US2497538A - Fluxes for use in the treatment of light metals - Google Patents

Description

enema at. 14, 1950 2,497,538

2,497,538 FLUXES FOR USE IN THE TREATMENT OF I LIGHTMETALS- Edward Frederick Emley and Alfred 'G. Jessum Clifton Junction, near Manchester, England, assignors to Magnesium Elektron Limited, London, England, aBritish company Noiira in Application August 2; 1947; serial No. 765,802. In Great Britain August 29, 1946 1' t This invention relates to fluxes :for use in the treatment of light metals consisting of magnesium,- magnesium base alloys; and aluminium base alloys containing magnesium all hereinafter included in the term metal. 5 a much more conspicuous corrosion mark on mag- Manysuch fluxes have-heretofore been prO- nesium-zinc-zirconium than on standard alloys. posed and thos maimy sed n a large oommer; This is not due to a difference in corrosion recial scalecomprise two main kinds namely: sistance of the alloys, but is caused by local sur- (a) An inspissatedflux intended for refining face discolouration developing on the magnesiumthe metal as well as for for preventing oxidation z ncr ni l y r r h r for toreandth main haracte isti of. which are d duce the incidence of these traces of flux below scribed in-Biitish Patent No. 539,024; and t n the s a a s, as j d v y by A thinly fluid r no'n jnspjs'sa ted fl of the exposure in ahumidity chamber of carefully low melting point intended mainly for protectmachined sections of the alloys, we have had to ing the metal against oxidation during melting, l5 devise o s f'p 'fi in s u gm x m of t type and ts n characzirconium alloys a degree of freedom from traces teristic's are described in British Patent No. of fiuxnot previously r a in Standard alloys- 539 023; We have also ascertained that when magne- The present invention is concerned with fluxes Sium alloy 5 ap containing zirsonium is melted of type (a) with normal fluxes a considerable amount of new These fluxes all contain chlorides and as is contamination is invariably introduced. Alwell known proper care u be exerci'ged both though light in nature, this secondary contamina in selecting suitable compositions for'the fluxes n Wldespread and renders the remelted and also in their use in order to minimise con- 9, fi for most commercialvpurpfies' 't'amination of the finished metal with chlorides P 5 kmwn m th Preparatmn, which give rise to corrosion of the metal. t m' m l alloys flux-free State 15 a This cliificulty is experienced with normal conimat-fiber of conslderable dlmculty and moon m ven ence.

31.1552; ofifiifiifilei ifiiutfifififiiii fii its wi h V e t m t P residual W have also met with chloridecont'amination diet-- 0f f m zlrmmum'contammg culties of a special nature when dealing with m "P Y have F exthe magnesium base alloys. described in British tensive exper ments on lines which have included Patent No. 511,137 namely alloys containing a the mlhwmg' Small pereentage of q' i n' e b e 1. Modification of known fluxes in various ways, l m Such a a1um1111um and 5111601} whlPh 55 for instance by use of fluxes in which the form high meltmg 130ml? Compounds Wlth MgGlz/Gal lz ratio is such as to produce a slight coniumnon-wetting action.

It has been the constant 9X p1l 1 '2. Modification of pouring technique, inparticuthat magnesium alloys conta ning zirconium are lar'by fitting specialtraps to the pouringlip dlfiicult to P p 1n a flux-free State, and WQTk of the crucible and special ingates to the mould. on this problem had resulted in the inventions 3.- Use of mechanical filters. forming the subject of co-p'ending British pat- 4. Use of special inhibitors to permit very careful ent applications Nos. 7,227, 18,890 and 20,870, all cleaning of the metal surface before pouring of 1945, according to which it is proposed to effect t0 fOIm Strong co ent o idtube dur alloying by means of zirconium fluoride dis- P g solved in a molten bath-of inert fluorides, or by M dtfi a l m il fluoride alloying bathpotassium fluozirconates either with or without 5' I n ?F P9 U the presence of a chloridebath. gt l t f a t f P m m m We have now found that even with the. alloyg i t uppez the m a ing methods described in these co-pending am ame a hlgher than the lower part during a settling period.

British applications it is very dinicult to remove undesirable traces of chlorides which may be in With the exception of (7) none of these methods troduced by chlorides present in the alloying mix has shown an appreciably beneficial efiect.

tures or which may be introducedlafter alloying In view of thevslight improvement following 2 by the subsequent treatment with chloride-containing flux.

We have also found that a given quantity of included flux produces on exposure to damp air adoption of settling under a favourable temperature gradient, it was decided to investigate the possibility of preparing a special high density flux of the inspissated type for use with magnesium alloys containing zirconium. Whilst it is obvious that such fluxes must contain a high proportion of barium and/or strontium halides in order to attain the necessary high density, it is nevertheless essential that such fluxes should not only introduce no barium or strontium into the fluxed alloy, but should actually be able to remove barium and strontium already in the alloy at least partially during the fiuxing process, since traces of barium and strontium are harmful to magnesium-zinc-zirconium alloys for certain purposes and particularly for preparation of sand castings.

