US2290026A - Aluminum alloy - Google Patents

Description

Patented July 1 942 ALUMINUM ALLOY Walter Bonsack, South Euclid, Ohio, assignor to The National smelting Company, Ohio, a corporation of Ohio Cleveland, 7

No Drawing. ApplicationFebruary 20,1942,

' Serial No. 431,683

9 Claims (01. 75-146) This application is a continuation-in-part of my copending application Serial No. 389,020, filed April 17, 1941. The invention relates to alloys, and particularly .to aluminum base alloys suitable'for casting and working, and having high strength at ordinary and elevated temperatures. It is an object of this invention to produce alloys having relatively high elongation and relatively high tensile strength.

It is a further object of this invention toprovide a relatively light alloy which may be easily cast and machined, which may be used at elevated temperatures without a rapid deterioration of desirable properties, and which may be readily treated with anodictreatment to give excellent lustre and finish.

It is a still further object of this invention to provide an alloy having a relatively high propor; tional limit and relatively high fatigue strength, and in which these properties may be obtained without heat treatment.

When magnesium and zinc are added to alumiproduces an alloy having high strength combined with high ductility, ood casting, rolling, extruding and forging properties, and good color.

In calculating the amount of magnesium and zinc that should be present in the aluminum alloy to form'the desired percentage of ternary 7 compound, only magnesium which is not combined with silicon is to be calculated, as it is only such magnesium that is available to combine with zinc and aluminum to form the ternary compound.

The ternary compound .is said by some investigators to have a composition having substantially the formula AlaMgvZne, and other investigators have considered the formula for the ternary compound as being AlzMgaZm. seen that the amounts of magnesium and zinc relative to each other are quite similar in both formulae. The magnesium and zinc should be present in about the proportion necessary to form the ternary compound of either formula or, preferably, the ratio ofthe magnesium to zinc in the alloy should be between the ratios in the I formulae.

An excess of zinc, over and above that which cooperates with magnesium and aluminum to It will be form a'ternary compound accordingto the above alloys. I

preference to most elements, each part by weight formula having the greatest proportion of zinc, increases the brittleness and decreases the ductil-. ity of the alloy. For this reason it is undesirable that zinc be present in quantities substantially greater than the amount to ract to form such a ternary'compound with magnesium and aluminum. The most desirable properties are obtained when the magnesium and the zinc are proportioned so that the ratio'of magnesium (uncombined with any silicon) to zinc is about equal ,to

the ratio represented by the iormulaeAlzMgaZm, or somewhat larger as represented by the formula AliMgqZne. A small amount of magnesium may be provided to replenish losses thatmay occur when the alloy metal is remelted.

- Magnesium adds to the hardness and machining qualities of the alloyand, as above stated, should be present in an amount suiiicient to combine with the zinc and aluminum present. In greater quantities, magnesium tends to make the alloy sluggish, decreasing castability.

The improved aluminum alloys may havethe ternary compound of aluminum, zinc and magnesium present in an amount ranging from about 2% to 20%, the preferred range being between about 3% and 15%. At room temperature the ternary compound goes into solid solution' in aluminum alloys in an amount of about 2%. The percentage in solid solution increasesat high temperatures and decreases upon cooling, the excess precipitating out. Aluminum alloys containing the ternary compound may, therefore, be

advantageously heat treated to improve their properties.

A small amount of silicon is usually present in aluminum alloys andup to 1.5% silicon may be present in the alloys-of the present invention. If the alloys are to be rolled or worked the silicon 'should be low, from about the minimum obtainable quantity of .04% or .05% to about 17%. More than 31% is frequently desirable in casting Silicon combines witlt magnesium 'in of silicon combining with about 1.75 parts, by weight, of magnesium to form MgzSi. At least suflicient magnesium is therefore added to the alloy to combine with the silicon uncombined with 'any calcium to form MgzSi, and in addition to combine with all the zinc and form the ternary compound according to the formula AlzMgaZna.

'MgzSi is more stable than the ternary compound above mentioned and may be maintained in solid; solution in aluminum alloys in an amount up to about 1.85%, which is the quantity of Mgz'Si present if the silicon is present in the alloy, and acts as a hardener which is sometimesdesirablein It has now been found that aluminum alloys containing magnesium (over that necessary to combine with silicon) and zinc in the proportions to form a ternary compound are greatly improved by incorporating in the alloy about .05% to 1.5% manganese, about .05% to 1.5% chromium, about .l% to 1.5% nickel and about .1% to 1.5% copper, with one or more of the grain refining elements, such as those selected from the group consisting of titanium, columbium, zirconium, boron, tungsten, molybdenum, tantalum and vanadium. The' grain refiners should be present in a total amount of .005% to .5% 'andthe total of the-copper, nickel, manganese and chromium should preferably be less than of the alloy.

