FRICTION STIR WELDING PROCESS FOR LARGE METALLIC COMPONENTS

Abstract

A method for forming a large metallic component, a friction stir welded component and a friction stir welded blank are provided. The method includes positioning a first metallic plate and a second metallic plate in an abutting arrangement. The first metallic plate and the second metallic plate have corresponding faying surfaces at a point of abutment. A backing plate is attached spanning the point of abutment adjacent the faying surfaces. The first metallic plate is friction stir welded to the second metallic plate to form a friction stir weld along the faying surfaces. The backing plate receives an end of a friction stir welding tool curing the friction stir welding. The backing plate is removed to form a welded blank. The welded blank is formed into a component form. The component is heat treated and aged to form the large metallic component. The friction stir weld in the welded blank has a stable microstructure having little or no abnormal grain growth during elevated temperature forming, heat treatment and aging.

Claims

1. A method for forming a large metallic component comprising: positioning a first metallic plate and a second metallic plate in an abutting arrangement, the first metallic plate and the second metallic plate having corresponding faying surfaces at a point of abutment; attaching a backing plate spanning the point of abutment adjacent the faying surfaces; friction stir welding the first metallic plate to the second metallic plate to form a friction stir weld along the faying surfaces, the backing plate receiving an end of a friction stir welding tool during the friction stir welding; removing the backing plate to form a welded blank; forming the welded blank into a component form; and heat treating and aging the component form to form the large metallic component; wherein the friction stir weld has a stable microstructure having little or no abnormal grain growth during elevated temperature forming, heat treatment and aging.

2. The method of claim 1, wherein the positioning a first metallic plate and a second metallic plate in an abutting arrangement is positioning in a weld fixture.

3. The method of claim 1, wherein forming the welded blank includes spin forming or stretch spin-forming the welded blank.

4. The method of claim 1, providing a first run-on/off tab and a second run-on/off tab at distal ends of the point of abutment of first metallic plate and the second metallic plate.

5. The method of claim 4, wherein the friction stir welding includes commencing the welding at the first run-on/off tab and ending the welding in the second run-on/off tab, the friction stir welding including positioning the end of the friction stir welding tool to form the bottom of the weld in the backing plate.

6. The method of claim 1, wherein attaching the backing plate includes mechanically retaining the backing plate in position with a clamp.

7. The method of claim 1, wherein attaching the backing plate includes welding or adhering the backing plate into position spanning the point of abutment adjacent the faying surfaces.

8. The method of claim 1, wherein the friction stir welding tool is a pin.

9. The method of claim 1, wherein the first metallic plate and the second metallic plate include aluminum or aluminum alloy.

10. The method of claim 1, wherein the backing plate backing plate width is greater than or equal to four times the thickness of one or both of the first and second metallic plates and a thickness greater than or equal to one third times the thickness of one or both of the first and second metallic plates.

11. A friction stir welded component comprising: a first metallic plate and a second metallic plate joined at corresponding faying surfaces by a friction stir weld; and a backing plate spanning the point of abutment adjacent the faying surfaces; wherein the friction stir weld terminates in the backing plate.

12. The friction stir welded component of claim 11, further comprising a first run-on/off tab and a second run-on/off tab at distal ends of the point of abutment of first metallic plate and the second metallic plate.

13. The friction stir welded component of claim 12, wherein the friction stir weld extends into the first run-on/off tab and the second run-on/off tab.

14. The friction stir welded component of claim 11, wherein the first metallic plate and the second metallic plate include aluminum or aluminum alloy.

15. The friction stir welded component of claim 11, wherein the backing plate backing plate width is greater than or equal to four times the thickness of one or both of the first and second metallic plates and a thickness greater than or equal to one third times the thickness of one or both of the first and second metallic plates.

16. A friction stir welded blank comprising: a first metallic plate and a second metallic plate joined at faying surfaces by a friction stir weld; wherein the friction stir weld has a stable microstructure having little or no abnormal grain growth during elevated temperature forming, heat treatment and aging.

17. The friction stir welded blank of claim 16, wherein the friction stir welded blank has a circular geometry.

18. The friction stir welded blank of claim 17, wherein the friction stir welded blank is a spin blank.

19. The friction stir welded blank of claim 16, wherein the first metallic plate and the second metallic plate include aluminum or aluminum alloy.

20. The friction stir welded blank of claim 16, wherein the backing plate backing plate width is greater than or equal to four times the thickness of one or both of the first and second metallic plates and a thickness greater than or equal to one third times the thickness of one or both of the first and second metallic plates.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0012] FIG. 1 shows a schematic view of a weld setup according to the present disclosure prior to welding.