It was also desirable that such fluxes should possess the following properties:

1. Suitability for use while stirring melts at fairly high temperatures (for example over 800 C.)

2. Suitability for use as an all purpose flux, i. e.

We have found it possible to prepare the following four types of heavy fluxes, three of which possess special properties as indicated below in addition to the general properties of high density, power of removing strontium and barium, and the properties numbered (1), and (3) above.

Type 1.Standard heavy flux, i. e., suitable for puddling, refining and covering the alloys. Type Zr-Flux with special suitability for remelting zirconium-containing alloy scrap (hereinafter termed superheavy flux).

Type 3.Flux with special suitability for alloys containing rare earth metals with or without zirconium.

Type 4.-Non-hygroscopic flux.

The use of these fluxes in conjunction, where zirconium is to be introduced, with the alloying method disclosed in British patent application No. 7,227 of 1945, has enabled us to prepare alloys containing (a) zirconium, (b) zirconium and rare earth metals, and (c) rare earth metals, which are of an extremely high degree of freedom from flux.

We have found that in order to avoid the introduction by the flux of traces of barium or strontium into metal, where such traces are undesirable, or to remove or reduce the content of barium and strontium which may already be present in the metal, it is necessary for the flux either to contain no fluorides of barium or strontium or for magnesium chloride to be present in chemical excess of the fluorides of barium and strontium present. For example, two chemical equivalents of magnesium chloride for each equivalent of strontium or barium fluoride present will give good results.

We have ascertained that the inspissated fluxes of the present invention may be used in the treatment of normal commercial type of magnesium base alloys, e. g. those containing magnesium and manganese, magnesium, aluminium and manganese, and magnesium, aluminium, zinc and manganese, and also with aluminium base alloys containing magnesium, with improved results, that is to say with an even greater degree of freedom from chlorides in the finished alloys than when using fluxes of the normal commercial types.

We have found that a protective base consisting of BaClz-MgClz-KC1 in the approximate proportions of 50:38:12 is very satisfactory for preparation of the fluxes of the types 1 and 2. For maximum density we inspissate this with BaFz which is added to the molten protective base, and the resulting product is cast into moulds, crushed, and milled. This superheavy flux has a density of 2.7 g. per cc. in comparison with standard fluxes of density 1.8 to 2.0 g. per cc. and consequently any inclusions of this flux which may be formed in the metal at any stage of the alloying process will have from five to ten times the settling rate of inclusions of standard flux oi the same volume, when calculated according to Stokes law. For this superheavy flux the whole or at least of the inspissating agents consist of barium fluoride and/or strontium fluoride and the chlorides preferably comprise barium and/or strontium chloride in quantity at least equivalent to 40% barium chloride. Alternatively, where the highest density is not required, a standard type of flux may be produced by mixing the BaFz with the milled protective base in powder form instead of by fusion, the density of the resulting flux being somewhat less (2.55 to 2.6 g. per cc.). The permissible latitude in composition of this flux is, however, extremely narrow, the BaFz content necessary to produce the required degree of inspissation being critical to 1 or 2% on either side of the optimum content, which we find may vary with the condition of the particular sample of protective base used and particularly with its degree of hydration.

With a view to increasing this latitude in composition and thereby rendering the production of a standard type of heavy flux practicable on a continuously operating plant, we have substituted MgFz for BaFz with considerable success. The density of this standard heavy flux (type 1) is 2.5 to 2.55 g. per cc. and therefore rather less than that of the superheavy flux, but we have found that this flux gives excellent results. To compensate for the slightly reduced density and to cheapen the product, we have also in certain cases introduced calcium chloride and sodium chloride into the protective base with satisfactory results, and we have also substituted (a) CaFz, (b) CaFz and MgO and (c) MgO for some, or even all, of the MgFz, though in the latter case we prefer to prefuse the MgO into the protective base.

We have prepared satisfactory fluxes for use with zirconium alloys containing rare earth metals by inspissating the following protective base with MgO and/ or CaFz:

50 BaCIz 25 CaClz 15 NaCl 10 KCI but such fluxes possess inconveniently narrow permissible latitude in composition and we prefer, therefore, to inspissate this base with MgFz which we have found provides a much wider latitude.

