JP2012500330A - Tempering method of aluminum alloy - Google Patents

Abstract

  A process that achieves high strength performance and resistance to stress corrosion cracking without the need for prior art steps of tempering large aluminum lithium alloy components and cold working alloy components. In addition to the use of two new soaking periods and the use of a new controlled temperature selection at two individual soaking times, the process carefully controls the temperature drop from one soaking time to the other. To achieve the desired material properties.

Description

  The present invention relates to the manufacture of metal domes and conical components used in launch vehicles, and more particularly to the manufacture of components produced using an aluminum lithium alloy known as 2195.

  The 2195 aluminum lithium alloy is attractive for its low density, high modulus and comparable strength, and desirable cryogenic service properties, so it is used in launch vehicle applications. If the component is manufactured in accordance with the industry guidelines for this material, the 2195 aluminum lithium alloy is also resistant to stress corrosion cracking. As the mass for launch vehicle payloads continues to increase, the use of this alloy in fuel tanks and airframe structures has come to be required by NASA and other launch vehicle operators. In responding to this requirement, it is necessary to supply 2195 alloy in a state where its strength is highest and resistance to stress corrosion cracking.

  To achieve high strength performance and resistance to stress corrosion cracking in this material, manufacturers apply a solution heat treat to the material followed by quenching in water or an aqueous glycol solution. After quenching, the material is uniformly cold worked. The cold working process is typically a stretching operation controlled to 1 to 3%. Once the cold work operation is complete, the component is then artificially aged, thereby achieving high strength and high resistance to stress corrosion cracking. The parameters of heat treatment and cold work are known and are defined as industry standards for achieving the ideal state of 2195 aluminum lithium alloy. In some of the launch vehicle tanks and structural components, due to the size and geometry of the parts, the cold work required to achieve the desired characteristics in the 2195 aluminum lithium alloy has been eliminated. Is impossible to apply. Included in this field are monolithic tank domes and cones produced from 2195 aluminum lithium plates / blanks using a metal spinning process. In manufacturing these components, current manufacturing methods are inadequate.

  One possible solution is to produce a metal spatula drawing device that can uniformly apply the cold work required to achieve the high strength and resistance to stress corrosion cracking of 2195 aluminum lithium alloy. It is to be. However, considering that the parts are relatively small, it is unlikely that a metal spatula manufacturer will invest in this device. Also, considering that industrial data is based on cold working using tensile force, the question of whether cold working using compressive force, developed from metal spatula, yields the desired state. There is also. The unfavorable return on investment and suspicious success of this solution make it an unattractive option.

  It is not yet known in the art how to produce these components and achieve high strength and resistance to stress corrosion cracking without the addition of cold working after solution treatment and quenching.

  The present invention is a method of manufacturing domes and cones using a metal spatula drawing process and alternative heat treatment parameters, which removes similar characteristics to those achieved when parts are cold worked. To achieve even if A preferred embodiment of the method includes forming and heat treating a dome and cone made of 2195 aluminum lithium alloy.

  One aspect of the present invention provides a method for treating 2195 aluminum lithium alloys to achieve beneficial properties similar to those obtained using prior art methods that require cold working of the parts produced. It is to be.

  Another aspect of the present invention is to provide a method for treating 2195 aluminum lithium alloys that can be used on very large parts that require spatula drawing techniques to produce.

  Yet another aspect of the present invention is to provide a method for treating 2195 aluminum lithium alloy with high tensile strength and yield strength.

  Another aspect of the present invention is to provide a method for treating 2195 aluminum lithium alloy having high resistance to stress corrosion cracking.

  Ultimately, one aspect of the present invention is to provide a 2195 aluminum lithium alloy processing method that provides a launch vehicle component that meets performance parameters achieved using existing manufacturing equipment.

  These aspects of the invention are not intended to be exclusive, and other features, aspects and advantages of the invention will become apparent to those skilled in the art when read in conjunction with the following detailed description and drawings. Will.

FIG. 5 is a multi-stage rocket diagram showing the types of components that can be made using the process taught by the present invention. 4 is a flow chart of a preferred embodiment of the method according to the invention.

