US2497540A - Fluxes for the treatment of light alloys - Google Patents

Description

Patented Feb. 14, 1950 '"Manchester;England, as'signorto Magnesium Elektron LimitedgLondon, England, a British company NdjDrawing. v.;.App1mamma ,am.26,.misz semi No: 7.1!],763. 'iIn'Great BritainAygu'st;29; l946 12 .Claims.

invention -relatesto fluxes forthe treatment I of light alloys consisting of -magnesium hbase 'alloys containing rare earth metals, and

tains substantially no magnesium chloride. {For dthis :purpose I haveendeavoured to develop a =flux which -contains .a :mixture of 'chlorides .-(which'3[s.term..aflprotectivevbase) having-a sufiiciently low melting pointe-to-eenable the flux to prevent burning of the metal'and to provide,

together with a suflicientlquantity of inspissating ia entsutor enable ..th8ifll=.1Xf.t0l':h&Ve the required iscosityrrawpastyviscous; coverin on ithebmetal. c- -lna.ctherawordslhavazendeavoured toi inspissate a mixture ..of .chlorides .-.not,.containing magnesium chloride in a manner in which it has .;previouslyabeenuproposed':to.einspissate.zchloride mixtures consisting largely ofsmagne'siumachldride. I have, however, found that the inspissation of chloride mixtures not containing magnesium chloride is accompanied by certain difiiculties. For example, attempts to inspissate a chloride mixture solely by means of an addition of magnesia, result in a tendency to liquation and dry top-effects, that is to say the flux cover on top of the molten metal is too dry near to its upper surface, and appears to consist mainly of magnesia insufficiently wetted by the chlorides. These difficulties are apparently due to the poor wetting capacity for MgO of chloride mixtures not containing magnesium chloride.

These difficulties can be overcome by prefusing the magnesia with the chloride mixture but this results in a flux, the composition of which must be adjusted somewhat critically to achieve the required degree of inspissation, and which is barely satisfactory in its ability to extinguish burning magnesium.

Accordingly I have attempted to inspissate these chloride mixtures with calcium fluoride.

The composition of these fluxes appeared to be very critical in so far as compositions tending to be somewhat fluid showed the pronounced non-wetting effects to be expected in the absence of magnesium chloride, whereas attempts to 55 .20 The use of "sdiu.m"'and "potassium* fluoride overcome this-difiiculty by'increasing' the amount or thecalcium fluoride until the "flux" 'was ,:so -viscous- -as-to-be--incapab1e" of "showing non' wettingiJcharacteri ticsmroduced: fluxes'gwhichewere 5 aitoo dry sforesatisfactery.gprotection :of the emetal .tagainst oxidation. 'flihetxrange of composition abetween, fluxes-showing qthe non-wetting attendency and-thoser whiohaarentoo; dry. isx-itooz narrow .iorasatisfactory :rcom-mercial. productiona: of-; such lfluxes-eand moreover tdzhe ipptimum .a.calcium s fluoride; acontent rvariestwith temperature of, the ametalv zunderet-reatment.

Attempts to use-.;calcium :fluoridel andimagnesia atg ether ;;save efiuxes gqpOSSessihg -to vsome extent ethe r-disadvantages 1:. associated with sthe separate use ofv both these inspissating agents.

"The -use of ;:strontium and "barium fluorides also produced disadvantages'similar to"thosei.ac-

companying the use'of'calcium fluoride.

gives rise; to introduction of "small amountsfof sodium and traces "of-potassiumintothe'metal nbqth sofewlhichuaiieimbjefltmnablajn addition to non-wetting difficulties.

The us of nma'gnesium ilfiuoride 'was :zinitially QQQXlSldBI'Bd 1impractitable; not 'onlyv-beca-use ituis sine-re. costly l-than-sanyeof ,"lihe fluorides :above .e-mentioned; abut more particularly: because it .:-is

- ..well-:.known that rqmagnesi-um v fluoride will react with the rare earth metals in the same way as magnesium chloride.

