JPS6360835B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method and apparatus for producing an Sr--Al master alloy, which is mainly used for refining the hypoeutectic structure of aluminum-silicon eutectic and hypoeutectic castings. [Prior art] Sr is added to 0.01 to refine the eutectic structure of eutectic and hypoeutectic aluminum silicon castings (silicon 12.6 wt% or more) and improve mechanical strength and machinability.
~0.05% is added, and excellent effects have been confirmed together with Na. In addition to the effect of refining the eutectic structure, Sr has an excellent feature not found in Na, in that the treatment effect lasts for a long time. Such additives include metal Sr, Sr-Al,
Sr--Si--Al alloys are known. When using metal Sr as a starting material as an additive,
It is desirable to use it once synthesized into the Sr-Al master alloy, but it burns during melting and is difficult to handle, the addition yield is low, and processing costs are high. Therefore,
From the point of view of processing cost, commercially available Sr-Si-Al
It is more advantageous to use a master alloy. However, in this case, the Sr-Si-Al master alloy contains hardly soluble SrSi,
Intermetallic compounds such as SrSi ₂ are generated, and Sr-Si
- Even if the matrix part of the Al master alloy melts, these intermetallic compounds exist in solid form, so they do not dissolve easily and take a considerable amount of time to dissolve.
For this reason, the Sr yield after addition also varied widely. Improvements such as raising the addition temperature and using fluxes made of SrCl ₂ and alkali metal chlorides and fluorides have stabilized the addition yield. Due to the high temperature, there remained unresolved problems such as occasional formation of gas occlusion cavities. [Problem to be solved by the invention] In order to take advantage of the advantages of Sr treatment and obtain stable treatment effects, it is desirable to use a Sr-Al master alloy with a low melting point. Because the method was to create a master alloy by alloying,
The disadvantage was that the unit price of the Sr--Al master alloy was high, and therefore the processing cost was also high. [Means for Solving the Problems] As a result of various studies on the manufacturing method of Sr-Al master alloy, the present inventors found that a melt of a strontium halide or a strontium halide and an alkali metal halide were used. The molten salt consisting of more than one type is on the upper layer, the molten Al is on the lower layer,
The lower end of the electrode is immersed in the upper molten salt as an anode, the lower molten Al layer is used as a cathode, and a DC voltage is applied to electrolyze the strontium in the molten salt onto the surface of the molten Al layer. We conducted analysis and discovered a method to obtain an extremely efficient Sr-Al alloy by quickly alloying this Sr with Al. According to the method of the present invention, Sr generated by electrolysis is
Negatively charged molten aluminum layer (or Sr
-Al layer), it quickly becomes an Sr-Al alloy. In short, at this time, the activity of Sr decreases, so an extremely efficient electrolytic reaction takes place. As the electrolytic bath, it is possible to use SrCl ₂ alone or a mixed bath of SrCl ₂ and an alkali metal halide which has a higher decomposition voltage and becomes molten at around 750°C. Among them, SrCl ₂ ―KCl type or SrCl ₂ ― is used from the viewpoint of separability from metal after reaction.
The KCl-NaCl system showed good results. Next, the composition of the molten salt bath during electrolysis will be explained. When the amount of Sr in the molten salt bath is within the range of 2 to 30%, the reduction reaction to elemental Sr by molten salt electrolysis proceeds efficiently, and an Sr--Al alloy can be advantageously obtained. However, if the Sr content in the bath is less than 2%, the separation of the molten salt and metal is good, but the current efficiency during electrolysis is poor, while if the Sr content exceeds 30%, the fluidity of the molten salt bath becomes poor. Separation from metal is also poor, resulting in lower electrical conductivity and lower current efficiency. The temperature of the bath during electrolysis is advantageously 660-900°C.
If it is lower than 660°C, separation of the molten flux and metal will be poor, while if it is higher than 900°C, the progress of electrolysis will become unstable, the current efficiency will decrease, and the life of the reaction crucible and other equipment will be shortened. The best results are obtained when the bath temperature is in the range of 700 to 850°C. The target composition of the metal bath is Sr5-20.
