US1572488A - Aluminum-silicon alloy - Google Patents

Description

Patented 9, 19 26. a a a ourrao STAT 1,572,488 PATENT tori-Tics.

ZAY JEFFRIEB, OI SHAKER HEIGHTS, AND ROBERT B. ARCHER, 01 LAKEWOOD, OHIO,

ASSIGNOBS TO LLUKIHUI 001mm OF AMERICA, PITTSBURGH, PENNSYL- VAN 1A, A CORPORATION 01' PEHHSYLVANIA.

Lam-saloon annoy.

No Drawing. priginal application fled January 4, 1921, Serial R0. 485,024. Divided and this applica- To all whom it may cmwernzz Be it known that we, ZAY Jmnms, of

Shaker Heights, and ROBERT S. Aaomm, of Lakewood, both in the county of Cuyahoga 5 and State of Ohio, have invented certain new and useful Improvements in Aluminum-Silicon Alloys, of which the following is a full, clear, and exact description.

The invention y 'hirh forms the subject of our present a plu tion (a division of our copcnding apphcat on Serial -N 'o. 435,024, filed January 4, 1921, now patent No. 1,508, 556, issued September 16, 1924) relates to the production of aluminum alloy castings, particularly castings made of alloys containing silicon or copper or both, with or without other metals, and its chief object is to provide a simple and efl'ective method which will produce light-weight castings with a hitherto unobtainable combination of physical properties, especially as regards elastic limit, tensile strength and ductility. 'Do this and other ends the invention consists in the novel method and product hereinafter described.

As will be seen from the subjoined descri tion, the invention is basedupon the com ination of certain steps, some of them novel with us, and in part the invention resides in the discovery that certain alloys are especially susceptib e to improvement by heat treatment after casting, and that certain methods of casting such alloys further and peculiarly adapt them to such treat-.

3 ment; and in the additional discovery of temperature and duration of heat treatment in combinations appropriate to the particular alloys and method of casting involved.

With the aid of these discoveries we have 4 been able to produce castings having improved physical properties with respect to elastic limit, tensile strength and ductility to an extent hitherto unattainable, with the result that it is now possible to use aluminum alloy castings fpr purposes for which their use has previously een impracticable. i It has been found that the addition of a substantial amount of silicon to aluminum 00 alloys very materially improves their castiiig qualities, .thus rendering it possible to successfully and easily make castings which would otherwise e very, diflicult to produce.

,strength of the resulting alloy and as retensile strength may tion fled lprll 38, 1924. Serial No. 709,748.

In particular, the presence of a substantial amount of silicon enables us to produce alloys having excellent casting qualities, even better than those of the well known alloy containing 8 er cent copper, with the use of only relative y small amounts of copper or-zinc or both. The possibility of limiting these heavy metals to amounts of say 5 per cent or less in the caseof copper, and 10 per cent or less in the case of zinc, is very advantageous, both as respects the 05 spects its specific gravit The silicon, by virtue of its lightnem, 0 sets, in a measure, the eflect of the heavy metals, copper and zinc, as well as permitting the use of the heavier metals in smaller uantities. We have discovered that these si icon alloys can be materially-improved by an appro riate heat treatment, which may affect hot the silicon and the heavy-metal constituents.

The tensile strength of commercially pure cast aluminum is about 12,000 pounds per square inch and its elongation about 25 per cent. By adding varying proportions of hardening metals, particularly copper and zinc, it is possible to increase the tensile strength so that the sand cast alloy will have an ultimate strength of nearly 30,000 pounds per s uare inch, but the elongation 1s the by re need to less than 5 per cent. By aiding a very lar e amount ofzincthe B5 raised to ap roximately 40,000 ounds per square inc but the elongation is reduced to almost nothing, and the alloy is very brittle. By casting any of these alloys in a chill mold, the tensile stre h may be increased'in general by approximately 5,000 pounds per square inch and the elongation may also be increased. But it has heretofore been impossible to simultaneously produce tensile strengths of over 30,000 unds per square inch and an elongation o 8 per cent or over.

