US2174645A - Method of treating aluminum alloys - Google Patents

Description

Oct. 3, 1939. H. H. WETZEL METHOD OF TREATING ALUMINUM ALLOYS Filed Dec. 11, 1935 F' 1 a6 Z6 I A? [-6 o 26 z/ A 0 0 um; 0 A9 /a By W Patented Oct. 3, 1939 UNITED STATES PATENT OFFICE 2,174,845 METHOD OF TREATING ALUMINUM ALLOYS Harry Herman Wetzel, Santa Monica, Calif., as-

signor to Douglas Aircraft Company, Inc., Santa Monica, Calif., a corporation of Delaware Application December 11, 1935, Serial No. 53,929

7' Claims.

- or bending operations and the aluminum alloy used must be in a soft condition in order that it may be shaped or formed without fracture or spring-back. The aluminum alloy in this soft condition is unsuited for use in service because of low strength and inferior resistance to corrosion. It is therefore necessary, after forming the parts, to subject them to treatment which will chemically change the alloy structure in order to produce the optimum percentage of alloying element in solid solution. When so treated there is imparted to the aluminum alloy the best possible physical properties and resistance to corrosion. Such treatment as practiced prior to my invention consists of heating the aluminum or aluminum alloy part or object to a predetermined temperature, holding the temperature for the necessary length of time and thereafter cooling the object from the temperature range to which it was heated. The rapid cooling as practiced prior to my invention was ordinarily done by plunging the objects into cold water. Such quenching is effective in rapidly cooling the part and in producing proper physical properties and resistance to corrosion, but the ob-' ject so treated is usually so seriously warped that it is not capable of withstanding the design stress. It has been the practice, therefore, to strengthen such warped parts immediately after the quenching operation and before the metal has hardened to any great extent. This period is ordinarily about thirty minutes and the work must be straightened within this period of time. In most cases, however, thirty minutes is not suflicient to do all the straightening, and after a part has once buckled it is very difficult to bring it back to its original shape. It will therefore be seen that it is practically impossible to completely and satisfactorily straighten a part or object particularly if the warping is at all serious. Obviously such a method is undesirable from the standpoint of dependability of the work produced.

It is anobject of my invention to provide a method of treating aluminum alloys which produces chemical changes in the material 'neces- 6 sary to improve the physical properties and corrosive resistance thereof without causing such warpage as will require subsequent straightening. Objects produced according to my invention are suitable for usewithout further 10 working, thus shortening the process and time of production, reducing the costs, and producing objects of uniform shape and characteristics.

It is an object of my present invention to provide a method of improving the physical properties and resistance to corrosion of aluminum alloys which consists of first heating the object as desired and thereafter rapidly and evenly extracting the heat from all surfaces thereof.

A further object of my invention is to provide a method of the character pointed out in the preceding paragraph in which the aluminum or aluminum alloy object after heating is subjected to the action of a heavy vapor, mist, or fog-like atmosphere to efiect the cooling thereof.

It is another object of my invention to provide a method of the character pointed out in the second preceding paragraph in which after heating the aluminum alloy object it is submitted to the action of a heavy vapor or fog-like atmosphere which substantially simultaneously contacts all surfaces thereof.

It is another object of my invention to provide a method of the character pointed out in the third preceding paragraph in which all parts of the object are cooled at substantially the same rate so that there will be equal contraction in all areas thereof.

It is a still further object of my invention to provide a method of the character pointed out 40 heretofore in which the aluminum alloy object is first heated and thereafter subjected to the action of moisture particles evenly suspended and distributed in an atmosphere, which moisture particles contact the surfaces of the ob- Ject and cool same evenly and rapidly.

It is another object of my invention to provide a method as pointed out in the preceding, objects in which the heavy vapor, mist, fog, or moisture dispersion in the atmosphere is drawn into contact with the aluminum alloy object to be quenched.

