US2290023A - Aluminum alloy - Google Patents

Description

without heat treatment.

Patented July 14, 1942 i Ohio, in i No Drawing.

The National Smelting Applicat Serial No. 431,680

Company, Cleveland,

a corporation of Ohio:

oil-Fe ruar 20, 1942,

a: 8 Claims; (01. 75-9146) This application is a continuation-in-part of my copending applicationserial No. 389,020, filed April.1'7, 1941. and particularly to aluminum y I able for casting and working, and having high strength at ordinary and elevated temperatures.

It is an object ofethis invention to produce base alloys suit;

The invention relates to-alloys,

alloys having relatively high elongation and 'relartively high tensile strength. i, I

It is a further object of this inventionto pro vide a relatively light alloy whichmay be easily cast and machined, which may bet used at ele vated temperatures without a rapid deterioration of desirable properties, and which may be readily treated with anodic treatmentto give excellent lustre andfinish. i v r v M t It is a still further object of this invention to provide an alloy having a rel atively high propor-f tional limit and relatively high fatigue strength, and in which these properties may be obtained by" the formula should lbe present combinewith the When magnesium and aincl are added aluQ minum in the properproportionsa ternary co nrelative to each preferably the ratio or tion in the aluminum,

pound of aluminum, agnesiumand zinc is formed, which ompound]isfsolublefin fsolid solu- Theg presence of this com-; pound in "a relatively. small amountgreatly: im

proves the characteristics'oi aluminum and produces an alloy having high strength combined with high ductility, good casting, rolling, extrud ing and forging properties, good color and. eitcellent corrosion resistance. ln calculating the amount of magnesium and zinc that should be present in the aluminum alloy to form the desired percentage of ternary compound, only magwnesium which is not combine'd'with silicon is to be calculated, as it' is only such magnesium that formula having-the greatest proportion of zinc, increases the brittleness and decreases the due: tility of the alloy. For this reason it is undesirable that zinc be present in quantities sub:- stantially greater than the amount to react to form such a ternary. compound with magnesium and alumlnum.- The most desirable properties are obtained when the magnesium and the zinc are proportioned so that the ratio of magnesium (uncqmbined withvany silicon) to zinc is about equal to the ratio, represented by the formula AhMs=zm,;or somewhatflareer, as represented i AlsMgvZIlo. A small-amount of magnesium may i that may occur when the alloy metal Magnesium adds ing qualities of remelted. to the hardness and machinthe alloyand, as above stated, [in an amount suflicient fto zinc and aluminum present. Ingreater quantities, magnesium tends to make the alloy sluggish, decreasing castability.

The improvedaluminum alloys may have the ternary compound of aluminum, zinc and magnesium present in an amount ranging from about 1%yor 2% to 20%,the preferred range being between about-3% and 15%. At room temperaurns ternarycompound goes-into solid solution inaluminum alloys in an amount of about 2%. "lThepercentage insolid solution increases at hightemperatures and decreases upon cooling, the excess precipitating out. Aluminum alloys containing the ternary compound may, therefore, be advantageously heat'treated to improve their properties.

is available to combine with zinc and aluminum to form the'ternary compound.

The ternary compound is said bysome investi; gators to have a composition having substan-, tially the formula AlaMgizna, and other investigators'have considered theformulaforvthe ter nary compound as being AlzMEaZllaQ It will be seen that the amounts of magnesium and zinc other are quite similarinboth formulae The magnesium andl zinc should be present in about the proportion necessary to form the ternary compound of either formulae, or} the magnesium to zinc in the alloy should be between the ratios in the formulae; l l in .7

An excess .of zinc, over and above that gwhich' cooperates with magnesiumand aluminumhto form a ternary compoundfaccording to the above i or silicon combining ,A small amount of silicon is usually present in aluminun alloys'and upto 1.5% silicon may be present in the alloys of the present invention. It the'alloys are to be rolled or worked the silicon should below, from about the minimum obtainable quantity of 5.04% or .05% to about 11%. More than 31% isfrequently desirable in casting alloys; Silicon combines preference to most elements, each part by weight weight, of magnesium rto form MgzSi. At least sufficient magnesium istherefore added to the alloy to combine with the silicon uncombined with any calcium to form MgzSi, and in addition tocombine. with all the zinc and form the ternary compound according to the formula AlzMgaZna.

