US2604394A

US2604394A - Magnesium base alloys

Info

Publication number: US2604394A
Application number: US120422A
Authority: US
Inventors: Edward F Emley
Original assignee: Magnesium Elektron Ltd
Current assignee: Magnesium Elektron Ltd
Priority date: 1949-07-04
Filing date: 1949-10-08
Publication date: 1952-07-22
Anticipated expiration: 1969-07-22

Description

Patented July 22, 1952 chester, England, assignor to Magnesium Elektron Limited, Manchester, England, a British omp any No Drawing. Application October 8, 1949, Serial N 0. 120,422. In Great Britain July 4, 1949 1 J .This invention relates to the production of magnesium-base alloys, and in particular to the introduction of one or more of the'rare earth metals into the alloy in quantities not exceeding 15 per cent and usually from 1 to 8 per cent.v For thispurpose, it is possible to obtainrare earth metals in metallic form which, however, are

usually contaminated with appreciable quantities of iron and silicon. These impurities are, however, deleterious when introduced into magnesium alloys, especially magnesiumalloys containing zirconium. It is found that even comparatively smallproportions of iron and silicon will militate to a considerable extent against the introduction of zirconium into the magnesium. I have, therefore, considered the possibility of introducing rare earth metals by means of reducible salts of these metals.

It has. been suggested in British Patent No. 342,586 to incorporate cerium chloride in-fluxes to be used with alloys containing rare earth metals, these fluxes containing magnesium chloride, and the object of the cerium chloride being to give rise to sufiicient cerium on reaction with the magnesium to offset the cerium loss which would otherwise be caused by reaction with the magnesium chloride. I have performed a number of alloying experiments with cerium chloride but this substance is deliquescent, volatile, readily hydrolysed and expensive, and is, therefore, not well adapted to serve as a commercial source for the introduction of cerium. Moreover, reduction of the cerium chloride by magnesium is far from complete. These remarks are also applicable to the chlorides of other rare earth metals.

I have, therefore, carried out experiments with a view to using the fluorides of the rare earth metals for alloying purposes. These fluorides are however highmelting pointsolids, and it therefore appeared to me desirable to search for some suitable solvent to assist in the reduction at temperatures suitable for treatment of magnesium. Experiments showed thatthe rare earth metal fluorides were insoluble in alkali metal chlorides and also in alkaline earth metal chlorides with which they did not react. I

therefore tried various low melting mixtures of It was found that various fluoride mix- 2 Claims. (01. 75-67) Considering the possible use of potassium fluoride, I discovered that potassium fluoride formed a low melting point mixture with rare earth fluorides if the proportions of the substances were kept within certain limits, and if sufiicient potassium chloride was added to prevent the mixture from reacting violently with magnesium, the resulting composition could be used for introducing rare, earth metals into magnesium. Itwas also found that the rare earth metal alloying efliciencies using such compositions were superior to those that obtained with rare earth chlorides.

I have considered the possibility of using sodium fluoride in place of potassium fluoride, and of using sodium chloride, calciumchloride, strontium chloride or magnesiumchloride in place of potassium chloride with a view to effecting further improvements in alloying efliciency. The use of'sodium fluoride results however in the incorporation into the final alloy of undesirably large amounts of sodium, which in all cases produces a marked increasein the tendency of the alloys to burn during casting, and inthe case of alloys containing zirconium exercises a deleterious effect on tensile properties, particularly in the sand cast state. The alloying composition should not contain more than 5 per cent sodium fluoride if any. Substitution of sodium chloride for the potassium chloride also gives rise to somewhat increased sodium contents in the final alloys. On substituting calcium chloride, strontium chloride and barium chloride for the potassium chloride, it is found that a reaction occurs in which the potassium fluoride is converted to potassium chloride 'With subsequent precipitation from solution of the rare earth fluoride, and deterioration in the alloying efliciency. It appears therefore that the most satisfactory chloride to use in order to prevent the mixture of rare earth fluoride and potassium fluoride from reacting violently with the magnesium during alloying is'potassium chloride.

According to the present invention therefore, an alloying composition' for introducing rare earth metals into magnesium consists of the fluoride of the rare earth metaLsufiicient potassium fluoride to dissolve the rare earth metal fluoride at the alloyingtemperature (e. g. 700 C. to 850 C.) and at least asufficient quantity of an alkali metal chloride to prevent violent reaction, other of the aforementioned chlorides, if any, not exceeding 5 per cent. In particular, magnesium chloride should be absent. a I

Whilst the minimum quantity of potassium fluoride is that required to dissolve the rare earth metal fluoride, a somewhatgreater proportion may be used in order to produce greater fluidityat the alloying temperature, and a corresponding 3 increase in the proportion of the alkali metal chloride is then used. The quantity of potassium fluoride is preferably at least an equimolecular proportion in relation to the rare earth metal fluoride. The proportion of alkali metal chloride should be at least one chemical equivalent of the potassium fluoride. 1

The quantity of alkali metal chloride is preferably from 5 to per cent of the total weight of I flux more than the quantity of potassium fluoride and from to per cent less than the quantity of rare earth metal fluoride. The alkali metal chloride and potassium fluoride together are preferably from 5 to 15 per cent less than the quantity of rare earth metal fluoride.

