US1915932A - Magnesium-cerium alloy - Google Patents

Description

Patented June 27, 1933 UNITED STATES PATENT OFFICE KARL HIEGE, OF BITTERFELD, GERMANY, ASSIGNOR, BY MESNE ASSIGNMENTS, '1'0 .MAGNESIUM DEVELOPMENT CORPORATION, A CORPORATION OF DELAWARE MAGNESIUM-CERIUM ALLOY No Drawing. Application filed April 8, 1930, Serial No. 442,691, and in Germany April 15, 1929. Renewed May 10, 1932.

The present invention relates to magnesium-cerium alloys and is more especially \conccrned with a method of refining magnesium-cerium alloys. The term cerium when employed in the present application is understood to refer not only to the chem1- cal element cerium but also embraces the socalled misch-metal containing besides cerium a comparatively large number of other rare.

earths in minor quantities. The following table gives an analysis of the average composition of miseh metal:

Percent Ce 50-60 La Dy, Sa and other rare earth metals- 15 Fe 1-2 These elements also participate in the same ratio in salts such as chlorides derived from misch-metal.

Processes are known for refining magnesium alloys by melting them together with saltfluxes containing for example magnesium chloride or carnallite or mixtures of both salts either alone or in combination with additives which act as thickening media. In U.-S. Patents 1,576,080 and 1,661,526 respectively, a number of such substances are disclosed as having a thickening ciiect of this kind upon the flux and it is particularly to these substances that the term thickening media refers when used in the present specification and claims. It is further known that these methods may be advantageously amplified by forming a protective layer of a salt mixture having the composition of the flux itself or containing its ingredients in proportions only vinoderat-ely diiierent therefrom on the surface of the molten metal after the refining process propercons1stmg in an intimate mechanical mixing of the flux with the molten v metal-is completed, and heating the molten metal thus protected to a high temperature before allowing it tocool down to the casting temperature.

When applying these methods to the treatment of magnesium alloys containing certain amounts of cerium I have observed that part of the cerium is eliminated from the metal alloy by the action of the flux and is thus hygroscopic flux preferably combines with the easily oxidizable cerium contained in the molten metal according to the equation Ce lthe cerium dioxide being taken up by the slag whereas the hydrogen escapes.

Objects of the present invention are, therefore, to prevent the elimination of cerium from molten magnesium alloys when the latter are contacted with refining fluxes and to produce refined magnesium-cerium alloys having a predetermined cerium content.

In order to carry my invention into practice I thoroughly mix a quantity of anh drous cerium chloride with the flux to o employed in the refining process. I preferably add so much cerium chloride to the flux that the percentage contents of cerium chloride in the former amounts to about twice the. percentage contents of cerium in the alloy to be treated. The cerium chloride may either be admixed in the solid state in comminuted form to the other solid fluxing salt or salts, or be melted together with the latter, the solidified melt then being ground in the usual manner. The flux thus obtained is then employed for refining magnesiumcerium alloys in exactly the same manner as the known fluxing compositions.

The following examples will serve to illustrate the particular advantages attending my new methodas compared with the method formerly in use for refining magnesiumcerium alloys,

Example 1.-(Sh0'wi1 ig the use of old flames) the molten metal 10 of a powdered flux substantially consisting of 10 parts of carnallite, 15 parts of magnesium oxide and 15 parts of fiuorspar, the latter two substances acting as thickening media, while thoroughly stirring the melt at a temperature of about 750 C. until practically all the flux had disappeared from the surface of the molten metal. The surface of the melt was then covered with a layer having a thickness of about 5-10 mm. of the same finely grained or powdered flux and the melt was then heated to above 850 C. and maintained above that temperature for about 5 minutes. It was then allowed to cool down until the selected casting temperature of 780 C. was reached, whereupon the protective layer of salt was broken in and the melt was cast, care being taken to prevent any fragments of the protective layer from being swept along by the metal. The cast alloy was found to contain only 8.5 percent of cerium misch-metal as compared with 10 percent of cerium misch-metal in the starting material.

Example 2. (Showing the we of the fl'ua'es according to the present invention) The same alloy was treated in exactly the same manner, the only difference being the composition of the flux. The latter contained besides the ingredients mentioned in Example 1, 25 percent (by weight of said inedients) of anhydrous cerium misch-metal chloride. The flux in this case thus had approximately the following composition:

Percent Carnallite Magnesium oxide 12.5 Fluorspar 12.5 Anhydrous cerium misch-metal chloride 20 in the bath, causes the formation of further amounts of oxide by decomposition, the latter also acting as a thickening medium upon the flux. When working in this manner it is preferable to slightly raise the amount of =cerium chloride added to the original flux,

whereas the amount of thickening substances contained in the latter may be, correspondingly reduced.