%, with the remainder being Al. If the Sr content is less than 5%, there will be a disadvantage that a large amount of Sr-Al alloy must be used, while if the Sr content is more than 20%, it will be difficult to extract the Sr-Al molten metal from the crucible. During this process, Sr burns and is wasted. In addition,
An alloy containing 7 to 12% Sr and the remainder Al is most advantageous from the viewpoint of manufacturing and use. If oxygen enters the crucible during electrolysis, the flux will be oxidized, so an inert gas atmosphere is preferable for the reaction atmosphere, but since Cl ₂ gas is constantly generated during electrolysis, it is necessary to prevent outside air from entering the crucible. If this is possible, there is no need to give special consideration to the atmosphere inside the crucible. Next, the present invention will be explained regarding a manufacturing apparatus. FIG. 1 is a longitudinal cross-sectional view of one example of the Sr--Al alloy production apparatus of the present invention, in which the side walls and bottom of the crucible 1 are supported by an insulating high alumina refractory 2. A graphite anode electrode 3 is vertically disposed within the crucible 1, and its lower end is immersed in molten flux during operation of the apparatus. In addition, a graphite cathode conductive part 4 is surrounded and buried in the side wall of the crucible, and the lowest end of the cathode conductive part 4 is exposed inside the lower part of the crucible and is exposed to the molten Al.
in contact with the layer. That is, since the side wall lining corresponding to the lower end of the conductive part 4 is cut out, this part is the Sr-- which is stored in the bottom of the crucible.
It is in contact with the Al alloy bath and can therefore conduct electricity to the bath through this part. Therefore, melting
The Al layer becomes the cathode. In addition, a discharge hole 5 for Cl ₂ gas generated by electrolysis is provided at the top of the crucible, and a thermometer 6 is inserted through the canopy 7.
is installed vertically. A heating unit 8 is provided around the outer periphery of the molten metal storage portion of the crucible. In the figure, 9 is a molten flux bath, and 10 is an Sr--Al alloy bath. Next, a method for producing an Sr--Al alloy using the apparatus shown in FIG. 1 will be explained. First, separately melted Al and a mixed molten salt of, for example, SrCl ₂ and KCl are charged into the crucible 1, and the anode electrode conductive part 3 is vertically placed so that its lower end is immersed in the molten salt bath and energized. do. As a result, a current flows through the molten salt, the Al molten metal, and the cathode electrode conductive part 4, and the Sr generated on the molten Al surface by the reduction reaction is liberated and enters the Al molten metal, where it is alloyed and becomes an Sr-Al alloy molten metal. Become. FIG. 2 is a longitudinal sectional view of another apparatus for manufacturing the Sr--Al alloy of the present invention. The device of this invention is similar in principle to the device of the invention shown in FIG. Flux and Al grains can be charged into the crucible from the hollow cylinder of the cathode electrode conductive section 4, respectively. Further, near the bottom of the crucible, a molten metal extraction hole 11 is provided that passes through the side wall and faces obliquely upward. Electric heating means for heat retention may be provided around the extraction hole 11 if necessary.
In the apparatus of the present invention shown in Fig. 1, electrolytic work is carried out in a batch manner, whereas in the apparatus of the present invention shown in Fig. 2, flux and Al metal powder can be charged continuously. Therefore, continuous melting electrolysis is possible, which is extremely advantageous in terms of thermal efficiency and labor savings. The material of the anode electrode 3 and the cathode electrode conductive portion 4 may be tungsten, tantalum, or carbon in addition to graphite. The above are just a few examples of the method and device of the present invention, but in actual electrolysis, flux and Al
For heating and melting, it is possible to adopt an internal heating method such as resistance heating or to charge the flux and Al as molten metal, and these means are naturally included in the present invention. Next, the present invention will be explained with reference to examples. Example 1 Al (99.5% Al), SrCl ₂ (SrCl ₂ 98.3%) produced by firing SrCl ₂ 6H ₂ O, and industrial NaCl, KCl
by electrolysis using the apparatus shown in Figure 1.
Manufactured Sr-Al alloy. The results are shown in Table 1.