Although the metals manganese, chromium and nickel each increase the hardness of the alloy, a given percentage of each of these elements improves certain of the properties more than it does others. Nickel increasesthe tensile strength, proportional limit and yield strength of the alloy without decreasing its elongation to any appreciable degree. In fact, with certainamounts of. nickel the elongation is increased, so that an alloy having exceedingly desirable and exceptional properties may be obtained.

Alloys containing nickel may be readily heat treated or age hardened to give somewhat superior properties, but very desirable properties which are almost equivalent to the heat treated alloys are also obtained when castingsare simply aged at room temperature, with or without quenching from the mold.

Nickel is quite an effective element in the alloy and appreciable improvements in properties of the alloy are noted when it is present in an amount of about .1%, or more. The preferred properties are obtained with about .3% to about .8% or 1% nickel, and in some cases it is desirable to have the nickel present in amounts as great as 1.5%.

Manganese, although it decreases the tensile strength and elongation to some degree, increases the yield strength, hardness and proportional limit of the alloy. It also makes the alloy more corrosion resistant.

Alloys containing manganese may be readily heat treated or age hardened to give somewhat superior properties, but very desirable properties are obtainable when castings are simply aged at room temperature, or'when quenched from the mold and aged.

Manganese is a very efiective element in the alloy and desirable improvements are noted when about .l% or even a little less, such as .05%, is present in the alloy. The preferred properties are obtained with about .2% to about 5% or .8% manganese, and in some cases it is desirable to have the manganese present in amounts as great as about 1%, or even 1.5%.

Chromium is a particularly effective alloying element in the alloy of the present invention. Although it does not appear to improve the proportional limit and yield strength of the alloy quite as much as does'manganese, it increases the elongation and further increases corrosion resistance. It is, therefore, particularly advantageous that both chromium and manganese be present. As little as .05% or .1% chromium, and particularly with manganese, is eflective in improving the properties of the alloy, but .2% or .3% to about 1%, or even 1.5%, is desirable. When manganese is also present, the total of manganese and chromium should preferably be between about .3% and 2.5% of the alloy.

Copper functions in a somewhat different manner than do manganese and chromium. Due to the fact'that copper is considerably more soluble in aluminum-at high temperatures than at low temperatures, copper acts as a precipitation hardening ingredient, so an alloy containing copper is benefited more by solution heat treatment.

Small proportions of copper even without solution treatment improve the proportional limit and yield strength of the alloy. As little as .1% of copper noticeably improves the alloy, but it is preferable, especially in alloys to be solution heat treated, that about .2% to about 1.5% of copper be present. The presence of from .4% or .5% to 1.5% of copper permits a reduction in the amount of ternary compound so that a desirable alloy is produced with as little as 1% of the ternary compound.

The quantity of each of the hardening metals desired in a given alloy also depends somewhat upon the quantity of'other hardening ingredients present and upon the amount of ternary compound, a given hardness and tensile strength often being obtainable either with a relatively large amount of strength-improving hardening metal and a relatively small amount of .ternary compound, or with a relatively small amount of such metal and a relatively large amount of magnesium and zinc in the propor- I tions of a. ternary compound.

An alloy containing 2%, or even 1%, of the ternary compound may be used for casting purposes. The castability, however, is improved with an increase in the amount of ternary compound and it is, therefore, preferred to have a larger percentage of the ternary compound present, such as 4% to 8% or 9% for casting purposes, 9% ternary compound containing about 5.4% zinc. When the casting is more or less intricately shaped, still greater percentages, such as 10% to 12% or 15%, of the ternary compound may be present. For alloys to be forged or shaped after casting, the ternary compound should be present in the lower ranges, such as 2% to 8% or so, as the metal is less hard with the lower percentages of the ternary compound A larger proportion of the ternary compound may be present in alloys which are to be given a so-called solution treatment" than in alloys to be given only an aging treatment, or those to b quenched from the casting mold and aged at relatively low temperatures. Thus, the desirable properties of the solution heat treated alloys may be obtained when they contain the ternary compound in amounts up to 10% or 12% or so, whereas less of the ternary compound, such as 4% to 6%, is preferred in alloys which are quenched upon removal from the mold and heat treated at a low temperature, or ged at room temperature.

