US2474538A - Alloying manganese with magnesium - Google Patents

Description

Patented June 28, 1949 2,474,538 ALLOYING MANGANESE WITH MAGNESIUM Charles H. Mahoney and Gerald L. Lee, Boulder City,

Nev., assignors, by mesne assignments, to

the United States of America as reprcsented by the Secretary of the Navy No Drawing. Application June; 10,. 1944, Serial No. 539,786

2 Claims.

This invention relates to magnesium alloys containingmanganese, and has for its object the provision of certain improvements in alloying manganese with magnesium.

Manganese is: commonly included in most magnesium base alloys employed for structural and other commercial uses. Binary magnesiummanganese. alloys commonly contain 1 to 3% manganese, and magnesium base alloys com=- monly' containfrom 0.05 to 3% manganese, with, for example, 0.1 to 12% aluminum and 0.05 to 5 zinc. The amount of manganese included in these alloys. is limited on the higher side by the solubility of manganese in magnesium and in magnesium base alloys and on the lower side by the. amount required to impart the. desired corrosion resistance and other properties to the alloy. In general, magnesium alloys contain from 0.05 to 55%. manganese, while the magnesium base alloys containing aluminum customarily contain from 0.05 to 1.0%. manganese.

The direct alloying. of metallic. manganese with magnesium is attended by considerable difficulties, and while the. literature casually mentions the melting together of metallic. manganese and magnesium or the. introduction of metallic manganese to molten magnesium or alloysv thereof, the-customary industrial practice: is to: introduce the; manganese inthe form of a. reducible: manganese. compound, commonly manganous' chloride.v Thus, dehydrated manganous. chloride, in flakeor granular form, is placed on. the surface of the. molten magnesiu-mor magnesium alloy, the. magnesium. replacing; manganese in the manganous. chloridewith the liberation. of metallic. manganese which. is. then available for alloying with the. magnesium. The resulting; magnesium. chloride: is: heavier; than: the molten. metal and sinks to. the bottom ofthe'bath. Manganous. chloride crystallizes with: four molecules: of water, (MGM-41120) and. while part of the water of crystallization is. easily driven oft; complete dehydration is diflicult withoutv converting somev oi; the: chloride to oxide. Moreover, the flake or granular dehydrated manganous chloride is; of light weight and: dusts easily thereby contaminating;v other melts in: the plantv in which manganese is not: desireoh. or is; objectionable. The-,replaaement of manganese. by magnesium: is never complete, and. withgood. alloying practice: emciencies: of about can be: accomplished. As aconsequence. the use. of: maganous chlorideinexp nsive; ,and-lthezresults;obtained. leave much; amer-desired withurespecuta: accurate control. of haalloncompositlom.

Where attempts have been made to alloy metallic manganese directly with magnesium or its alloys, much of the manganese is oxidized. Moreover, because of its relatively high specific gravity, much of the manganese settles rapidly through the molten magnesium and collects in the sludge or flux layer at the bottom where it tends to become coated with the chloride fluxes. As" aresult, low and unpredictable efliciencies are attained, andaccurate control of the alloy composition is impossible. In an attempt to overcome these difiiculties, manganese has been introduced into the molten magnesium in the form of" an intermediate alloy with another metal as a hardener. However, the use of the intermediate manganese alloy is limited. to alloys in which the-presence of the other hardening metal is. contemplated, and moreover the additional cost of producing the intermediate alloy is objection able.

The present invention aims to provide a commerciallysafisfactory' and economical method of directly alloying. metallic manganese, and particularly electrolytically produced manganese, with: magnesium As a result of our investigations; we: have discovered: that the presence of aluminum. in molten magnesium adversely affects the direct. alloying of manganese with the magnesium by lowering or retarding the solubility of the. manganese. We have further found that metallic; manganese in a moderately coarse condition can. be: directly alloyed with magnesium with satisfactory efliciency. For optimum results, themoltenmagnesium should be substantially; free' of chloride-containing fluxes, and the temperature; of. the molten magnesium should be above 740?" C. before: adding the metallic manganese.