. The ingredients of the-composition should fall 7 within the following limits:

For example, a mixture consisting of 55% rare earth metal fluoride, 17% potassium fluoride and 28% alkali metal chloride gives satisfactory results. 1 In practice, I prefer to use potassium chloride as the alkali metal chloride.

Certain ingredients otherthan those hereinbefore mentioned may be incorporated into the composition viz:

1. One or more rare earth metal chlorides or oxides preferably not exceeding 10 per cent each andnot exceeding 15 per cent in total. These should however preferably not exceed 4 per cent.

2. Up to 5 per cent of one or more oxides inert to magnesium and'which do'not react with rare earth metal chlorides e. g. MgO (preferably not more than 2 per cent).

3. Up to 5 per cent of one or more fluorides of alkaline earth metals including magnesium. The total of these fluorides and the oxides mentioned under 2 should not exceed 5 per cent (preferably however not exceeding 2 per cent).

4. Up to 10 per cent (preferably not more than 5 per cent) of bromides of alkali metal and alkaline earth metals.

5; Some lithium chloride and/or bromide, e. g. up to 10 per cent (preferably less than 5%) The total proportion in the alloying composition of rare earth metal fluorides, potassium fluoride and alkali metal chlorides, should be at least,80 :per cent and preferably at least 95 per cent;

In the production of magnesium base alloys containing for example about 3 per cent. rare earth metals, the following procedure may be adopted. The magnesium or magnesium alloy to be melted is charged to the'crucible and a quantity of the composition equal to about 12 percent of the weight of metal also added. When melting is complete, the temperature of the metal is raisedto about 830 C., and the metalis'puddled for 10 to 15 minutes using an alloying tool consisting of a perforated plate with a handle attached at right angles. During the puddling process, it is desirable to use a flux which does not contain magnesium chloride, e. g. the flux described in the specification of British Patent No. 652,235.

In addition to the method described, the composition may be contacted with the magnesium or magnesium alloy in other ways, e. g., the composition may be added in the form of lumps or powder to the melt when the metal is molten, or the metal may be poured on to the composition, the latter being either in the solid or molten state. Mechanical stirring'may be substituted for puddling by hand.

When preparing alloys containing both ziricomum and rare earth metals, the addition of i the zirconium can be'made before or after the introduction of the rare earth metal or may be simultaneous therewith. For introduction of the zirconium, the alloying composition of U. S. Patent 2,452,914 may conveniently be used, and this can be chargedto the crucible with the metal to be melted or may be contacted with the molten alloyv in other ways, e. g., by stirring the alloying composition either in the form of lump or powder into the molten metal, or the metal may be poured on to the composition, the latter being in either the solid or liquid state. Mechanical stirring may be used. j

In remelting ingot or scrap alloy containing rare earth metals it is desirable to introduce a further quantity of the alloying composition into the crucible and conveniently this'isadded to the crucible before or at the same time as the scrap. It can however be added at a later stage. The Weight of alloying composition required in remelting alloy containing 3 per cent of rare earth metals will for example be from one to two per cent of that of the alloy, and its use will enable the rare earth metal content of the final alloy to be closely controlled.

In the production'of magnesium base alloys containing zirconium as well as rare earth metals, the zirconiurn alloying substance may be introduced into the molten magnesium at the same time as or after introducing the rare earth metal alloying composition.

I claim.

1. A composition of the character described, for use in producing magnesium base alloys, consisting of 45 to of at least one rare earth metal fluoride, 12 to 25% of potassium fluoride and 20 to 40% of at least one alkali metal chloride.

'2. A composition for use in producing magnesium base alloys consisting of from 80 to 98% of a main component and from. 20 to 2% of a subsidiary component, the main component consisting of: rare earth metal fluorides 45 to 65% by weight of the component, potassium fluoride 12 to 25% by weight of the component and alkali metal chloride 20 to 40% by weight of the com- .ponent, the subsidiary component consisting of at least one of the following: 0 to 5% of sodium chloride, 0 to 5% of an alkaline earth metal chloride, 0 to 10% of a chloride of a rare earth metal, 0 to 10% of an oxide of a rare earth metal, 0 to 5% of an oxide inert to magnesiumyO to 5% of anoxide inert to rare earth metals, 0 to 5% of a 'fluoride of an alkaline earth metal, 0 to 10% of a bromide of an alkali metal, 0 to 10% ofa' bromide of an alkaline earth metal, EDWARD F. EMLEY.

REFERENCES orrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name 1 Date 2,250,687 Von Zeppelin July 29, 1941 2,251,088 Von Zeppelin July 29, 1941' 2,452,914 Emley i Nov. 2, 1948

Claims

1. A COMPOSITION OF THE CHARACTER DESCRIBED FOR USE IN PRODUCING MAGNESIUM BASE ALLOYS, CONSISTING OF: 45 TO 65% OF AT LEAST ONE RARE EARTH METAL FLUORIDE, 12 TO 25% OF POTASSIUM FLUORIDE AND 20 TO 40% OF AT LEAST ONE ALKALI METAL CHLORIDE.