CN1587424A - Magnesium alloy smelting method using 1,1-difluoroethane as protective atmosphere - Google Patents

Abstract

A magnesium alloy smelting method using 1,1-difluoroethane as a protective atmosphere, mixing 1,1-difluoroethane with a volume content of 0.01-4% and auxiliary diluent gas in a gas mixing device to produce magnesium The atmosphere protective agent for the melt, put pure magnesium or magnesium alloy in a closed crucible to heat up, then pass the mixed gas into the crucible, so that the gas covers the surface of pure magnesium or magnesium alloy melt to form a dense oxide protective film, through The per minute flow rate of the mixed gas is 0.05-8% of the volume of the closed gas, continue to heat up and refine and deteriorate under the protection of gas, and then carry out gravity pouring or pressure casting after standing still. The protection gas adopted in the invention can effectively prevent the oxidation and combustion of the magnesium alloy during the smelting process, and has good protection effect, low price and low greenhouse effect.

Description

Magnesium Alloy Melting Method Using 1,1-Difluoroethane as Protective Atmosphere

technical field

The invention relates to a high-temperature oxidation and combustion protection technology in the smelting process of pure magnesium or conventional magnesium alloys, in particular to a pure The invention relates to a smelting protection process for magnesium or magnesium alloy, which belongs to the technical field of material metallurgy.

Background technique

Due to the oxophilicity of metal magnesium, pure magnesium or magnesium alloys are easily oxidized in the air. Since the density coefficient of its oxidation product, magnesium oxide, is less than 1, this naturally occurring oxide film cannot constitute an effective barrier to prevent the internal Further oxidation of the metal, pure magnesium or magnesium alloys are also prone to combustion at high temperatures. Therefore, in the industry, the mixed gas containing sulfur hexafluoride is generally used as the protective atmosphere for magnesium alloy smelting and production, which is one of the most effective protection methods for magnesium alloy smelting. In recent years, with the rapid development of the magnesium industry, the amount of protective gases such as sulfur hexafluoride required for the smelting and production of pure magnesium or magnesium alloys is increasing. However, the global warming potential (GWP) of sulfur hexafluoride reaches 23900 (the GWP value of carbon dioxide is 1), and the atmospheric life is as long as 3200 years. The pressure is increasing, and it is listed as a substance that needs to be reduced by international environmental protection organizations. The "Kyoto Protocol" signed at the 5th United Nations Framework Convention on Climate Change requires the industry to minimize sulfur hexafluoride in the next 10 years Gas emissions, to achieve zero emissions of sulfur hexafluoride by 2015 (U.S.EPA, 2003b). Therefore, the International Magnesium Association (IMA) requires that the use of sulfur hexafluoride be reduced by improving the efficiency of use, and that the magnesium industry should achieve zero emission of sulfur hexafluoride before 2015.

In order to achieve the above goals without affecting the development of the magnesium industry, international efforts are being made to find a substitute for sulfur hexafluoride and to develop a melting protection process for pure magnesium or magnesium alloys. The results of the survey on the new protective atmosphere with low environmental impact found that only a few alternative atmospheres have been proposed. The most typical representatives are three alternatives that are being evaluated by the International Magnesium Association for their protective effects and environmental loads: AMCover ^TM ( HFC-134a), HFE7100 (C ₄ F ₉ -O-CH ₃ ) and Novec ^™ 612 (C ₃ F ₇ COC ₂ F ₅ ). The former was invented by the Australian CAST Research Center, and the latter two were invented by 3M. Although these three gases and smelting protection processes have been initially confirmed to be effective for pure magnesium or magnesium alloys, and their greenhouse effect is only as strong as that of sulfur hexafluoride. It is more environmentally friendly than sulfur hexafluoride, but the GWP values of these three gases are still high, all exceeding 1000, and the protective effects of the latter two gases are still under evaluation and have not yet been confirmed; meanwhile, HFE7100 and Novec The price of ^TM 612 is relatively high, and there is no domestic production, which will obviously limit the feasibility of its industrial application. Therefore, it has always been the goal of the magnesium industry to continue to look for alternative gases with lower prices and less environmental impact and their smelting protection processes.