We have also succeeded in preparing a nonhygroscopic mix from a protective base-of :Bacn, KCl and NaCl. It was found that if CaFz; BaFz orxSrFz were. used as inspissating agents for the protective base, the resulting fluxes were all strongly non-wetting. If at least 75 per cent of the inspissating agents in the flux consist of MgFz, the non-wetting was eliminated. Barium fluoride and strontium fluoride are preferably absent or at any rate constitute not more than of the total inspissating agents. Preferably the whole of the inspissating effect for this purpose should be provided byv MgF2 but if some proportion of other inspissating agent is present this should preferably not comprise any other fluoride. The resulting flux was very satisfactory in behaviour except in its lack of ability rapidly to ex tinguish burning metal which rendered the flux unsuitable for use in melting magnesium alloys. By profusion of the constituents of the protective base it was found possible to overcome this disadvantage and so produce a completely non-hygroscopic flux which was entirely satisfactory as a flux in all respects.

We have found that the BaClz may, if desired be replaced at least partially by SrC12 in an of the heavy fluxes described.

The fluxes may contain minor proportions of inert impurities such as Si02, FezOs, A1203, CaO and carbon, which may be present either as impurities in the constituents of the flux or may be added for their inspissating action in amounts up to 35%.

Certain variations may be used both in the ingredients of the inspissated fluxes according to the present invention, and also in their relative proportions'but the following features must be taken into consideration.

1. The strontium chloride and/or barium chloride may be wholly replaced by strontium fluoride and/or barium fluoride. In this case the inspissated flux must contain at least 12% of barium fluoride, i. e. equivalent to of barium chloride based on the total flux which is approximately equivalent to of barium chlorides based on the weight of the chlorides alone. Alternatively the flux may contain both barium and strontium fluorides in amounts equivalent to at least 12% barium fluoride, reckoning 1% strontium fluoride equivalent to 0.35% barium fluoride.

2. If desired the strontium and/or barium chloride may be partly replaced by strontium and/or barium fluoride. In this case the barium and strontium halides must be equivalent in total to at least 20% (of the total flux) of barium chloride reckoning 1% barium chloride equivalent to 1.4% strontium chloride, 0.6% barium fluoride, and'lfi strontium fluoride.

3., In the flux incorporates strontium and/or barium fluoride it must also include at. leas a stoichiometrically chemical equivalent of magnesium chloride to avoid the reduced wetting tendencyv and to prevent entry of strontium and barium into the metal. in cases where this is. not desirable.

4. The chlorides in the flux when melted alone, apart from the inspissating agents, should have a-liquidus temperature not greater than 75090., and preferably not greater than 610 C., that is to say a slightly greater liquidus temperature can be tolerated when the chlorides are used in an inspissated fluxfor refining and covering than when used aloneas a melting flux.

5. The inspissated flux will consist solelymf chlorides and fluorides of alkali metals and al- I kaline earth metals including magnesium together with, if.desired', substantially-inertoxides suitable for use as inspissating agents.

6. The quantity of inspissating agents, that is to say the fluoride: and/or oxides, mustbe sufficient to cause the flux to produce a pasty viscous cover on. the surface. of the molten metal at 750 C.

7. If calcium chloride and magnesium chlorid are absent, then at least of the inspissating agents should consist of magnesium fluoride; other fluorides should preferably be absent'and the protective baseofthe'flux. should preferably be prefused.

8. Preferably, if strontium and/or barium chloride are. absent, the strontium and/or barium fluoride is/are prefused with one or more of the chlorides.

9. Preferably sodium and potassium fluorides are omitted from the flux, but these fluorides can be tolerated to some extent if sufficient magnesium chloride is present to avoid contamination of the metal by sodium and potassium and to prevent the reduced wetting effect.

10. The density of the fluxes of the present invention is at least 2.2 and preferably at least'2.4-.

According to the present invention therefore the fluxes are composed as described under (a) below or in the modified form described under (1:) produced by wholly or partly replacng, the barium chloride and/or strontium. chloride by barium fluoride and/or strontium fluoride.

(a) The flux contains at least two chlorides of the group consisting of the chlorides oi the alkali and alkaline earth metals including magnesium, at least 25% of the chlorides being barium chloride, together with a. sufficient proportion of one or more inspissating agents (other than barium fluoride and strontium fluoride) to enable the flux to provide a pasty viscous covering on the surface of the molten metal at 750 C., the flux having a specific gravity of at least 2.2 at 800 C.; the barium chloride being partly. or wholly replaceable by strontium'chloride reckoning 1% strontium chloride equivalent to 0.7% barium chloride.

(b) The modified flux contains one or more of the salts of the group consisting of barium chloride, barium fluoride, strontium chloride, and strontium'fluoride, including at least one of these fluorides, the total quantity of these salts being equivalent to at least 20% barium chloride reckoning 1% barium chloride equivalent to 1.4% strontium chloride, 0.6% barium fluoride, or 1.6% strontium fluoride, the flux also containing magnesium chloride in quantity at least stoichiometrically equivalent to the barium fluoride and/ or strontium fluoride and having a specific gravity of at least 2.2 at 800 C. and being adapted to produce a pasty viscous cover on the metal at 750 C.

