US2823996A - Magnesium alloy - Google Patents

Description

MAGNESIUM ALLOY DanielGardner, NewYork,-N. Y.

N Drawing. Application August 3, 1953 Serial No. 372,170

1 Claim. (Cl. 75-168) keep the alloy as light as possible and at the same time achieve satisfactory physical properties without upsetting the equilibrium between the ingredients which enter into a finally acceptable formula.

Magnesium is abundant in nature and belongs to the group of raw'rnaterials which are plentiful in theouter shells of the earth. With its low density of 1.74 itis available for many purposes where such a light metal'is desirable. In accordance with my invention I am able to utilize the lightness of magnesium by achieving chemical and physical properties in a magnesium alloy without materially departing from the low density of magnesium. In doing this, I am able to bestow upon the magnesium alloy the physical, chemical and physico-chemical properties which magnesium itself does not possess. I am able to accomplish this, as mentioned above, without departing substantially from the density of the prevailing ele ment in the alloy, i. e., magnesium.

Before proceeding with the description of the present invention the following table of some of the pertinent elea't Patent 2,823,996 Patented Feb. 1 8, 1 1958 Aluminum is desirable for many purposes, particularly aircraft needs and can be alloyed in desirable ways. However, notwithstanding the properties that can be achieved by alloying, it is not possible to go very much below its density of 2.7. In instances where a lighter alloy is' desirable aluminum cannot be used as the entire base.

In accordance with my invention, I obtain an alloy having a density not appreciably different from the density of magnesium, but having marked improvements over magnesium in terms of physical and chemical properties, whichovercome the inherent weaknesses of magnesium as indicated in the above table.

The magnesium alloy of my invention comprises four essential'components: (1) pure magnesium as the primary component, a minor part of which may be replaced by aluminum insome insta'nees if the increase density of the alloyfor the wantedpurpose is not objectionable; (2) asmall amount of an interstitial metal; (3) a small but requisite amount of a filler for the interstices of the interstitial metal selected from the group consisting of silicon or boron or both, preferably silicon in most instances; and in some instances antimony alone or in admixture with silicon and/or boron; and (4) a small but requisite amount of an auxiliary metal selected from the group consisting of calcium, beryllium, chromium, cobalt, nickel, manganese and yttrium, which facilitates the incorporation of the silicon or other third component.

The term interstitial is used to refer to an element capableof forming a compound with metalloid elements in which the metalloid atoms occupy the interstices between'the at'omsof the metal lattice.

Thefollowing is a brief discussion of each of the four components (1) The properties of the pure magnesium, or magnesium a minor portion of which has been replaced by aluminum, are we'll'known together with the manner in which they'aremade and can be utilized as the primary component of my alloy. These need not be furments and some of their properties may be noted: 40 ther explained. The magnesium, and aluminum if it is TABLE I E1 e t Densit; Hardness oin oin a lo 0 asm n y (MP), (BP), BP/Ml ticity B 111 1.85 6.9 .27 1 350 1, 550 1.13 B35111??? 2. a 9. 5 .24 2: 300 2, 500 1.1 Magnesium 1. 74 2 87 651 1, 110 1. 7 Aluminum 2. 7 2. 9 659 2, 450 a. 7 Silicon 2. 4 7. 0 .34 1, 420 2, 600 1.8 Calcium 1. 55 1. s 1. 03 845 1, 240 1. 47 Antimony s. 68 3. o 2. 2 650 1, 380 2. 2

From this table it will be seen that magnesium has-a desirably low density. However, it has an undesirably low melting point and low boiling points, as well as a low ratin of boiling point to melting point. In addition, it has a relatively low modulus of elasticity.

used, must be pure and have boiling points of 1110 C. and 2450 C., respectively.

(2) The interstitial metals which are listed as the second component of my alloy, and their properties are as follows:

TABLE II Hard- Melting Boiling Modulus of De1]1)s)lty 1213s; D/H (ED211 31: a??? BP/MP Elasticity p. s. C. O.

All of the elements above listed belong to the so-called transition metals of the periodic table, and are shown in the above listing as they stand in the vertical columns of the fourth, fifth, and sixth groups of the periodic table. Of the interstitial metals I prefer for the purpose of my invention titanium, columbium and tantalum, but

4 first two mentioned as the fourth component of my alloy, and the properties of which are listed in Table I, I may include as the metals functioning as the fourth component, as mentioned heretofore, chromium, cobalt, nickel, manganese and yttrium. Their properties are shown in the following table:

any can be used alone or in admixture with each other.

