DE1483471A1 - Method for joining aluminum parts together - Google Patents

Description

Method for joining aluminum parts to one another. For the burner elements In nuclear reactors, aluminum is used for thermal purposes because of its low cross-section Neutron absorption and because of its generally quite satisfactory mechanical properties widely used as a cladding material. In contrast, the mechanical strength of aluminum is not sufficient if it is in Reactors intended to be used for high temperatures. Higher strength properties are particularly necessary when the burner, for example, in the form of a Connection such as U02 is used, which does not take the burden of the 'entire burner assembly has to bear. Since now the aluminum compounds have better strength properties at high temperatures have as pure aluminum and also satisfactory Have neutron cross-sections, they are special good for that. Suitable for use in nuclear reactors. From the aluminum alloys used for Use in reactors for high temperatures and for many other uses are suitable in which a greater strength than that of aluminum metal is required, the class of commercially viable aluminum alloys stands out which consist of about 4 to 10 percent by weight of aluminum oxide (A1203), which is dispersed in an aluminum matrix. In the following description shall now use the word aluminum, unless other definitions are expressly given are, as a collective term, both metallic aluminum and aluminum alloys include. The tight, leak-tight connection of aluminum parts with one another is a urgent requirement in the manufacture of burner elements. It is there it is of particular importance that the closing parts are

linked to prevent fission products from escaping to prevent the inside of the reactor or the environment and that the burner itself is protected against corrosive or erosive attacks by the coolant. For example, a burner element can be made up of a number of tubular parts an aluminum alloy containing UO2, and such an arrangement must be closed with a leak-proof and tight closure cap. So far took place joining metallic aluminum with an aluminum alloy or joining an aluminum alloy with parts from a Aluminum alloy by applying high pressures, a particularly strong connection, for example using a pressure of 2100 to 5600 kg / cm 2o this. Procedure requires takes a considerable amount of time and can also lead to the discarding of the aluminum parts, it is on the other hand too

unsuitable for a manufacturing process involving thousands of terminations for burner rods required for a single core load are. The use of welding processes destroy the favorable properties of the Negations of aluminum and aluminum oxide at high temperatures.

The invention is based on the object of a new and improved one To create a method for joining aluminum parts. The invention is intended to the following purposes are fulfilled: 1.) The new procedure is to liaison lead, which have approximately the strength of the starting material.

2.) It aims to provide a method of diffusion bonding for the union created by aluminum alloys. 3.) With the new process terminations

for reactor burner rods that can also be produced at high temperatures remain absolutely gas-tight.

4.) The new method should be able to be carried out quickly even at moderate pressures be. 5.) It is also part of the objective of the invention, a method to create, in which the binding layer between the to be united Parts extremely thin and free of crumbly connections between the metal parts is. 6.) The new method is also intended for large-scale manufacturing processes be conveniently applicable. Further purposes and advantages of the invention will be apparent from US Pat now emerge from the following description. According to the invention, there is the new method essentially that a layer of at least one binder metal, which is optional Silver, copper, gold, tin or zinc can be, on at least one of the related Surfaces is applied and that these surfaces while maintaining an intimate Contact are placed on top of each other, and that the whole is then brought to one temperature is brought between the temperature for the eutectic transformation of the binder metal and the aluminum on the one hand and the melting point of the aluminum parts on the other lies. With the help of the method according to the invention, aluminum points can be at a Joint are united, the strength of which is the strength of the starting material almost reached and which does not decrease at higher temperatures. So can for example, end seals on fuel rods are made that are gas-tight and remain completely undamaged when the temperature cycle at higher temperatures repeated over a long period of time. The formation of the junction appears through the formation of a eutectic between the aluminum surfaces and adjust the binding metal, which after the eutectic transformation from the intermediate surfaces diffused away to leave an extremely fine connecting line. In the practical Carrying out the method according to the invention is a very thin layer of at least one binding metal, which is optionally silver, copper, gold, tin or Zinc can be applied to at least one of the surfaces to be connected, but preferably only on one of these surfaces. It has been found that it is it is advisable to apply only a very thin layer of the binding metal: for example the film should be no thicker than 0.0254 mm, with a film from about 0.00254 to 0.000254 mm is preferred. Thicker films can also be used with success but these lead to the formation of connections between the metals on the interface, which is friable and, as a result, of reduced strength are. The film can be customized by the application methods that are specific to this Metals are known to be applied to surfaces. So you can, for example Films can be regulated by vacuum evaporation or electrolytic precipitation Manner. In detail, the process takes place in such a way that initially at least one of the surfaces to be connected to one another in the usual way, for example through Washing with organic reagents and alkali formers as well as with sprays the end Acid cleaned, that the binding film is applied thereon and that finally the surfaces are brought together and kept in intimate contact. the latter can be effected, for example, with the aid of a collet or other holding devices will. Only one pressure needs to be applied to the holding devices themselves sufficient to maintain intimate contact during the heating period. The temperature at which the connection occurs is dependent on the special type of eutectic binder used. This temperature lies between about 242 ° C for the eutectic formation between tin and the Aluminum part and is 3820C for zinc, 5290C for gold and about 545C for copper up to about 555.C for silver. The maximum temperature is a function of the melting points or the deformation point of aluminum and is for metallic aluminum at about 5930C and for the aluminum alloy mentioned above at about 6480C. Is there it is desirable to set the temperature for the formation of the eutectic for that special eutectic material around. about 0.5 to 160C to increase the diffusion to promote the eutectic in the starting material and thus the formation of a thin Interlayer to lighten, which adds quite considerably to the good properties contributes to the resulting connection. For example, it is a very cheap one Temperature for a compound from a silver eutectic a temperature from about 571 ° to 588 ° 0, with generally a temperature of about 58800 being preferred is given. The heating itself is expediently carried out either in air or in the atmosphere of an inert gas: Keeping intimate contact between the Surfaces to be connected to one another are upright, then an oxidation occurs on the Interfacial reliably prevented when the temperature has been increased, and the heating of the air, for example by an induction coil, is sufficient for the Carrying out such a manufacturing process completely.

