US1920963A - Process of improving aluminum and alloys thereof - Google Patents

Description

Patented Aug. 8, 1933 PROCESS OF IHWPROVING ALUMNUM ALLOYS THEREOF Walter Bonsack, Cleveland, Ohio, assignor to The National smelting Company, Cleveland, Ohio,

a Corporation of Ohio No Drawing.

Application September 4, 1930,

Serial No. 479,789. Renewed October 21, 1932 12 Claims. (Cl. 75-58) This invention relates to aluminum and alloys thereof, and more particularly to an improved process for imparting desirable characteristics to such metals and is an improvement of the process generically described and claimed'in my copending application, Serial No. 479,790, filed on September 4, 1930.

An object'of my invention is to provide an improved'process for treating aluminum and alloys thereof to improve their characteristics.

A further object of the invention is to provide a simple, effective, inexpensive, more exact and more rapid process for introducing boron into molten aluminum and alloys thereof.

Another object of this invention is to provide an improved process for treating aluminum and alloys thereof with boron, whereby the treated metal will exhibit superior properties for casting, forging, rolling, drawing, extrudin welding and other purposes.

An additional object of theinvention is to provide an improved method of treating aluminum and alloys thereof to impart improved characteristics thereto, which treatment-may accom-i pany the fluxing of the molten metal and require no additional steps or equipment.

Anotherobject of the invention is to provide an improved method of treating aluminum and alloys thereof with boron to impart improved casting properties thereto, such as better mold filling characteristics in sand and metal molds,

, uniform and fine grain structure and homogeneous characteristics, with substantial reduction of porosity andshrinkage cracks.

A further object of my invention is to provide an improved and simple process for treating aluminum and alloys thereof with boron to impart to such metals improved characteristics which are relatively permanent and do not disappear upon remelting the treated metal, or upon overheating molten treated metal.

Another object of my invention is to provide a process of producing boron in contact with aluminum or alloys thereof at a greatly accelerated rate, which boron may enter said aluminum or alloy thereof to improve its characteristics.

Another object of this invention is to provide a simple and convenient process for treating aluminum and light alloys thereof with boron to obtain a substantially permanent refinement of grain sizeand improvement of physical and mechanical properties of the treated metal.

A further object of the invention is to provide an advantageous method of treating secondary aluminum and alloys thereof to impart to such metal advantageous characteristics for casting and other purposes.

Another object of my invention is to provide an improved rapid method of imparting substantially permanent improvement with respect to grain refinement and physical and mechanical properties to aluminum and alloys thereof by the treatment thereof with boron in a solid, non-metallic form.

A further object of this invention is to provide an improved method of treating aluminum and alloys thereof with boi'bn to impart relatively permanent improvement in physical and mechanical characteristics, which method may be carried out by the use of boron in an inexpensive and readily available form and which may be carried out at relatively low temperatures and in shorter time than previously attained.

Other objects of the invention will be apparent to those skilled in the art from the disclosures herein made.

Fine grain size and uniform dispersion of alloy constituents are extremely desirable in aluminum and light alloys thereof. The desirability of fine uniform grain size throughout the cross section of all typesof castings made from such metals is apparrit'sTurthermore, the presence of a fine, uniform grain size is very desirable in various aluminum alloys which are to be forged, rolled, welded, or used for other purposes. Such fine grain structure of aluminum and aluminum alloys in general has not been obtainable in the past until the discovery that treatment of aluminum or aluminum alloys in molten condition with boron under proper conditions would impart properties .to the molten metal such that, upon solidification, a marked grain refinement of the aluminum and alloyed constituents occurred.' It was found. moreover, that such improvement of the aluminum or aluminum alloy was relatively permanent in that the treated metal exhibited marked grain refinement and improved physical and mechanical properties even after repeated melting and solidification. However, the previous methods of treating aluminum and aluminum alloys with boron to accomplish the desired improvement of the metal have been relatively complicated, difficult and expensive. My invention, on the other hand, contemplates an inexpensive, simple and more effective method of treating aluminum and alloys thereof with boron which may be carried out in relatively short times and at relatively low temperatures to effect a substantially-permanent improvement of,physical no and mechanical properties.

