US2290016A - Aluminum alloy - Google Patents

Description

Patented July 14 1942 NITED-"STAT S PATENT OFFICE ALUMINUM my Walter Bonsack, South Euclid, Ohio, assignor to The National smelting Company, Cleveland, Ohio, a corporation of Ohio 1 No Drawing. Application April 17, 1941,

Serial No; 389,020

7 Claims. ((21. 75-142) This application is a continuation-in-part of my co-pending application Serial No. 284,527, filed July 14, 1939. 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 alloy, the magnesium and zinc should be present in about the proportion necessary to form the ternary compound of either formula.

alloys having relatively high elongation and relatively high tensile strength.

It is a further object of this invention to provide a relatively light alloy whichmay be easily cast and, machined, which may be used at elevated temperatures without a rapid deterioration of desirable properties, and which may be readily have these properties improved by heat treatment. l a

When magnesium and zinc are added to aluminum in the proper proportions, a ternary com-,

pound of aluminum, magnesium and zinc is formed, which compound is soluble in solid solution in th aluminum. The presence of this compound in relatively small amounts greatly improves the characteristics of aluminum and produces an alloy having high strength com-' bined with high ductility, good casting "and forging properties, good color and excellent corrosion resistance. In calculating the amount of magnesium and 'zinc that should'be present in the An excess of zinc, over and above that which cooperates with magnesium and aluminum to form a ternary compound according to the above formula having the greatest proportion of zinc, increases the brittleness and decreases the ductility of the alloy. For this reason it is undesirable that zinc be present in quantities substantially greater than the amount to react 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 theratio of magnesium (uncombined with any silicon) to zinc is about equal to the ratio represented by the formula V AlzMgaZna, or somewhat larger as represented desirable properties, and because the zinc con-- aluminum alloy to-form'the desired percentage of ternary compound, only magnesium which is not combined with silicon is to becalculated, 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 AhMg- Zm, and other investigators have consldered the formula for the ternary compound as. being AlzMgaZm. It will be seen that theamounts of ma'gnesiumand zinc relative to each other are 'quite similar in both formulas and, for the purposes of-the improved 11% is frequently desirable in casting alloys.

by the formula AlaMg-z Znu. A small amount of magnesium may be'provided to replenish losses that may occur when the alloy metal is remelted.

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

Magnesium and zinc have heretofore been added to aluminum in the proportion represented by the formula MgZnz. It has been found, however, that a given percentage of ternary compound is more effective in producing tent of the temary' alloys is less they have a lower density.

The improved aluminum'alloys may have the ternary compound of aluminum, zinc and magnesium resent 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 3 aluminum alloys in an amount of about 2%.

The percentage in solid solution increases at high temperatures and decreases upon cooling; the excess precipitating out. Aluminum alloys containing the ternary compound may, therefore, be'advantageously properties. p a

A small amount of silicon is usually present in aluminumalloys and from to about-3% is desirable in alloys of the present invention which are to be forged or drawn; more than Silicon combines with magnesium in preference to'most elements, each part by weight of silicon heat treated to improve their 1 vpound 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 MgzSi present if the silicon is present in the Alloys containing nickel may be readily heat treated or age hardened to give somewhat superior properties, but very desirable properties alloy, and acts as a hardener which is sometimes desirable in conjunction with the ternary compound. MgzSi does not, however, make as efiicient use of the magnesium as does the above mentioned ternary compound. Therefore, it is desirable to have the magnesium present on the rich side to prevent the silicon from being present in excess and taking magnesium away from the ternary compound.

If the alloy is desired particularly for casting purposes, more silicon, such as up to about 1.5%, may be present. If however a somewhat larger amount of silicon is present in the alloy than is desirable for the purpose for which the alloy is intended, and such amount of silicon is not too excessive, then a small amount of calciuinmay be added. Calcium has an even stronger afinity for silicon than has magnesium and, therefore, it can be used to reduce the-amount of silicon available for combination with magnesium. The amount of the relatively expensive magnesium available for the formation of the ternary compound may thus be increased. Although much more than 1.85% silicide acts as a supplemental hardener and more than about 3% or so makes the alloy more sluggish and adversely affects the castability of the alloy, up to 3% is desirable and more than 3% may in some cases be desirable in the production of hard castings having less intricate shapes, particularly when a large amount of the ternary compound is present in the alloy.