By our method, however, we have been able to extend very greatly the range of the tensile strength and elongation, and of the combination of the two, so that we have obtained castings having very much higher tensile strengths than those hitherto known in the art, and yet elongations better than those at present obtained with castin alloys 105 having only moderate tensile strengt s.

. strength alloys previously knownhave required the presence'of substantial amounts of zinc, even in many cases up to 33 per cent, and have therefore been considera ly heavier thanpure uminum, while we obtain our results with an addition, in general, of

- lot more than to per cent of total heavier alloying metal or metals and yet produce a casting which is not only stronger and more ductile but likewise lighter than would otherwise be obtained.

Various prior investigators have proposed to obtain castin possessing'the desirable combination of figh tensile strength and ductility by heat treatment of a properly made castin but their contributions to the art have so ar not led to commercially useful results. For example, the best results ublished prior to our work are those of gVilm, who reports having obtained chill castings with a tensile strength of about 32,000 pounds per square inch and an elontion of 5 to 7 per cent. More recently fierica and Karr have by heat treatment of an alloy containing 00 per and a large amount of zinc obtains a tensile strength of 41,200 pounds per square inch but with an elongation of only 4 per cent. This allo contained about 19 per cent of heavy allbying metals and hence had a specific 'avity greater than 3. With lighter a]loys,- r example one containing small amounts of copper, magnesium and manganese, they obtained a tensile strength of 35,500 pounds per square inch and an elongation of 2.3 per cent. In none of the three cases men- A tioned above were the properties enough cent copper and 0.2

better than those ssessed by untreated castings to justify t e cost of the treatment.

Our invention involves the discovery of important reasons for previous lack' of practical success along-this line, and embraces a combination of old and new steps so that we are now able by means of our improved method to reduce articles, cast in either sand or molds, having physical properties far superior to those of any such castings hitherto produced. B means of our novel method we have r uced sand castin'gs of an aluminum al 0y contain ng 4 per r cent ma esium, ha a tensile strength of about 50,000 per square inch and an elon tion of 8.5 per cent, with relatively big elastic limit; also chilled cast ,having a tensile strength of 54,000 un 'per square inch and an elongation o 18 .per cent, with rela- 'tively high elastic limit.

This combination of high tensile strength 7 'the castings at t and elongation enables these castings to be used for purposesfor which aluminum castings have not hitherto been suitable and for which it has been necessary to use the much heavier ferrous materials such as steel or malleable iron. g 2 One example of our process comprises as its first step the preparation of an aluminum alloy containing about'3 to 5.5 per cent copper, preferabl 4 per cent, with no magnesium or' wit magnesium up to about 0.3 per cent, the iron content in particular eing as low as possible, preferably not to exceed 0.25 per cent. Iron and silicon are always present as im urities in aluminum as now obtainable, an a part of our invention consists in so choosing the raw materials as to limit the iron content of the finished alloy to an amount as low as possible, preferably not over 0.25 per cent. The use of silicon in substantial amounts will be considered hereinafter. 7 w

The ingredients are mixed in the molten state, care being taken to avoid excessive temperatures at all stages of the melting operation, and the mixture is poured'into either a sand mold or a chill mold, and caused to solidify. After solidification a microscopic examination reveals masses of an aluminum-rich constituentsurrounded by a network of a hard, brittle constitutent, which has been reported to be chiefly CuAl,,. In the form of a sand-cast test bar about one-half inch in diameter the alloy has a tensile strength of 18,000 to 25,000 pounds per square'inch with an elongation of 2.5

to 4 per cent in two inches. A chill cast test bar of the same size has 'a tensile strength of about 24,000 to 28,000 pounds per square inch and an elon tion up to 6 per cent in two inches. he iron in the alloy is found both in the form of needles, reported to be FeAl,, and in a different form, apparently as a silicide of iron. The presence of the iron (FeAl,) needles up to a certain amount is beneficial to the strength and ductility of the alloy in the cast condition, probably due to the fact that the ordinar path of fracture in the cast allo is throng the brittle network of anal; which is stren hened by the iron needles. It is foun that these iron needles are very detrimental to the physical properties of the casting after the cat treatment discussed below.