The more common boron compounds, such as aluminum to form metallic boron and aluminum oxide. For example, I have found that if boric oxide is disposed on the surface of a bath of molten aluminum and the aluminum maintained in molten condition at approximately 900 degrees C. for about an hour and then allowed to solidify without pouring, a deposit of crystalline metallic boron is found on the surface of the aluminum. This reaction between the boron compound and the aluminum, which results in the production of metallic boron and aluminum oxide, proceeds relatively slowly, due to the high viscosity of the melted boron compound and also due to the deficient ability of said boron compound to dissolve the aluminum oxide resulting from the reaction.

I have discovered that the reaction between a boron compound and molten aluminum will take place much more rapidly and at considerably lower temperatures if the boron compound be dissolved in a molten flux which is also capable of dissolving the aluminum compound or compounds resulting from the reaction. Under these conditions the boron compound is in a much more reactive state, and can react more readily with the molten metal with which the flux is in contact, and the metallic boron produced by the reaction can more readily diffuse into the molten metal. Furthermore, the solution of the aluminum compound or compounds resulting from the reaction, and the diffusion thereof into the flux and the consequent removal of said aluminum compound or compounds from the contacting surface of the flux and the molten metal where, according to my present opinion, the reaction takes place, greatly assists in causing the reaction to go forward more rapidly to substantial completion.

The invention contemplated by this application is the further acceleration of the production of boron by the use of suitable alloying constituents in connection with the aluminum or aluminum alloy bath. Thus, I have found that if relatively small amounts of one or more of certain metals be alloyed with the aluminum or aluminum alloy, the boron compound will react preferentially with such alloying constituent and produce boron more rapidly than by the corresponding reaction with aluminum. In such case, the alloying constituent, for example, magnesium, reacts with the boron compound and reduces the same, forming metallic boron. Since the alloying constituents which I employ have a greater tendency to oxidize than aluminum and produce more exothermic heat as the result of the reaction with the boron compound, the pro-. duction of metallic boron takes place more rapid- 1y and/or at lower molten bath temperatures than would otherwise be the case. To further increase the rate of reaction I prefer to agitate the molten metal and flux, whereby the contacting surfaces of flux and molten metal are greatly increased.

The accelerator metal may be any one of a relatively large group represented principally by the alkali or alkaline earth groups. -I have found calcium and magnesium to give the best results as an accelerator, but the other accelerator metals to be hereinafter mentioned may also be employed with satisfactory results. Thus, besides calcium and magnesium, I may employ any one or more of the following metals: Sodium,

potasium, barium, strontium, lithium, thorium, or beryllium. In general, I may employ as accelerator any metal whose reaction with a boron compound produces more exothermic heat than the corresponding reaction between the same boron compound and aluminum. It will be understood, of course, that one or more accelerator metals may be employed for the purposes at hand. Ordinarily, I find that the presence of the accelerator in the molten bath in amount from 0.01 to 3 percent to be satisfactory to accomplish the modification of the molten bath. The specific percentage will depend somewhat on the nature of the alloy to be modified, as will be obvious to those skilled in the art. An excess of the accelerator metal is ordinarily not harmful, unless the presence of the accelerator metal in the finished product is not desired.

The boron material, wherewith my invention is carried out and which is incorporated in a suitable flux coating, may comprise one or more of a large variety of boron compounds. For example, I have found boric acid, borax, boron oxide and calcium boride to be very satisfactory. Alkali, alkaline earth, and other borates, boron sulphide, boron phosphate, boron nitride and boron carbide likewise may be employed. Furthermore, double salts may be successfully used, such as ammonium boro-fluoride and potassium borofluoride. The above boron compounds are merely illustrative. In general I have found most solid and many liquid inorganic boron compounds tion. The boron material is preferably present in appreciable amount up to 1% perecent by weight of the metal bath. I have employed boron compounds in amounts as low as a small fraction of one percent with satisfactory results. If desired, boron compounds in excess of 1 percent may be used It will be understood that the boron compound may be introduced into the flux covering after the flux is melted, or may be incorporated with the flux materials in making up the flux.