Usually, however, the amount of silicon should be between .5% and 1.5%, especially in castings not heat treated. This is true even when calcium is present, although with the latter element more magnesium is available for formation of the ternary compound.

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 im- P oved by the addition of one or more members of the group of hardening elements, consisting of .1% to 1.5% nickel, .1% to 1.5% manganese and .05% to 1% chromium in a total amount of about .2% or .3% to 5%, with or without one or more of the grain refining elements selected from the group consisting of titanium, columbium, zirconium, boron, tungsten, molybdenum, tantalum and vanadium in a total amount of .005% to .5%.

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. It is therefore preferred that more than one of these elements be present in the alloy. Nickel increases the tensile strength, proportional limit and yield strength of the alloy without decreasing its elongation to any appreciable degree. In fact, with certain amounts of nickelthe'elongation is increased, so that an alloy having exceedingly desirable and excep- K tional properties may be obtained.

which are almost equivalent to the heat treated alloys are also obtained when castings are 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 effective element in the alby and desirable improvements are noted when about .l%, or even a little less, 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, although it does not appear to improve the proportional limit and yield strength of the alloy, increases its elongation. It is, therefore, particularly advantageous that both chromium and manganese be present. As little as .05% or .1% chromium, particularly with manganese, is effective in improving properties of the alloy, but .2% or .3% to about .8% or even 1% is desirable. When manganese is also present, the total of manganese and chromium should preferably be between about .3% and 1.5% of the alloy. When both manganese and chromium are present, they may be in about equal proportions, or preferably with a slightly greater amount of manganese than chromium.

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 a such metal and a relatively large amount of magnesium and zinc in the proportions of a ternary ccmpound.

As silicon decreases the ductility of the alloy to a substantial degree, it is best that when the alloy contains nickel present in the upper portion of the above mentioned range that the silicon does not exceed .7% or .8%, as the presence of too much of the hardener MgzSi may decrease the ductility to such an extent that the alloy is undesirable for many purposes. Alloys containing nickel. and free magnesium and zinc in the ratio of a ternary compound may contain as much as 1% or 1.5% silicon. While 2% or 3% of the ternary compound of aluminum, magnesium and zinc improves the properties of aluminum or aluminum alloys having low silicon content, alloys containing such low percentages of a ternary compound are relatively diflicult to cast.. a

An alloy containing 2% of the ternary compound may be used for casting purposes.

The castabiiity, however, is improved with an increase in the amount of ternary compound and it is,

being obtainable with a relatively larger amount of iron and a relatively smaller amount of ternary compound, or a relatively smaller amount of iron and a relatively larger amount of ternary.

The hardening elements and the grainrefining elements are particularly desirable in an-alumitherefore, preferred to have a larger percentage of the ternary compound present, such as 4% to 8% for casting purposes. -When the casting is more or less intricately shaped, still greater percentages, such as 10% to or 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 and metals of the above hardening'g-roup may be present in alloys which are to be given a socalled "solution treatment than in alloys to be given only an aging-treatment, or those to be num alloy containing both iron and the ternary compound. Although the iron itself improves the properties of the alloy, the hardening elequenched from the casting 'rnold 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 20% or so, whereas less ,of the ternary compound, such as 4% to15%,

is preferred in alloys which are quenched upon removal from the mold and heat treated atalow temperature, or aged at roomtemperature.

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 above described ternary compound, with or without one or more of the above mentioned groupof hardening elements, and with or without one or more of the above group of grain refiners, is

ments and the 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 the proportion of a ternary compound, when cast in molds of a design such that chilling takes place substantially simultaneously in the various portions of the casting, solidify without the use of grain refining agents toform good castings. However, ithas been found that certain grain refining elements substantially improve the properties of the 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 I true when the metal is cast in molds of more or less intricate shape where the chilling may not be so uniform throughout the casting.

The grain refiners which I have found improve .the properties of the'alloy are members of the group consisting of boron in theamount of .0051% to .l%, zirconium in the amount of .01% to .5%, tungsten in the amount of .01% to .5%, molybdenuin in the amount of .01% to 5%, vanadium in the amount of .01% to .5i%. t an um in the amount of .05% to .5%, columbium in the amount of .01,% to .5%and tantalum in the amount of .05% to .5%. These grain refining elements should preferably be present in a total amount of from .005% to 5% and it is frequently-deimproved by the presence of iron in suitable proportion.