The interstitial metals according to my experience, can all be obtained by reducing their oxides by pure magnesium, with the exception of thoria. Also, their halides are reduced by magnesium and a pure interstitial metal is obtained.

.t has long been known that the interstices of the interstitial metals are filled with metalloids and other elements such as hydrogen, oxygen and nitrogen. Halogens may also fill the interstices as well as carbon, sulfur, selenium and tellurium.

(3) In the magnesium alloy of my invention, containing an interstitial metal, I have made the important observation that silicon and/ or boron and/ or antimony can fill up the interstices of these interstitial metals, thus preventing the air, gases and other elements mentioned above from occupying the instertices. Silicon is generally preferred as the third component of my alloy, although any of the three may be used or mixtures of two or three. Hereinafter I will refer to silicon as representing the best embodiment but it is to be understood that in all references to silicon hereinafter, prior to the illustrative example, boron and antimony or mixtures thereof may be substituted for a part or all of the silicon.

Silicon is of interest in this connection because the interstitial metals can readily be converted to their respective silicides whereby the interstices of the metals are filled with silicon or boron or antimony if these are employed in their purification. it is important during all of such operations to avoid working with products containing moisture, and it should be removed entirely by calcining. and their compounds and salts is essential.

Silicon is not directly soluble in magnesium, only about 0.003% being soluble at 600 C. While the presence of the silicon increases the hardness of the magnesium alloy up to about 5 for the magnesium silicide, the problem is presented as to the easy incorporation of silicon in magnesium.

(4) it is because of this problem that I introduce the fourth component in my alloy, which plays the important function of facilitating the introduction of silicon into the magnesium alloy. Thus, for instance, calcium is included as a metal representative of the fourth component of the alloy, because it not only lowers the density of the magnesium alloy containing it, but because silicon is easily introduced in calcium with the formation of CaSi which has a density of 2.46, a hardness of 3.5 and a melting point of 1020". This formation is easy and goes according to the following equation:

2Si+Ca CaSi +224.6 calories Also complete absence of alkaline metals Chromium, magnesium, cobalt and nickel, in addition to being utilized as their silicides similar to that of the calcium and beryllium, may also be used to increase the modulus of elasticity and the general workability of the alloy. While their density is far greater than that of magnesium or of calcium or beryllium, their introduction so much improves the metal that it can be used for other purposes and the increase in the density is not so great as to make this undesirable for such purposes. In addition only small amounts are used so the increase in density is negligible.

Amongst these metals I should like to mention particularly yttrium, which has the properties of the metals mentioned in the previous paragraph, and is of special interest because it crystallizes in a hexagonal-system like magnesium. This element is often found in the interstitial metals and such minerals as those containing titanium and tantalum, colnmbium and uranium. Yttria is reduced by magnesium to metal according to the following equation:

2 2+ g- 2Y+3MgO+77.4 calories The silicon plays a number of roles in the alloy which can be summarized as follows: (1) It forms silicides with magnesium, the interstitial metals and the additional metals, in which the ratio of the silicon to the metal is 2:1; (2) silicon fills the interstices of the interstitial metals, such as titanium, zirconium, tantalum, molybdenum, etc, which renders the use of the interstitial metals suitable for the purpose of obtaining the high grade magnesium alloys and solid solutions; (3) the silicon forms a silicide with calcium which facilitates the obtention of the molten alloy providing an even distribution of the individual ingredients whereby the mechanical properties of the alloy are improved; (4) the structure of the silicides are exactly similar to that of the alloy, the bonds of the silicon atoms remaining unaltered and appearing exactly as in the case i of silicon; (5) not only does the silicon form silicides with the magnesium and calcium, but also with any other metals that may be included, such as aluminum, chromium, manganese, nickel, cobalt, yttrium, and these may be prepared in the silicide form; (6) the silicon acts as a scavenger in the initial stages of preparing the silicides so that allowance should always be made for a certain percent loss during the process in which silicon is in- :cluded.

The relative amounts of the ingredients comprising the alloy are generally as follows:

(1) At least of the alloy is magnesium which forms the alloy base, or if a portion of this is substituted by aluminum the magnesium-aluminum mixture comprises at least 90% of which the magnesium in the alloy which, as will be seen further, is desirable, Magnesium silicide is soluble in the presence of calcium silicide.

