Study of some issues in the field of aluminum, porous ceramic filter

Adtech specializes in the production of porous ceramic filter, which filters impurities in molten aluminum.

Contents

1. Gas in molten aluminum

2. How hydrogen is produced in molten aluminum

3. Effect of gas on aluminum ingot

4. Source of inclusions 5. Interaction between inclusions and hydrogen
1. Gas in molten aluminum
The gas in molten aluminum is mainly hydrogen, with a content of 80%-90%, followed by nitrogen, oxygen,
Carbon monoxide; Hydrogen is practically insoluble in solid aluminum, but very soluble in the liquid. The solubility of hydrogen above and below the solidus line is 0.65mL and 0.034mL per 100g of aluminum liquid (hydrogen is at 0.1MPa), that is, the solubility of hydrogen in the solid-liquid two-phase difference is 19.1 times, and per 100g of molten aluminum The normal hydrogen content in the blood is 0.1~0.4mL. Due to the difference in solubility, hydrogen tends to escape from the melt. When the hydrogen pressure is greater than the surface tension and hydrostatic pressure, bubbles are formed, which in turn produces pinholes in the casting. Therefore, in the purification of aluminum alloy melt, the main problem is that the hydrogen content of the aluminum alloy is high, and the existing methods cannot meet the production requirements of high-quality aluminum alloy castings. Usually, when the hydrogen content per 100g of aluminum is 0.1~0.2mL, it can basically meet the production requirements. For castings with special requirements (such as aviation castings), the hydrogen content per 100g of aluminum should be below 0.06mL.
2. How is hydrogen produced in molten aluminum (1)?
Hydrogen is a gas that can have a certain solubility in molten aluminum. It is caused by the liquid aluminum and moisture under melting conditions.
There are several sources of moisture generated by the reaction: 1. Moisture in the air 2. Fuel combustion products 3. Moisture adsorbed on the surface of the charge 4. The residual grease on the waste is melting Hydrogen gas is released when the scrap is submerged at high temperature, when the grease reacts with the molten metal, or when the scrap cracks. 5. Moisture absorbed by tools in the furnace Some tools used for feeding, stirring, or skimming will naturally absorb moisture. 6. Absorbed or chemically bound moisture on solid scouring agents or their residues. A by-product of refining with chlorine is the chloride salts of aluminum and magnesium. These chlorides are highly absorbent and cling to tools or the inside walls of the furnace.
2. How is hydrogen produced in molten aluminum? (2)
7. Before the surface of the dry container is in contact with the molten aluminum, the coating of refractory mud, the melting or holding furnace made of refractory materials, the furnace lining or the launder made of refractory materials are not completely dried, all of which are harmful to hydrogen. the formation has an impact. 8. Gas The gas introduced into molten aluminum for various refining purposes may contain moisture. If you insist on using some methods to reduce the moisture entering the molten metal, the hydrogen content will be reduced. In addition, because the dissolution of hydrogen and the formation of oxides increase with the increase in temperature, the temperature in the furnace should be strictly controlled. If possible, the maximum temperature during melting should be lower than 760°C. During melting, in addition to dissolving, hydrogen will also be generated and enter the molten aluminum due to the reaction between the molten aluminum and the moisture in the air during the transportation or pouring of the aluminum liquid, especially when the oxide film on the liquid surface is due to When rolled over and destroyed. The dissolution of hydrogen is slower when the liquid level is still.

Adtech specializes in the production of porous ceramic filter, which filters impurities in molten aluminum.

3. Effect of liquid aluminum gas on aluminum quality (1)
Hydrogen exists in the atmosphere and is very soluble in molten aluminum. Hydrogen trapped in molten aluminum can produce white spots or pores, adversely affecting the final product. For example, these aluminum articles may not achieve acceptable mechanical or physical properties and may adversely affect tensile strength. Hydrogen inclusions may also cause fatigue cracks in materials. Casting rejections may be caused by pinholes in castings or machined surfaces, or leaks when castings are required to withstand pressure without leakage. Porosity may cause blistering in forged products, extruded products, and thin and thick plates when processed from round ingots. The poor surface properties of the material, such as spalling during casting and foaming during heat treatment of the material, also indicate the presence of hydrogen.
3. Effect of molten aluminum gas on aluminum quality (2)
Hydrogen is about 20 times more soluble in liquid aluminum than in solid aluminum. Due to the difference in solubility, hydrogen tends to escape from the solution during the solidification process, or slowly diffuse, or quickly form bubbles to generate hydrogen molecules. Bubbles form when the hydrogen pressure is greater than the surface tension and hydrostatic pressure. In this way, if the hydrogen content in the aluminum liquid is high during the solidification process, the hydrogen will exist in the form of a solid solution, pores, or breakpoints. Therefore, it is important to control the hydrogen content at a low level of high-quality castings are to be obtained.

So the degassing unit produced by Adtech can solve the problem of excess gas in molten aluminum.
3. Sources of inclusions in molten aluminum
Inclusions refer to any solid above the liquidus line, any solid, and any substance other than liquid. Common non-metallic impurities in molten aluminum include oxides, nitrides, carbides, borides, etc., mostly in the form of particles, and the typical particle size is in the range of 1-30 microns. In addition to coming from the charge, it is mainly the product of chemical reactions during the melting process. The thickness of the oxide film on the aluminum surface is 2-10 microns, and it increases to 200 microns when it is close to the melting point. The oxide film on the liquid surface is not only thicker but also the structure has changed; the dense layer on the side facing the aluminum liquid has a protective effect on the aluminum liquid. The outer side of aluminum is loose, and there are small pores of 5-10 microns inside, which are filled with hydrogen, air, and water vapor. If the liquid film is stirred into the aluminum, it will add impurities and gas. In addition, there will be some undesirable primary intermetallic compounds in high-alloy aluminum products, such as aluminum-zirconium, aluminum-titanium, etc., and iron-containing aluminum alloys will also form iron-rich aluminum-iron phases and aluminum-silicon-iron phases. These impurities, directly affect the mechanical properties of the product.
3. Interaction between inclusions and hydrogen in molten aluminum

Adtech specializes in the production of porous ceramic filter, which filters impurities in molten aluminum.

There is a strong interaction between the inclusions and the gas in the aluminum alloy, and the hydrogen content in the molten aluminum is greatly affected by the inclusions. When the inclusion content is 0.002% and 0.02%, the corresponding hydrogen content is 0.2ml/100gAL and 0.35 ml/100gAL. In the case of the same hydrogen content, the higher the inclusion content, the higher the pinhole rate; on the contrary, when the impurity content in the aluminum liquid is very low, the hydrogen content is also very low, even if the hydrogen is artificially introduced, it will automatically precipitate, quickly returned to its original content.

Adtech specializes in the production of porous ceramic filters, which can adsorb and filter impurities in molten aluminum.