Iron in suitable amounts further increases 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 the properties desired with a smaller amount of magnesium and zinc. These alloys containing iron may be readily heattreated or age hardened to give somewhat superior properties, but theiron in combination with the ternary elements in the above proportion is also outstanding in that almost as desirable properties are obtained when castings are aged at room ing.

Iron has generally been considered to crystal-. lize in large platelike crystals-which weaken the alloy. Iron in the presence of the ternary com pound appears to crystallize in finely dispersed form and the ternary compound also seems to be dispersed, thus producing a highly desirable alloy.

, Iron in the amount of 3% or more in the alloys of the present invention gives noticeable effects in improving the properties of the alloy,

and as much as 2% has been found to be desirable for some purposes. For most castings it is desirable that the alloy have .6% or 11% to 1.5%

temperature without a heat treatment or quenchsirable to, have more t an one of these elements. present in a given allo 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 selected in any'given instance depends upon the particular condition which must be satisfied. The grain refiners selected from the I group consisting oftitanium, tungsten, molybtantalum do not appear to appreciably. increase the strength or elongation of the alloy and are usually used where appearance, finish and corrosion resistance are most important and where strength is of lessconsequence. Certain grain of iron, although about 1% is' usually "preferred.

The quantity of iron desired in the alloy depends also upon the quantity of other hardening ingredients and upon the amount of ternary prescut, a given hardness and tensile strength often refiners, such as cerium, were found to be rela- 'tively undesirable in the alloy.

The above described hardening elements, manganese, chromium and nickel, substantialy decrease the hot shortness, improve the properties of the'alloy and assist in maintaining the improved properties at high temperatures such as are encountered in internal combustion engines. The above grain refining elements, particularly members of the group consisting of tungsten,

molybdenum, vanadium and'titanium, also have. this property when present in substantial amounts, such as .2% or .3% or so. It is therefore,.especially desirable to have up to 5% or so of these latter elements present when other hardening ingredients are absent.

If it is desirable to make the alloy more responsive to heat treatment, as is sometimes the case, it is preferable that from .2% to about 1%, or even up to about 1.5%, copper be present in the alloy. Copper is a precipitation hardening ingredient, and the benefits of this element are obtainable when the alloy is subjected to conditions of heat treatment which precipitate the element from the solid solution. The presence of from .5% to 1.5% copper permits a reduction in the amount of the ternary compound, which may be as low as 1%, and preferably should not exceed about or 12%.

When copper is present in the above alloy containing magnesium in the proportion to combine with the silicon to form MgzSi, and with the zinc and aluminum to form a ternary compound as above described, iron as above set forth may or may not be present, although superior properties are obtained with .4% to 1.5% or 2% iron.

The alloys containing copper, with or without iron as an ingredient, are also substantially improved, as are the alloys without copper, when at least one member of the above group of hardening elements and/or at least one member of the group of grain refining elements are also present.

Example 1 An alloy containing about 1% copper, .2% sili- I nell hardness of 86, a proportional limit of 20,000 lbs/sq. in., and a yield strength of 28,400

lbs/sq. in. The same alloy when aged seven days at room temperature had a tensile strength of 40,300 lbs/sq. in., an elongation of 6.5%,. a

alloys are light in weight and are, therefore, especially adapted to aircraft construction and the like. This is particularly true whenthe quantity of ternary compound is sufiiciently low so 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 (MgaSi) before any ternary compound will be. formed. For example, if 2% of the ternary compound on the basis of AlzMgsZm 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 and zinc in an alloy containing .7% free silicon and 20% AlaMgvZns would be about 7% and 12%, respectively. The alloys described herein include aluminum, magnesium and zinc, the zinc being present in the amounts of 1.2% to 12% of the alloy, and the magnesium, uncombined with silicon, being proportioned to the zinc in the ranges of the formulas given for the ternary compound. The proportions for the formation of the ternary compound in the alloy exist when the magnesium is about to 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 examples 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 of its initial value by aging at room temperature for relatively long Brinell hardness of 82, a yield strength of 23,900

lbs/sq. in., and a proportional limit of 17,500 lbs./ sq. in. When the above castings were simply air cooled and aged seven days at room temperature the tensile strength was about 39,000 lbs./ sq. in.

