Degassing methods commonly used in the industry of

2022-07-25
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Magnesium alloy depends on whether the brand and after-sales service are the commonly used degassing methods in the formal and perfect smelting industry

① the method of introducing inert gas flail nitrogen and neon spoon: generally, 0.5% of the melt mass is introduced into the melt at ℃. The nitrogen content in the melt can be reduced from CM 3/kg to 100cm 3/kg. The ventilation speed should be appropriate to avoid melt splashing. The ventilation time is 30min. Too long ventilation time will lead to grain coarsening

② introduce active gas (chlorine scoop method: generally, chlorine is introduced into the melt at ℃.

when the melt temperature is lower than 740 ℃, the mgc12 generated by the reaction will be suspended on the alloy surface, so that a compact coating cannot be formed on the surface and the combustion of magnesium cannot be prevented. When the melt temperature is higher than 760 ℃, the reaction between the melt and chlorine will intensify, generating a large number of mgc12 and forming inclusions. The amount of chlorine should be appropriate, and the chlorine content volume ratio of the melt is generally controlled below 3% (2.5'-3) l/min is preferred. Carbonaceous substances such as ccl4 C2c16 and SiC have obvious grain refinement effect on mg Al alloys. If the mixed gas accounting for the melt mass (()%c12+0.25%cc14) is used for degassing at ℃, the dual effects of degassing and refining can be achieved, and the degassing effect is better, but it is easy to cause pollution

removal of inclusions. The main inclusions in the magnesium alloy are mgo'and MgF2' mgc12. The melting of MgO and MgF2, B. are 26420c and 12630c respectively, which are higher than the melting temperature of the magnesium alloy, and appear in solid form in the magnesium alloy liquid. The density of MgO is 3.5 8g/cm3, which is higher than that of magnesium. Therefore, MgO will settle at the bottom of the alloy liquid and be discharged as oxidation slag. As magnesium is easy to oxidize, a large amount of MgO will be produced at high temperature, which cannot be completely discharged, so a part of MgO slag will remain in the magnesium alloy; The melting point of mgc12 is 7180c, which is within the melting temperature range of magnesium alloy. Therefore, mgc12 appears in liquid form in the magnesium alloy liquid. In addition, the density of mgc12 in liquid state is close to that of magnesium. Therefore, the probability of mgc12 remaining in the magnesium alloy liquid is high. If necessary, it should be well conditioned;, In addition, mgc12 also has strong moisture absorption, which will accelerate the corrosion of magnesium alloys

these problems make it necessary to refine magnesium alloys during melting. Hexachloroethane is usually added to magnesium alloys for refining treatment (c2cq, mgc03, caco. and other refining agents, which are mainly due to MgCO and CaCO. It is easy to decompose and produce a large amount of co: gas, thus playing the role of degassing and slag removal.

the flux refining treatment is to use the flux to wash the magnesium melt, use the full contact between the flux and the magnesium melt to wet the inclusions, polymerize them in the flux, and deposit them at the bottom of site a along with the flux and the magnesium melt. The basis of this refining method is that the flux must have Good ability of wetting and absorbing inclusions. In production, c2c16 is used as refining agent for different experimental objects, which has the dual effects of modification and refining. The advantage of this method is especially outstanding when there is no flux refining. 4. The operating environment of the equipment is also a noteworthy point. The mechanism of the method is that c2ch rapidly decomposes into C1 in magnesium melt C and other elements can react with magnesium to form mgc12, which can play a refining role, while carbon can play a role in refining grains. In addition, the gas produced by c2c16 decomposition also has the function of hydrogen removal

during the refining process, flux is continuously sprayed on the metal surface, and the flux melts and enters the metal. After refining, the covering agent shall be sprayed on the metal surface to prevent oxidation and combustion of the surface metal. The covering agent is a mixture of 20% sulfur powder and 80% refining agent. After the surface refining agent is melted, it gradually penetrates into the metal. Even if the protective film on the metal surface in the inclined ladle is broken during the casting process, the covering agent shall be sprinkled on the metal surface to be cast. These refined works undoubtedly add foreign impurities to the metal. Some manufacturers adopt nitrogen protection method to prevent the entry of gas impurities, but it is only effective to refine and cast in a relatively closed nitrogen environment. Spraying Nitrogen on the surface of open containers has little effect on preventing surface combustion. When the refining and casting temperature is not too high, it is better to prevent the surface oxidation and combustion of molten metal by spraying sulfur powder. A certain amount of air flow is introduced into the box containing sulfur powder with the outlet pipe facing the molten metal, and the ejected sulfur powder rushes to the metal surface for combustion, reducing the surface oxidation of the metal and preventing the entry of foreign refining agents

The modifier used in

magnesium alloy is easy to form high melting point metal intermediate compound with other high melting point impurities and settle at the bottom of the furnace. The solubility of these refractory impurities and modifiers in magnesium alloys is small, the melting point is high, and the specific gravity is larger than that of magnesium. When they interact with each other, the fusible impurities in the alloy can be removed, which is beneficial to magnesium alloys, but reduces the effect of the modifier, or even fails

reduce Fe, Ni in magnesium alloy The content of Si impurities can improve its corrosion resistance. Because ti has a large solubility in magnesium at ℃, when it is lower than 700 ℃, the solubility decreases sharply, and forms a high melting point intermetallic compound with Fe "Si and settles. Therefore, in recent years, iron waste and low-quality chin chloride have been used in industry to remove Fe" Si and some Ni from the melt, so as to improve the corrosion resistance of the alloy. For example, after MB3 alloy is treated with low-quality chloride (tic13+tic1) and Mg Ti master alloy (ti24%), the content of Fe and Si in the alloy can be reduced from fe0.01% SiO. 01% reduced to feo 002% "sio.001% Zr containing magnesium alloy, the content of Si, Al and Mn impurities shall be strictly limited. When the. Mn content exceeds 0.1% respectively, the error content in the alloy will be greatly reduced

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