It is also an object of my present invention to provide an apparatus whereby the process of my invention, the objects of which have been prises 4.0% copper, 0.15% manganese, 0.5% magnesium', and the remainder aluminum and its normal impurities, and which is commonly known as 17$, for example, it is first raised to a temperature of between 930 and 950 F. The

aluminum alloy is held within the specified temperature range for a sufficient length of time, depending upon thickness of the metal, heating medium used, and circulation of heating medium, to insure that all alloying elements are in solution. When the heating step has been completed the aluminum alloy is then quenched as rapidly as possible from within this temperature range in order to insure the best possible physical properties and corrosion resistance. Adjacent the heating apparatus I provide a chamber and in and through this chamber I circulate a fog-like atmosphere, or a heavy mist, or an atmosphere having liquid particles in substantially even dispersion therein. Immediately upon completing the heating step the aluminum alloy object is moved into the chamber where it is fully and completely enveloped by the quenching atmosphere therein and it is rapidly and evenly cooled from the temperature range. By such a process t e quenching is quickly done; that is, a minimum amount of time is lost between heating and quenching medium, and the nature of the quenching medium is such that the heat is extracted at a very high rate, thus producing the maximum percentage of alloying elements in solid solution and in finely divided and evenly dispersed form throughout the alloy. Furthermore, the quenching operation is such that warpage of such a degree as will require straightening of any of the aluminum alloy parts or objects does not occur, and the part may be used without further treatment.

In order that those skilled in the art may be instructed in the performance of my invention a detailed description of a preferred form of the method of my invention and an apparatus for performing the method will'be given in connection with the accompanying drawing.

Referring to the drawing.

Fig. 1 is a sectional view showing a furnace, a quenching chamber, and other parts whereby my invention may be practiced.

Fig. 2 is a sectional view through the quenching chamber takemon the line 2--2 of Fi 1.

Fig. 3 is an elevational view of a fog or mist producing or liquid dispersing nozzle which I utilize in the form of my invention shown.

Fig. 4 is a sectional view taken on the line 4-4 of Fig. 3.

Referring to the drawing in detail. the numeral represents a furnace having a door l2 which may be opened very quickly and closed very quickly by common types of mechanism not illustrated. This furnace is of such a design that temperatures within relatively narrow ranges may be produced in order that aluminum alloy objects may be raised to and maintained at such a temperature that the alloying elements will be placed. in solution in the aluminum alloy Parts. For the purpose of supporting the obiects both during heating and quenching there is provided a rack ll having wheels l5 whereby the rack is movable on a track It in the furnace The rack I4 is essentially a frame construction so that the objects as illustrated by the numerals i1 and I8 are freely accessible from all sides thereof, and so that heat may be applied from all sides, and so that the cooling medium, as will be pointed out shortly, may be brought into contact with the objects l1 and i8 from all sides thereof.

Placed adjacent the heating furnace II is the quenching apparatus IQ of my invention which consists of walls in which are mounted tracks 20 so that the rack M with the objects l1 and I8 may be run into the quenching chamber 2|. There is a door 22 at the end of the quenching device I!) adjacent the furnace II, and when the doors 2,2 and I2 are opened the rack l4 may be moved along the track l6 and the track 20 and into the quenching chamber 2|. There is a door 23 at the opposite end of the quenching device quenching medium under suitable pressure. De-

pending from the pipes 24 is a multiplicity of nozzles 28 which break up the liquid from small streams into relatively small particles of even dispersion in order to form an atmosphere of substantially even liquid or moisture dispersion or to form what I term the fog-like atmosphere or heavy mist.