In addition to calcium and beryllium, which are the base is the primary component.

(2) The interstitial metal which comprises the second component of my alloy should be present in an amount of 0.01 to 2.0% preferably 0.01 to 1.0%.

L relation to preferable ratio is 0.01% beryllium'to 3% silicon. When chromium is introduced into any specific alloy it pref- (3) The silicon (or boron orantimony aonmiXture thereof) may be present in an amount of 1.0 to 5%.

(4) The elements comprising-the fourth group vary in amounts depending somewhat upon the metal selected from this group. ln-the'case of calciumlarger amounts can be -employed, i. --e., -amounts up to 7.99% When beryllium is included 'it may bepresent in :amounts 1 of 0.001% to 0.005 --When-the other-metalsof the fourth component-are includedthey maybe-present in an amount it of 0.01%-to Z-%,-preferably 0.01-%-to 1.0%.

-It is preferred that whenber-yllium is employed as a component its amount should be kept relatively low in the amount, of silicon so that-the maximum erably should be not more than-1 mol of chromium for 2 mols of silicon. If yttrium is. included in the formula its relation to the amount of silicon preferably should be chosen so that not more than one part yttrium is present to .20 .parts. .ofsilicon.

The method of making thealloy. does not involveany particular complications. Theingredients .forming .the alloy .arebrought togetherinafluid.phase,..either liquid or-gaseous. .In..view. of the natureofmagnesitu'n, some of thewwork must becarried outinan atmosphere of an inert gas such as helium, argon, neon or the like. Work- 1ng"invacuo,because it is rather expensive,-sl1ou1d be avoided if possible, but can be employed if this is-feasib'le mechanically and economically.

"In perfecting the alloy, at least a part of the silicon (or boron or antimony) should be addedto the bulk of the magnesium in the form of a ternary alloy such as, for instance, a silicon-calcium-magnesium alloy. The interstitial metal or metals can be added in combination with silicon asha .silicide. .A ,magnesium;siliconetitanium alloy represents one of thepreferred.fotmsm a g t .first threetcomponents of the alloy ofmyinvention. A aquaternary alloy can also be producedby introducing calciumsilicideor titaniumsilicide and then introducing the latter into a molten bath containing pure magnesium in addition to which is. added a solid. solution of the calcium-magnesium alloy.

-Iintentionally avoid copper as an element in my alloy because copper weakens the resistance of magnesium to corrosion. The following examples areillustrative of the invention:

Example 1 Percent Magnesium 95.00 Titanium .10 Silicon 4.60 Nickel .15 Chromium .15

This alloy can be made by first preparing the silicides of nickel, chromium and titanium and adding these to the, remaining silicon whereupon this mixture may be. in-

troduced into the molten magnesium with the adequate precautionary measures mentioned heretofore. The alloy has a melting point far higher than themelting point of magnesium and has good resistance to corrosion and asubstantial increase in modulus of elasticity as compared With magnesium. All of thespeciiic examples hereinafter share. in these properties.

Example 2 Percent Magnesium 90.00 Tantalum .01 Silicon 2.35 Calcium 7.50 Manganese .10 Chromium .02 Nickel .02

In this example the introduction of calcium into the alloy 1g re atly-.simpli fies the introduction of silicon. The other ,metals. are prepared as ,silicides ,and introduced. ,into the final charge working in an atmosphere of an inert gas. The manganese in this 6X8Illli2zlfifil1d in other examples containing it increases the resistance of magnesium to corrosion and facilitates its weldability.

Example 3 .Percent Magnesium 90.00 Columhiu m .02 :Sili on V 72.3.5 Calcium 7.50 'Yttrium .23

This example is interesting and important: because it introduces the element yttrium, an element as plentiful as vanadium, nickel, and zinc in the outer shell of the earth. In addition, this element often occurs with columbium,

tantalum and titanium and can be introduced into the alloy Without separation. The low melting magnesium 651 C.) is greatly fortified by the higher melting yttrium (1490 C.). Yttrium, in addition, has the same crystal- ;line structure as magnesium and beryllium, and since it :follows the other two metals in the table of electromotive arrangement, it provides a strongly positive alloy.