[0013] FIG. 2 shows a sectional view of FIG. 1 taking in direction 2-2.

[0014] FIG. 3 shows a schematic view of a weld setup according to the present disclosure after welding.

[0015] FIG. 4 shows a sectional view of FIG. 3 taking in direction 4-4.

[0016] FIG. 5 shows a flowchart illustrating a process according to the present disclosure.

[0017] FIG. 6 shows a schematic view of two welded plates that have been welded according to a method of the present disclosure.

[0018] FIG. 7 shows a schematic view of the welded plates of FIG. 6 having the backing plate removed according to a method of the present disclosure.

[0019] FIG. 8 show an elevational view and a sectional view of exemplary friction stir welding tool geometries according to an embodiment of the present disclosure.

[0020] FIG. 9 shows photomicrographs from welded samples welded according to known friction stir welding procedures.

[0021] FIG. 10 shows photomicrographs from welded samples welded according to a friction stir welding procedure not utilizing a backing plate.

[0022] FIG. 11 shows a photomicrograph illustrating the effect of AGG on weld properties of a welding procedure not utilizing a backing plate.

[0023] FIG. 12 shows a photomicrograph showing the microstructure of a weld without the use of a backing plate after an annealing cycle.

[0024] FIG. 13 shows a photomicrograph showing the microstructure of a weld after a solution heat treatment wherein the backing plate is in position below the point of abutment.

[0025] FIG. 14 shows a photomicrograph showing the microstructure of a weld formed according to an embodiment of the present disclosure where the backing plate was removed prior to annealing.

[0026] FIG. 15 schematically illustrates a spin forming apparatus utilizing a blank formed by a method according to the present disclosure.

[0027] FIG. 16 shows a welded spin blank according to an embodiment of the present disclosure.

[0028] FIG. 17 shows a shaped component formed from a welded spin blank according to an embodiment of the present disclosure.

[0029] FIG. 18 shows a final component formed from the shaped component of FIG. 17 after heat treatment, aging and machining.

[0030] Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts.

DETAILED DESCRIPTION OF THE INVENTION

[0031] Embodiments of the present invention include a friction stir welding, forming, and heat treatment process that may be applied to large aerospace structures, and maintain a stable microstructure through both forming and heat treatment to yield high strength welds of greater than 95% joint efficiency. The methods according to the present disclosure permit procurement of narrower commodity metallic plates, such as aluminum plates, which may be sourced from multiple manufacturers, in a far more cost-effective manner, than procuring large monolithic plate stock sourced from a single manufacturer, as is done currently, to avoid undesirable welding effects.

[0032] The method according to the present disclosure includes a single-sided weld approach that utilizes a friction stir welding process, wherein the tip of the friction stir welding tool extends past the thickness of abutting metallic plates into a backing plate that is removed in a subsequent machining operation prior to further manufacturing heat treatments or deformation process steps. The removal of the sacrificial backing plate aids in formation or maintenance of a stable microstructure in the formed and heat-treated component. By stable microstructure, as utilized herein, it is meant that the microstructure has little or no abnormal grain growth (AGG) in subsequent elevated temperature forming and heat treatment and/or aging.

[0033] FIGS. 1-4 shows a welding setup 100 according to an embodiment of the disclosure and FIG. 5 illustrates a flowchart illustrating method 500 according to an embodiment of the disclosure. Method 500 according to the present disclosure includes a method for formation of large metallic components. As utilized herein, large components include components that exceed a diameter or other dimension that is difficult or impractical to obtain without utilizing a joining technique, such as welding. For example, large components may be components having a dimension greater than 100 inches, greater than 150 inches, greater than 200 inches or greater than 250 inches. As shown in FIG. 1 and FIG. 2, the final geometry of the spin blank 115 prior to forming is superimposed on the welding setup 100 to show the size of the spin blank 115 that will result after welding and machining. Specifically, spin blank 115 includes a large diameter 117 corresponding to a large component 1700 (see for example, FIG. 17).