It has been found that the formation of a eutectic and_de diffusion 3n the starting material with the aim of getting a solid connection, at the temperatures mentioned above is relatively rapid, so that the aluminum parts can be conveniently connected to one another in a short time. The parts will last for about 7.5 to 10 minutes at the temperatures noted above heated, the heating time of: 2.5 to 5 minutes being preferred. After completion During the heating process, the interconnected parts are allowed to reach ambient temperature cool, preferably still held together with the help of the clamping devices will. This process takes about 30 minutes

long. It has been found that the cooling of the parts while they are still in the clamping device does not exert any critical influence, but accelerates further diffusion of the eutectic into the starting material. The following exemplary embodiments explain the essence of the invention in detail recognize clearly. Example 1 This example relates to the production of an end closure for a fuel rod on a tube with an inner diameter e #, before ; , 62 + 0, (`.76 r @ x # and a wall thickness of 0.762 mm. The tube consisted of an aluminum with 4 to 8% aluminum oxide alloy, which is known under the trade name" Alcoa M-257 ". The end screw connection was Forged from the same material and made from a forged bar 9.5 mm in diameter, the diameter of the portion of the end plug to be inserted into the tube was 7.54 mm + 0.05 mm.

Samples. were cleaned by first washing them with liquid and vaporous trichlorethylene degreased and then with an aqueous one Lye were cleaned, then rinsed with water, what-a treatment with nitric acid (50 percent by volume) followed by a rinse Water was made, followed by drying. The end plug was with silver in a plating bath with silver cyanide at a concentration of 6 ounces per 3.7 liters and sodium cyanide at a concentration of 12 ounces per 3.7 Liters electroplated. The sample was applied for 30 seconds at 40 amps per 900 cm2 electroplated, whereupon a precipitate of silver from about 10-5 to

1-0`4 inches. Revealed. The end cap was then in the tube inserted and in a six-part jig with an open Pressurized inner diameter of 9.5 mm. The whole thing was then by way of Induction heating brought to a temperature of 5710C to 593 ° C. The pressure was then tightened by tightening the jig at intervals of about 1500C and 499 ° C and: after reaching the temperature, maintain intimate contact to be maintained after expansion due to heating. The temperature was for a period of about 2.5 minutes, after which the sample is in the Jig allowed to cool for about 20 minutes before being removed became. At the other end, the tube was closed in a similar manner. Both ends proved to be tight against helium, using a plug for the purpose of testing was pierced. After performing the control, this hole was made by hot cutting locked at 6480C, with a copper-clad aluminum welding rod inserted into the Bore was introduced to stop the occlusion. facilitate.

The tube was then subjected to an external positive pressure in an autoclave at 427 ° C. As soon as this overpressure reached the value of 161 kg / cm, the pipe broke, but the end seal was still intact and proved to be helium-tight. The tubes were also subjected to various pressure cycles at 399 ° C. A sample was subjected to 50 cycles from zero to 70 kg / cm 2 and remained helium-tight. Another pipe failed due to the plating, but the, end seal remained intact. The samples also remained tight after being placed in an air-filled oven at 5350C for 90 days and after 1000 hours in a terphenyl solution at 399 ° C. Example 2 The same samples were used as in Example 1, with the only difference that copper was used as the eutectic binder. The copper was electroplated onto the aluminum end plug from an aqueous plating bath containing copper cyanide at a concentration of 6 to 8 ounces per 3.7 liters - as well as free KCN, 1.2 to 1.5 ounces per 3.7 liters and KOH , 3 to 4 ounces per 3.7 liters. A copper layer of about 10-5 to 10-4 inches was applied to the sample; this happened in about 30 seconds at a specific current strength of 50 ampo per 900 em2.