Example 2 st ength of 32,400 lbs/Sq. in., a proportional limit of 19,300 lbs/sq. in., a Rockwell E hardness of 86:9 and an elongation of 5.9%.

Example 3 When the aluminum base alloy of Example 2 contained about .75% copper instcad'of .5% copper, the test bars showed a tensile strength of about 39,500 lbs/sq. in., a yield strength of 34,200

lbs/sq. in., a proportional limit of 21,900 lbs./

sq. in., a Rockwell E hardness of 86.5, and an elongation of 3.9%.

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 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.

The improvement of properties is illustrated by the following table showing the improvement in an alloy containing a small percentage of silicon, about 6% ternary compound, about 1% iron, and about .2% titanium. The test bars were chill cast, quenched from the mold, and tested after aging at room'temperature for the period indicated.

Table Tensile Hardness Aging time Emllgamn strength Rockwell E Percent None 12 31, 200 56 3 days..- 7. 9 36, 700' 76 1 week- 1. 3 38,300 80 2 weeks. 6. 6 39, 700 82 3 weeks. 6. 6 40, 000 84 4 weeks. 6. 3 40, 300 83 5 weeks. 6. 6 40, 900 85 2 months. 6. 0 41, 350 85. 1 3 months" 4. 8 41, 600 88. 5 4 months. 4. 8 42, 500 87. 6 5 months. 5. 2 43, 400 89. l 6 months.. 5. 1 43, 700 80. 1

ment in properties.

be used as sheets, rods, wire, structural shapes,

castings, machine parts, etc.- These alloys have a desirable color, high corrosion resistance, and

may be anodically finished or highly polished with excellent results, and are suitable for many uses, among them being the production of castings which are shaped or formed to some extent I 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.

eners and grain refiners to increase strength, ductility or hardness of the alloy, with the balancesubstantially all aluminum and minor impurities, the amount of zinc in the alloy being about .6% to 12%, and the amount of magnesium in the alloy uncombined with the silicon being about 35%- to 45% of the zinc content, the total magnesium being within the range of about It is to be understood that in considering the be made without departing from my invention as defined in the appended claims.

WhatIclaimis: 1. An aluminum base alloy containing magnesium, zinc, about .15% to 1.5% silicon, about 2% to 1.5% copper, and one or more metals for hardening or grain refining, with thebalance substantially all aluminum and minor impurities, the percentage of zinc in the alloybeing about .6% to 12%, the amount of magnesium uncombined with the silicon being about to about of the zinc content, the total magnesium being within the range of about ..5% to 2. An aluminum alloy containing magnesium, zinc, about .2% to 1.5% copper, silicon in amount up to 1.5%, and one or more metals 0! the hard- 3. An aluminum alloy containing magnesium, zinc, about 2% to 1% copper, silicon in amount up to 1.5 and one or more metals of the hardeners and grain refiners to increase strength, ductility or hardness of the alloy, no one of such metals being {present in amounts more than 1.5%, with the balance substantially all aluminum and minor impurities. the amount of zinc in the alloybeing about 1.2% to 7.2%, and the amount of magnesiiun' in the alloy uncombined with the silicon being about 35% to 45% oithe zinc content, the total magnesium being within the range of about .5% to 7% 4. An aluminum alloy containing magnesium, about .6% up-to about 6% zinc, about .2% to 1.5% copper, silicon in amountup to 1.5%, and

one or more metals of the hardeners and grain refiners to increase strength, ductility or hardness oi. the alloy, no one of such metals being present in amounts more than 1.5%, with the balance substantially all aluminumand minor impurities, and the amount of magnesium in the alloy uncombined with the silicon being about 35% to 45% of the zinc content, the total magnesium being within the range of about .5% to 6%.

5. The alloy set forth in claim 4 in which the zinc content is about .6% to 4.8% and the magnesium content is within the range of about .5%

to 5%. V I

6. The alloy set forth in claim 4 in which manganese is present in the amount of about .1% to 1.5%. Y

'1. The alloy set forth in claim 4 m which chromium is present in the amount of about wan-ma BONSACK.