Contents of the invention

The object of the present invention is to address the deficiencies of the prior art, to provide a magnesium alloy smelting method, using a material whose protective effect on the magnesium melt is equivalent to that of sulfur hexafluoride, and whose environmental protection effect is better than that of sulfur hexafluoride. It replaces sulfur hexafluoride as an atmosphere protective agent for magnesium melt, reduces process cost, has good smelting protection effect, and does not cause pollution to the environment.

In order to achieve such purpose, the present invention adopts 1,1-difluoroethane to replace sulfur hexafluoride as the atmosphere protective agent of magnesium melt, and the smelting process mainly includes the following steps:

1. Mix 1,1-difluoroethane (its trade name is R152a) with auxiliary diluent gas in the gas mixing device, and the volume content of 1,1-difluoroethane in the mixed gas is 0.01-4% . The auxiliary diluting gas may be dry air, dry carbon dioxide or other inert gases, or a mixture thereof.

2. Put pure magnesium or magnesium alloy in a closed crucible and heat up.

3. When the temperature of pure magnesium or magnesium alloy reaches 400°C, start to feed the mixed gas into the crucible so that the gas covers the surface of pure magnesium or magnesium alloy, and the flow rate of the mixed gas per minute is 0.05-8% of the volume of the closed gas .

4. Continue heating until the pure magnesium or magnesium alloy melts, so that the protective gas quickly forms a dense and protective oxide film on the surface of the melt.

5. When the temperature of the pure magnesium or magnesium alloy melt is raised to 700-850°C, it is refined and modified under gas protection, and then it is left to stand for 30-40 minutes before gravity pouring or pressure casting.

During the melting and pouring process of pure magnesium or magnesium alloy, the mixed gas containing 1,1-difluoroethane undergoes a complex chemical reaction with the surface of the molten fresh magnesium liquid, which improves the structure of the natural oxide film and makes the surface film change. It is dense, complete and elastic, closely combined with the molten metal, and completely covers the surface of the melt, separating the magnesium melt from the air, greatly reducing the oxidation or burning speed of the magnesium melt, making pure magnesium or Magnesium alloys are protected during smelting. When the old oxide film is removed during smelting or pouring, a dense protective new oxide film will quickly form on the surface of the melt, covering the surface of the magnesium melt again, and continue to effectively protect the magnesium melt from being oxidized or burned.

与六氟化硫相比，前者在镁熔炼时的用量和效率几乎一样，而且熔炼保护工艺简单。因此，用1，1-二氟乙烷代替六氟化硫作为纯镁或镁合金的保护气氛的经济效应是十分可观的。The characteristics of the present invention are: (1) the protective effect of the atmosphere containing 1,1-difluoroethane on the magnesium melt is equivalent to that of the atmosphere containing sulfur hexafluoride. In the entire melting temperature range, 1,1-difluoroethane When the content of magnesium is 0.01-4% (volume), it has a good protective effect on the magnesium melt. (2) Under optimized conditions, the density, smoothness, and thickness of the formed surface film are very similar to those formed by the atmosphere containing sulfur hexafluoride, and the protective effect on the magnesium melt is almost the same. (3) 1,1-difluoroethane is a stable, non-toxic and non-corrosive substance at room temperature, and it will decompose at high temperature, and its decomposition products can be consumed by chemical reaction with magnesium, and the exhaust gas will not affect Hazards to the environment and operators; (4) The global warming potential (GWP) of 1,1-difluoroethane is about 140 (about that of sulfur hexafluoride ), the atmospheric life is only 1.4 years, and even if 1,1-difluoroethane is emitted into the atmosphere during the magnesium alloy smelting process, its impact on the greenhouse effect is far lower than that of sulfur hexafluoride and significantly lower than that of foreign inventions Containing R134a, HFE7100 and Novec ^TM 612 magnesium alloy melting protective gas. (5) 1,1-difluoroethane has been produced industrially in China, is easy to buy, and the price is low. Its market price is about that of sulfur hexafluoride.

Compared with sulfur hexafluoride, the amount and efficiency of the former in magnesium smelting are almost the same, and the smelting protection process is simple. Therefore, the economic effect of replacing sulfur hexafluoride with 1,1-difluoroethane as the protective atmosphere of pure magnesium or magnesium alloy is very considerable.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the examples.