The next step in the example of our process now being described consists inheating the castings to, and maintaining them at,

a temperature of 500 to 540 C. for a period of time depending ulpon the results esired and themanner in w ich the casting was made. The principal object of heatin e temperature mentioned is to cause the CuAlin the network to go into solution in the solid aluminum-rich constituent. It is found that at the tem oratures"'referred to, this CuAl, disso ves slowly, in fact surprisingly slowly. In sand castings the time necessary for maximum solution of this CuAl may be as much as 48 hours, at the temperatures mentioned;

while in chill castin because of thefiner' the freezing int of the eutectic, some of the CuAl, wi remainin the network after heat treatment, and the physical properties of the obtained with will notbe as good ascan be a lower copper content. In

most if not all cases the best combination of physical pro stantially al of the CuAl in the network has been dissolved in the aluminum-rich constituent.

A temperature of heat-treatment high I enough to fuse the eutectic, that is, the temerature of incipient fusion of the alloy, is

in most cases unfiavorable to the best ultimate results, and it has been found that in some instances 540 C. is too high unless the rateof heatin up to that int is very slow or the time o heating be ow that point is comparatively. long.

A further result of heating the castings at 1 the tem turc mentioned-is to re-dissolve any C 1 which may have'precipitated in small particles within the aluminum-rich constituent rather than in the network during the previouscooling of the castings,

After the heating period the castings are preferably cooled-rs idly, as b uenching in water. .By the a ve descm procedure, sand castings of an alloy containing 4 per cent copper, 0.2 per cent magnesium and less than 0.25 per cent iron have been produced within a tensile strength, after aging,

of about 50,000 pounds per square inch and an elongation of 8.5 per cent. Chill castin s have been madeby the same process, of t e same alloy, having a tensile strength of 54,000 pounds per square inch after aging and an elongation of 18 per cent.

As stated above, quenchi is preferable to slow cooling, but good' resu ts can in some. cases be obtained by cooling in a current of air. A marked difference has been observed between the results obtained by cooling in a current of air and those obtalned by cooling in still air. Even slow cooling, however, produces improvement as compared to the cast condition, not only in the physical properties, but also in resistance to-corrosion.

The physical properties of castings subjected to t e treatments above referred toca-n be further changed by artificial aging, that is, by heating them, immediately after cooltime, one hour being in many cases sufii ies results only when submethod, say at a temperature around 520 C.

ing, to 'a temperature of 100 to 150 C. for a cient. As a' resu of ;such heati the tensile strength is increased and the e ongation decreased, and the elastic. limitis inc vei iqlmarkedly.

e method of casting is-an important factor. Thus a method reducing fine grain and improved physio l lproperties, yields castin which are gene y more amenable to the heat-treatment than does a casting method which roduees'coarse grain. For example a bar aving a cylindrical test section two inches lon and a half-inch in diameter, composed o alloy containin about 4 per cent copper and cast in a sun mold,

has a tensile strength of about 18,000 pounds per square inch and an-elongation of. about 4 per cent. If the bar is heat-treated'by our for 24 hours, the tensile strength ma be more than dpubled' (increasing to a ut 37,000 pounds per square inch) and the elongation is increased to about 12 r cent, or three times its original value. n the other hand, if the bar is cast in such a manner as to cause rapid solidification, sa by chill casting in an iron mold, it will ave, after heat-treatment by our method, a tensile strength of about 40,000 oundsper square inch, and an elongation of about 20 per cent.

In sand castings of alloys containing sub-' stantial amounts of silicon a considerable portionof the latter appears in the form of relatively large lates or needles, and in chill the s' 10011 is found generally in smaller particles, some of which at least are more or less rounded. The heat-treatment the shape chan and sometimes the. size of the silicon particles, tending toward'a more 105 rounded form, and the improvement in phys ical properties reduced by the heat-treatment of such change.