  As shown in FIG. 1, the illustration of a multi-stage rocket 10 is a typical structure with parts that can be made using the methods taught herein. The payload 15 is disposed inside a payload fairing structure. The second stage rocket engine 17 powers the payload 15 during the last stroke of the navigation, thereby achieving a good trajectory. Note that in the first stage of the rocket 10, the main tank 12 and the auxiliary tank 14 have dome-shaped top and bottom portions 16, 18 respectively. These tanks have a very large diameter 11 and are particularly suitable for being manufactured using the present invention. Thrust cone 17 (usually a composite material) is also a suitable component to be made using the methods disclosed herein.

  Referring now to FIG. 2, a flowchart is shown illustrating step 54 for tempering the 2195 aluminum lithium alloy. The starting material form 20 is in a mill temper known as the F state. In step 22, the material plate 20 is annealed according to industry standards for 2195 aluminum lithium alloy. In step 24, the dome or cone is formed by a spatula drawing process. Dome or cone molding is performed in steps 26 and 28 using a metal spatula drawing process and / or a tensile molding process developed as disclosed in US Pat. No. 6,199,419. It is performed at a controlled temperature of ± 25 degrees. When the forming operation is complete, the component is solution treated again in accordance with industry standards for 2195 aluminum lithium alloy, as shown in step 30, and quenched in water or aqueous glycol solution. If necessary, the component is straighten in step 32 after the solution treatment to remove small distortions caused by quenching. The component is then artificially aged at step 34. In step 36, the temperature of the component is raised to 340 degrees Fahrenheit ± 5 degrees Fahrenheit. The component is then subjected to “soaking” (a technical term that means keeping the component at that temperature) for 32 hours ± 5 minutes. Next, in step 38, the temperature of the component is lowered to 250 degrees Fahrenheit ± 5 degrees Fahrenheit at a rate of 45 degrees Fahrenheit per hour. The component is then “soaked” again at step 40 for 72 hours ± 5 minutes. Finally, in step 42, the component is air cooled to room temperature. After completion of the above steps, the component characteristics are inspected in step 44 and thereafter. The various parameters that are examined are the hardness at step 46, the electrical conductivity at step 48, the minimum step 50 in practicing the present invention, and finally, the defined SCC inspection, step 52. .

  Although the present invention has been described in connection with some preferred embodiments, other variations will be apparent to those skilled in the art with respect to the preferred embodiments contained herein.

Claims (15)

A process for tempering an aluminum alloy blank to achieve high strength performance and resistance to stress corrosion cracking,
Annealing the alloy blank according to industry standards for the particular alloy used;
Applying a hot spatula to a desired shape at a first controlled temperature for the annealed alloy blank; and
Solution treating the desired shape according to industry standards for the particular alloy used;
Quenching the desired shape in a liquid;
Subjecting the desired shape to a first aging at a second controlled temperature;
Applying a first soak to the desired shape for a first predetermined length of time;
Lowering the second controlled temperature of the desired shape to a third controlled temperature at a predetermined reduction rate;
Applying a second soak to the desired shape for a second predetermined length of time;
Tempering the aluminum alloy blank, including air cooling the desired shape until it reaches room temperature.   The process of claim 1, comprising correcting the desired shape to remove small distortions caused by the quenching step as an additional step after the quenching step.   The process of claim 1, including the step of inspecting the desired shape as an additional step for measuring characteristics of the desired shape.   4. The process of claim 3, wherein the step of inspecting includes at least one inspection selected from an inspection group consisting of hardness, electrical conductivity, mechanical ASTM inspection, and SCC inspection.   The process of claim 1, wherein the liquid for quenching is water.   The process according to claim 1, wherein the liquid for quenching is an aqueous glycol solution.   The process of claim 1, wherein the first controlled temperature is within a temperature range of 725 degrees Fahrenheit.   The process of claim 1, wherein the second controlled temperature is within a temperature range of 340 degrees Fahrenheit.   The process of claim 1, wherein the third controlled temperature is within a temperature range of 250 degrees Fahrenheit.   The process of claim 1, wherein the rate of temperature decrease is in the range of 45 degrees Fahrenheit per hour.   The process of claim 1, wherein the first soaking time is in a range of 32 hours.   The process of claim 1, wherein the soaking time is within a range of 72 hours.   The process of claim 1, wherein the aluminum alloy blank comprises a 2195 aluminum lithium alloy.   The process of claim 1, wherein the desired shape is a dome-shaped upper portion of a rocket.   The process of claim 1, wherein the desired shape is a rocket thrust cone.

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