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技术简介 INTRODUCTION
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‘steel hot dip aluminum’ technology introduction

‘Hot dip aluminum steel’ is the steel or steel products into molten salt under a certain temperature in the liquid, make the steel base surface activation and fully after purification, put forward and put into molten in rare earth aluminum liquid rapidly, after dipping appropriate time, the steel substrate to form a certain thickness of inter metallic compound, the aluminum layer of dense homogeneous and 3 oxidation 2 aluminum oxide film. The two bath process hot dip aluminum technology can make the steel and metal products for the steel matrix composites, and the energy conservation and environmental protection new materials. In high temperature, high pressure and strong corrosive medium environment have the excellent anticorrosion performance. Ten years of practice and application proves that the 'steel hot dip aluminum steel and steel products is the most effective anti-corrosion methods.

‘Hot dip aluminum steel’ products including plate, pipe, wire, profiles and suitable for hot dip aluminum anticorrosive equipment, etc. This composite material is refers to the compound layer on the surface of the steel substrate, including basic - iron alloy layer closest to the steel substrate; The middle - pure aluminum layer; Outer - dioxide three aluminum oxide film. Iron alloy layer is extremely hard and high melting point metal compounds, has excellent high temperature oxidation resistance and wear resistance. Pure aluminum layer has excellent corrosion resistance and decorative, so steel heat capacity dip aluminum technology products produced by the hot dip aluminum steel, are a mechanical strength of steel matrix, and the corrosion resistance of aluminum and aluminum alloy of high temperature oxidation resistance and wear resistance of highly efficient steel. Because of the hot dip aluminum steel has much special performance; therefore they are widely used in petroleum, chemical industry, metallurgy, machinery, building, transportation, light industry, shipbuilding, electric power, automotive, marine engineering and highway engineering and other fields.

Technological process

Raw material-Pretreatment-Surface inspection-Preheat-High temperature liquid salt purification surface-Dip aluminum plating-Slow refrigerating treatment-Post treatment-Surface Check- entering warehouse- Product packaging

The microstructure characteristics of hot dip aluminum steel

Hot dip aluminum steel make the combination between iron and aluminum to atom, by metallic bonding tightly together, as shown, reveals the microscopic from outside to inside with AL2O3 oxide film, the order of the pure aluminum, iron, aluminum alloy layer formed a composite layer. Is carbon steel, banded structure and composite layer in parent metal close contact.

Thickness of the composite layer: If is carbon steel, the pure aluminum layer of 0.04-0.07 MM, iron, aluminum alloy layer is about 0.05 MM. Will the thickness of each layer for steel type, carbon content and dip aluminum temperature and time are different

If the parent metal is alloy steel, the composite layer is different from the above

The performance of hot dip aluminum:

The corrosion resistance mechanism:

Immersion corrosion resistance of aluminum steel is through AL203 oxide film stability and self-healing, the corrosion resistance of iron alloy layer and play out.

(1) The weather

Dip aluminum products can damp in the sea areas, industrial zone and sulfurous springs, such as corrosive environment for long-term use

Dip aluminum, galvanized steel corrosion experiment results mg/cm

Test name Test condition Galvanized steel Dip aluminum steel Type 1 Type 2
SO Test contains 16%SO Air -2825 -130.0 -104.0
Nitric acid test contains 20%HNO Air Prototype disappear -2.0 -3.0

(2) Sea water resistance

Hot dip aluminum steel is very good for seawater corrosion, not only in the Marine environment, is also have the same effectiveness in tidal and wave

Dip aluminum steel, resistant to salt water corrosion is very excellent, listed in the table below 3 steel corrosion test results in 3% NaCl aqueous solution.

Three kinds of corrosion of steel in 3% NaCl aqueous solution

material original weight Surface area Amount corrosion
24H 72H 480H
mg mg/cm mg mg/cm mg mg/cm
Carbon steel 26.6378 27.90 6.3 0.260 16.7 0.600 136.7 4.860
Dip aluminum steel 29.0568 27.90 1.7 0.061 1.7 0.057 2.8 0.100
13Gr steel 26.6982 27.90 3.2 0.115 14.8 0.532 26.0 0.934

(3) Resistance to water

Generated to the aluminum surface passivation of alumina membrane and alloy layer corrosion resistance, so dip aluminum products have strong water resistance.

