US1908023A - Aluminum silicon alloy - Google Patents

Description

Patented Ma e, 1933 more w; mrr, or cnnvnnnnn, onio,

ABSIGNOR 'IO ALUMINUM comm OI mamas, or rrrrsnunen, rmmsnvam. A conroaa'rron or rmmmvmu ALUMINUM sxmcon nnnov Drawing.

This invention relates to aluminum base alloys which contain silicon as the principal alloyingelement and to certain novel alloys of such nature.

for construction material do not possess t e. necessary strength and hardness, and in other cases the hardness alone is inadequate. It is well known that when aluminum-silicon allo is used in the form of castings, partic arly when the alloy contains high amount of silicon such as to -per cent, castings with superior physical properties are usually only obtainable when the structure of the alloy is modified in some manner. a The socalled modification processes involve. either casting the metal in a chill mold or adding to the metal some substance which has in itself the desired modifying efiect. The modifying 1 substance may be a metal such as sodium or ,it ma be a salt such as an alkali fluoride.

' 'The iscovery that these alloys mi ht be modified and that increased strengt and hardness might be obtained has called attention to the inherent possibilities of aluminum base alloys containingsilicon and the more or less extended use or these alloys is the result of the discovery of such modification.

However, the aluminum silicon alloys so modified do not possess the stren h, hardaces, or fati no resistance desire for, some purposes; oreover, in the unmodified state, the allo s do not readily machine, and in the modifiex condition, considerable care is sometimes necessary to avoid dross inclusions in casting.

The alloys which are the subject of the present invention not only do not have the" Application fled June 24, 1980. Serial No. 488,578.

disadvantages enumerated above, but they retain all 0 erto made the aluminum base alloys containmg silicon a desirable material for use in many varied applications,

I ave discovered that a small amount of magnesium added to aluminum allo s con taining more than about 5 per cent 0 silicon produces an effect in those alloys which, inview of the amountof constituent added, is entirely out of pro ortion to what might be expected. The ad ition of ma esium imparts to the alloy a hardness w ich ishigh as com ared to the aluminum-silicon alloys hereto ore produced, and give tothe alloys the advantages which have hithproperties which are much more conducive to satisfactory machining than the older aluminum-silicon' alloys. Furthermore, the

small amount of added magnesium produces an alloy which responds to heat treatment to a marked degree and rmits the of aluminum-silicon filbys of big strength as compared with those previously known.

Hitherto, in order to produce such strength and hardness and machinabili't as I have produced in the aluminum base oys containin silicon by the addition of small amounts 0 magnesium, it was thought necessary to add comparatively large amounts of other allo ing elements, such as copper. Because of t e amount of alloyin constituent which was necessarily added, t e characteristic advantageous features of the aluminum-sflicon alloys, such as lightness and corrosion-resistance, wereito some degree changed and the resulting alloy was for many purposes not as desirable. The present invention eliminates these difiiculties in that the inherent defects of the aluminum-base silicon allo are overcome without changin essentia y the nature of those alloys, and e beneficial properties imparted b the silicon to the alu minum are not diminis ed. a

To obtain these effects, I have added from 0.02 to 3 per cent of magnesium with good reproduction .fact, there is a strength caused,I

sults. Ihavefoundflmttheadditionof as little as 0.02 per cent of magnesium will produce appreciable improvements over the entire sihcon range, the lower limit of which is about 4 or 5 per cent. (The upper limit is for practical reasons about 25 per the extreme difliculty of machining the alloys when the content is materiall greater than the amount named and the oys are quite brittle and diflicult to cast.) The ma nemum may be added to the alloy by an we known metall ell allpying meth and the aluminumcon-magnesium alloy may be made into castings of an nature in ractically any type of mold. I ve found, owever, that the best-results are obtained when the metal is modified at the time of casting either by the use of an added agent or by the use of a chill mold.