[ MgzSi is more stable than the ternary compound be maintained in solid alloys in an amount up is th quantity of MgzSi ispresent in the alloy, and

solution in aluminum present if the silicon above mentioned and may to about 1.85%, w ch be provided to replenish losses with magnesium in wlth'about 1,75 parts; by I Although it does not desired in a given in conjunction with the ternary compound. MgzSi does not, however, make as eflicient use of the magnesium as does the above mentioned ternary. compound. Therefore, it i desirable to have the magnesium present on the rich side to prevent the silicon being present in excess and taking magnesium nary compound,

It has now been found that aluminum alloys containing magnesium (over that necessary to combine with silicon) and zinc in the proportions away from the termanganese and 'Alloys containing manganese may" be readily 7 heat treated or age hardened to' give somewhat superior properties; butvery 'desirable properties are obtainable"whe n castings are simply aged at room'temperaturejonwhen quenched from themold and age Q Manganese is a very efie'c'tive element in the alloy and desirable improvements are noted when about .1% or even a little less, such as .05%,' is presentin the alloy. The preferred properties are obtained'with about .'2%' to about 5% or .8% manganeseyand in'som'e cases it is desirable .to have the manganese present as about 1%, or even 1 .5%.

Chromium is a particularly effective alloying element in the alloy. of the presentinvention.

' appear to improve the roportional limit and yield strength of the alloy sistance. 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 improvin'gthe properties of the alloy,'but .2%' 'or .3% to about 1%, or even 1.5%, is desirable. manganese is also present, thetotal of manganese and chromium should preferably be between about .3% and 2.5%of the alloy.

The quantity of each of the hardening metals compound and it is, therefore, preferred to; havea larger percentage of the present, such as 4% to 8% may be present.

acts as a hardener which is sometimes desirable 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 For alloys to be forged or shaped after casting, the ternary compound should be present in the lower ranges, such as or so, as the metal is less hard with the ternary compound.

I v refining metal such as is set forth in the above group, is improved by the presence of iron in suitable proportion.

ternary compound Iron in suitableamounts further increases the hardness and tensile strength are aged at room temperature without a heat treatment or quench- 1 duetiiity' fingering-nee du nt z d'eSimme-m anamminumi ano i eomgming i ron;

nuni allo be present n h n ofethes me fiswlpre e-is 40 1 o isho s n s me ev' the naep m rbpdrtiqn'tq comb-me wnhthe silicon and "t0" orin.1 o i"the ternary 1 compound 2' AlsMgqzne, with"the balance substantially am minum and minor impurities was prepared and hi eesi ntote i; 3 7 1 n e he n e Seven aaysgau .rqomrtefiiper mre.whe tested they properties of" the anew, the man um and grain refining" elements w ther improvement independent? v The alnminfilinf allpysggqf the tiqn eontaining" magnesi silicon, and zinc in' e cbmpound'; when east 1"] M I that chilling takeis'jlacefsq ta y, nebusly in the Lvariqus fbottiqn's of the 19,000'1bs./sq.'in. the hardness was '80 Rockwell chilling may not be l ys re m er ol tween?" esi fiin 7 bor'on m-th amoumonp0 ;to1.1 coniiim ast 1; rs were quenched and n a re lower a q tnegeastability is decl eased 'wExa mpZea3-- a w n w n w, a wnenwhe'ial dy oiniahlpleziontainedxoava 9? 0 t e mrefine ee e t heme; vanaamnrmsmm-,zorymhgsfiefi; the test bars we W T 53 93 0? F 29? 45 which were"emueast,fqumnenmagedseven f m of r fi s s e n W33 SFa P Q days at mamtembeiawr new hardness of '14-, d p 4 9 QW FF EP E WWW??? w m an '-1Qnat'1QiigQrsW; a. brobdrtional limit or mustbe t s ed- Th exa ur ne i el c ei 16600 lbs/sci; a Mad strength 6: 24,900 r m the grounv sye E' WF PmJ D SR Q tensilestength of 38300 m percem rnolybdenum, "zijx egnium and yanadijum"; .and of Vanadium m me aneSs-wasso, the