The addition to thea-luminum-copper loys, of a small amount of magnesium, say 0.2 or 0.3 per cent increases the tensile strength an elastic limit',but is less favorable to'ductility or elon tion. Magnesium may also be added to t e aluminum-silicon alloys, the effect, generally, being to increase the tensile strength and diminish the elongation.

For the best results, our e. erience indicates thatthe iron content 0 num copper alloy should be low, but if care is taken to make thecastin'gs by the chill method, a higher ercentage of iron can be used, good results eing obtained with chill castings containing even more than 0.4 per cent of iron. Onthe other hand, in the case of heat treated' sand castings, more than thatamount of iron gives less advantageous physical properties. The presence of the iron is evidenced by crystalline oys is due in part to this the alumi- 'tai plaice while the CuAl, is absorbed into the metal can be heated above the melting p y of the solid-solution crystals of aluminum during heat-treatment. The iron needles tend to have a beneficial effect on the physical properties of the alloy-as cast that is before eat-treatment, but after the luAl in the network has been dissolved into the aluminum-rich constitutent by heat-treating, the iron needles are a source of weakness, diminishing both tensile strength and elongation.

' The complete elimination of the iron needles is therefore highly desirable, but the complete avoidance of iron or even its reduction below about 0.25' per cent is not always racticable commercially. However when si icon is resent in excess of the iron the quantity 0 lfeAl, formed is lessened, and some of the iron combines with the silicon to form what appears to be an iron silicide. We have discovered that the latter compound freezes in a form less harmful thanthe needles of FeAl In the case of chill castings, it is found that the FeAl,

needles are much smaller than in the sand castings, and hence. they are not so objectionable in the heat-treated casting. Since there is considerable difliculty in commercially roducing aluminum free from or containing less than 0.25 per cent of iron, the desired silicon-iron relationship is most advantageously obtained by adding silicon when necessary. For example, if the iron.

content of the aluminum ingot is 0.35 per cent and the silicon 0.3 per cent, we nd it advantageous to add about 0.35 per cent silicon. We have also found that the addition of a small quantity of zinc, say 0.25 per cent, improves both the tensile strength and elongation of the heat-treated castings. Chromium up to 0.5 er cent or alittle more increases the tensile strength in the heat-treated casting, but reduces the elontion. With regard to the limits of copper content, we have observed that up to about 2 per cent copper, nearly all the CuAl remains in solution upon solidification, and that beyond 5.5 per cent copper some of "the (hull, usually remains out of solution even after heat-treatment. In some cases tfihe 0 nt of the eutectic of CuAl, and aluminum without impairing its physical properties providedthe metal is cooleqL to a temperature slightly below that of complete solidification and held there for some time before quenching. When substantial percentages of iron, silicon, magnesium and zinc are present, or any of them, the higher permissible temperature is lowered.

A. very important class of alloys embraced by our invention includes the use of silicon in substantial amount, say from 3 to 15 percent, With the silicon class of alloys the bestresults are usually obtained when the castings are made in a chill mold. For example, a chill cast test bar of an alloy contalnin about 10 per cent silicon and no copper s owed a tensile strength around 30,000 pounds per square inch and an elongation of about 7.5 per cent in two inches. After heating at 560 C. for 40 hours, followed by quenching, the tensile strength was about 27,500 pounds per square inch, but the elongation was found to have been increased to 21 able to produce y our method a casting of aluminum-silicon alloy having great ductility and at the same time a tensile stren th twice or more than twice that of aluminum, with the further advantage of cod casting qualities as mentioned above. be addition of copper to this aluminumsilicon alloy increases the tensile strength enormously but decreases the elongation. Chill cast bars of an alloy containing 6 per cent silicon and 4 per cent copper, heated 45 hours at 500 to 515 C. followed by quenching, showed a tensile strength as high as 42,000 pounds per square inch and an elongation of 8 per cent. In the high silicon alloys the most advantageous copper content is from 2 to 5 per cent. should be noted that the eutectic of the aluminum-silicon system melts at 570 to' 580 'C., which is higher than the melting pointof V the aluminum-cop er eutectic which is at 540 C. and there ore it is not only permissible but advantageous to heattreat the former alloys at higher temperatures-say 530 to 570 C. When copper is, added to the aluminum-silicon alloys a ternary eutectic may form with a melting point of abou 520 C. and consequently the eat-treatment tem erature should be lowered accordingly. inc and magnesium also er cent. We are therefore lower the maximum heat-treating temperacent. In case only silicon and zinc are.

