JPS61124540A - Method for dehydrogenating molten al or al alloy - Google Patents

Abstract

PURPOSE:To remove efficiently hydrogen from a molten Al or a molten Al alloy by treating the molten metal with gaseous halogen or a compound contg. halogen to reduce the concn. of hydrogen in the molten metal to a specified value and by treating the molten metal with an inert gas in the form of fine bubbles. CONSTITUTION:The molten Al or the molten Al alloy is treated with gaseous halogen and/or a compound contg. halogen to reduce the concn. of hydrogen in the molten metal to <=0.15cc/g by 100g molten metal. The inert gas such as nitrogen is then blown into the molten metal from a porous plug in the form of fine bubbles to reduce the concn. of hydrogen in the molten metal to <=0.1cc/g by 100g molten metal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for efficiently removing hydrogen mixed in Al or Al alloy molten metal in a relatively short time.

[Conventional technology]

Hydrogen gas dissolved in the molten Al or Al alloy (hereinafter referred to as Al alloy) becomes bubbles due to a decrease in solubility as the temperature falls during casting, causing casting defects such as pinholes and surface roughness. , must be removed as much as possible at the molten metal stage. The currently widely used dehydrogenation methods for this purpose are: 1. Injecting halogen gas and/or halogen-containing compounds into the molten metal to dehydrogenate, and 2. Injecting an inert gas into the molten metal through fine bubbles. This method uses the partial pressure of an inert gas to promote hydrogen dissipation.

[Problem that the invention seeks to solve]

The above dehydrogenation method ① is extremely excellent as a dehydrogenation method for molten Al alloy with a large amount of dissolved hydrogen, but it is difficult to reduce the hydrogen concentration of molten Al alloy to 0.12 to 0.14 cc/100y. is the limit, and the hydrogen concentration cannot be lowered below this value, and therefore casting defects caused by hydrogen cannot be eliminated. On the other hand, if the inert gas fine bubble injection method (■) is adopted, the hydrogen concentration can be reduced to O, lcc/100y.
Although it is possible to substantially eliminate casting defects caused by hydrogen, the treatment requires a long time and productivity is significantly reduced.

In view of these circumstances, the present invention aims to establish a dehydrogenation technology that can reduce the hydrogen concentration in molten Al alloy to about 0.1 CC/1002 or less in a relatively short period of time.

[Means for solving problems]

In the dehydrogenation method according to the present invention, first, Al or Al alloy molten metal is treated with a halogen gas and/or a halogen-containing compound to reduce the hydrogen concentration in the molten metal to 0.15cc/1.
The key point is to reduce the temperature to 00y (molten I!1) or less, and then to treat it with fine bubbles of inert gas.

[Effect]

As mentioned above, the dehydrogenation methods for molten Al alloy are: (1) treatment with halogen gas and/or halogen-containing compound (hereinafter referred to as halogen treatment method), and (2) treatment with fine bubbles of inert gas (hereinafter referred to as fine bubbles). The advantages and disadvantages of each method are as described above. Incidentally, FIG. 2 shows the relationship between the treatment time and the hydrogen concentration in the molten metal when these methods (1) and (2) are adopted. However, the experimental conditions were as follows.

Experimental conditions〉 Processing molten metal: JIS A 5056 alloy Processing temperature near 50°C Injection gas in case of ■: Chlorine gas, 200 N//mi
Blow conditions for n ■: Porous plug: Use 1 o porous plug (40 mφ cylindrical plug with 40 μmφ through hole) disclosed in Japanese Patent Publication No. 56-85625, Inert gas... Nitrogen, 50 Nl/min As is clear from Figure 2, in the case of halogen treatment method ■, even when applied to molten Al alloy with a high hydrogen concentration, it takes a short time (80 Nl/min).
The hydrogen concentration can be reduced to about 0.15 cc/100 y in about 1 minute).

However, even if the treatment time is extended as it is, the subsequent decreasing gradient of the hydrogen concentration is extremely small, and the maximum value of the hydrogen concentration is 0.12 to 0.14 cc/1002. On the other hand, if the micro-bubble IG treatment method (■) is adopted, the hydrogen concentration can ultimately be lowered to 0.1 cc/100y or less, but the downward slope of the hydrogen concentration over time is extremely gradual, making it difficult to reach the target hydrogen concentration. It takes a long time to lower the temperature to a certain level, which not only makes it impossible to expect an improvement in productivity, but also reduces economic efficiency because a large amount of inert gas is required.

The present invention attempts to effectively combine the advantages and disadvantages of these prior art techniques to enable effective dehydrogenation in a short period of time. However, even if methods (2) and (2) above are combined, the purpose cannot be achieved just by combining them at random, and various ingenuity is required. However, the inventors have confirmed through preliminary experiments that depending on the combination procedure and the timing of switching dehydrogenation methods, the dehydrogenation efficiency may be lower than in the case of single treatment, and more effective The conclusion was reached that procedures, etc. should be strictly stipulated.