peeiany tungsten am} nielypljd'en th 0 mean lixnit was the strength and d 'trength 1was25500 'th was 40,400

v w elqeeieeq w HROOW -l e swine used, b'utfwhen 'sfiecial pro-perms I I gated article are" important it. desyraple Itd se lect} e in" r fln ri h'e 1 1 9 fl li e' en SQ ILP OPQ S?T5 3 lumbilim and'l tantal mgm Titanimnbeing .r

- When man alloy Of Exam le 2' the when qu nch ewand aseeeve d y' t: oom e "The abdv'e' descrihed handeniing e ganese and ehl ominni; substantially d r e-leh- J 1" thegy dgst e gth was 25,800 lbs/sq. imi' and thq tensilestrength was 42,000 lbs./ sq. in. wnen thegtest bars-wexge simply air cooled and aged seven days at room temperature, the elongation was 9.3%, the px opprt'lonal limit was 18,200 1bs./sq. in, the yield strength was 25,800 1bs'./-sq. in and the tensilestrength was 40,600 5% t f I 1b$. /sd."in. When the molybdenumawas increased a g j 7 A v 1' td.-'12%;test bajrs whichwere-chill cast, quenched ,7 f -endagedsevendaysfatif Itemperature had'an e1ongation* "of*121%," a. prbportional limit of 16,700 lbssq. in., a yield strength of 24,500 lbs./sq. 75 in., and a tensile strength of 41,400 lbsjsq- 1 T the present invention:

tune was 11 .2%, theprqpprtional limit wa s 18,100

the amount Example 5 and the hardness was,80 Rockwell E.

Example 6 Sand cast test bars were prepared from an al-- loy having the composition of about 1.8% magnesium, about 3.5% zinc, about 28% silicon, about .5% iron, about 28% manganese, about .3% chromium and about .2 titanium and aged seven days at room temperature. These; bars had a tensile strength of 33,300 lbs/sq. in., a proportional limit of 14,700 lbs/sq. in., a yield strength of 21,400 lbs/sq. a hardness of Rockwell E 72.5 and'an elongation of 6.2%.

Example 7 An aluminum base alloy containing magnesium, zinc andsilicon in proportions to form 6% of a ternary compound, based on the formula Alr'MgvZnc, .6% iron, .25% chromium, .2% titanium and .3% manganese was prepared. Test bars made from this alloy, quenched from the mold and aged seven days at room temperature, 7

had a tensile strength of 42,300 lbs/sq. in., a

strength of 24,300 lbs/sq. in., a hardnessRockwell E 80.8 and an elongation of 10.3%. When of manganese in the same alloy was increased to .5 similarly prepared and treated test bars had a tensile strength of 41,600 lbs./sq. in., a proportional limit'of 17,600, lbs./sq. in., a yield strength of 23,500 lbs/sq. in., a hardness of Rockwell E 801 and an elongation of 9.6%. When manganese was present in the amount of about 35%, test bars similarly prepared and treated had a tensile strength of 41, 00 lbs/sq. in., a proportional limit of 18,400 lbs/sq. in., a yield strength of 24,300 lbs/sq. in., a'hardness of Rockwell E 80.5 and an elongation of 8.4%.

'When manganese was present in the amount of 1%, test bars similarly prepared and treated had a tensile strength of'39,900 lbs/sq. in., a proportional limit of 19,000 lbs.'/sq. in., a yield strength of 25,900 lbs/sq; in., a hardness of Rockwell E 81.1 and an elongation of 5.9%.