present, it is found that the heat treatment I nuracae has a less beneficial effect on the tensile strength, but the elongation is very favorably afi'ected. For example, in an alloy containin 8 per cent silicon and 10 per cent zinc, a 0 ill cast test bar gave a. tensile strength of 29,250 pounds per square inch and an elongation of 4 per cent, whereas after. heat treatment the tnsile strength was 30,500 pounds per square inch and the elon ation had increased to 11 per cent. It is a so found that the heat-treatment 'can be used in conjunction with the process for improving the physical properties of these alloys by the ad ition of alkali metals to the molten allog, as described in the atent of Junius D. dwards, Francis 0. rary and Han V. Churchill, No. 1,410,461,1ssued Mare 21, 1922, on their application Serial No. 426,796, filed November 17, 1920. For example, chill cast test bars of an alloy containing 8 er cent silicon and 10 er cent zinc, to w ch alkali metals were added before pouring, gave an average tensilestrength of over 41,000 pounds per square inch and an elongation of 6.2 per cent in two inches. Heat-treatment reduced the tensile strength to 34,000 pounds per square inch, but increased the elongation to 14 per.

cent.

To obtain the best results it is desirable, in all the above mentioned aluminum-silicon allo s, to keep the iron content low, preferab below 0.6 per cent.

It is ound that the coarser the grain reduced in casting, the longer must the heat-treatment be continued to reduce the most beneficial .result's. Accor ingly sand casting with large cross-sectional areas reuire longer heating than chill castings. suall holding at temperature for about 7 hours is suflicient for chill castings, whereas 24 hours may be necessary with sand casts. In addition to the production of a superior grade of sand castings, permanent 'mold or chill castings (including die castings), the application of our invention is also most important in'connection with the forging and pressing of aluminum allo s. If it is desired to roduce a forging o a given sha e, a casting of suitable composition, sa per cent copper and 0.2 per cent ma esium, is made, preferably in a chill mo (1, and 1S subjected to heat-treatment by our method to produce a'starting material for for ing.

In this case, instead of quenchin from the heat treatment temperature and t en reheatin the article to forging tempewature, we fin it preferable to simply cool slowly from the heat-treatment temperature to the forging temperature. The P1866 is then fin-' ished to size under the presso'r hammer, after which it is given a short heating, say at 520 0., followed by quenching.

of our method depends, in large measure,

other conditions being the same, upon the degree of improvement desired in the physica roperties of the casting.

T e essential thing to be kept in mind is the relatively long time reqmred for east alloys in general, as com ared to those rolled aluminum-copper al oys, known to the priorxhcat-treating art. his is caused, in t e case of the cast copper alloys, by the reater difiiculty in getting the unbroken uAl network into solution in the aluminum, and in the case of the silicon alloys by the slowness of change of form 'of the silicon. In case both copper and silicon are prese "in substantial uantities, time must be allowed for both of these changes to take place to the extent necessary for the desired 1m rovement.

n the copper alloys containing about 4 per cent copper, for example, it is found;

that heating for very long periods, say 48 hours or more, at temperatures only slightly below 500 C. will not, in general, produce as good results as a. five hour treatment at 520 C. In chill castings of the copper alloys it has been found that even two hours heating at 250 0. produced sgbstantially as good results as about 22 hours at 500 C. 11 order to reduce the time to a minimum, we prefer, if suitable temperature control is available, to use as high a temperature as can be safely employed without spoiling the castings by overheating.