The halogen treatment method described in (2) is more suitable as a method for dehydrogenating materials with a high hydrogen concentration, and the method described in (2) that can further reduce the hydrogen content of materials with low hydrogen concentration is described in (2). With the conviction that the IG treatment method is more suitable, when assembling the combination process of first performing method ■ and then performing method ■, we decided to proceed from method ■ to ■.
We believed that it was necessary to clarify the most effective time to switch to the method, so we conducted the following experiment.

That is, 500 kg each of several kinds of AI alloy melts IIh (all JIS A 5056) with different hydrogen concentrations were prepared, and a micro-bubble treatment method (plugs: using 10 40 mφ cylindrical plugs with countless 40 μmφ through holes, Active gas: Nitrogen, 50 N//min) is used for dehydrogenation, and 0,0, which is considered to be the limit value for hydrogen reduction in this method.
The time required to reduce the temperature to 9% was investigated. The results are shown in Table 1.

As is clear from Table 1, the lower the initial hydrogen concentration, the shorter the time required for dehydrogenation treatment. If the initial hydrogen concentration is 0.154 or less, the dehydrogenation time will be 80 minutes, but if the initial hydrogen concentration is lower than 0.15%, for example, 0.11% or 0.12%. However, the time required for dehydrogenation is not shortened at all.

That is, as long as dehydrogenation is performed using the microbubble IG method, a treatment time of at least 80 minutes is required until the hydrogen reduction limit value is reached, and in this case, the upper limit of the initial hydrogen concentration is 0.15%. Therefore, as mentioned above, (1) the gradient of decrease in hydrogen concentration is gentle when employing the microbubble IG method, and (2) on the other hand, the halogen treatment method shows better dehydrogenation efficiency at higher hydrogen concentrations. Considering the characteristics of both, ``In the initial dehydrogenation stage where the hydrogen concentration is high, a halogen treatment method is used to rapidly reduce the hydrogen concentration, and after the hydrogen concentration has fallen to 0.15% or less, microfoam IG is used. The present invention introduces a dehydrogenation method unique to the present invention in which the hydrogen concentration is reduced to 0.1% or less by switching to the method.

As for how to combine the methods (6) and (6) above, there are two methods: (1) treatment with the microfoam IG method followed by (6) halogen treatment, or (6) (6) carrying out (6) and (6) in parallel. ,
However, with these combinations, not only is it not possible to shorten the processing time, but also it is not possible to reduce the hydrogen concentration to 0.196 or less. Also adopting the procedure of the present invention,
The timing of switching to the microbubble IG method is determined by changing the hydrogen concentration to 0.2% or 0.
．． It is also possible to set the temperature at the point when 3% is reached, but in this case, the switching to the micro-bubble IG method is too early and the purpose of shortening the processing time cannot be achieved.

However, as mentioned above, if the application types of the halogen treatment method and the micro-bubble IG method are defined, and the timing of switching to the micro-bubble IG method is strictly set, the shortcomings of both can be mutually compensated for and dehydrogenation can proceed extremely efficiently. I can do it. In the present invention, the microbubble IG treatment is performed after the halogen treatment, and the halogen dissolved in the molten metal in the halogen treatment process also functions to promote dehydrogenation during the microbubble IG treatment, improving dehydrogenation efficiency. Contributing. By the way, Figure 1 shows microfoam IG.
This is a graph showing the relationship between the presence or absence of halogen gas (chlorine) in molten Al alloy (A 5056) and dehydrogenation efficiency during treatment (plug and inert gas are the same as in the previous example), and the coexistence of halogen gas itself It can be seen that this promotes dehydrogenation during microfoam IG treatment.

[Example 1] As shown in Table 2, 15 molten Al alloys of various types were used.
The results shown in Table 2 were obtained by preparing a sample of 1000 ml (100 ml) and dehydrogenating it under the following conditions.

<Dehydrogenation conditions> 1st dehydrogenation (halogen treatment) Treatment temperature Near 20℃ Halogen gas: Chlorine 40ON 7/min Treatment time -30 minutes 2nd dehydrogenation (microbubble IG treatment) Plug: Numerous 40μmφ holes has 40txtx
φ cylindrical plug, 10 inert gas: nitrogen, flow jet
5ONl/min, pressure 0.8 Ky/preparation temperature 10-720°C, treatment time = 80 minutes As is clear from Table 2, the present invention exhibits an excellent dehydrogenation effect on all kinds of products.

〔Effect of the invention〕

The present invention is constructed as described above, but the point is that by strictly setting the order of implementation and switching timing of halogen treatment and microbubble IG treatment, dehydrogenation of molten Al alloy can be carried out extremely efficiently. Became.

[Brief explanation of drawings]

Figure 1 shows the presence or absence of chlorine gas in the Al alloy molten metal.
A graph of experimental results showing the influence of treatment on the dehydrogenation effect, and FIG. 2 is a graph showing the relationship between treatment time and hydrogen concentration when a conventional dehydrogenation method is applied.

Claims (1)

[Claims] Al or Al alloy molten metal is treated with halogen gas and/or halogen-containing compound to reduce the hydrogen concentration in the molten metal to 100% of the molten metal.
A method for dehydrogenating Al or Al alloy molten metal, which comprises treating the molten metal with fine bubbles of inert gas after reducing the hydrogen content to 0.15 cc or less per gram.