The flux with which the molten metal bath is covered during the carrying out of my invention and into which the boron material is introduced maybe of widely varying composition, the requisites being that it be molten and not too volatile at the temperature of the metal bath, and that said flux be capable of dissolving the particular boron compound being used, and of dissolving aluminum oxide, and compounds formed by the reaction of the boron compound and accelerator metal. The flux preferably has a melting point relatively close to that of the metal, in order that the molten bath need not be heated too highly. Thus, I have found a flux consisting of potassium chloride, sodium chloride, cryolite and calcium fluoride to be very satisfactory. I have also employed a flux consisting of.calcium chloride with good results. Moreover, many other fluxes having characteristics outlined above may be employed. For the purpose of this invention the fluxes preferably should be present in appreciable amounts up to 3 percent by weight of the metal bath. I have employed fluxes in amounts as low as a fraction of one percent with satisfactory results- If desired, flux in amounts in excess of 3 percent may be used.

In carrying out my invention, .the aluminum or aluminum alloy, with which the accelerator metal has been suitably alloyed, is maintained in molten condition. The boron material, conthe flux has been associated with the molten bath. The metal bath containing the alloyed accelerator metal preferably is maintained at relatively low temperatures and need not be heated to temperatures much more than 100 degrees C. higher than the melting point thereof. In many cases I have carried out the invention at temperatures relatively close to the melting point of the metal bath and less than 100 degrees C. higher than the same. The metal bath and flux may be agitated for a short time, and may then be permitted to stand longer before pouring, if desired.

The result of the reaction between the boron compound or compounds and the accelerator metal of the bath, as previously stated, I believe to be the formation of finely divided metallic boron, which boron becomes disseminated throughout the metal of the bath. While the mechanism whereby the aluminum or aluminum alloy is improved by the boron is not definitely known, it is believed that during solidification boron forms a very large number of crystal nuceli throughout the molten bath, resulting in the growth of a very large number of relatively small crystals of aluminum and alloyed constituents rather than a small number of relatively large crystals.

By way of specific example, I have carried out my invention as follows: An alloy consisting of 92 parts by weight of aluminum and 8 parts copper was melted in a suitable container. Magnesium to the extent of 0.2 percent was then alloyed therewith. A flux consisting of 8.2 parts by weight of potassium chloride, 33.3 parts sodium chloride, 8.2 parts cryolite, and 38.8 parts calcium fluoride was prepared. To this fiux was added 11.2 parts boric acid. The flux to which had been added the boric acid was disposed on the surface of the metal bath, which was maintained at a temperature of about 700 degrees C., the melting temperature of the bath being about 620 degrees C. The total of the flux plus boron material was 1 percent of the weight of the molten metal bath. The molten metal and flux were agitated vigorously for about five seconds, and after one minute the metal was poured. The resulting solidified metal was found-to exhibit an extremely fine grain size and to have higher tensile strength, greater elongation, and somewhat greater hardness than corresponding alloys not subjected to suitable boron treatment. Moreover, the improvement in properties persisted throughout several subsequent operations of remelting and resolidification.

.Further by way of illustrating my invention,

an alloy consisting of 90 parts by weight of aluminum and 10 partssilicon was melted in a container and calcium alloyed therewith to the extent of 0.2 percent. A fiux of calcium chloride to which had been added boric acid was disposed on the surface of the metal bath, the calcium chloride and boric acid being in proportions of to 30. The boric acid was present in amount of 1 percent of the weight of the molten metal bath, the latter .being maintained at a temperature of about 700 degrees C, the melting temperature thereof being about 590 degrees C.

,The bath and flux were agitated vigorously for two minutes, and after five minutes the metal was poured. The resulting solidified metal showed the improved characteristics referred to above in connection with the previous specific example.

It will be observed that if the accelerator metal be present in amount insufiicient to react with all of the boron compound, nevertheless, certain advantages are obtained in that such accelerator metal as is present causes the reaction to go forward at a rapid pace, the reaction being completed by the boron compound and the aluminum of the bath.

It will be noted that I have provided an improved method not requiring the use of expensive alloying materials, whereby there may be imparted to aluminum and alloys thereof improved mechanical and physical properties, ,such as greater tensile strength and elongation, increased elasticity and resistance to fatigue, low gas content, decreased crystalline shrinkage upon solidification, and decreased grain size of the aluminum constituent. Moreover, such improvement takes place without impairment of the thermal or electrical conductivity of the metal, while yet facilitating subsequent heat treatment thereof. Furthermore, the influence of undesirable impurities, such as iron, is decreased, while the treated metal in molten form exhibits greater fluidity, whereby its casting properties are improved.

It will be observed that I have provided an improved method of treating aluminum and its alloys with boron which needs no additional equipment beyond that used in present day practice, and which has the combined advantages of economy, with speed and ease of operation. Furthermore, the fact will be duly appreciated that my improved process may be practiced in connection with the usual step of fluxing with the obvious attendant advantages.

