DE1237326B - Process for refining aluminum-silicon alloys - Google Patents

Description

GERMAN PATENT OFFICE

EDITORIAL

German class: 40 b-21/04

Number: 1237 326

File number: R 37144 VIa / 40b

237 326 Filing date: February 3, 1964

Opened on: March 23, 1967

Aluminum-silicon alloys, in particular those with a eutectic or near-eutectic composition, are subjected to a so-called finishing treatment in order to improve the mechanical properties. According to the state of the art (German patents 897 922, 866 551, 897 758), the melt of the alloy is either mixed with metallic sodium at temperatures of 700 to 750 ° C. or brought into contact with salt mixtures, which are an essential component those sodium salts are which, at the present temperature, are capable of releasing a greater or lesser proportion of their sodium content to the melt. Be mentioned here is primarily sodium fluoride having a melting point of about IOOO ⁰ C by mixing with suitable other alkali metal halides such. B. NaCl and / or KCl, or other alkali salts, e.g. B. Na ₂ CO ₃ , partly in the presence of other compounds, partly fluoridic, partly non-fluoridic nature, is reduced so far that it is already liquid at the temperatures of the aluminum-silicon alloy melt and is thus reactive.

Further sodium salts successfully used for processing are sodium azide (German patent 1 017 796), sodium peroxide (patent application by the inventor dated September 28, 1961, file number T 20866 VIa / 40b) and disodium cyanamide (patent application by the inventor dated August 28, 1962, file number R 33411 VIa / 40b).

The latter salts are distinguished by the fact that they have melting or decomposition points below the treatment temperature of the aluminum-silicon alloys and thus the use Make melting point-lowering additives unnecessary.

Recently, preparations have been proposed for the refinement to be marked thereby are that they are conventionally known sodium compounds found useful for the finishing treatment - Alone or in a mixture with other alkali salts - in the presence of finely divided bring metallic aluminum and / or magnesium to use. This ensures that the Sodium yield is significantly increased and thus the amount of preparation required for the treatment decreases (German Patent 1 023 232, German Auslegeschrift 1 155 915).

It has now been found that a particularly effective metallothermal reaction is achieved when calcium as a reducing metal in the form of an alloy with silicon, which has approximately the composition CaSi is used. The suitability of such processes for refining aluminum-silicon alloys

Applicant:

Dr. Riedelbauch & fabric rain
Foundry chemical products,
Meisenheim / Glan

Alloys, however, only come to light when they are in the right proportion with the respective sodium carrier or sodium carrier mixture combined are used, whereby "correct ratio" does not include "Stoichiometric ratio" is to be equated. Becomes the optimal range of the mixing ratio If this is not observed, either the metallothermal reduction of the sodium does not start at all or so spontaneous and explosive that the desired refinement effect does not occur either. (As a guide to the correct ratio, please refer to the example given at the end of the description referenced.)

Provided this is the correct mixing ratio, the sodium compounds used must be used containing salt mixture by far not as much melting point lowering components contained as is the case with the already known preparations. This in turn means that one more time smaller amounts of preparation are sufficient for a successful refinement - which has handling advantages is synonymous -, and on the other hand, that the risk of contamination of the treated melt with low-viscosity components of the treatment preparation that are not capable of reacting with the reducing alloy is significantly reduced.

Salt matrix containing sodium compounds and released with the reducing alloy of sodium or the formation of easily decomposable sodium compounds capable of refining capable, that of compounds of Na and oxygen acids of the non-metals of the III. until VI. Main group of the periodic table of the elements, especially with sodium salts of carbonic acid - alone or in a mixture with one another - proven to be useful. It can be as such or in addition

709 520/334

Claims (4)

Mixture with alkali or alkaline earth halides, especially the fluorides, are used. A mixture has proven to be particularly effective, which consists of 44 percent by weight of CaSi, 45 percent by weight of Na2CO3 and 11 percent by weight of NaF. Patent claims: 1. Process for the refinement of aluminum-silicon alloys, especially electrical ones and near-eutectic composition, with the help of salt mixtures containing sodium salts, characterized in that this together with finely divided calcium-silicon alloy, which corresponds approximately to the composition CaSi, are introduced into the melt and in it with the added alloy react exothermically, releasing sodium. 2. The method according to claim 1, characterized in that the salt mixture containing sodium salts one such is used, the sodium compounds of the oxygen acids of the non-metals the III. to VI. Main group of the periodic table of the elements - preferably sodium salts contains carbon dioxide - alone or in a mixture with one another. 3. The method according to claim 2, characterized in that the salt mixture containing sodium salts additionally alkali and / or alkaline earth halides, preferably fluorides, are included. 4. Process according to claims 1 to 3, characterized in that the mixtures in Form of compacts or castings with a diving bell or a similar device in the melt can be introduced. Considered publications:
German Patent Nos. 744 035, 1023 232, 155 915;
German interpretative document No. 1 184 506. 709 520/334 3.67 O Bandesdruckerei Berlin