As shown in Figs. 3 and 4, each nozzle is constructed as follows: The nozzle has a threaded portion 29 which is threadedly secured in an opening of the pipes 24 and has a central passage 30. Formed in the side walls of the nozzle is a series of radial downward extending ducts 3| and a series of radial upward extending ducts 32, the outer ends of which meet at an annular channel 33 as illustrated. Near the lower end of the nozzle is a series of downwardly directed ducts 35 formed around the central body projection 36 of the nozzle, and there is also a series of outwardly extending ducts 31. The outer ends of the ducts 35 .and 31 meet as indicated The water or other quenching medium is supplied through the pipes 24 under a relatively high pressure. This liquid flows outwardly through the ducts 3|, 32, 35, and 31 and adjacent streams are brought into forcible contact with each other, thus breaking the streams up into small water particles and causing them to fly outwardly in all directions. This produces the quenching atmosphere 'of my invention which I have defined using various terms in order that the characteristics thereof may be understood. The nozzles break up the moisture or liquid into particles which are substantially evenly dispersed in the atmosphere. This produces what I term a fog-like atmosphere or heavy vapor or mist. Since the nozzles are located in the upper part of the quenching chamber 2|, the quenching chamber 2| is filled with quenching atmosphere which I have illustrated by a multiplicity of dots in Fig. 2.

The lower wall 40 of the quenching chamber 2| is provided with a multiplicity of outlet openings 42 which communicate between the quenching chamber 2! and an exhaust chamber N. This exhaust chamber 42 is connected to an exhaust conduit 44 which is in turn connected to a suction producing means in the form of a suction blower 45 or its equivalent. To prevent water which has settled from the atmosphere from passing through the, exhaust apparatus I provide a water pocket 46 having a water drain 1, in the lower part of the exhaust chamber 43, and which catches water so that it will not pass through the exhaust conduit 44.

During the operation of the apparatus and during the performing of the-quenching step of my invention the blower 45 is in operation so that the quenching atmosphere which is formed by the nozzles 28 is drawn downwardly through the quenching chamber 2| and caused to completely envelop the objects l1 and I8. Arrows 49 have been used in Fig. 2 to illustrate the passage of the quenching atmosphere through the quenching chamber 2| and around the objects I! and IS. The rate of travel of the quenching atmosphere, however, is not so great that the quenching atmosphere will not be brought into contact with the bottom surfaces of the objects II and [8, but on the other hand is sufliciently fast so that the quenching atmosphere will be continuously brought into enveloping relationship with the objects.

In performing the process of my invention, the aluminum or aluminum alloy objects I! and I8 are first placed on the rack II in such a manner that all surfaces thereof are exposed. Where pieces are laid flat, as indicated at l8, they are supported by a very coarse screen as indicated in Fig. 2. The rack, including the parts therein, are placed in the furnace II and the doors thereof are closed. The objects I! and I8 are then subjected to the suitable heat treating step, the temperature and duration of the treatment depending upon the particular size 'or shape or characteristics of the objects being treated. The purpose of this heat treating step is to place in solution the alloying elements of the aluminum alloy, and particularly the copper. The quenching apparatus I9 is preferably a portable device which is positioned in front of the furnace ll just prior to the time that the heat treatment is completed. It is placed in the position shown so that the tracks 20 are in alignment with the tracks l6 of the furnace. When the heating step is finished the valve 26 is opened and the blower 45 set into operation, thus continuously forming the quenching atmosphere of the character defined heretofore in the quenching chamber 2|. The quenching atmosphere is fully establishedbefore the objects are moved into the quenching chamber. The doors 22 and I2 are then opened and as quickly as possible the rack I4 is moved into the quenching chamber 2|, and thereupon the doors 22 and I2 are immediately closed. In the apparatus which I employ I provide a means for moving in the neighborhood of twenty-five seconds or less, the heat must be very rapidly extracted with the result that considerable steam is produced. As the quenching properties of the quenching atmosphere are spent, fresh quenching atmosphere is continuously circulated around and in contact with the objects I1 and II by the action of the suction blower Ii.

When the quenching operation has been completed the valve 26'is closed and the blower l5 shut down. The door 23 may then be opened and the rack I4 removed from the quenching apparatus l9.

The quenching atmosphere forming means has been illustrated as being positioned in the upper part of the quenching chamber 2|. It should be understood, however, that the quenching atmosphere forming means might be remotely lo= ing chamber. The essential element in the proc-- ess is forming the quenching medium and passing it into or through a quenching chamber in order that the parts or objects to be quenched may be enveloped by the' quenching medium. I believe my invention to be broadly new and therefore desire it to be broadly construed in accordance with the appended claims.