We have also found that in the case of alloy containing substantial amounts of silicon, the effect upon the silicon particles is produced more quickly and more completely at relatively high temperatures. In these alloys, heating for about 12 hours at 520 C. produces very substantial improvement, but the time may be extended, with slight additional im rovement, if desired. At a temperature 0 550 to 570 C. the aluminum-silicon alloys may be heattreated with more beneficial results than can be produced at 500 C. or thereabouts.

It is; to'be understood that the invention is not limited; to the' specific details herein described but can be practiced in other ways without departure-from its spirit.

We claim: v

1. In the art of making aluminum alloy castings, .the method comprising prepar' an alloy containing substantial amounts 0 silicon and zinc, casting the allo heating thecastingto a temperature slig tlybelow the melting point of the eutectic, and maintaini such temperature until the silicon partic eshavebeen sufliciently altered to materially improve the physical properties of the cast alloy.

2. In the art of making aluminum alloy castings, the method comprising preparing an, alloy containing substantial amounts of silicon and zinc, casting the allo and causing the silicon therein to take t e form of re atively small particles in the solidfied al- 10y, heating the castin to a tem erature slightly below the melting point 0 the eutectic, and maintaining such temperature until the silicon particles have been sufliciently altered to materially im rove the physical roperties of the cast al 0y.

3. In t 0 art of making aluminum alloy castings, the method comprising preparin an alloy containing substantial amounts 0 silicon and zinc, chill casting; the alloy whereb the silicon is caused to take the form 0 relatively small particles in the solidified allo heatin the castin to a tern-- perature slightly be 0w the me ting point of the eutectic, and maintaining such temperature until the silicon particles have been sufliciently altered to materiall improve the physical roperties of the a 0y.

4. In t e art of making aluminum alloy castings, the method comprising preparingan alloy containing 3 to 10 per cent silicon and 5 to 15 per cent zinc, casting the alloy, heating the casting to a temperature slight- 1y below the rneltin point. of the eutectic, and maintaining sue temperature until the silicon particles have been sufficiently altered to materially im rove the physical properties of the cast al 0y.

5. In the art of making aluminum alloy castings, the method comprising preparin an alloy? containi substantial amounts 0 silicon, copper an zinc, casting the alloy, heating the casting to a temperature slight ly below the meltln point of the eutectic, and maintaining sue temperature until the silicon particles have been sufficiently al tered and a suflicient amount of the intergranular copper-rich constituent has been dissolved to materially improve the physical properties of the cast alloy.

, silicon,

6. In the art of making aluminum alloy castings, the method comprising preparin an alloy containi substantial amounts 0 silicon, copper an zinc, casting the alloy, and causing the silicon therein to take the orm of relatively small particles in the solidified allo heating the casting to a temperature slig tly below the melting point of; the eutectic, and maintaining such tem perature until the silicon particles have been sufficiently altered-and a suflicient amount of the inter-granular copper-rich constituent has been dissolved to materially improve the physical roperties of: thecast alloy.

7. In e art of aluminum alloy castings, the method comprising preparing an alloy containing substantial amounts 0 copper an zinc, casting the alloy, heating the casti at a temperature slightlybelow the'meltinguntil the silicon particles have been sulfian alloy containin point of the eutectic all ciently altered and a suflieient amount of the inter-granular copper-rich constituent has been dissolved to materially im rove the physical properties of the cast loy, and cooling the castin rapidly.

S. In the art 0 making aluminum alloy castings, the method comprising preparing substantial amounts 0 silicon, copper an zinc, casting the alloy and causing the silicon therein to take the form of relatively small' articles in the solidified "alloy, heati e casting at a temperature slightly low the melting point? of the eutectic until the silicon particles have been sufliciently altered anda sufficient amount of the inter-granular copperrich constituent has been dissolved to materially improve thel hysical properties of the cast alloy, and cooling the casting rapidly.