In. addition to the SICIz and/or BaClz present in all fluxes, the following groups of additional chlorides and inspissating agents give fluxes which are particularly suitable for thepurposes cited.

Type 2.--(For alloys containing zirconium):

Chlorides of Mg and K with or without minor proportions of chlorides of Ca and Na, together with one or more fluorides selected from the group MgFz, CaF2 and BaFz with or without minor amountsof MgO.

Ty'pe.3.--(Foralloys containing/rare earth elements with or'without zirconium:

=75v Chlorides :of Ca, K and Na with one or more nesium, and the alkali metals, said flux contain ing at least two of the aforementioned chlorides, said flux including at least one inspissating agent selected from the group consisting of such oxides and fluorides including the said barium fluoride and strontium fluoride as are chemically inert to molten magnesium, the quantity of inspissating agents being between 13% and 43%, and such as to enable the flux to provide a pasty viscous cover on the surface of the molten metal at 750 C., the flux having a specific gravity of at least 2.2 at 800 C. and being substantially free from sodium fluoride.

Inert Impurities For various purposes:

Suitable for Al- N on-deli- Suitable for loys containing quesccnt flux Standard rare earth metals suitable for Alloys with orwithout Zr all alloys Example reference. (G) (H) (I) (I) Inert Impurities The following specific compositions are quoted by way of further example, the small letter references corresponding with the similar above quoted capital letter references:

2. An inspissated flux as claimed in claim 1 which includes at least one of the fluorides selected from the group consisting of barium fluoride and strontium fluoride, and magnesium chloride in quantity at least stoichiometrically equivalent to the barium and strontium fluorides.

3. An inspissated flux for use in the treatment of magnesium and magnesium base alloys consisting of barium chloride from 20% to 45%, magnesium chloride from 15% to 42%, potassium chloride from 4% to 16%, and the balance consisting of from 18% to 38% of at least one inspissating agent selected from the group consisting of calcium fluoride, magnesium fluoride and magnesium oxide, the flux having a specific gravity of at least 2.2 at 800 C.

EDWARD FREDERICK EMLEY. ALFRED C. JESSUP.

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

UNITED STATES PATENTS Number Name Date 1,359,851 Whitmyre Nov. 23, 1920 1,968,984 Binder Aug. 7, 1934 1,980,152 Beck Nov. 6, 1934 2,148,664 Wille et al. Feb. 28, 1939 2,170,863 Junker et al. Aug. 29, 1939 2,261,906 Nelson et al. Nov. 4, 1941 2,286,869 McDonald June 16, 1942 2,453,444 Loonam Nov. 9, 1948 FOREIGN PATENTS Number Country Date 489,700 Great Britain Aug. 2, 1938 503,953 Great Britain Apr. 12, 1939 OTHER REFERENCES Ser. No. 387,769, Light Metals and Their Alloys, Henry Lepp (A. P. 0.), published May 4,

Claims (1)

1. AN INSPISSATED FLUX FOR USE IN THE TREATMENT OF MAGNESIUM AND MAGNESIUM BASE ALLOYS CONSISTING OF AT LEAST ONE HALIDE SELECTED FROM THE GROUP CONSISTING OF THE CHLORIDES AND FLUORIDES OF BARIUM AND STRONTIUM, IN TOTAL AMOUNT AT LEAST EQUIVALENT TO 20% BARIUM CHLORIDE RECKONING 1% BARIUM CHLORIDE EQUIVALENT TO 1.4% STRONTIUM CHLORIDE, 0.6% BARIUM FLUORIDE, OR 1.6% STRONTIUM FLUORIDE, AT LEAST ONE CHLORIDE SELECTED FROM THE GROUP CONSISTING OF THE CHLORIDES OF CALCIUM, MAGNESIUM, AND THE ALKALI METALS, SAID FLUX CONTAINING AT LEAST TWO OF THE AFOREMENTIONED CHLORIDES, SAID FLUX INCLUDING AT LEAST ONE INSPISSATING AGENT SELECTED FROM THE GROUP CONSISTING OF SUCH OXIDES AND FLUORIDES INCLUDING THE SAID BARIUM FLUORIDE AND STRONTIUM FLUORIDE AS ARE CHEMICALLY INERT TO MOLTEN MAGNESIUM, THE QUANTITY OF INSPISSATING AGENTS BEING BEWEEN 13% AND 43%, AND SUCH AS TO ENABLE THE FLUX TO PROVIDE A PASTY VISCOUS COVER ON THE SURFACE OF THE MOLTEN METAL AT 750* C., THE FLUX HAVING A SPECIFIC GRAVITY OF AT LEAST 2.2 AT 800*C. AND BEING SUBSTANTIALLY FREE FROM SODIUM FLUORIDE.