I claim as my invention:

1. The method of treating an aluminum alloy which contains at least one alloying element to improve its physical properties and resistance to corrosion, including the steps of: heating the aluminum alloy to such a temperature and for such period of time as to cause at least a part of the alloying element to go into solution;

forming a fog-like quenching atmosphere by improve its physical properties and resistance to corrosion, including the steps of: heating the aluminum alloy to such a temperature and for such period of time as to cause at least a part of the alloying element to go into solution; forming a fog-like quenching atmosphere by spraying water into an induced current of air; and

cooling the heated aluminum alloy by substantially simultaneously contacting all of the exposed surfaces of said aluminum alloy with said fog-like quenching atmosphere.

3. The method of treating an aluminum alloy which contains at least one alloying element to improve its physical properties and resistance to corrosion, including the steps of: heating the aluminum alloy to such atemperature and for such period of time as to cause at least a part of the alloying element to go into solution; forming a fog-like quenching atmosphere by atomizing water in air; and cooling the heated aluminum alloy by substantially continuously moving such fog-like quenching atmosphere into contact with substantially all of the exposed surfaces of said aluminum alloy by air currents.

4. The method of treating an aluminum alloy which contains at least one alloying element to improve its physical properties andresistance to corrosion, including the steps of: heating the aluminum alloy to such a temperature and for such period of time as to cause at least a part of the alloying element to go into solution; forming a fog-like quenching atmosphere containing water particles dispersed therein, by spraying water into air; placing said heated aluminum alloy in a quenching chamber; and cooling the heated aluminum alloy by substantially simultaneously contacting all of the exposed surfaces of said aluminum alloy with said fog-like quenching atmosphere; withdrawing steam from said chamber formed by contact of said moisture particles with said heated aluminum alloy; and replacing said steam by fresh quenching atmosphere.

5. The method of treating an aluminum alloy which contains at least one alloying element to improve its physical properties and resistance to corrosion, including the steps of: heating the aluminum alloy to such a temperature and for such period of time as to place at least a part of the alloying element in solution; forming a iog-like quenching atmosphere containing moisture particles dispersed therein, by spraying water into air; placing said heated aluminum alloy in a quenching chamber having an outlet; cooling the heated aluminum alloy by substantially simultaneously contacting all of the exposed surquenching atmosphere;

faces of said aluminum alloy with said fog-like rapidly withdrawing steam through said outlet formed by contact of said moisture particles with said heated aluminum alloy; and replacing said steam by fresh quenching atmosphere.

6. The method of treating an aluminum alloy which contains at least one alloying element to improve its physical properties and resistance to corrosion, including the steps of: heating the aluminum alloy to such a temperature and for such period of time as to cause at least a part of the alloying element to go into solution; forming a fog-like quenching atmosphere by spraying water into air adjacent the upper end of a quenching chamber; placing said heated aluminum alloy in said quenching chamber; cooling the heated aluminum alloy by substantially simultaneously contacting all of the exposed surfaces of said aluminum alloy with said fog-like quenching atmosphere; withdrawing steam, formed by contact of said moisture particles with said heated aluminum alloy, through an outlet at the lower end of said chamber; and replacing said steam by fresh quenching atmosphere.

'7. The method of treating/a strong aluminum alloy-including the steps of subjecting the alloy to a solution heat treatment: iorming a foglike quenching atmosphere by atomizing liquid in gaseous medium; and cooling the alloy by introducing it at substantially the temperature of the solution heat treatment into; said quenching atmosphere. HARRY HERMAN WETZEL.

CERTIFICATE OF CORRECTION. Patent No. 2,17LL,6L;5. October 19 9.

' HARRY HERMAN WETZEL. It is hereby certified that error appears in the printed specification 'of the above numbered patent requiring correction as follows: Page 1, second column, line 22; strike out the words "aluminum or"; .and that the said Letters Patent shonld be read with this correction therein that the same may conform to the record of the case inthe Patent Office.

Signed and sealed this 19th day of December, A. D. 1959.

Henry Van Arsdale, S Acting Commissioner of Patents.

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