Example 9 Chill cast impact test bars of the standard V- notch and keyhole types were prepared from an aluum base alloy containing 6% of the ter- .25% manganese, .6% iron,

at room temperature, elevated temperatures and low temperatures.

Copper is frequently an impurity in aluminum alloys and, unlike the hardeners present in alloys of the present invention, copper is a precipitation hardening ingredient which is much more soluble at high temperatures than at low temperatures. Substantial amounts of copper are desirable when the alloy is to be solution heat treated. Alloys of the present type containing copper in an amount of more than .1 or so form the subject matter of copending applications.

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 sufliciently 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 (MgzSi) before any ternary compound will be formed. For example, if 2% of the ternary compound on the basis of AlzMgaZm 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% A13Mg'lZn8 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 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% or! the zinc.

A very astounding fact has been discovered, however, in connection with these alloys, namely, that the tensile strength may increase up to approximately 50% Olf 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 abo've room temperature.

To obtain properties even of, the same order of so that they can be rolled or rods, wire, structural shapes, castings machine ,sults, and are lution heat treat for improvement in properties. The alloys of the present invention have good fatigue and tensile strength and a relatively high to be heat treated if it is although such heat and they have sufiicient treatment is not required; ductility and hardness .formed into sheets,

parts, etc. These alloys "have a desirable color, high corrosion resistance, and may beanodically finished or highly polished with excellent resuitable for many uses, among them being the production of castings which are shaped or formed to someextent after castings percentages of ter- The, alloys having the lower nary compound may even be forged at room temperature and are thus. useful for many special purposes. l

It is to be understood that, in considering the 1 amount of zinc and magnesium to add to alu- 1 minum alloys to form of aluminum, magnesium and zinc in the alloy,

the ternary compound such magnesium as is necessary to combine with the unoombined silicon is not to be considered 1 as part of the magnesium necessary to form the specified amount of ternary compound.

As pointed out above, grain refiners are usually desirable in alloys of the present invention. However, it. has been foundv that the alloys of the present invention have relatively high base alloy containing mage silicon in an amount up grain refining metals to 1.5%, and one or more proportional limit, even at relatively high temp peratures; they have desired to improve and modify their'properties, content, the total magnesium strength, high proportionallimit and ductility without solution heat treatment,-even in the ab- .1% to about 1.5% iron, manganese, about .05% to nesium, zinc,

with the balance substantially all aluminum and minor impurities, the amount of zinc in the alloy being about .6% to about 9%.and the amount of magnesium in the alloy uncombined with silicon being about to about of the zinc being within the range of about .5% to about 7%.

2. An aluminum base alloy containing magabout .1% to about 1.5% iron, about .05% to 1.5% manganese, about .Q5% to about 1.5% chromium, silicon in an amount up to 1.5%, and one or more grain refining metals in a total amount of about .005% to about .5%; with the balance substantially all aluminum and minor impurities, the amount of zinc in the alloy being about .6% to about 9%, and the amount of magnesium in the alloy uncombined with silicon being about 35% to about 45% of the zinc content, the total magnesium being within the range of about .5% to about 7%.

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

4. The alloy set forth in claim-l in which the zinc contentis about 1.2% to 4.3% and the magnesium content is within the range of about 5% to 5%.

5. The alloy set forth in claim, 2 in which titanium is present in theamountof about ,05% to .5%. y i

6. The alloy set forth in claim 2 in which molybdenum is present in the amount of "about 01% to .5%. l i .7. The alloy set forth conium is present in the amount of about .05% to .5%. i

8. An aluminum base alloy containing magnesium, zinc, about .1% to about 1.5% iron,

about .05%. tov 1.5% manganese, about .05%

-,the amount of zinc in the alloy being about 6% to about 9%, and the amount of magnesium in the. alloy uncombined with silicon being about 25%. to about 45% of the zinc content,

,the total magnesium being within the range of about .5% to about 7%..

WALTER. BONSACIGI.

in claim 2 in which zir-v