Based on the: foregoing inventionvinuolves directly alloying metallic manganese: with magnesium by adding relatively coarse manganese to molten magnesium at a temperature of from 750 to 800 C. and prior to adding: aluminum.. The. magnesium should be essentially-- aluminum-free for optimum alloying efficiencya. although reasonably satisfactory re.- sults can. be obtained with magnesium containing only a few tenthsv of a percent of aluminum. The: metallic" manganese, preferably electrolytic manganese, is crushed; tomoderate fineness, so that. approximately all; passes through a 4 mesh standard. Tyler screen or sieve and a minimum passes a 150' mesh screen. We have found that too. finely. ground manganese, that is through or minus L mesh, oxidizes rapidly with resultdiscoveries, the present.

metal is melted under a suitable protective cover r (inert gas or flux). The molten metal is then heated to a temperature of between 750 C. and 800 C., and the calculated amount of moderately coarse metallic manganese (preferably electrolytic manganese) is added. It is necessary prior to adding the manganese that the magnesium metal be refined as free of chloride-containing fluxes as possible in order to achieve maximum manganese efficiency. The manganese is preferably laid on the bare surface of the clean molten magnesium, and gradually sinks therethrough. Preferably, to minimize burning losses, a suitable protective cover of inert gas or fiux is applied to the surface of the molten metal as soon as the manganese is added. After an in erval of 5 to minutes, the molten alloy is agitated by stirring or plunging. The agitation may be done by plunging with a hand tool or by mechanical stirring. If aluminum, zinc or other metal additions are to be made to the alloy, they are added to the molten magnesium-manganese alloy if maximum manganese efiiciency is to be obtained.

Although a substantally chloride-free molten magnesium metal is necessary in order to achieve maximum alloying efficiency, alloying efficiencies of 70% or better can be obtained by adding to the molten magnesium metal a mixture of relatively coarse manganese and commercial magnesium refining flux, the proportion of manganese exceeding 50% of the mixture. We have found that the customary thin chloride melting flux tends to set the manganese and thus impairs the alloyin efiort. Hence, in the preferred practice of the invention, we carefully refine out any chloride melting flux in order to obtain maximum alloying efficiencies. On the other hand, we have found that the customary thick refining fluxes do not greatl -impair the alloying efi'iciency of the manganese. These commercial refining fluxes consist generally of a chloride salt base,

for example a mixture of alkali chlorides and alkali-earth chlorides, and contain 20 to 40% of inspissating agents such as magnesia and calcium fiuoride (e. g. fluorite). When such a mixture of relatively coarse manganese and com mercial refining fiux is added to the molten magnesium metal, the flux apparently protects the manganese fines, such as pass a 150 mesh sieve, from oxidation or loss, and the presence of certain amounts of such fines does not deleteriously affect the efficiency of the alloying effort and may be tolerated. The mixture of moderately coarse metallic manganese, preferably electrolytic manganese, with commercial magnesium refining flux constitutes a new and useful article of commerce for the direct introduction of manganese into molten magnesium metal in accordance with the principles of the invention.

As a specific example or the practice of the invention in the manufacture of a binary magnesium-manganese alloy containing approximately 1.5% manganese, 150 pounds of electrolytic magnesium metal essentially aluminum-free was melted under a chloride-containing magnesium melting flux, and the resulting melt was heated to a temperature of approximately 760 C. At this temperature, the magnesium melt was refined by stirring in a magnesium refining flux containing magnesium oxide and calcium fluoride along with chloride-containing base salts. To this refined magnesium melt was then added 3 pounds of electrolytic manganese crushed to pass' a 30 mesh sieve and essentially all coarser than mesh. In this example, the metal was immediately stirred by hand plungin for a few minutes and re-stirred at 10 minute intervals for approximatly 30 minutes. At the end of 30 minutes a sample of the metal showed 1.4% manganese, and 20 minutes later, after intermittent stirring, the metal contained 1.68% manganese. The metal was then superheated at a temperature of 900 C., cooled to 740 C., and cast. The cast metal contained 1.68% manganese, the manganese alloying efiiciency being thus about 86%.