【table】

[Table] From Table 1 above, it can be seen that the Sr yield is greatly influenced by the Sr content in the molten salt of the electrolytic bath, and as the amount of SrCl ₂ increases, the Sr yield decreases rapidly. The current efficiency is extremely good, but the reason is
This is because Sr electrolytically deposited on the surface of the Al bath immediately becomes an Sr-Al alloy, reducing the activity of Sr. Example 2 Continuously using the apparatus of the present invention shown in FIG.
A Sr--Al alloy was manufactured under the following conditions. The starting mixture is Al 1000g SrCl ₂ 1017g KCl 1000g NaCl 1000g, Al is charged first, then SrCl ₂ , KCl,
The entire amount of NaCl mixture was charged. After raising the temperature to 700℃ and confirming that the charge has melted, set the anode electrode.
A current of 26.5 A was applied for 3.51 hours, or 93 ampere hours. After that, the Sr-Al alloy overflowing from the extraction hole was poured into the casting bed while electricity was applied and the raw materials were continuously fed at a feeding speed of basic composition Al 47.5g/10 minutes SrCl ₂ 9.7 〃 KCl 4.8 〃 NaCl 4.8 〃 I washed it away. The amount of raw material charged is adjusted to such an extent that the molten flux occasionally flows out from the taphole.
Check the flux level from time to time through the inspection hole,
If the flux level decreases, add KCl/
A flux of NaCl=1/1 was charged and the flux level was adjusted. These results are shown in Table 2.

【table】

[Table] According to the present invention, a low melting point Sr--Al alloy can be stably produced with high current efficiency and high yield.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of an example of an apparatus used in the batch method, and FIG. 2 is a longitudinal sectional view of an example of an apparatus used in the continuous melting method. 1... Crucible, 2... High alumina refractory for insulation, 3... Anode electrode, 4... Cathode electrode conductive part, 5... Chlorine gas outlet, 6... Temperature meter, 7
...Canopy, 8...Heating unit, 9...Salt bath, 1
0...Sr-Al bath (cathode), 11...extraction port,
12... Electrode holder, 13... Heating unit,
14... Granular aluminum, 15... Strontium compound raw material.

Claims (1)

[Scope of Claims] 1 An electrode immersed in a molten salt of any one of strontium halide flux on a molten aluminum bath and a flux consisting of strontium halide and an alkali metal halide is an anode. and strontium in the molten salt is reduced by electrolyzing the molten salt with the molten aluminum layer as a cathode, and at the same time, strontium is electrolytically deposited on the molten aluminum of the cathode and alloyed with the molten aluminum. A method for manufacturing Sr-Al alloy. 2. The material of the electrode used to make the molten aluminum as a cathode and the electrode used to make the anode whose tip part is immersed in flux molten salt is one selected from tantalum, tungsten, and carbon. The method according to claim 1, which is a method according to claim 1. 3. The electrode used to form the molten aluminum as a cathode and the electrode used to form the anode immersed in the flux molten salt are each hollow cylindrical, and the hollow cylinder of the cathode electrode has aluminum grains. 2. The method according to claim 1, wherein the molten salt electrolysis is carried out while charging flux into the hollow tube of the anode electrode. 4 A crucible lined with an insulating refractory that is equipped with a heating unit on the outside of the side wall and the bottom, and has a canopy and an exhaust gas discharge hole on the top; Most of the crucible is buried in the side wall of the crucible, but the tip thereof is a cathode formed by a molten aluminum layer, only a portion of which is in contact with the lower end of the cathode electrode conductive part exposed in the lower part of the crucible; and a lower end located above the molten aluminum layer cathode part in the crucible; 1. An anode electrode which is suspended in such a way that the apparatus is in operation, and whose lower end is immersed in molten flux during operation of the apparatus. 5 A crucible lined with an insulating refractory, which is equipped with a heating unit on the outside of the side wall and the bottom, and has a canopy and an exhaust gas discharge hole on the top; Most of the crucible is buried in the side wall of the crucible, but the tip thereof is A hollow cylindrical cathode electrode conductive part, only a portion of which is exposed in the lower part of the crucible, and which is in contact with a lower end of a hollow cylindrical cathode electrode conductive part having a passage communicating with the inside of the crucible bottom at its lower end, is constituted by a molten aluminum layer. The cathode is suspended so that its lower end is located above the molten aluminum layer cathode portion in the crucible, and a passage is provided in which the lower end is immersed in the molten flux during operation of the device. An apparatus for manufacturing an Sr--Al alloy, characterized in that it mainly comprises: a hollow anode electrode;