It, has generally been considered that aluminum alloys of magnesium containing iron much above the impurity value in commercial aluminum are of little commercial value; but it has also now been found that an alloy containing the magnesium, zinc and silicon proportioned as herein described, and also containing manganese,

chromium, nickel, copper and a grain refining metal such as is set forth'in the above group, is improved by the presence of iron in suitable proportion. a

Iron in suitable amounts furtherincrea'ses the hardness and tensile strength of the alloy without decreasing its ductility a substantial amount. A small amount of iron thus permits one to obtain th properties desired with a smaller amount of. magnesium and zinc.- Iron also improves castability. These alloys containing iron may be readily heat treated or ag hardened. to give somewhat superior properties, but theiron in combination with manganese, chromium and the ternary elements in the above proportion is pends upon the quantity of other hardening .in-

gredients present, upon the amount of ternary I present, and upon what properties are most important. A given hardness and tensile strength is often obtainable with a relatively larger amount of iron and a relatively smaller amount 1 of ternary compound, 'or a relatively smaller amount of iron and a relatively larger amount of ternary. Iron may be present :in the alloy of the present invention in amounts between about 0.1% and about 1.5%. centage of iron in the alloys, th percentages of manganese and chromium may be reduced considerably. If both manganese and chromium are present in substantial amounts and if workability, ductility and corrosion resistance are not to be impaired, the iron shouldbe low, i. e., about 0.1% or less to about .6% or .7% of the alloy. If yield strength and high tensile strength are most important and ductility less important, the

amount of iron may be greater.

The grain refining elements are particularly desirable inan aluminum alloy containing iron, manganese, chromium and the ternary com pound. Although the iron itself improves the properties of the alloy, the manganese, chromium, copper and nickel, and grain refining elements exert a still further improvement independently of iron.

The aluminum alloys of the present invention containing magnesium, uncombined with silicon, and zinc in th proportion of a ternary compound, when cast in molds of a design such that,

chilling takes place substantially simultaneously in th various portions of the casting, solidify without the use of grain refining agents to form 'good castings.

certain grain refining elements substantially im- However, it has been found that prove the properties of th aluminum alloy containing the ternary compound, whether or not it contains one or more of the above hardening metals, with or without iron, This 'is especially true when-the metalis cast in molds of more or less intricate shape where the chilling may not be so uniformthroughout the casting.

The grain refiners which I have found exert greatest improvement in the properties of the alloy are members of ,the group consisting of With the larger perin the amount of .01% to .5%, tungsten in the amount of .01% to .5%, molybdenum in the boron in the amount or new to 1 zirconium.

amount of .01% to .5%, vanadium'in the amount of- .01% to .5%, titanium in'the amountof 05%.

to .5%, columbium in the amount of .01% to .5% and tantalum in th amount of .05% to .5%.

These grainrefining elements shouldpreferably be present, in a total amount of from 005% to .5% and it is frequently desirable to have more than one of these elements present-in a given alloy. v

Whilethe grain refiners in the above group are desirable in the alloys of. the present invention,

not all of the grain refiners affect the properties in the same way. The particular refiner or group of refiners selectedin any given instance depends .upon th particular condition which must be satisfied. The grain refiners selected from the group consisting of titanium, tungsten, molybdenum, zirconium and van-adiur'n, and especially tungsten and molybdenum, improve both the strength and th elongation Of the castings.

Titanium being readily available is frequently used, but when special properties of the fabricated article are important it is desirable to select the grain refiner that is most suitable for such properties. The grain. refiners boron,

' columbium and tantalum may advantageously be used where appearance, finish and corrosion resistance are important.

The above described hardening elements, manganese and chromium, substantially decrease the hot shortness, improve the properties of the al- 10y, and assist in maintaining the improved prop-' erties at high temperatures such as are encountered in internal combustion engines. The above grain refining elements, particularly members of the group consisting of zirconium, tungsten, mo lybdenum, vanadium and titanium, also have this property particularly when present in larger amounts, such as .2% or .3% or so. It may, therefore, be desirable to have up to .5% or so of these latter elements present.

The following example illustrates the alloys of the present invention: I

An aluminum base alloy containing magnesium, zinc and. silicon in proportion to form 6% of a ternary compound based on the formula AlaMgwZm, about .3% manganese, about .25%

chromium, about .6% iron, about .2% titanium,

about .2% nickel, and about .2% copper, with the balance substantially all aluminum and minor impurities, was prepared and chill cast into tive properties of those air cooled from the mold and those quenched from the mold were: tensile strengthsdOAOO lbs/sq. in. and 41,900 lbs. /sq. in.; proportional limits 18,800 1bs./sq. in. and 17,700

lbs/sq. in.; yield strengths 26,600 lbs/sq. in. and

25,400 lbs/sq. in.; Rockwell E hardness 84.2 and 80.7; and elongation 5.9% and 7.7%.

Since the molecular proportion of zinc is never more than the molecular proportion of the relatively light magnesium in the ternary compound,

-it is seen that in addition to high strength the alloys are light in weight and 'are, therefore, especially adapted 'to aircraft construction and the like. This is particularly true when the quantity of ternary compound is sufficiently low so grain refiners.

that'the alloy may be drawn or rolled into structural members.