Due to the different water quality, PH, temperature, flow rate, the dip aluminum corrosion endurance also to have certain differences

Dip aluminum wire (room temperature) (liquid temperature)

Galvanized steel wire, liquid temperature (room temperature)

The corrosion loss

Dipping time

Alkaline acid

The hot dip aluminum and galvanized amount of corrosion in the water

Material and measure Amount corrosion Dip aluminum steelCorrosion depth
hot dip aluminum 0.007 0.007
galvanized 0.038 0.038

(4) Resistance to stress corrosion cracking

Some special steel, carbon steel such as if in a solution containing chloride and sulfide in the medium (low resistance), stress corrosion cracking happens, if the dipping aluminum can prevent them. Use dip aluminum tube in the heat exchanger experiment, whatever the heat exchanger, has not been any stress cracking phenomenon.

(5) Other corrosive solution

Corrosion resistance of hot dip aluminum products type aqueous solution, refining enterprise heat exchanger in the oil and water resistant sulfur ions, chloride ion, and organic acids' inorganic salt has excellent corrosion resistance.

For organic acid, nitric acid, sulfuric acid, ammonium (more than 1% and less than 1%), water for hydrogen sulfide, sulfurous acid aqueous solution, urea, water, salt water 'potassium chloride calcium chloride, hot spring water containing sulfur has corrosion resistance

Heat resistance

(1)high temperature oxidation resistance

Ordinary steel quickly oxidation under high temperature is at 500 degrees Celsius, and dip aluminum steel has strong high temperature oxidation resistance and high temperature sulfur corrosion and SO. This is due to the oxide film aluminum surface to prevent the proliferation of oxygen, and iron alloy layer on the running of the (as mentioned in the reactive), also has the very strong heat resistance.

The choice of aluminum can prevent the oxidation of iron oxide

Several kinds of steel heat resistance test (100 h) after gasification increment (g/cm)

Heating condition 600c 800c 1000c
oxidation increment raw material raw material Dip aluminum incremental ratio raw material Dip aluminum incremental ratio
material —— —— —— —— —— —— ——
Carbon steel —— 0.075 0.0011 68;1 0.41 0.0055 75;1
Forged steel 0.0032 0.0074 0.0095 78;1 0.41 0.0077 52;1
Ordinary steel 0.0024 0.1 0.0023 43;1 0.37 0.012 31;1
13CY steel —— —— —— —— 0.22 0.0062 35;1

(2) Resistance to permeability, decarburization

Dip aluminum composite layer on the surface of the steel can restrain the invasion and spread of carbon. In addition, under the environment of high temperature reducing gas can also prevent the raw material (steel) decarburization.

Hot dip aluminum steel welding:

Dip aluminum steel to be welded, dipped aluminum steel special electrode (A312SL) are available, and the corrosion resistance of the welding parts of the same as the leaching performance of the aluminum and steel. During welding, aluminum layer of high temperature diffusion penetration, parent metal also protected

Note:

(1) and other metal contact corrosion electrochemical corrosion)

All kinds of metal in the electrolyte solution (fresh water, sea water) have their own potential. Due to the potential difference, interaction of different metal can form the battery, caused electrochemical corrosion. Hot dip aluminum steel should also pay attention to in the use of this influence.

2) As heat resistant, above 500 degrees Celsius conditions make it for a long time will be stripped. Should be around 850 degrees Celsius temperature heating in advance 1-2 hours for diffusion treatment, the surface of pure aluminum layer spreading matrix permeability of formation of Fe - Al alloy layer.

3) Due to the leaching aluminum alloy layer is very hard, ductility is small, processing should be paid attention to avoid bending radius is too small.

4) After dipping aluminum steel size precision of the change, so the bolt, nut and other joint position allowance.

Visual inspection Aluminum layer continuous, good surface, without slag, no needle the plating
Characterization of inspection In the score line on both sides of the 2.0 MM aluminum layer peeling off
Aluminum layer thickness and quantity Coating coverage thickness

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