DE1608245B2 - Process for the production of master alloys containing strontium - Google Patents

Description

The invention relates to a method for producing strontium-containing master alloys which are used for refining are determined by aluminum-silicon alloys.

It is known to introduce small proportions of alkaline earth metals into silicon-containing aluminum alloys in order to refine the structure of these aluminum alloys (DT-PS 4 59 408). Another known proposal provides for calcium in the form of metallic calcium or calcium master alloys in aluminum-silicon alloys in contents of 0.005 to 0.5% to produce a refinement of the structure of these alloys (DL-PS 19 324). Is allowed, it is further known to introduce strontium into ferro-silicon, strontium compounds, preferably with fluxes at temperatures above 1500 ⁰ C with a ferro-silicon, which only low levels of aluminum and calcium have reacted (DT-AS 12 22 518). The silicon contained in the ferro-silicon is supposed to reduce the strontium compound and the resulting strontium is absorbed into the melt.

In technical practice, however, the latter process is not economically viable, since the yield of metallic strontium, which goes into the alloy melt, is below 10%. The familiar way of working for the production of strontium-containing ferro-silicon could therefore for the production of a refining alloy for aluminum alloys, which contain strontium, do not serve, since the alloys from the known methods have insufficient reducing power for introducing strontium into silicon alloy melts own.

According to another known method, further metals, such as barium, are alloyed into silicon-calcium alloys by introducing, for example, the oxide or carbonate of barium into the melt and reducing it at high temperatures in an electric melting furnace. The silicon-calcium alloys of the known process are used in particular in iron metallurgy (DT-AS 11 51 129). Furthermore, a method for alloying silicon alloys is known, according to which in the melt of a silicon-aluminum alloy at temperatures up to 1800 ⁰ C oxidic compounds of z. B. strontium can be reduced and the reduced component is alloyed. Insofar as the known process uses electrical melting units, it is a high-frequency furnace, with the slag guidance, such as liquid slags of eutectic composition, being of particular importance (GB-PS 5 10 759).

The invention is based on the object of providing a simple and economical process for the production of silicon alloys with a high content of strontium for the refinement of aluminum-silicon alloys. The invention solves the problem with a method for producing strontium-containing master alloys, which are intended for refining aluminum-silicon alloys, by introducing a compound containing the alkaline earth metal into a silicon alloy melt at high temperature with vigorous bath movement and the use of additives. The method according to the invention consists in that in a mains frequency furnace in the presence of carbonaceous substances a Siüciumschmelze containing at least 0.5% and together at most 70% magnesium and / or calcium and / or aluminum at a temperature of 650 to 1700 ⁰ C, preferably 1000 to 1450 ° C, reacted with strontium oxide, carbonate or sulfate and the metal is alloyed. These strontium compounds are used in a well-dried state in order to avoid explosive outbreaks due to trapped moisture when treating the melt. Alkali halides, alkaline earth halides, borax, aluminum chloride, coal or high-carbon masses such as coke powder, coal dust, coal tar can be used as additives or flux additives to the strontium compounds. The addition of carbon or carbon-containing substances advantageously facilitates the melting of the strontium compounds. In particular, when carbonates are used, a favorable course of the egg melting process is brought about.

Suitable starting alloys for the production of the strontium-containing silicon master alloys are binary silicon alloys with 0.5 to 50% magnesium, preferably 5 to 30% magnesium, the remainder being silicon with the usual impurities such as iron or manganese. In these alloys, magnesium is that reactive alloying element that reduces the strontium compound.

Other suitable starting materials are binary silicon alloys with 0.5 to 50% calcium, preferably 5 to 30% calcium, the remainder silicon with usual impurities. In such alloys, this is calcium able to reduce the strontium compounds under the conditions according to the invention.

Binary silicon alloys are also suitable, with 0.5 to 50% aluminum, preferably 5 to 40% Aluminum, the remainder silicon with the usual impurities. In these alloys, aluminum is the reducing agent Element for the strontium compound.

But it can also be used ternary and quaternary silicon alloys, the magnesium and / or calcium and / or aluminum. Of the-

like alloys are composed of 0.5 to 50% magnesium, preferably 5 to 30% magnesium and / or 0.5 to 50% calcium, preferably 5 to 30% calcium and / or 0.5 to 50% aluminum, preferably 5 to 40% aluminum, but not more than 70% if they are common, the remainder silicon with usual Impurities such as iron and manganese.

In order to achieve good contact between the strontium compound to be added and the silicon alloy melt and to always create a new reactive bath surface, it is essential that the melt bath is moved well. A mains frequency furnace is used to carry out the method according to the invention. The melt is equenzofen ^r In such Netzf electromagnetically moved in the crucible to reach a good mixing of the bath, at the same time a renewal of the bath surface is effected again.

While using a mains frequency oven an intense electromagnetic stirring effect (pinch effect) occurs, there is practically no stirring effect when using a high-frequency oven, as in one Melting unit the intensity of the stirring effect decreases with increasing frequency.