9. In the art of making aluminum alloy castings, thegmethod com rising preparing an ,alloy containing 3 to 1 per cent silicon, 2 to 5.5 {per cent copper, and 5 to 15 er cent zinc approximately, casting the al oy, heating the casti to a temperature slight ly below the melti point of the eutectic, and maintaining suc temperature until the silicon particles have been siliciently altered and a sullicient amount of the interranular copper-rich constituent has been ties of the cast al 0?. p

10. In the art 0 making aluminum alloy castings, the method comprising preparing an alloy containing substantial amounts of issolved to materially rove the physical proper the cast a 0y, and cooling the casting rapidly.

11. In the art of making aluminum alloy castings, the method comprising preparing an alloy containing 3 to 10 per cent silicon, 2 to 5.5 per cent copper, and 5 to 15 er cent zinc, approximately, casting the al oy and causing the silicon therein to take the form of relatively small particles in the solidified alloy, heating the casting to a temperature slightly below the meltin point of the eutectic, and maintaining such temperature until the silicon articles have been sufliciently altered an a sufficient amount of the inter-granular copper-rich constituent has been dissolved to. materially improve the physical properties of the cast 0y. 12. In the art of making aluminum alloy castings, the method comprising preparing an alloy containiiw substantial amounts of silicon, copper an zinc, casting the alloy, heating the casting to a temperature slightly below the melting point of. the eutectic, maintaining such temperature until the silicon particles have been sufficiently altered and a sufliuent amount of the inter-granular coppei rich constituent has been dissolved to materially improve the physical properties of the cast alloy, and rel-heating the casting at a relatively low temperature to increase the tensile strength of the alloy.

13. In the art of making aluminum alloy castings, the method comprising preparing an alloy containing substantial amounts 0 silicon, copper and zinc, casting the alloy and causing the silicon therein to take form of relativley small particles in the solidified alloy, heating the casting at a tern Jerature slightly below the melting point 0 the eutectic until the silicon particles have been sufliciently altered and a sullicient amount of the inter-granular copper-rich constituent has been dissolved to materially improve the physical properties of the cast alloy, cooling the casting rapidly, and reheating the casting at a relatively low temperature to increase the tensile strength of the alloy ,14. As a new article of manufacture, a heat-treated casting of an aluminum alloy containing zinc,'and containing silicon in amount between 3 and 15 per cent, characterized by the silicon being in the form of small finely dispersed more or less rounded particles and substantially devoid of large plates and needles of silicon, withconsequent high tensile strength and elongation.

15. As a new article of manufacture, a heat-treated castin of an aluminum alloy containing zinc an substantial amounts of silicon and copper, characterized by the silicon befiig in the form of a small finely dispersed more or less rounded particles and substantially devoid of large ,silicon plates or needles and of undissolved inter-granular copper-rich constituent, with consequent high'tensile strength and elongation.

16. As a new article of manufacture, a

heat-treated casting of an aluminum alloy containing zinc and silicon and a substantial amount of copper, and having a low iron content, characterized by the substantial absence of undissolved inter-granular copperrich constituent, and having high tensile strength and elongation.

17. As a new article of manufacture, a heat-treated casting of an aluminum alloy containing zinc and 3 to 15 per cent silicon, containing between about 2 and 5.5 per cent of copper, and havinga low iron content; characterized by the silicon being in the form of small finely dispersed moreor less rounded particles and substantially devoid of large plates and needles of silicon, with consequent high tensile strength and elongation.

18. As a new article of manufacture, a heat-treated and artificially aged casting of an aluminum alloy containing zinc and substantially amounts of silicon and copper, characterized by the silicon being in the form of small finely dispersed more or less rounded particles and substantially devoi of large silicon plates or needles and of undissolved inter-granular copper-rich constituent, with consequent high tensile strength and elongation. I

In testimony whereof we hereto afiix our signatures. ZAY J EFFRIES.

ROBERT S. ARCHER.

and causing comprising preparing an alloy containiiw substantial amounts of silicon, copper ant zinc, casting the alloy, heating the casting to a temperature slightly below the melting point of the eutectic, maintaining such temperature until the silicon particles have been sufiiciently altered and a sufi'nlent amount of the inter-granular copper rich constituent has been dissolved to materially improve the physical properties of the cast alloy, and re-heating the casting at a relatively low temperature to increase the tensile strength of the alloy.