Example 1:

Protective Melting of AM60 Magnesium Alloy with 1,1-Difluoroethane

The implementation steps are: (1) 1,1-difluoroethane is mixed with dry air or carbon dioxide in the gas mixing device according to the various mixing ratios given in Table 1; (2) 3 kilograms of clean AM60 alloy are mixed in Heat and melt in a 5 kg resistance crucible furnace; (3) when the alloy temperature reaches 400°C, start to feed the mixed gas into the crucible according to the flow parameters given in Table 1, so that the gas covers the alloy surface; (4) continue to heat the magnesium alloy After heating up to melting, the protective gas quickly forms a dense and well-protected oxide film on the surface of the melt; (5) The magnesium alloy melt is heated to 700-850°C, and refined and metamorphosed under the protection of the gas , and then stand for 30 to 40 minutes before gravity casting or pressure casting.

During the whole melting process, the protection effect of various melting process parameters was continuously observed, and the observation results were also recorded in Table 1. It can be seen from Table 1 that when AM60 magnesium alloy is smelted under the protection of a mixed atmosphere containing 1,1-difluoroethane, under the various smelting temperatures, various blowing flow rates and holding times set in Table 1, even When surface agitation occurs, a dense, non-combustible surface protective layer can be formed relatively quickly.

Table 1 serial number Protect process parameters Smelting protection effect Melt temperature °C Mixed gas ratio (volume) Mixed gas flow(%/min) diluent gas Hold time (minutes) surface agitation film color, smoothness Film formation rate film thickness Flammability 1 620 0.01% 0.5 Air 15 have bright, wrinkled quick Thin non-combustible 2 650 0.24% 0.5 Air 20 have bright, wrinkled quick Thin non-combustible 3 670 0.12% 1 carbon dioxide 13 have bright, wrinkled quick Thin non-combustible 4 700 0.24% 1 carbon dioxide 19 have bright, wrinkled quick Thin non-combustible 5 720 0.3% 2 carbon dioxide twenty four have bright, flat quick Thin non-combustible 6 750 0.3% 2 air + carbon dioxide 14 have bright, flat quick thick non-combustible 7 780 0.3% 3 air + carbon dioxide 10 have bright, flat quick thick non-combustible 8 800 4 8 air + carbon dioxide 20 have bright, wrinkled quick thick non-combustible

Example 2:

Protective Smelting of Pure Magnesium with 1,1-Difluoroethane

The implementation steps are: (1) 1,1-difluoroethane is mixed with dry air or carbon dioxide in the gas mixing device according to the various mixing ratios given in Table 2; (2) 3 kilograms of clean pure magnesium are mixed in 5 kg resistance crucible furnace heating and melting; (3) when the pure magnesium temperature reached 400 ℃, began to feed the mixed gas into the crucible according to the flow parameters given in Table 2, so that the gas covered the surface of the magnesium; (4) pure magnesium Continue heating until melting, so that the protective gas quickly forms a layer of dense and well-protected oxide film on the surface of the melt; (5) The magnesium melt is heated to 700-850 ° C, and refined under the protection of the gas Deterioration, and then after standing for 30 to 40 minutes, carry out gravity casting or pressure casting.

The protection effect of various melting process parameters was continuously observed during the whole melting process, and the observation results were also recorded in Table 2. It can be seen from Table 2 that when pure magnesium is smelted under the protection of a mixed atmosphere containing 1,1-difluoroethane, under the various smelting temperatures, various blowing flow rates and holding times set in Table 2, even if the Surface agitation can quickly form a dense, non-combustible surface protection layer.

