US2148151A - Copper alloy - Google Patents

Description

Patented Feb. 21, 1939 UNITED STATES COPPER ALLOY Ernest R. Darby, Detroit, Mich, alsignor to Federal-Mogul Corporation, Detroit, Mich, a corporation of Michigan No Drawing.

2 Claims.

My invention relates to a copper alloy. It has to do particularly with copper alloys designed for use in the making of cylinder heads and other parts for internal combustion engines, although 5 such alloys are not necessarily limited to this use.

In the prior art, cylinder heads for internal combustion engines have been made from copper alloys wherein the copper constituted the major ingredient and had, associated therewith, chromium and silicon. The silicon was introduced mainly as a deoxidizing agent while the chromium served advantageously as a hardening agent and as an agent which rendered the alloy subject to a precipitation hardening treatment for increasing the conductivity as well as the hardness. The silicon had the further function of combining with the chromium to form a silicide which, like chromium alone, was relatively insoluble at low temperatures but would enter into solution "with the copper at high temperatures and, upon dropping to the precipitation hardening range, would be precipitated out with a resultant increase in conductivity and strength of the alloy. The silicon tended to increase the fluidity of the metal to some extent by virtue of its deoxidizing powers so that casting of the metal was facilitated. However, the permissible amount of silicon is severely limited because of the fact that excess silicon enters into solution with the copper and lowers the conductivity of the resultant product and possibly the hardness thereof.

One of the objects of this invention is to provide a copper-rich alloy containing chromium and having a degree of fluidity higher than such alloys wherein silicon is utilized as a deoxidizing agent.

Another object of this invention is to provide a copper-rich alloyfor use in such fields as the making of cylinder headsand other parts for automotive engines and the like, which copper-rich alloy may be subjected to precipitation hardening so that the ultimate product will have a rel- Another object of this invention is to provide a deoxidizing agent which may be used in excess of the amount required for deoxidation and which by its nature will result in an increase in fluidity over and above the increase in fluidity resulting from the deoxidation.

Phosphorus is commonly used as a deoxidizing agent for copper, to which other materials are to be added. However, the ordinary practice in the use of phosphorus as a deoxidizing agent has been to introduce it in such amounts that the residual proportion remaining in the melt after deoxidation does not exceed .01 or .02 per cent. The general belief has been that the use of higher percentages of phosphorus in the deoxiatively high conductivity and adequate hardness.

Application September 4, 1936, Serial No. 99,431

mally be expected in view of the general recog-7 nition that the use of percentages over the aboveindicated amounts for deoxidation of copper results in marked decrease of conductivity. Thus, I have found that the behavior of phosphorus in a copper-rich copper-chromium-phosphorus alloy is such that it may be used in percentages substantially in excess of the above-indicated percentages, with the result that, in addition to the deoxidation of the copper'whlch is effected by the phosphorus, the fluidity of the melt is greatly increased so that casting can be effected much more readily without drosslng and with a consequently marked decrease in the scrap loss resulting from the casting operation. I have also found that when the percentage of phosphorus bears a proper relation to the chromium content of thecopper-chromium-phosphorus alldy, effective deoxidation and high fluidity are attained and, in addition, the product will be of such a nature that it may have its conductivity and hardness markedly improved by heat treatment, such as precipitation hardening.

.More specifically, my tests to date show that in making a copper-chromium-phosphorus alloy wherein the phosphorus content ranges from .01 to .1 per cent while the chromium content is in the neighborhood of .4 per cent or over, with the balance copper, substantially complete deoxidation is effected, which in itself increases the fluidity of the melt. In addition, the phosphorus content over and above that normally considered for deoxidation additionally increases the fluidity of the melt to a marked extent so that the melt thus formed may be readily cast with much less drossing and much less scrap loss than is possible in the casting of a copper-rich copper-chromium alloy wherein silicon has been used as a deoxidizing agent. Also, with the percentages of phosphorus and chromium specified, my tests indicate that, while a portion of the chromium reacts with the phosphorus to form a compound, there is an excess of chromium which appears in the product as such, which upon proper heat treatment will enter into solid solution with the copper and which upon further heat treatment in accordance with the well known principles of precipitation hardening will be precipitated out to form an ultimate product having unusually high conductivity and adequate strength for use in cylinder heads, engine parts and other products wherein high conductivity and strength are desirable.

In thepractice of my invention, the copper is melted to approximately the proper casting temperature and, in the course of this melting op eration, and while the bath of copper is covered with a layer of charcoal, I preferably introduce the full percentage of phosphorus. This phos-.

chromium is fully dissolved and the melt is brought to the proper pouring temperature which will, of course, vary somewhat with the article to be produced.