As another example, pounds of essentially aluminum-free electrolytic magnesium metal was melted and heated to a temperature of 780 C., using a chloride-containing magnesium melting flux for protection against oxidation. The metal was refined, using a commercial magnesium refining fiux containing magnesium oxide, calcium fluoride in addition to the chloride-containing base salts. To this magnesium melt was added sufiicient electrolytic manganese crushed to pass a 12 mesh sieve to give theoretically 0.3% manganese in the finished alloy. In this example, the melt was immediately stirred by hand plunging, and after intermittent stirring for 15 minutes, pure ingot aluminum and pure ingot zinc were added to give an alloy containing approximately 4% aluminum and 0.5% zinc, After alloying the aluminum and zinc, a sample of the metal showed the alloy to contain 0.25% manganese. The metal was then heated to 815 C., cooled to 720 C., and cast. The resulting product contained 0.25% manganese, the manganese alloying elficiency being thus approximately 83%.

In another example, 150 pounds of essentially aluminum-free electrolytic magnesium metal was melted and heated to 760 C., using a commercial magnesium melting flux for the purpose. The molten metal was refined, using a commercial magnesium refining flux. Sufiicient electrolytic manganese, crushed to pass a 12 mesh sieve, to give theoretically 2.0% manganese in the alloy was then mixed with approximately l pound of the commercial magnesium refining flux and the mixture was stirred into the molten metal. The metal was restirred at 5 minute intervals and. after 25 minutes a sample of the metal showed a manganese content of 1.25%. The metal was restirred again and, after 20 more minutes, a sample of the metal showed 1.6% manganese. The metal was then heated to 900, cooled to 720 C. and cast into ingots. The manganese content of the ingots was 1.6%, the manganese alloying eificiency being approximately 80%.

The invention provides an improved method of .alloying manganese with magnesium in a rapid,

efiective and economical manner. It is particularly characterized by the high and superior manganese alloying efficiency, that is the ratio of the amount of manganese actually present in the finished alloy to the amount of metallic manganese initially added to the molten magnesium. Moreover, the invention enables the production of magnesium-manganese and magnesium base alloys containing definite amounts of manganese with high alloying efliciencies. No dust is raised in the necessary handling of the moderately coarse metallic manganese, and hence other melts in the plant are not contaminated with manganese. The manganese alloys promptly with the magnesium, alloying times of from 15 to 45 minutes being usually adequate, depending to some extent upon the percentage of manganese to be included in the alloy. With manganese contents up to about 1%, it is preferable to place the manganese upon the bare surface of the clean molten magnesium, immediately apply a protective cover, and wait for 5 to minutes before stirring or agitating. Alloying is completed in about minutes. With higher manganese contents, earlier and more frequent stirring and longer alloying times are usually desirable.

We claim:

1. The improvement in permanently alloying manganese with magnesium which comprises introducing crushed metallic manganese into essentially aluminum-free molten magnesium at a temperature of from 750 to 800 C., the particle size of the manganese being in the range minus 4 mesh and plus 150 mesh.

2. The improvement in alloying manganese with magnesium which comprises adding crushed metallic manganese of a particle size which is in the range of minus 4 mesh and plus 150 mesh to molten magnesium and stirring the melt to facilitate alloying.

CHARLES H. MAI-IONEY. GERALD L. LEE.

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

6 UNITED STATES PATENTS Number Name Date 2,029,898 Schmidt et a1. Feb. 4, 1936 2,235,508 Zeppelin et al Mar. 18, 1941 10 2,236,831 Nelson April 1, 1941 2,262,106 Leech Nov. 11, 1941 2,267,862 Hanawalt et a1 Dec. 30, 1941 2,317,980 Dean et al May 4, 1943 2,370,320 Moss Feb. 27, 1945 15 2,373,515 Stroup et a1 Apr. 10, 1945 FOREIGN PATENTS Number Country Date 336,498 Great Britain Oct. 16, 1930 OTHER REFERENCES