[0034] Method 500 includes positioning a first metallic plate 101 and a second metallic plate 102 in an abutting arrangement (step 501). The first metallic plate 101 and the second metallic plate 102 include faying surfaces 105 at a point of abutment 107. While FIG. 1 shows only two metallic plates, including the first metallic plate 101 and the second metallic plate 102, any number of plates may be used, provided the plates are in an abutting arrangement such that they may be friction stir welded together. The first metallic plate 101 and second metallic plate 102 may be any suitable metallic material that may be friction stir welded together to form a spin blank 115. Suitable materials may include, but are not limited to, aluminum or aluminum alloy plates. In one embodiment, first metallic plate 101 and second metallic plate 102 may be provided in either the F (as-rolled), O temper (annealed), or T3 temper (SHT, quench, cold worked). In one embodiment, first metallic plate 101 and second metallic plate 102 are rectangular and substantially identical in size and thickness. For example, in one embodiment, first metallic plate 101 and second metallic plate 102 may be 109 inches or greater in width, 218 inches or greater in length, and ? inch or greater in thickness. In addition, as shown in FIGS. 1 and 3, run-on/off tabs 103 are attached, adhered, or formed at distal ends of the point of abutment 107 of the first metallic plate 101 and second metallic plate 102. In one embodiment, run on/off tabs 103 are attached by tack welding. Run-on/off tabs 103 provide additional material to the welding setup 100 at the point of initiation of the stir welding operation and at the point of termination of the stir welding operation. Method 500 further includes attaching a backing plate 201 spanning the point of abutment adjacent the faying surfaces 105 (step 503). The backing plate 201 may include the material of the same alloy as first metallic plate 101 and second metallic plate 102 or may include other compatible materials (see FIG. 2). The backing plate 201 is position in the welding setup 100 such that the backing plate 201 receives at least the tip of the welding tool 401 (see for example, FIG. 4) during welding. That is, the backing plate 201 is positioned so that, after welding, the weld root 405 terminates in the backing plate 201. In one embodiment, the sacrificial backing plate 201 includes a width greater than or equal to 4T (four times the thickness) of the plates 101, 102 and a thickness greater than or equal to ? T (one third times the thickness) of the plates 101, 102. The backing plate 201 may extend below the run-on/off tabs 103.

[0035] The first metallic plate 101, second metallic plate 102 and the backing plate 201 are welded together with a friction stir welding apparatus 403 to form a friction stir weld 108 using a single-sided, fixed tool, friction stir welding process with a low RPM and slow feed rate. The stir welding apparatus 403 is configured to rotate a welding tool 401 at a speed sufficient to accomplish friction stir welding and advance the welding tool 401 along a path at the faying surfaces 105 to form the friction stir weld 108. The welding tool 401 may be any tool suitable for use with a friction stir welding apparatus 403. In one embodiment, the welding tool 401 is a pin. The geometry of the welding tool 401 is any suitable geometry for friction stir welding faying surfaces 105. While the welding tool 401 according to the present disclosure is not so limited, FIG. 8 shows examples of alternative friction stir welding tool geometries suitable for use with the friction stir welding apparatus 403 according to the present disclosure. As shown in FIG. 8, the upper section of the figure shows an elevation view of the friction stir welding apparatus 403 and the lower portion of the figure shows a cross-sectional view of the welding tool 401. As shown in FIG. 8, different geometries may be used. While not so limited, as shown in FIG. 8, suitable geometries may include geometry (a), which is a cylindrical pin geometry, geometry (b), which is a cylindrical pin geometry having threads, geometry (c), which is a tapered cylindrical pin geometry, geometry (d), which is a square tool geometry, and geometry (e), which is a triangular geometry. The friction stir welding tool 401 has a sufficient length to extend past the faying surfaces 105 of the first metallic plate 101 to the second metallic plate 102 into backing plate 201 (step 505). In one embodiment, the welding tool 401 extends at least halfway through the thickness of the backing plate 201 during welding. In another embodiment the welding tool 401 extends at least 75% of the thickness of the backing plate 201. However, in embodiments of the present disclosure, the welding tool 401 is not permitted to extend through the entire thickness of the backing plate 201. This single side/single pass low rpm and slow feed rate welding process yields a deposited friction stir weld 108 with material properties as similar to metal of the first metallic plate 101 and the second metallic plate 102 as possible. In certain embodiments of the present disclosure, the friction stir welding may include welding parameters in accordance with AWS D17.3 (2021), including speeds, feed rates, and iterations utilized to match material chemistry variations as well as subsequent effective heat treatments to maximize the weld properties. The method 500 according to the present disclosure maximizes weld formability and allows formation of large aerospace structures without formation of a brittle weld that is typical of as-welded known aluminum friction stir weld assemblies. Effective friction stir welding parameters will vary depending on weld joint thickness. Suitable friction stir welding parameters may include, but are not limited to, tool rotational speed in a range of 50 to 150 rpm, with feed rate range of 0.5 and 2.5 inches per minute (IPM). As shown in FIGS. 3, the friction stir welding process begins with providing the friction stir welding tool 401 to entry point 109 and run along the faying surfaces 105 of first metallic plates 101 and second metallic plates 102. The welding is continued until the welding tool 401 has advanced into the run-of/off tab 103 to exit point 111 to form friction stir weld 108. As shown in FIG. 4, the weld root 405 terminates in the backing plate 201. Weld root 405 is the point in weld at or near where friction stir welding tool 401 terminates during the welding process (see also FIG. 6). FIG. 6 shows a schematic view of the first metallic plate 101, second metallic plate 102 and the backing plate 201 after welding.