The refining process according to the present invention may further advantageously be combined with an incorporation of cerium into the metal or alloy. This is effected by adding the amount of metallic cerium required to produce the desired cerium content of the finished alloy to the molten magnesium or magnesium alloy underneath the protective layer of the flux containing anhydrous cerium chloride.

I claim: v

1. A method of refining magnesium-cerium alloys, comprising adding cerium chloride to a flux which, in the absence of cerium chloride, extracts cerium from a magnesiumcerium alloy melt and treating such a molten magnesium-cerium alloy with the flux thus obtained.

A method of refining magnesium-cerium alloys, comprising adding anhydrous cerium chloride to a flux which, in the absence of cerium chloride, extracts cerium from a magnesium-cerium alloy melt and treating such a molten magnesium-cerium alloy with the flux thus obtained.

3. A method of refining magnesium-cerium alloys, comprising adding anhydrous cerium chloride to a flux which, in the absence of cerium chloride, extracts cerium from a magnesium-cerium alloy melt, in such quantities that the percentage of cerium chloride in'the flux is approximately twice as large by weight as the percentage of cerium contained in the alloy to be treated, and treating such a molten magnesium-cerium alloy with the flux thus obtained.

4. A method of refining magnesium-cerium alloys comprisin treating the molten metal with a flux main y consisting of magnesium chloride and containing minor quantities of a thickening medium and anhydrous cerium chloride.

5. A method of refining magnesium-cerium alloys comprising intimately mixing the molten metal at a temperature not far above its melting point with a flux mainly consisting of magnesium chloride and containing a minor quantity of cerium chloride, until the flux has disappeared from the surface of the molten metal, then forming a protective layer of a flux having substantially the same composition on the surface of the melt, heating the melt to at least about 850 C. and

keeping it above that temperature for some anhydrous cerium chloride, until the flux has disappeared from the surface of the molten metal, then forming a protective layer of a flux having substantially the same composition on the surface of the melt, heating the melt to at least about 850 C. and keeping it above that temperature for some time, then cooling it to the casting temperature and casting the metal.

7. A method of producing magnesium alloys containing a predetermined quantity of cerium which comprises intimately mixing the molten metal still free from cerium at a temperature not far above its melting point with a flux mainly consisting of magnesium chloride and containing a minor quantity of cerium chloride until the flux has disappeared from the surface of the molten metal, then forming a protective layer of a flux having substantially the same composition on the surfaces of the melt and introducing the amount of metallic cerium required to form the alloy desired into the melt underneath the protective layer.

8. A method of producing magnesium alloys containing a predetermined quantity of cerium which comprises intimately mixing the molten metal free from cerium at a temperature not far above its melting point with a flux mainly consisting of magnesium chloride and containing minor quantities of a thickening medium and anhydrous cerium chloride, until the flux has disappeared from the surface of the molten metal, then forming a protective layer of a flux having substantially the same composition on the surface of the melt and introducing the amount of metallic cerium required to form the alloy desired into the melt underneath the protective layer.

9. A process of refining magnesiumcerium alloys which comprises heating a melt of such an alloy with a flux containing magnesium chloride and cerium chloride, the latter being present in a percentage equal to about twice the percentage of cerium in the alloy.

10. The process of refining magnesium cerium alloys which comprises heating a melt of such an alloy with a flux comprising carnallite, fiuorspar, magnesium oxide and cerium chloride.

11. The process as defined in claim 7 wherein the flux contains cerium chloride in a percentage equal to about twice the percentage of cerium in the alloy treated.

12. A flux for refining magnesium-cerium alloys While preventing oxidation of the cerium in the alloys comprising magnesium chloride and cerium chloride.

13. A flux for refining magnesium-cerium alloys. while preventing oxidation of the cerium in the alloys comprising magnesium chloride, cerium chloride and a thickening agent. I

14. A flux for refining magnesium-cerium alloys while preventing oxidation of the cerium in the alloys comprising magnesium chloride, cerium chloride, carnallite and a thickening agent.

15. A flux for refining magnesium-cerium alloys while preventing oxidation of the cerium in the alloys comprising magnesium chloride, cerium chloride, carnallite, fluorspar and magnesium oxide.

. In testimony whereof I have hereunto set my hand.

KARL HIEGE.