It is a feature of my new alloy that while the hardness of the alloy in the as cast condition, i. e., before solution heat treatment, is increased by the addition of the ma sium, the tensile strength is not iucreasedi znd in t decrease in tensile eve by-theeflect of the magnesium on the particular modification process used in casting the alloy. However, this decrease is slight and any dis'advanta resulting from it is overcome by e large percen increase In hardness'caused by the magnesium.

Thus in the aluminum-silicon eutectic range in the neighborhood of about 1 percent of amounts of m silicon where modification has its most pronounced eifect, I have found that increasing agnesium have a tendency to interfere with this phenomenon and consequent- -Taking as anexam alloywhich contains no ly there is little or no increase in tensile strength but a decided increase in hardness. is an aluminum alloy of P about 12 per cent of silicon which has been cast in a chill mold to obtain asuitable modification elfect, the following table clearly shows the results of mcrhasmg quantities of magnesmm:

J Tumlial Alumina alloy: 18 per cent silicon it a... miner an a. 22% hi an an no as: lam 11.0 0.41 sum can 1.. man 57.1

Itwillbeobservedfromthesefiguresthates little asILOS perqent of magnesium produced an increase in Bnnell amountingto over 25,-per cent of the Brinell hardness of the This increasemhardnesnnashas hitherto menbound. of great importance for many purcent, because of the same 7 without heat treatment has an endurance limit of 5,000 pounds value represents the limit for aluminuin,-sili-- poses, and..the value of aluminum-silicon aloys in the as cast condition is thus greatly enhanced.

I have also found that such alloys have mechining properties which are notably better than those 0 the aluminum-silicon alloyscontaining no ma esium. Another important feature of the a oys represented above is their relative resistance to corrosion. Aluminum base alloys containing silicon are in themselves, on a comparative basis, corrosion-resistant to a considerable d and as between alloy A and .alloy C o the'above table, for instance, I have found but little to choose from in point of corrosion-resistancc, but in respect to this property my new alloys are advantageousl superior'toaluminum-silicon al-. loys in whic equal properties are obtained by the addition of copper or similar alloying elements, such as zinc and nickel.

It is also an advantageous feature ofmy new allo that their strength and hardness are cape 1c of further increaseby the application of thermal treatments which are used in connection with other aluminum alloys for aging heat treatments such as are regularly. other alloys, did

practiced in connection wi 7 not increase but on the other hand decreased the tensile strength and h dness. Thus, for instance, a castin of su an alloy 'asallo A, if heat treated or abou 2 hours at 565 and later a will actua g undergo a decrease in tensile strength an Brinell hardness. On the other hand, if 0.4 per cent of magnesium is added to this alloy, the same thermal treatment will increase the tensile strength to about 51,000 pounds per square inch and the Brinell hardness to about 114. The efiect ofheat treatment on other properties than the ones above mentioned is also pronounced. For example, a heat treated casting of alloy containing per cent of silicon and 0.2 r cent of magnesium has an endurance lilmt to fatigue of 9,000 pounds per square inch whereas without the magnesium alloy in the modified condition but per square inch, which con alloys of this composition unless the alloy 7 is made susceptible to heat treatment. Fur-. thermore, between the two alloys just mentioned, the. one contain" magnesium and in a modified and heat treated condition has a yield point of 16,000 pounds 'per' square inch; while the other, without magnesium but in the unheat' and modified condition, has a yield point of 14,500 pounds .persquare inch. If this latter alloy is heat treated by substantially heat which d for about hours at 150 C.

produced a yield point of 16,000 pounds per square inch m the aluminum alloycontaimng both silicon and magnesium, the yield point will decrease to about 12,000 pounds per square inch.

* Tum No. 2

Aluminum alloys containing 5 per cent silicon Brinell Per cent at magnesium Because of the'lower. amounts ofsilicon in the above alloys, the results are vnot equal to those set forth in the precedin table but they afiord striking evidence of t e markedeflect of small amounts of magnesium on aluminum-silicon alloy castings containing relatively small amounts of silicon.