[0036] Optionally, after the friction stir welding is completed, the friction stir weld 108 may be inspected in the welding setup 100 via any suitable weld inspection technique. Suitable weld inspection techniques include, but are not limited to, phased array ultra-sonic (PAUT) volumetric inspection for defects to a NASA-STD-5009 (revision B, May 8, 2019) standard or better.

[0037] After inspection, the backing plate 201 is removed from the weld set-up 100 to form a welded blank (step 508). In addition, the backing plate 201, run-on/off tabs 103 are removed from welded plates 101, 102 by machining. The machining may be accomplished with any known machining process known for machining the material of the first metallic plates 101 and second metallic plates 102. In one embodiment, the weld may be machined flush to the weld plates 101,102 on one side and the backing plate 201 is removed and the weld is machined flush on the opposite side.

[0038] In addition, the spin blank 115 as shown in FIGS. 1, 3 and 15 may be a round or circular diameter. However, the geometry is not so limitation and other suitable geometries may be utilized for the spin blank 115. For example, FIG. 16 shows a round spin blank 115 after welding ready for forming of the component 1700.

[0039] After formation of the welded blank, method 500 further includes forming the welded blank into a component form (step 509). The forming may be any suitable forming process for forming large components. Particularly suitable processes may include, but are not limited to, known spin-forming or stretch spin-forming processes. An exemplary apparatus for use with the method 500 according to the present disclosure, is shown in FIG. 15. Suitable known processes for spin forming are likewise disclosed in NASA Report #NESC-RP-13-00884 Section 7.6 and U.S. Pat. No. 6,199,419131, both of which are hereby incorporated by reference in their entirety. FIG. 17 shows a formed component 1700 according to an embodiment after the welding of step 509.

[0040] FIG. 15 shows an exemplary spin forming apparatus for spin forming the spin blank 115 into component 1700. As shown in FIG. 15, the spin blank 115 is mounted onto a shaft 1501 extending between a tailstock 1502 and a headstock 1505. The spin blank 115 rotated on the shaft 1501 with a spindle 1503 driven by a motor (not shown) in a headstock 1503. The spin blank 115 is retained in position with a clamp or follower 1507 that retains the spin blank 115 in position along shaft 1501. A forming roller 1509 is directed into and along spin blank 115 to deform the metallic material of the spin blank 115 into a desired shape. A mandrel 1511 is positioned between the spindle 1503 and the spin blank 115 and has an outer surface having geometry corresponding to the desired geometry of the spun formed or finished component 1700 (see for example, FIG. 20). The forming roller 1509 is directed into and along spin blank 115 until a surface of the spin blank 115 contacts and conforms to the outer surface of the mandrel 1511.

[0041] After the effective spin-forming deformation formation (step 509), the spun component 1700 may be heat treated (step 511) to achieve the desired material properties. The temperature and process times for each aluminum alloy are specific to that alloy's chemistry. Examples of suitable heat treatment steps for metallic components are disclosed in at least U.S. Pat. Nos. 5,066,342, 6,562,154, 7,490,752, and 9,090,950, each of which is incorporated by reference in their entirety.

[0042] In certain embodiment, a recovery anneal, or intermediate annealing treatment may be utilized. If a recovery anneal or intermediate annealing treatment IAT is used, the temperature will typically be several hundred degrees below the alloy's solvus temperature. Following the IAT the component is solution heat treated and quenched in a water or water-glycol solution quench bath. The IAT, if utilized, may be performed as a separate process step, or performed in conjunction with the solution heat treatment process. For example, a suitable heat treatment process in aluminum alloy 7075 is to perform the IAT at 500? F. and then air cool to room temperature, followed by a solution heat treatment at 870? F. for 180 minutes and quenching into a 16% water-glycol solution quench bath.