13, In the art of making aluminum alloy castings, the method comprising preparing an alloy containing substantial amounts of silicon, copper and zinc, casting the alloy the silicon therein to take form of relativley small particles in the solidified allo heating the casting at a temperature slig tly below the melting point of the eutectic until the silicon particles have been sufliciently altered and a suilicient amount of the inter-granular copper-rich constituent has been dissolved to materially improve the physical properties of the cast alloy, cooling the casting rapidly, and reheating the casting at a. relatively low temperature to increase the tensile strength of the alloy ,14. As a new article of manufacture, a heattreated casting of an aluminum alloy containing zinc,'and containing silicon in amount between 3 and 15 per cent, characterized by the silicon being in the form of small finely dispersed more or less rounded particles and substantially devoid of large plates anl needles of silicon, withleonsequent high tensile strength and elongation.

15. As a new article of manufacture, a heat-treated casting of an aluminum alloy containing zinc and substantial amounts of castings, the method siliconpnd copper, characterized by the silicon being in the form of a small finely dispersed more or less rounded particles and substantially devoid of large ,silicon plates or needles and of undissolved inter-granu lar copper-rich constituent, with consequent hightensile strength and elongation.

16. As a new article of manufacture, a heat-treated casting containing zinc and silicon and a substantial amount of copper, and having a low iron content, characterized by the substantial absence of undissolved inter-granular copperrieh constituent, and having high tensile strength and elongation.

17. As a new article of manufacture, a heat-treated casting of an aluminum alloy containing zinc and 3 to 15 per cent silicon, containing between about 2 and 5.5 per cent of copper, and having a low iron content; characterized by the silicon being in the form of small finely dispersed moreor less rounded particles and substantially devoid of large plates and needles of silicon, with consequent high tensile strength and elongation.

18. As a new article of manufacture, a heat-treated and artificially aged casting of an aluminum alloy containing zinc and substantially amounts of silicon and copper, characterized by the silicon being in the form of small finely dispersed more or less rounded particles and substantially devoid of large silicon plates or needles and of undissolved inter-granular copperich constituent, with consequent high tensile strength and elongation.

In testimony whereof we hereto affix our signatures.

ZAY J EFFRIES. ROBERT S. ARCHER.

Certificate of Correction.

' t is hereby 192 on the a )lication of Zay'Jeffries of Lakewood,

appear in the printed specification requiring T Gambian-$37, 19930.; same page,

9, for the mispelled word for November 17, 1920 read A 02 read 520; page 6, line 94, ,auficiently; page 7, line 43, cla

a same page, line and that the said the same may conform Signed and sealed this 9th day of ifsmu] to the record of 5, after the wen? 71, claim 18, for the Word Letters Patent should be read the case in March,'A. D. 1926.

certified that in Letters Patent No. 1,572,488, granted February 9,

of Shaker Heights and in, for an improvement in Aluminum-ilicon Alloys, errors Robert S. Archer,

correction as follows: Page 5, line 19, line, 94, for 250 Sfiiciently read 8* of strike out/the article antially read substantial; with these corrections therein that the Patent Olfice.

M. J. MOORE, Actmg of Patents.

.sufziciemly; page 7, line 43, ch

Certificate of Correction.

It is hereby certified that in Letters Patent No. 1,572,488, granted February 9, 1926qgpn the a plication of Zay'Jeffries, of Shaker Heights, and Robert S. Archer, of Lakewood, hio, for an improvement in Aluminum-Silicon Alloys, errors appear in the printed specification requiring correction as follows: Page 5, line 19, for November 17, 1920 read N mbei' i', 7990.; same page, line, 94, for 250 read 520; page 6, line 94, 9, {or the mis elled word sificiently read 5, after the of strike out the article a same page, line 71, claim 18, for the word slit 'antially read substantzhl; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 9th day of 1\[arch,'A. D. 1926.

issue] M. J. MOORE,

Acting of Patents.