,It is known in the art that specimens separatel out under commercial conditions whic are tested without machiningofl' any of the metal of the outer skin develop more favorable properties than specimens machined out of heavier sections of commercial castings, this because heavier sections solidify more slowlyand are more susceptible to internal shrinks and defects than .the more rapidly cooled and more satisfactorily fed m fecting a distinct advance.

s ens, a goodly portion of which is in c osely roximity to the cool walls of the mold. fhave discovered it characteristic of this particular series of alloys that-the diver nce between separatel cast. specimens an those out from the interior of the heavier sections is not at all as marked as it is in the case of other commercial alloys. It is,

of course, recognized in the case of all alloy castings that such a drop in strength and elongation must anddoes progress towards the heavier sections but efi'orts are being made to cut this variation to a minimum and in the alloys within the scope of this invention I believe that I have succeeded in ef- As an illustration of the superiority of aluminum base silicon alloys to which has been added a small quantity of magnesium, I have taken a casting of commercial designv and cut test specimens from the interior'of oneof the heavier sections to be compared.

with other similartest specimens of the same alloy which were simultaneously cast to test size in separate molds. One alloy-was made up with 10 r cent silicon and 0.2 per cent magnesium in analuminum base. The separately cast bars had an average tensile strength of 20,890 lbs. perv sq. in. and an elongation of 8.3 per cent in 2-inches and the bars machined out of the casting had an. average tensile strength of 26,800 lbs. per

separately cast bars had a tensi a strength of 30,000lbs. per sq. in. and an elongation of 7.8 per cent in 2 inches. The bars cut from the heavy section had an average tensile strength of 23,300 lbs. per sq. in. and an elongation of 2.7 per cent in 2 inches. This represents a 22 per cent decrease in tensile strength and a decrease in elongation of 65 per cent. Significantly, the separately cast bars of the latter alloy had higher tensile strengths than those within the scope of our claims, and'whereas in the commercial aluminumbase copper alloy the loss in tensile strength amounted to 6800 lbs. peiasq. in.

and the. difl'erence in elongation amounted to 5.1 per cent in 2 inches, in the alloy made under the provisions of this invention the loss in tensile strength was only 3090 lbs.

per sq. in. and the diilerences in elongation "only 2 percent.

This superiorstrength in heavy sections is an indication of improved castin properties and it is interesting to note at a large foundry devoted to the casti 'g of aluminum base alloys-found it impossib e to make castings from a pattern of rather unusual designby the use of certain standard commercial alloys and it was only by utilizing an alloy made according of this invention that a satisfactory casting was produced.

Aluminum base silicon alloys to which to the precepts have been added small quantities of magnesium are corrosion-resistant to a very high degree. In a comparative test extending over a period of a year, I have subjected a series of aluminum base alloys, widely known and commonly used. to the action of a salt corrosive agent. Along with these standard alloys, I subjected to the .test two aluminum base silicon alloys with a silicon content of about 10 per cent with added quan- .tities'of magnesium, in one of which; alloys the ironirnpurity was held below 0.15 per cent, the other having slightly -more than the usual iron content, say about 0.7 per cent.

The ell'ect of the corrosive agent was measured by determining the loss in tensile subtractin the average tensile strength 0 the corrode specimens from the average tensile strength of specimens'from the same ineltwhichhad been retained for simultaneous and strength sufi'ered by the alloys-by reason of the con-osion and obtained. I?

remarked} which hadbeen protected from corrosive intest Him-h that treatment fluences by a protective which staudardfurflusalloy.

The four standard commercial allo reparesenting probably the four most wid used y aluminum base casting alloys suife a de- M preciation of strength about as follows: MW 5% -m 1 51 4 "a Allo A. 19.1 per cent in strength 22:3 :i m A110; B; "17.1 per cent lossin strength mm i v -QR A110 0 "12.5 per cent oss in strength l All; D