Table 2: serial number Protect process parameters Smelting protection effect Melt temperature °C Mixed gas ratio Mixed gas flow(%/min) diluent gas Hold time (minutes) surface agitation film color, smoothness Film formation rate film thickness Flammability 1 680 0.04% 0.5 Air 40 have bright, wrinkled quick Thin non-combustible 2 700 0.04% 0.5 Air 17 have bright, wrinkled quick Thin non-combustible 3 720 0.1% 1 carbon dioxide 25 have bright, flat quick Thin non-combustible 4 750 1% 1 carbon dioxide 10 have bright, flat quick Thin non-combustible 5 780 1% 2 air + carbon dioxide 25 have bright, flat quick Thin non-combustible 6 800 4% 8 air + carbon dioxide 10 have bright, wrinkled quick Thin non-combustible

Example 3:

Protective Melting of AZ91 Magnesium Alloy with 1,1-Difluoroethane

The implementation steps are: (1) 1,1-difluoroethane is mixed with dry air or carbon dioxide in the gas mixing device according to the various mixing ratios given in Table 3; (2) 3 kg of clean AZ91 alloy is mixed in Heat and melt in a 5 kg resistance crucible furnace; (3) when the alloy temperature reaches 400°C, start to feed the mixed gas into the crucible according to the flow parameters given in Table 3, so that the gas covers the surface of the alloy; (4) continue to heat the magnesium alloy After heating up to melting, the protective gas quickly forms a dense and well-protected oxide film on the surface of the melt; (5) The magnesium alloy melt is heated to 700-850°C, and refined and modified under the protection of the gas , and then stand for 30 to 40 minutes before gravity casting or pressure casting.

The protection effect of various melting process parameters was continuously observed during the whole melting process, and the observation results were also recorded in Table 3. It can be seen from Table 3 that when the AZ91 magnesium alloy is smelted under the protection of a mixed atmosphere containing 1,1-difluoroethane, under the various smelting temperatures, various blowing flow rates and holding times set in Table 3, even When surface agitation occurs, a dense, non-combustible surface protective layer can be formed relatively quickly.

table 3 serial number Protect process parameters Smelting protection effect Melt temperature °C Mixed gas ratio (%) Mixed gas flow(%/min) diluent gas Hold time (minutes) surface agitation film color, smoothness Film formation rate film thickness Flammability 1 650 0.01% 0.5 Air 40 have bright, wrinkled quick Thin non-combustible 2 680 0.05% 0.5 Air 10 have bright, flat quick Thin non-combustible 3 700 0.1% 1 carbon dioxide 17 have bright, wrinkled quick Thin non-combustible 4 720 0.1% 1 carbon dioxide 10 have bright, flat quick Thin non-combustible 5 750 0.15% 1.5 air + carbon dioxide 10 have bright, flat quick Thin non-combustible 6 780 1% 2 air + carbon dioxide 20 have bright, flat quick thicker non-combustible 7 800 4% 2 air + carbon dioxide 15 have gray, wrinkled quick thick non-combustible

The above examples illustrate that the use of mixed gas containing 1,1-difluoroethane as the protective atmosphere to melt and protect the magnesium melt has a good protective effect in the entire temperature range of pure magnesium or magnesium alloy smelting. The protection effect of sulfur hexafluoride is equivalent, and the smelting process is simple, which has more environmental protection and economic advantages than sulfur hexafluoride.

Claims (2)

1. A magnesium alloy smelting method using 1,1-difluoroethane as a protective atmosphere, characterized in that it comprises the following steps: 1) Mixing 1,1-difluoroethane and auxiliary diluent gas in a gas mixing device, the volume content of 1,1-difluoroethane in the mixed gas is 0.01-4%; 2) placing pure magnesium or magnesium alloy in a closed crucible to heat up; 3) When the temperature of pure magnesium or magnesium alloy reaches 400°C, start to feed the mixed gas into the crucible so that the gas covers the surface of pure magnesium or magnesium alloy, and the flow rate of the mixed gas per minute is 0.05-8% of the volume of the closed gas ; 4) Continue heating until the pure magnesium or magnesium alloy melts, so that the protective gas forms a dense oxide protective film on the surface of the melt; 5) When the temperature of the pure magnesium or magnesium alloy melt is raised to 700-850°C, it is refined and modified under gas protection, and then left to stand for 30-40 minutes before gravity casting or pressure casting. 2. The magnesium alloy smelting method using 1,1-difluoroethane as a protective atmosphere according to claim 1, characterized in that said auxiliary diluent gas is dry air, dry carbon dioxide or a mixture thereof.