US2293864A - Aluminum base alloy - Google Patents

Description

atented Aug. 25,

ATENT oF icE ALUMINUM BASE ALLOY Philip '1. Stroup, New Kensington, Pa., assignor to Aluminum Company of America, Pittsburgh, 1%., a corporation of Pennsylvania No Drawing. Appiication September 19, 1939, Serial No. 295,644

5 Claims. (Cl. 75-142) Aluminum base alloys containing substantial amounts of magnesium have recently enjoyed wide use because of their desirable fabricating characteristics, high mechanical properties, and

excellent resistance to corrosion. These alloys, however, have the disadvantage that when they are in a molten state, some of the magnesium alloying constituent tends to burn out of the alloy by. combining with oxygen, nitrogen, and atmostheir oxidation.

, I have found that the formation. of the above described crust of dross upon the surfaces of molten aluminum base alloys containing appre ciable amounts of magnesium may substantially be prevented by the addition of a very small amount of beryllium and lithium to such alloys.

These alloys containing beryllium and lithium may be handled in the manner usually followed in foundries, it being unnecessary to use a protective' atmosphere or a covering flux to prevent My invention, accordingly, consists in the utilization of this discovery to prevent formation of dross and the attendant loss of pheric moisture, especially when the alloy. is-

maintained for a considerable period of time in the molten condition. Under ordinary circumstances, a black nodular dross formation appears upon the molten alloy which, upon continued heating, changes to a white porous crust containing a considerable amount of entrapped metal.

For the purpose of convenience, this formation of dross is considered to be the result of oxidation. In addition to the-magnesium which is lost by oxidation and inclusion in this crust of dross, added amounts of magnesium are lost from the molten alloy when the dross is skimmed or otherwise removed from the metal. Further, the presence of any substantial amount of dross in the molten alloy tends-to make the metal sluggish and less -fluid, rendering casting of the alloy more diflicult since the metal "does not properly fill the molds and sincenon-metallic'inclusions may be introduced into the casting during the pouring operation.

One of the principal objects, then, of this in vention is to minimize the loss of magnesium from molten aluminum base alloys containing this element. A further object is to prevent the formation of the crust of dross which ordinarily forms upon the surfaces of aluminum base alloys containing magnesium. An additional object of the invention is to provide a means for dispensing with protective fluxes and inert atmospheres heretofore considerednecessary in melting aluminum base alloys containing magnesium. An-

other object is to provide an aluminum base alloy venient means readily adaptable to prevailing plant practices. Other objects will appear in the following description of the invention.

metal from molten aluminum base alloys containing magnesium.

For the purposes of my invention, only very small amounts of beryllium and lithium need be added to the alloy, from about 0.001 per cent to about 0.02 per cent of each of these elements being suflicient. The total amount of beryllium and lithium, however, should not exceed about 0.03 per cent of the alloy. I generally prefer to use equal parts of each of these elements in the alloy, but it may be desirable to increase the amounts of lithium and to decrease the amounts of beryllium, which is the more expensive of the two elements, while, of course, maintaining the total amount ofthese elements used in the alloy within the ranges indicated .above. These amounts of beryllium and lithium, while small, serve to render the alloys resistant to oxidation and thus substantially prevent dross formation and loss of magnesium content from aluminum.

base alloys containing from 1 per cent to per cent magnesium. Additions of these elements are particularly beneficial commercial alloys which contain magnesium in amounts from about 1 per cent to about 15' per cent, and especially in alloys which comprise from about 4 per cent .to about 12 per cent of magnesium. Since formation of dross does not. present a serious problem in the melting of aluminum base alloys containing less than 1 per cent of magnesium; there is little need for application of my invention to these alloys. As for the amounts of beryllium and lithium which maybe added to these alloys, I have found that at least a total of 0.0005 per cent of these elements should be present in order to impart the desirei beneficial effect to the molten alloys, and in the preferred practice of my invention 1 recommend the use of 0.001 per cent to 0.02 per cent each of beryllium and lithi alloys in their molten state and may even cause an increase in the amount of dross formation and,

it is relatively fluid and eifectively fills the mold .without introducing non-metallic inclusions into the casting.

The desired amountoi' beryllium and lithium may be added to the alloy in any convenient manner. For example, it may be added in the form of metallic beryllium and lithium, or as a rich aluminum-beryllium-lithium alloy. ever, I prefer to add the beryllium and lithium to the alloy by the decompositionof compounds of these metals.