Although I do not desire to be bound by theories, it is believed that the reaction which takes place consists in the formation of chromium phosphide which goes into solution with the melted copper but which separates out upon the solidification of the melt. Micrographic examinations of the solidified product show a copper background having dispersed therethrough particles which are apparently chromium phosphide. Upon heating the solid alloy to a temperature at which chromium normally goes into solution with the copper, these particles do not enter into solution with the copper which indicates that their solubility is extremely low. It is difiicult to detect the excess chromium by micrographic examination. However, chemical analysis indicates that with the percentages specified above the indissoluble particles are compounds of chromium and phosphorus and that substantial amounts of excess chromium are present in the alloy.

Upon heating the solidified product to a temperature in the neighborhood of 1700 F., the excess chromium apparently goes into solid solution with the copper while the particles which are presumably chromium phosphide do not. Upon thereafter quenching in water and then dropping to a temperature from 850 to 950 F. and holding at this temperature .for a period ranging from 1 hours to 20 hours, depending upon the temperature used, the excess chromium is apparently precipitated out in a manner characteristic oi the usual precipitation hardening processes.

Comparative tests to determine the conductivity of my precipitation hardened copperchromium-phosphorus alloy and of copper-chromium alloys which have been deoxidized by the use of silicon with the silicon constituting not over to of the chromium content show that my copper-chromium-phosphorus alloy when made by usual practices can be given a conductivity of from to per cent of that of pure copper whereas thecopper-chromium alloy made with silicon according to usual practices ordinarily has a conductivity lower than 80 per cent of that of pure copper. In actual tests to date, I have obtained a product having a conductivity of 88 per cent of that of pure copper. That satisfactory hardness is attained, is shown by the fact that my alloy which had an 88 per cent conductivity had a Brinell hardness of over 100, which is'amply adequate. Y

My investigations to date give a sound basis for the belief that the results attainable with my invention may be obtained by the use of .01 to .2 per cent phosphorus and from .25 to 2 per cent chromium and an alloy containing P centages of phosphorus and chromium within these ranges is within the scope of my invention.

During the course of my tests in connection with this invention, I have utilized iron as a substitute for the phosphorus and-found that it has a somewhat similar behavior. For example, one of my tests involved the making of a copper-rich copper-chromium-iron alloy wherein .15 per cent of iron was used with approximately from .4 to .5 per cent chromium. The iron acted as a deoxidizing agent. It also reacted with the chromium to form an intermetallic compound which was soluble in the melt. When the alloy solidified, there appeared to be a background of copper having dispersed therethrough particles. formed of intermetallic compounds of iron and chromium, while chemical analysis indicated that the alloy also contained excess chromium. Upon subjection to precipitation hardening treatment, the conductivity of the alloy was about the same as a similarly made copper-chromium alloy that had been deoxidized with silicon.

It is within the scope of my invention to produce a copper-rich alloy containing either phosphorus and chromium or iron and chromium together with small percentages of either silver, cobalt, iron, zirconiumor nickel in amounts up to .2 per cent. In some cases, these metals will serve as a substitute for a portion of the chromium so that smaller percentages of chromium can be used without detracting from the ability of the alloy to yield high conductivity values upon heat treatment.

It will be seen from the above that I have produced a superior alloy with markedly increased fiuidity and castability. I have likewise found that this alloy is superior from the standpoint of soundness and, as indicated above, this alloy may be caused to have unusually high conductivity and ample hardness for use in the preferred field specified.

Having thus described my invention, what I claim is:

1. A copper base alloy consisting of from .01 to .2 per cent of phosphorus, from .25 to 2 per cent of chromium, and the balance substantially all copper, the phosphorus being present in an amount exceeding that required to deoxidize the copper, the phosphorus content and the chromium content being so adjusted relative to each other that the said excess of phosphorus reacts with a portion of the chromium to form chromium phosphide and that an excess of chomium remains as such in the alloy, the alloy being precipitation-hardened, the alloy having a conductivity at least 80 per cent that of pure copper and having a Brinell hardness in excess of 100.

2. A cylinder head for internal combustion engines composed of a copper base alloy consisting of from .01 to .2 per cent of phosphorus, from .25 to 2 per cent of chromium, and the balance substantially all copper, the phosphorus being present in an amount exceeding that required to deoxidize the copper, the phosphorus content and the chromium. content being so adjusted relative to each other that the said excess of phosphorus reacts with a portion of the chromium to form chromium phosphide and that an excess of chromium remains as such in the alloy, the alloy being precipitation-hardened, the alloy having a conductivity at least 80 per cent that of pure copper and having a Brinell hardness in excess of 100.

ERNEST R. DARBY.