PM m in ms e m-get: se i-sass? :s; The two alloys which I have especiallf ad 017 m bf devised and compounded gave these f 'llowform asimila to determine the ingresultsvariation of: a usedby-in 7 Table B the ten: h -The55his tcspec1 'menswere r oursat an y E (with higher iron) P M1053 quenched.- The results are given in Table D1 emsmmgth Talon. Alloy F (with lower iron) 2.4 per ccntloss in I 1 A In connection with this test, it should be noted that the corrosive influence was an arti- 4 ficially aggravated case and that such 'COI'ldl- 31:3 tions would conceivably never be encountered 015 (1 v in the t majority of uses to which the al- P7 H loymi tbe put. Inspecific instancesas,for It 'will be observed that although Ih'ave" examp e, when alloys of my invention are used along the sea coasts as parts ofseaplanes, ships, etc., conditions approximating those of the test will be encountered and the almost negligible corrosion efiects on my all- 35 10 will be particularly in demand when consi cred in con'unction with the high endurance limit an the retention of satisfactory phgsical properties with increasing section. asting o aluminum-base alloys containing silicon and small amounts of are also susceptible to increase in hardness and strength by the use of low temperature aging pr without previous h gh temperature solution treatment, and me alloys 'respondreadily to an of thewell known heat treatments which ave been hitherto described for use in connection with' aluminum alloys in eral.

I- have ound it chars. teristic of my alloys that the physical properties are not varied by previous changes in pouringtemperature to the extent of the ordinary commercial aluminum base alloys. It is well known in i 56 the art that when the molten metal, through inadvertence or nity, is poured at temhigher than usual for that particular alloy, the physical properties sufier a decrease which in some alloys ;is especially As a basis for comparison, I tool: a commercial aluminumbase .heat treated alloy .seontaining copper and poured test specimens from the same melt at 3 difierent temperatures, with the results given in-Table C. The

msandorin V 'sium, ma

about 0.02'and 1 used a higherpouring temperature for one of the tests on' my alloy, the efiect on tensil strength ismuch less than in the alloy of The term 1.1mm use alloy, as used herein and in'the appended comprebends for the of avoi undue details and prolixi use only the oy as Well as the molds or in any combine? can of these casting methods 1 Whilecertain and limits' of I silicon and um content have been stated, within which limits my best results were obtained, and although certain partieular wellknown heat treatments have been described, be understood that these factors maybe varied without departing f fromthe invention. .1 claim- 1. Au aluminum base alloy consist offrom about 5 to 25 per cent of silicon, about 0.02

2.'Anal'uminumb ase mg of aboiit 12 per cent of silicon, between the rest aluminum.

3; As a new product acasting of an aim.

' a loy consistcenlttopercentofma'gne percent of magnedum,and

I 1,noa,oaa 5 25 per cent of silicon and from about 0.02 to 3 per cent of mum, and the rest aluminu m, characterized by high hardness and relatlvely lugh corrosion-resistance in the as 5 cast condltiom In testimony whereof I hereto aflix my signature. I v

LOUIS'W. KEMPF.

CERTIFICATE or CORRECTION.

Patent No. 1,908,023. May 9. 193a.

Loulsw. Km.

It is herehy certified that error appears in the printed specification of the 'above numbered patent requiring correction as follows: Page 1, line 8, for "flow" read "low"; 2, line 57, in column 3 of the boxed table, for "31,500" read "31,550"; and that the said Letters Patent should he read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 18th day of July, A. D. 1933.

M. J. Moore.

(Seal) I Acting Gomnliesioner of Patents.

I 1,noa,oaa 5 25 per cent of silicon and from about 0.02 to 3 per cent of mum, and the rest aluminu m, characterized by high hardness and relatlvely lugh corrosion-resistance in the as 5 cast condltiom In testimony whereof I hereto aflix my signature. I v

LOUIS'W. KEMPF.

CERTIFICATE or CORRECTION.

Patent No. 1,908,023. May 9. 193a.

Loulsw. Km.

It is herehy certified that error appears in the printed specification of the 'above numbered patent requiring correction as follows: Page 1, line 8, for "flow" read "low"; 2, line 57, in column 3 of the boxed table, for "31,500" read "31,550"; and that the said Letters Patent should he read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 18th day of July, A. D. 1933.

M. J. Moore.

(Seal) I Acting Gomnliesioner of Patents.