While the presence of beryllium and lithium has beneficial effects ,upon binary aluminum base alloys containing various amounts of magnesium, Ihave found that it is also advantageous to use these elements in alloys containing magnesium with additional ingredients. For example, from 0.1 to 5 per cent copper, or from 2 to 14 per cent zinc, or from 0.3 to 5 per cent silicon, or combinations of these elements may be present in the alloy along with the magnesium. In addition, the alloy may contain small amounts of on or more of a group of insoluble metals which serve to increase the hardness of the alloy. These include manganese, chromium, titanium, vanadium, molybdenum, tungsten, zirconium, uranium, nickel, boron, and cobalt. These elements may be employed individually in the following amounts: manganese 0.1 to 2 per cent; chromium 0.1 to 0.5 per cent; titanium 0.01 to 0.5 per cent; vanadium 0.1 to 1 per cent; molybdenum 0.1 to 1 per cent; tungsten 0.1 tol per cent; uranium 0.1 to 1 per cent; zirconium 0.05 to 1 per cent; nickel How-' 0.1 to 2 per cent; boron 0.01 to 0.1 per cent; and.

cobalt 0.1to 2 per cent. The total amount of these hardening elements should in no case exceed about 2 per cent of the composition of the alloy. Since magnesium is susceptible to oxidation regardless of the presence of the above elements in the molten alloy, the addition of berylliumand lithium effectively prevents dross formation 'and magnesium losses in any of these magnesium-containing aluminum base alloys.

- being aluminum.

of beryllium and lithium seems to have no 'appref and lithium being added to the other portions as indicated in the table below. Samples were taken from each alloy prior to the soaking period to determine the exact magnesium content. These melts then were held, or soaked, at a temperature between 1400 and 1500 F. for a period of about 6 hours in order to simulate the most severe conditions sometimes encountered in foundry practice and to promote the formation of dross. While the melts were held at this temperature, substantial amounts of dross only appeared upon the surface of the alloy which contained no beryllium and lithium. After the soaking period, all of the melts were cast in molds and subsequently analyzed to determine the magnesium content of the alloys after soaking at the elevated temperature as compared to the amount of magnesium which they had contained prior to this soaking treatment. The following table summarizes the results of the tests.

The above table indicates that a considerable amount of the magnesium content was lost from the alloy which contained no beryllium and lithium, whereas but slight losses occurred during the soaking period in the alloys containing those elements. Under less severe conditions than usually obtain in commercial operations, the losses are smaller; however, even losses of the magnitude shown above in the beryllium-lithium-containing alloys would be permitted in practice. Moreover, the alloys which contained beryllium and lithium did not acquire a black nodular crust such as formed upon the beryllium and lithium-free alloy during the soaking period, and the surfaces of the castings of the beryllium and lithium-containing alloys were clean and attractive as compared with the dull appearance of the alloys which had not been treated with beryllium and lithium. The term aluminum as herein employed relfers to aluminum as commercially produced, and the term aluminum base alloy" refers to those alloys containing at least 50 per cent aluminum regardless of whether the alloy is binary, ternary or of .a more complex character.

I claim:

1. An aluminum base alloy containing from 1 to 15 per cent magnesium and from 0.001 to 0.02 per cent beryllium and from,0.00l to 0.02 per cent lithium, the total amount of said beryllium and lithium not exceeding about 0.03 per cent, and from 0.1 to 5.0 per cent copper, the balance 2. An aluminum base alloy containing from 1 to 15 per cent magnesium and from 0.001 to 0.02 per cent beryllium and from 0.001 to 0.02 per cent lithium, the total amount of said beryllium and lithium not exceeding about 0.03 per cent, and from 2.0 to 14.0 per cent zinc, the .balanc being aluminum.

3. An aluminum base alloy containing from 1- to 15 per cent magnesium and from 0.001 to 0.02

'per cent beryllium and from 0.001 to 0.02 per cent lithium, the total amount of said beryllium and lithium not exceeding about 0.03 per cent, and

from 0.3 to 5.0 per cent silicon, the balance being aluminum.

4. An aluminum base alloy containing from 1 to about 15 per cent magnesium and from about 0.001 to 0.02 per cent beryllium and from 0.001

- to 0.02 per cent lithium, the total amount of said beryllium and lithium not exceeding about 0.03

' per cent, said alloy being characterized by a higher resistance to oxidation in the molten 0011-,

ditiont athan characterizes an alloy of the same I0 composition but devoid of said amounts of beryllium and'lithium, said higher resistance being attributable substantially to said beryllium and lithium content and said alloy being devoid of elements materially subversive to the aforesaid effect of the beryllium and lithium content.

' not exceeding about 0.03 per cent.

PHILIP 'r. mow.