An examination of the product, which had been produced according to the method of Example 1, showed that the resulting end closure was helium-tight and no leaks could be found after running through the pressure cycles, the temperature cycles and the washing processes with organic substances, Example 3 Same requirements as in Example 1 with the exception of the following changes. In this example the tube made of aluminum and aluminum oxide was closed with an end plug made of metallic aluminum. A tube with an outside diameter of 6.35 mm and a wall thickness of 0.4 mm served as a closure; the end cap had a shoulder with a diameter of. 6.35mm and ½mm thick for easy insertion. The clad area was 5.55mm in diameter and 12.7mmo in length

The end cap made of metallic aluminum was plated by that it was vapor-deposited with silver in a vacuum until the thickness 9 Q 10 # -5 to 1.8 0 10-4 Inch scam. Before plating, the parts were as in the working example 1 cleaned. The parts were then put together and placed in a jig, who was attracted to one

To exert pressure on the entire assembly, the jig with the end cap was then placed in the center of an induction coil and at about 5710 to 59300 for 2.5 minutes

warmed up for a long time. The jig was tightened every thirty seconds, to keep the pressure open during heating o The closure could be in the Jig about

25 minutes left to cool down. After removing the Closure from the jig was the closure for tightness at room temperature tested and proven to be helium-tight.

The closure was subjected to 1'7'5 thermal cycles, which were between 25 ° 0 and 48.2a0 and took about 30 minutes per cycle. The sample also remained helium-tight.

Finally, the end closure was subjected to gas pressure after he had been soaked at 39900 for 30 minutes. The pipe went at a pressure of 161 kg / cm 2 to break while the closure was still intact. The sample was then examined metallographically, and it was found that the Diffuson at the The connection surface and the actual connection itself remained completely intact was.

The above examples serve only to explain the essence of the invention and are not intended to limit it in any way; also becomes the expert in this special field within the scope of the invention. Changes and modifications that are not mentioned in: the exemplary embodiments,

Claims (1)

F ate, related procedure. for connecting aluminum parts to one another, characterized in that a layer of at least one binding metal, which can optionally be silver, copper, gold, tin or zinc, is applied to at least one of the associated surfaces and that these surfaces are in intimate contact are placed on top of one another, and that the whole is then heated to a temperature which brings about the formation of a eutectic layer between the binding metal and the aluminum parts, so that the corresponding parts are firmly connected to one another. 1, characterized in that the entire arrangement is heated to a temperature which lies between the temperature for the eutectic transformation of the 'binding metal and the aluminum on the one hand and the melting point of the aluminum parts on the other hand, characterized in that the entire arrangement is heated for 1 , 5 to 10 minutes. 6. The method according to claim 1 or dependent claims, characterized in that the arrangement is heated in air. 7. The method nach.einem of claims' t to 6, characterized in that the film of the binder is produced on the corresponding surface of the aluminum part by electrolytic precipitation. B. The method according to any one of claims 1 to 7, characterized in that at least one of the aluminum parts consists of an aluminum alloy which contains approximately 4 to 12 percent by weight A1203, while the remaining parts consist of metallic aluminum. 9. Method of joining aluminum parts; with each other, characterized in that a thin silver layer is applied to at least one of the associated surfaces of the aluminum parts, that these two surfaces are placed on top of one another and remain in intimate contact and that the whole is then heated to a temperature between about 555 ° C and below the melting point of the aluminum parts. 10. The method according to claim j, characterized in that the heating is carried out at a temperature between approximately 570 ° C and 59,000. r11: Method according to claim 9 or 10, characterized in that the thickness of the silver layer on the corresponding surface of the aluminum part is a maximum of approximately 10-3 inches (0.0254 mm). 12. A method for joining aluminum parts to one another, characterized in that a layer of silver is applied to a thickness of approximately 10-4 to 10-5 inches on one surface of the parts to be joined together so that the associated surfaces are brought into intimate contact with one another and that the entire assembly is finally brought to a temperature of about 571 to 5880C for a period of 1.5 to 10 minutes, so that the parts are firmly connected to one another. 13. Method according to claim 12, characterized in that the parts to be connected to one another are heated in air for a period of approximately 2.5 to 5 minutes. 14. The method according to claim 12 or 13; characterized in that the aluminum parts consist of an aluminum alloy containing approximately 4 to 12 percent by weight A103, while the remainder is metallic aluminum. 15. The method according to any one of claims 1 to 14, characterized in that the resulting arrangement is cooled to the temperature of the ambient air after heating in air and that the intimate contact is maintained during this time.