It will be seen that my invention has great commercial advantages in that aluminum and alluminum alloys of either virgin or secondary sources or combinations thereof may readily be provided with those properties of fine grain size, high tensile strength and elongation, which are of so much importance with respect to metals which are to be subjected to forging, rolling, drawing, extruding, welding and other purposes, and the production of more perfect. billets for such purposes is made possible.

My invention furthermore makes readily available aluminum and aluminum alloy sand and metal mold castings of uniform grain size throughout their cross-section, making unnecessary such careful control over pouring and metal mold temperatures as has hitherto been necessary, and making the manufacture of more diificult castings commercially practicable: Furthermore, by my invention, the use of secondary aluminum and alloys by reason of the relative ease with which the improvement of their characteristics may be obtained, becomes more feasible for casting purposes, with attendant increasing value of such secondary aluminum, on the one hand, and on the other hand, decreasing cost of both sand, and chill cast or metal mold aluminum castings by reason of the fact that more secondary metal may be employed therein with equal, if not better, results than has hitherto been readily possible by the use of more expensive metal.

It will further be noted that metal treated according to my invention may be poured at temperatures considerably higher than heretofore possible to produce solid sound castings relatively free of shrinkage cracks, gases and porosity, and having in many instances a superior surface finish.

Furthermore, it is to be understood that the particular materials and compounds disclosed and the procedure set forth, are presented for purposes of explanation and illustration and that various equivalents can be used and modifications of said procedure can be made without departing from my invention as defined in the appended claims.

What I claim is:

1. The method of imparting improved physical and mechanical properties to aluminum and alloys thereof, which comprises melting the metal to be treated, alloying therewith a metal of an arbitrary class comprising calcium, magnesium, sodium, potassium, barium, strontium, lithium, thorium, and beryllium, and causing to come into intimate contact with said molten metal, a fused solution of a boron compound whose reaction with'the metal of said arbitrary class produces more exothermic heat than the corresponding reaction with aluminum whereby rapid reaction resulting in the production of metallic boron may take place with consequent improvement of the treated metal.

2. The process of improving aluminum and alloys thereof by an accelerated treatment with a boron compound, which comprises maintaining the metal to be treated in molten condition, there being present in said molten metal a metal more readily oxidized than aluminum, holding a fused solution of a boron compound in contact with said molten metal, and continuously dissolving the compound or compounds resulting from the reaction between the boron compound and molten metal, whereby said reaction may proceed at a high rate to cause an improvement of the molten metal.

3. The method of improving the characteristics of aluminum and alloys thereof, which comprises maintaining the aluminum or aluminum alloy to be treated in molten condition and at a temperature relatively close to its melting point, introducing into said molten metal as an accelerator a metal whose reaction with a boron compound produces more exothermic heat than the corresponding reaction between the same boron compound and aluminum, holding a fused solution of the boron compound in contact with the molten metal to be treated, and continuously dissolving the compound or compounds resulting from the reaction between the boron compound and accelerator metal, whereby said reaction may proceed at a very rapid rate to cause an improvement of the molten metal such that upon solidification the aluminum constituent of the treated metal will exhibit relatively fine grain size.

4. The process of imparting improved properties to aluminum and alloys thereof, which comprises maintaining in molten condition the metal to be improved, said molten metal containing in alloyed condition therewith accelerator metal of an arbitrary group comprising calcium, magnesium, sodium, potassium, barium, strontium, lithium, thorium, and beryllium, associating with tl-e surface of said molten metal a molten solvent flux, dissolving in said flux a boron compound whose reaction with the-accelerator metal of said arbitrary group produces more exothermic heat than the corresponding reaction with aluminum, dissolving in said flux aluminum oxide from the surface of said molten metal, whereby the dissolved boron compound may contact directly with said molten metal, and dissolving compounds formed from the reaction between the boron compound, and accelerator metal and aluminum, whereby said reaction may proceed rapidly and improve the molten metal such that upon solidification the treated metal will exhibit superior physical and mechanical properties of substantially permanent nature.