I have now made the surprising discovery that unlike the fluorides of sodium, potassium, calcium, strontium, or barium, magnesium fluoride is substantially insoluble in certain chloride mixtures not containing magnesium chloride and I have used this discovery to make fluxes which are very satisfactory for use with alloys containing rare earth metals. I inspissate such chloride mixtures with magnesium fluoride and because the latter is practically insoluble in the chloride mixtures non-wetting does not arise. Furthermore, when the flux melts the particles of magnesium fluoride are readily wetted and coated with the protective base in which they do not dissolve and the magnesium fluoride is thereby protected from contact with the rare earth metals in the alloy and so does not react therewith.

The flux may, however, contain a minor proportion of inspissating agents other than magnesium fluoride. Some small amount of ma nesium chloride may be tolerated in the flux but this should not exceed 2% and is preferably less than 0.5%.

According to the present invention therefore,

a flux suitable for the treatment of the aforesaid light alloys is substantially free from magnesium chloride and consists essentially of at least two chlorides of the alkali metals and alkaline earth metals, other than magnesium, these chlorides in the absence of inspissating agents have a liquidus temperature not greater than 610 C., the flux also containing a sufficient quantity of one or more inspissating agents to enable the flux to provide a pasty viscous covering on the molten metal, and at least 75% of the inspissating agents consisting of magnesium fluoride.

I find in particular that mixtures of calcium,

potassium, and sodium chlorides are suitable for inspissation by magnesium fluoride especially in the following percentages of the chloride mixture(s) Per cent Calcium chloride 40-70 Potassium chloride 6-30 Sodium chloride Q. 24-40 Examples of inspissated flux compositions which we have found satisfactory are as follows:

CaClz 41 25.5 49 NaCl 26 23.5 KCl 9 47 BaClz 7 .5 SIC12 7.5 MgFz 24 20 20 In these examples the figures indicate percentages by weight of th compositions.

Magnesium base alloys containing one or more rare earth metals can be treated with fluxes made in accordance with the invention with regular production of finished alloys having at least equal freedom from traces of chloride contamina- 4 tion as commonly produced magnesium base alloys containing aluminium.

I claim:

1. An inspissated fluxsuitable for the treatment of magnesium alloys-containing-a rare earth metal, which flux is substantially free'from magnesium chloride and consists of at least two chlorides of the alkali metals and alkaline earth metals, other than magnesium, which chlorides when in mixture alone have a liquidus temperature not greater than 610 C., the balance of the flux being a quantity of inspissating agent such as to provide a pasty viscous covering on the molten metal, and at least of the inspissating agent consisting of magnesium fluoride, the quantity of magnesium fluoride being about 20% by weight of the flux.

2. A flux as claimed in claim 1 wherein the chlorides consist of the chlorides of calcium, po-

tassium and sodium, in the following percentages of the total chloride mixture:

Per cent Calcium chloride 40-70 Potassium chloride 6-30 Sodium chloride 24-40 EDWARD FREDERICK EMLEY.

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

UNITED STATES PATENTS Number Name Date 2,121,292 Haughton et a1. June 21, 1938 2,327,065 Reimers Aug. 17, 1943 2,396,604. Reimers Mar. 12, 1946 FOREIGN PATENTS I Number Country Date 342,586 Great Britain Feb. 5, 1931 403,891 Great Britain Jan. 4, 1934 489,700 Great Britain Aug. 6, 1938 OTHER REFERENCES Marande, Materials and Methods, February 1946, pp. 418-424.

Claims (1)

1. AN INSPISSATED FLUX SUITABLE FOR THE TREATMENT OF MAGNESIUM ALLOYS CONTAINING A RARE EARTH METAL, WHICH FLUX IS SUBSTANTIALLY FREE FROM MAGNESIUM CHLORIDE AND CONSISTS OF AT LEAST TWO CHLORIDES OF THE ALKALI METALS AND ALKALINE EARTH METALS, OTHER THAN MAGNESIUM, WHICH CHLORIDES WHEN IN MIXTURE ALONE HAVE A LIQUIDUS TEMPERATURE NOT GREATER THAN 610*C., THE BALANCE OF THE FLUX BEING A QUANTITY OF INSPISSATING AGENT SUCH AS TO PROVIDE A PASTY VISCOUS COVERING ON THE MOLTEN METAL, AND AT LEAST 75% OF THE INSPISSATING AGENT CONSISTING OF MAGNESIUM FLUORIDE, THE QUANTITY OF MAGNESIUM FLUORIDE BEING ABOUT 20% BY WEIGHT OF THE FLUX.