If the alloy contains uncombined silicon, about 1.75% magnesium is required to combine with each percent of uncombined silicon to form magnesium'silicide (MgzSi) before any ternary compound will be formed. For example, if 2% of the ternary compound on the basis of AlzMgaZna be desired in an alloy having .3 silicon, the amount of magnesium to be added to form the ternary compound will be .45%, or about .5%, and the magnesium to combine with .3% silicon will be about .5%, making a total of about 1%.

The magnesium andzinc in an alloy containing .7% free silicon and 20% AlaMEvZne would be about 7% and 12%, respectively. The alloys described herein include aluminum, magnesium and zinc, the magnesium, uncombined with silicon, being proportioned to the zinc in the ranges of the formulae given for the ternary compound. The proportions for the formation of the ternary compound in the alloy exist when the magnesium is about 35% to 45% of the zinc content plus 175% of the silicon content. Most desirable properties may be obtained when the magnesium (uncombined with silicon) is in the lower portion of this range, or about 35% to 40% of the zinc.

In the above example of alloys of the present invention, it is to be noted that excellent tensile strength and hardness are obtainable in a relatively short time by aging at room temperature. A very astounding fact has been discovered, however, in connection with these alloys, namely, that the tensile strength may increase up to approximately 50% of its initial value by aging at room temperature for relatively long periods of time, such as a few months. The same improvement in tensile strength can, of course, be obtained relatively quickly by aging at temperatures above room temperature.

To obtain properties even of the same order of magnitude in aluminum base alloys commonly in use, one has to resort to a solution and aging heat treatment, whereas in alloys of the present invention it is not necessary to solution heat treat desired to improve and modify their properties,

although such heat treatment is not required;

and they have suflicient ductility. and hardness so that they can be rolled or formed into sheets, rods, wire, structural shapes, castings, machine parts, etc. These alloys have a desirable color and are suitable for many uses, among them being the production of castings which are shaped or formed to some extent after casting. The alloys having the lower percentages of ternary compound may even be forged at room temperature and are thus useful for many special purposes.

As pointed out above, grain refiners are usually desirable inalloys of the present invention. However, it has been found that the alloys of 'the present invention have relatively high strength, high proportional limit and ductility without solution heat treatment, even in the absence of the The alloys may be cast, rolled, forged or otherwise shaped with or without grain refiners.

It is to be understood that, in considering the about .4% to 7%.

uncombined silicon is not to be considered part of the magnesium necessary to form the specified amount of ternary compound.

It is to be understood that the particular compounds disclosed and the procedure set forth are presented for purposes of explanation and illustration, and that various equivalents can be used, and modifications of said procedure can be made, without departing from my invention as V defined in the appended claims.

What I claim is:

1. An aluminum alloy containing magnesium, zinc, about, .1% to 1.5% iron, about .05% to 1.5% manganese, about .1% to 1.5% nickel, about .05% to 1.5% chromium, about .1% to 1.5% copper, silicon in an amount up to 1.5%, and one or more grain refining metals, with the balance substantially all aluminum and minor impurities, the amount of zinc in the alloy being about .6% to 7.2%, and the amount of magnesium in the alloy uncombined with silicon being about 35% to 45% of the zinc content, the total magnesium being within the range of about .4%

.tially all aluminum and minor impurities, the

amount of zinc in the alloy being about .6% to 7.2%, and the amount of magnesium in the alloy uncombined with silicon being about 35% to 45% of the zinc content, the total magnesium being within the range of about .4% to 7%.

3. The alloy of claim 1 in which the zinc content is about 1.2% to 6% and the magnesium content is within the range of about .5% to 6%.

4. The alloy of claim 1 in which the zinc content is about 1.2% to 4.8%, the magnesium content is within the range of about .5% to 5%, and the copper content is within the range of .2% to 1.5%.

5. The alloy set forth in claim 2 in which the copper is present in the amount of .l% to .5%.

6. The alloy set forth in claim 2 in which titanium is present in the amount of .05% to .5%.

7. The alloy set forth in claim 2 in which zirconium is present in the amount of .01% to .5%.

8. The alloy set forth in claim 2 in which molybdenum is present in the amount of .01% to .5%.

9. An aluminum alloy containing magnesium, zinc, about .1% to 1.5% iron, about 05% to 1.5% manganese, about .1% to 1.5% nickel, about .05% to 1.5% chromium, about .1% to 1.5% copper, and silicon in an amount up to 1.5%, with the balance substantially all aluminum and minor impurities, the amount of zinc in the alloy being about .6% to 7.2%, and the amount ofv magnesium in the alloy uncombined with silicon being about 35% to 45% of the zinc content, the total magnesium being within the range of WALTER BONSACK.