can also improve the corrosion resistance of the coating, because the segregation of silicon at the grain boundary, the formation of silicon oxide, inhibit the oxidation of beta Zn phase.When Si is less than 0.01%, its effect is not obvious (inhibited by aluminum). Silicon cannot react eutectically with aluminum or zinc on grain boundary, and cannot improve the corrosion resistance of coating.When w (si) more than 2.00%, beyond its solubility in zinc, in the coating was dispersion-like precipitation, on the surface of the coating formed small spots, making its mechanical processing performance damaged, so the ohm (si) should be 0.02%~1.00%.

1.3 mn element

It is found that when manganese is added to hot dip galvanizing liquid, the bottom of molten zinc pot produces a lot of powdery slag, and the amount of powdery slag increases with the increasing amount of manganese.Further studies show that manganese can promote the growth of the phase phase layer in zinc coating, inhibit the growth of the 'phase layer, and manganese can promote the phase phase from broken to compact.

Manganese can improve the corrosion resistance and oxidation resistance of the coating.Manganese content in the coating is very low, usually in the form of particles d less than 2 microns, because manganese did not fully melt in zinc.Because the relative density of liquid manganese is less than the relative density of liquid zinc.As a result, it accumulates near the surface of liquid zinc. When the sample is lifted, the coating surface forms dispersed small manganese rich particles (manganese also has a certain surface aggregation effect). Manganese in the air will generate a continuous dense oxide protective film, improving the oxidation resistance and corrosion resistance of zinc coating in the air.

The microstructure of zinc coating will change with the addition of manganese in hot dip galvanizing solution.In hot dip galvanizing liquid.Omega (Mn) less than 0. 50%, the coating is mainly composed of delta, zeta and eta, manganese can promote uniform density and or phase formation, zinc plating thickness with the plating solution, omega (Mn) increase and decrease.When the hot dip galvanizing liquid in (Mn) is 0.5.%, manganese in the alloy layer, zeta phase in particular, is conducive to photograph the delta and the uniform of the zeta phase, close, and affect the delta/zeta interface diffusion process;When hot dip galvanizing liquid.When ohm (Mn) exceeds 0.70%, scattered 8 particles appear in the layer, and the coating thickness increases significantly;When hot dip galvanizing liquid.(Mn) > 5. 00 %, coating corrosion resistance, adhesion and ductility can be improved.

Addition of Mn has been considered to be an effective substitute for Ni in thermal zinc solution.However, due to the addition of Mn in hot dip galvanizing liquid, the coating roughness will be increased and the coating will be dark.Meanwhile, the inhibition effect of Mn on fe-zn reaction of hot dip galvanized reactive steel is weaker than that of Ni.The latest findings suggest that.Manganese has no obvious inhibiting effect on the growth of coating thickness of Q345 steel, but has obvious inhibiting effect on the reactivity of Q235 and fe-0.08% Si.Therefore, adding manganous in hot dip galvanizing liquid has not been widely used in industry.

1.4 tin element

Generally, tin is added to hot dip galvanizing liquid in order to get a better appearance of the coating, get a variety of beautiful zinc flowers, so usually, tin and aluminum at the same time in hot dip galvanizing liquid will get a good effect, such coating not only has the advantages of adding aluminum, but also has the beautiful appearance of adding tin.The presence of tin can not only obtain beautiful zinc flowers, but also reduce the melting point of hot dip galvanizing solution (the melting point of tin is 217 ℃).Because tin erodes iron about half as fast as zinc does;After adding tin, the dry degree of hot dip galvanized solution will increase, so the thickness of galvanized layer will also increase.Studies have shown that when the hot dip galvanizing liquid in (Sn) more than 1.00% can make the coating thin;When ohm (Sn) is higher than 0. 30%, tin accumulates at the grain interface of zinc to form zinc-tin eutectoid, causing local microbattery, corrosion after the formation of pits, increase the corrosion rate of coating, corrosion resistance to decline.

In the silicon containing hot dip galvanizing liquid, when adding human ohm (Sn) for 3% - 12%, on the 0.37% Si steel hot dip galvanizing layer thickness changes show that hot dip galvanizing liquid.Omega (Sn) is 3% - 5%, can inhibit the activity of high silicon steel galvanized layer of abnormal growth, galvanized layer thickness decreased significantly, and its inhibition mechanism is: due to Sn difficult to soluble in Fe - zinc alloy layer, in hot galvanizing process is accompanied by the growth of a Fe zinc alloy layer, the Sn row to the Fe zinc/liquid interface on the growth of zinc layer, when it comes to an adequate amounts of Sn will grow in a Fe zinc alloy layer of leading edge to form a continuous layer, block mutual diffusion of Fe and zinc, thereby inhibit the growth of a Fe zinc alloy layer.According to the zinc-tin binary phase diagram, it can be clearly seen that at 450 ℃, the solubility of tin in zinc reaches 100 %, so the addition of tin can have a large range, but tin easy to produce grain boundary corrosion, make coating corrosion resistance decline, so the mass fraction of tin in hot dip galvanized liquid to strictly control red.

Galvanizing production line

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