Both acidic and basic ramming masses have proven useful as lining for the reaction space. However, it is particularly advantageous if the reactants in a coal or predominantly carbonaceous Masses lined reaction space or melted in a carbon or graphite crucible and be alloyed.

The reaction is carried out at temperatures of the melting bath 650 to 1700 ⁰ C. With good movement of the melt due to the electromagnetic stirring effect of the mains frequency furnace, however, temperatures of 1000 to 1450 ^° C. are advantageously used.

The strontium compound is, if necessary, in association with additives such as fluxes or coal, placed in portions on the Badooer surface, the furnace heating switched off, the material melted down and stirred in after the furnace heating has been switched on again. It has proven to be useful to let the substances to be added trickle continuously onto the bath surface. This will make a good one Causes the additive to be absorbed by the bath. With the process according to the invention, yields Up to 100% of the strontium metal to be alloyed, based on the strontium compound, is achieved.

The method according to the invention has advantages. It enables the economical production of master alloys, which serve to refine aluminum-silicon alloys, and which contain high levels of Have strontium and which can be produced with high yields. For the production of the master alloy the process according to the invention can start from commercially available, inexpensive strontium compounds which is already a prerequisite for economic viability. In addition, from a silicon carrier can be assumed that already contains calcium or aluminum and is cheaply available is like calcium silicide. In addition, the method according to the invention does not require a large outlay in terms of equipment compared to the production of refining alloys, starting from the metallic Components. Furthermore, there is also the direct reductive step for the production of the refining alloy easier than the route via the alloying process, since burn-off and loss of strontium occurs there.

The process according to the invention is illustrated using the examples below.

example 1

3 kg of an alloy consisting of 20% magnesium, the remainder silicon with the usual impurities such as iron, aluminum, calcium, were placed in a graphite crucible which was used in a mains frequency furnace. This insert was melted down and heated to 1300 ^0C. The furnace heating was then switched off and 250 g of strontium carbonate were added. This mixture sintered, melted and was stirred into the bath after the furnace heating was switched on. The furnace heating was then switched off again and 250 g of strontium carbonate were again placed on the bath surface and melted. After switching on the furnace heating again, this strontium carbonate was stirred into the melt.

After switching off the furnace heating again, the resulting slag settled on the bottom of the crucible and the melt above it could be poured off. Analysis of the material yielded a silicon alloy containing 16.2% magnesium and 8.5% strontium, the remainder being silicon. Since the abandoned If strontium carbonate contained 54% strontium, it was found that a 100% conversion of the strontium carbonate with the magnesium took place and the strontium was completely absorbed into the alloy became.

Example 2

3 kg of a silicon-calcium alloy containing 10% calcium with the usual impurities were placed in a graphite crucible which was inserted into a mains frequency induction furnace and heated ^{to 1300 ° C. within about 1/2 hour.} After switching off the furnace heating, 250 g of dried strontium carbonate were added. This material was melted within 20 minutes and stirred in after the furnace heating was switched on. This addition was repeated three more times, so that a total of 1 kg of strontium carbonate was added. Using this method, an alloy was melted which consisted of 16.6% strontium and 0.9% calcium, the remainder being silicon. The yield of strontium was 100%, based on the strontium carbonate used.

Example 1 3

In a mains frequency furnace, which was lined with a carbon-containing ramming mass, were 30 kg of a silicon alloy, consisting of 10% magnesium, the remainder silicon with usual impurities presented and melted. At 1400 ° C., after the furnace heating was switched off, 5.5 kg of a mixture were obtained consisting of 5 kg of dried strontium carbonate and 0.5 kg of electrode carbon powder. To After a waiting time of 10 minutes, the furnace heating was switched on again and the loose loading by means of stirred into the molten metal due to the electromagnetic stirring effect. After complete incorporation and dissolution of the charging material, the silicon alloy formed contained 7.5% strontium and 6.9% Magnesium, the remainder silicon. This corresponds to a yield of 89% based on the strontium content of the Strontium carbonate.

Claims (2)

Patent claims: 1. A process for the production of strontium-containing master alloys, which are intended for the refinement of aluminum-silicon alloys, by introducing a compound containing the alkaline earth metal into a silicon alloy melt at high temperature with vigorous bath movement using additives, characterized in that in a mains frequency furnace in the presence carbon-containing substances a Siüciumschmelze containing at least 0.5% and together at most 70% magnesium and / or calcium and / or aluminum at a temperature of 650 to 1700 ⁰ C, preferably 1000 to 1450 ⁰ C, with strontium oxide, carbonate or sulfate Reaction brought and the metal is alloyed. 2. Application of the method according to claim 1 to silicon alloys from 0.5 to 50%, preferably 5 to 30%, magnesium and / or calcium and / or 0.5 to 50%, preferably 5 to 40%, aluminum, if they are both present, however, a maximum of 70%, the remainder being silicon with the usual impurities, like iron and manganese.