Example'4 Percent Magnesium 90.00 Titanium .02 Silicon 2.35 Calcium 7 .50 Yttrium .23

This example is similar to Example 1 except for the inclusion of calcium and yttrium and differs from Example 3 by substituting..titanium fol-columbium. The alloy. has the advantagesimparted by titanium and yttrium and the alciumiacilitatfis the introduction and interaction of thesehelementsinto,the alloy along with the silicon. v1t also has .a higher melting point and better" resistance to wear .and tear.

Example 5 Percent Magnesium 97.05 Zirconium .02 Silicon 2.78 Manganese .10 Chromium .05

In thisexample zirconium replaces titaniumand all of the metals, .zirconium, manganese and chromium are present .as slicides.

The introduction ofmanganese, which together with vanadium is first converted into a silicide, greatly facilitates the formation of a stable alloy. The melting point of vanadium silicide is quite high, namely, 1654 C. and this property is imparted to the alloy. In addition, the alloy has marked hardness as compared with magnesium.

This example is similar to Example 6 except that a part of the molybdenum is replaced by tungsten, and manganese replaces nickel.

Example 9 Percent Magnesium 98.20 Titanium .01 Columbium .01 Silicon 1.73 Manganese .05

This example is somewhat similar to Example 3 except that calcium and yttrium are replaced by manganese and titanium. The alloy is resistant to wear and tear, resist corrosion admirably and. has improved mechanical properties. If desired the columbium can be replaced by tantalum.

Example 10 Percent Magnesium 98.20 Titanium .02 Tantalum .01 Silicon 1.70 Beryllium .01 Manganese .06

All of the metals, including beryllium, are present in the form of silicides. The alloy is stable, has a high melting point and resists corrosion. It also has a high and stable modulus of elasticity.

This alloy is unique because calcium and cobalt both have the same crystalline structures. Boron also forms the compound Mg B whereby the boron and magnesium unite readily and directly.

Example 12 Percent Magnesium 98.00 Titanium .01 Tantalum .01 Silicon 1.74 Nickel j .02 Chromium i l Q .02

Thisalloy is similar to Example 10 except that the beryllium and manganeseare replaced by chromium and O (:1 nickel. All of the metals are present in the form of silicides and give a very efiicient alloy.

Example 13 Percent Magnesium 65.50 Aluminum 32.50 Tantalum .01 Silicon 1.70 Manganese .25 Chromium .02 Nickel .02

This alloy is of particular interest since it shows the possibility of incorporating magnesium into aluminum and vice versa, without introducing transition metals other than the interstitial ones.

Example 14 Percent Magnesium 60.00 Aluminum 30.00 Titanium 0.20 Silicon 1.75 Calcium 7.40 Manganese 0.25

This example is similar to the previous example except that calcium is introduced into the alloy. Calcium is a splendid diluent and is especially useful in this alloy because it possesses two structures, i. e., that of both magnesium and aluminum.

Example 15 Percent Magnesium 96.00 Titanium .01 Antimony .25 Silicon 3.49 Titanium .01

Inasmuch as antimony dissolves in molten silicon it is best prepared the silicide SbSi This is then introduced into the molten titanium (which can be replaced by tantalum, columbium, zirconium, or vanadium, separately or in admixtures) followed by introducing the ternary alloy into the molten magnesium adding it in small portions with the stirring after each addition. These alloys show a marked increase in modulus of elasticity, general improvement in mechanical properties, and also greater resistivity to corrosion.

The above light alloys, based on magnesium of high purity, into which small amounts of the specified elements have been introduced, play an important role in light weight metal construction, where resistance to wear and tear and other chemical and physical properties are demanded. These alloys may be processed by recognized techniques such as quenching, annealing, aging, etc., as will be obvious to one skilled in the art.

I claim:

An alloy having the following composition:

(Other references on following page) ear-3399s 1 Chambers Technical Dictionary, pub- Sauerwald et a1. Oct. 22, 1940 Tweney et a1; Canac et al June 30, 1942 lished by the Macmillan C0., New York, N. Y. (1944), page 456. FOREPGITI PATENTS Merlub et al.: Metals and Alloys Dictionary, pub- Great Brltagn Oct 16, 1930 5 lished by Chemical Publishing 00., Brooklyn, N. Y. Great Britain Apr. 12, 1939 (1344), page 116. OTHER REFERENCES Serial No. 420,578, Canac et al. (A. P. C.), published July 13, 1943.