5. The method of imparting improved properties to aluminum and alloys thereof, which comprises holding a fused solution of a boron compound in contact with molten aluminum with which has been alloyed accelerator metal of an arbitrary group comprising calcium, magnesium, sodium, potassium, barium, strontium, lithium, thorium, and beryllium, said boron compound being one whose reaction with the accelerator metal of the arbitrary group produces more exothermic heat than the corresponding reaction with aluminum, agitating the molten metal and dissolved boron compound to expose large and fresh surfaces for reaction, and continuously dissolving the compound or compounds resulting from the reaction between the boron and accelerator metal, whereby said reaction may go forward rapidly to cause improvement of the molten metal.

6. The method of imparting improved properties to aluminum and alloys thereof, which comprises melting the metal to be improved, alloying with said molten metal an accelerator of an arbitrary group comprising calcium and magnesium, dissolving a non-metallic boron compound in a molton flux disposed on the surface of the molten metal, causing relatively large surfaces of flux and molten metal to come into contact for reaction, and removing the compound or compounds resulting from such reaction from the contacting surface between the compound and molten metal, whereby the molten metal may be rapidly improved so as to exhibit superior physical and mechanical properties upon solidification.

7. The method of improving the characteristics of aluminum and alloys thereof, which comprises melting the metal to be treated, alloying therewith an accelerator metal capable of reacting with a boron compound more rapidly than aluminum, associating with the surface of said molten metal a molten flux capable of dissolving aluminum oxide and boron compounds, dissolving in said flux a non-metallic boron compound of an arbitrary group comprising alkali, alkaline earth and other borates, boric acid, boron oxide, calcium boride, boron sulphide, boron phosphate, boron nitride, boron carbide, aluminum bore-fluoride, potassium born-fluoride, causing said flux to contact with relatively large surface areas of molten metal, dissolving in said flux compounds formed from the inter-action of boron compound and molten metal, and maintaining said metal molten until metallic boron formed from said reaction has become disseminated throughout said molten metal.

8. The method of improving aluminum and alloys thereof, which comprises melting the metal to be treated, alloying with said metal an accelerator metal of an arbitrary group comprising calcium and magnesium in appreciable amount up to about 3 percent of the weight of the molten metal, disposing on the surface of said molten metal a flux comprising sodium chloride, potassium chloride, cryolite and calcium fluoride, dissolving in said molten fiux an appreciable amount up to about 3 percent of the weight of the molten .metal of boron compound of an arbitrary class consisting of alkali borates, alkaline earth borates and boric acidpand agitating said molten metal and flux to produce a more vigorous reaction between the boron compound and the molten metal.

9. The process of imparting improved characteristics to aluminum and alloys thereof, which comprises preparing a molten bath of the metal to be treated, said molten metal containing from 0.01 to 3 percent of an accelerator metal of the alkali and alkaline earth groups, disposing a flux of calcium chloride on the surface of said molten bath, ,dissolving boric acid in said flux in an appreciable amount up to about 3 percent by weight of the molten metal, agitating said bath for several minutes to promote the reaction between the boric acid and molten metal, and permitting said metal to remain molten for several minutes longer to permit the dissemination of boron formed from said reaction through -said molten metal. I

10. The method of improving aluminum and alloys thereof, which comprises preparing a molten bath of the metal to be treated; said molten metal containing in alloyed form therewith from 0.1 to 3 percent of a metal of the arbitrary group consisting of alkali and alkaline earth metals, associating with said molten metal a flux of the composition sodium chloride about 33.3 parts, potassium chloride about 8.2 parts,

cryolite about 8.2 parts, and calcium fluoride about 38.8 parts, dissolving in said flux about 11.2 parts boric acid, said flux being in appreciable amount up to about 3 percent of the weight of the molten metal, agitating said molten metal and flux vigorously for several seconds, and permitting said molten metal to stand for a short time to permit substantial reaction between said boric acid and said molten metal.

11. As a new and useful product; improved cast metal of an alloy of aluminum with an alkali or alkaline earth metal, resulting from the treatment of said alloy in molten form with a normally solid boron compound and characterized I by fine grain structure of the aluminum constituent persisting through repeated meltings of said metal.

12. As a new and useful product, an alloy of aluminum with a metal of an arbitrary class of calcium and magnesium treated while in molten condition with boric acid in molten dissolved con-- dition, whereby the aluminum metal upon solidification exhibits refined grain structure of the aluminum constituent and improved physical and mechanical properties capable of persisting through repeated melting and solidification of the treated metal.

WALTER, BONSACK'.