[0043] In another embodiment, the component 1700 may require a T8 material property. In this embodiment, a cold spin-forming deformation process may be carried out after the solution heat treatment and before the final precipitation heat treatment. The component 1700 will then be age heat treated to final temper requirements using a precipitation heat treatment cycle. Suitable heat treatments will vary depending on alloy, some may require a period of natural aging at ambient room temperature before performing a precipitation heat treatment cycle. For example, a suitable age heat treatment process in aluminum alloy 7075 is to allow the component 1700 to naturally age in ambient conditions for 96-100 hours following quenching then to precipitation heat treat by soaking the component 1700 at 250? F. for 16 hours then soaking the component 1700 at 325? F. for 16 hours.

[0044] Test coupons may be removed from the formed and heat-treated component 1700 to verify weld metal and base metal properties. The component 1700 may further include traditional, known manufacturing sequences (milling/turning/drilling etc.) to complete the product to its dimensional requirements. FIG. 18 shows a final component 1800 formed from the shaped component 1700 after heat treatment, aging and machining.

[0045] Friction stir weld 108 formed by the method according to the present disclosure includes a weld efficiency of from about 95% to 98% or greater than 95% or greater than 97% or greater than 98% weld efficiency compared to base metal of first metallic plates 101 and second metallic plates 102, required minimum properties for room temperature tensile strength. Weld joint efficiency is defined as FSW Ultimate Tensile Strength divided by Base Metal Ultimate Tensile Strength.

Examples

[0046] In a known comparative process performed by NASA, samples were welded on opposites sides of the abutting surface with friction stir welding (double pass FSW) performed utilizing known conditions. (NASA Document ID #20140001083: Investigation of Abnormal grain growth in a Friction Stir welded and Spin-Formed AL-LI Alloy 2195 Crew Module). FIG. 9 shows photomicrographs of the weld with various process treatments; as-friction stir welded (FSW), FSW+25% hot rolling reduction (HR)+solution heat treatment (SHT), and FSW+25% HR+intermediate annealing treatment (IAT)+SHT. All The welds shown in FIG. 9 include AGG growth in the center/overlap of the double pass friction stir weld. AGG with the FSW poses the greatest risk in terms of meeting mechanical property specifications from NASA document ID 20140001083.

[0047] In another comparative example, FIG. 10 shows photomicrographs from welded samples welded according to a friction stir welding procedure not utilizing a backing plate. As can be seen in FIG. 10, AGG formed at the weld root. FIG. 11 shows a photomicrograph of the welded sample from FIG. 10, that was friction stir welded, solution heat treated, quenched, and aged, showing weld properties at various locations along the weld. As can be seen in FIG. 11, the AGG formed in the weld (present in the Bottom as shown on the chart of FIG. 11) detrimentally affect properties, including ultimate tensile strength (UTS) and % elongation.

[0048] FIG. 12 shows a weld formed without a backing plate 201, where AGG nucleated from the weld root through the crystalline matrix of majority of the weld metal when subjected to the alloy's solution heat treatment per AMS 2770 (2020). FIG. 12 illustrates an example of how the AGG can nucleate from the tip of the tool, as shown in FIG. 11, and can propagate through the crystalline matrix of most of the weld metal when subjected to the alloy's solution heat treat temperature of typically 900-1000? F.

[0049] FIGS. 13 & 14 show photomicrographs from the same friction stir weld 108 after an annealing heat treatment per AMS 2770. FIG. 14 includes an example according to the present disclosure, where backing plate 201 has been removed prior to forming and heat treatment. In FIG. 13 the backing plate 201 was left on during the during the annealing heat treatment and in FIG. 14 the backing plate 201 was removed prior to the annealing heat treatment and is an embodiment of the present disclosure. In the FIG. 13 photomicrograph, AGG is present in the tip of the weld after the annealing heat treatment. In the FIG. 14 photomicrograph, the microstructure is stable and no AGG is present in the weld. FIG. 13 shows an example of welding with a backing plate 201 showing AGG starting in the tip of the weld after an annealing cycle at 775? F. FIG. 14 shows an example of how AGG can be controlled by removing the backing plate 201 before forming and heat treatment. The sample of FIG. 14 was annealed at 775? F. and remained stable.

[0050] While the exemplary embodiments illustrated in the figures and described herein are presently preferred, it should be understood that these embodiments are offered by way of example only. Accordingly, the present application is not limited to a particular embodiment but extends to various modifications that nevertheless fall within the scope of the appended claims. The order or sequence of any processes or method steps may be varied or re-sequenced according to alternative embodiments.

[0051] It is important to note that the construction and arrangement of the various exemplary embodiments is illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present application. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. In the claims, any means-plus-function clause is intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the exemplary embodiments without departing from the scope of the present application.