Patent Application
20180050419
The present invention relates to metal welding, in particular friction stir welding.
Friction stir welding (referred to as “FSW”) is a method of joining a first metal, such as an aluminum alloy sheet or plate, to a second metal, such as a steel, copper, nickel or other metal sheet or plate. The sheets/plates are softened, but not melted, and the softened metals and/or alloys are mechanically mixed by stirring and joined by applying pressure from a FSW tool to interlock the metal sheets or plates.
Aluminum alloys are increasingly replacing steel and other metals in manufacturing and various applications. Increased use of aluminum alloys requires a broader range of characteristics of the aluminum alloy parts, such as thicker gauges. Joining aluminum alloys with steel or other metals is challenging, especially when joining thicker gauges.
The terms “invention,” “the invention,” “this invention” and “the present invention,” as used in this document, are intended to refer broadly to all of the subject matter of this patent application and the claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the patent claims below. Covered embodiments of the invention are defined by the claims, not this summary. This summary is a high-level overview of various aspects of the invention and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification, any or all drawings, and each claim.
Provided herein is a tool for FSW thick gauge, dissimilar and/or other metal sheets (i.e., 3.5-8 mm) and plates (i.e., 8-16 mm) such as, but not limited to, aluminum alloy and steel, copper, nickel or other metal sheets and plates. As used herein, the term metal includes alloys. In some cases, the FSW tool includes a pin having a plurality of planar surfaces separated from one another by a plurality of teeth. In some cases, the tip of the pin is curved/domed. The pin extends from a shoulder, which may be concave in some examples. In some cases, a diameter of the shoulder is increased relative to a length of the pin. For example, a ratio of the diameter of the shoulder relative to the length of the pin may be greater than approximately 2.5:1, such as but not limited to approximately 3:1 or approximately 3.5:1.
Also disclosed are systems and methods for reducing heat generated in FSW. In some cases, a heat sink, such as but not limited to a copper anvil, and/or cooling nozzles are used. In some cases, the system additionally or alternatively includes clamps to help maintain the position of the metals during FSW.
Moreover, methods of welding dissimilar metals, including thick gauge metals, without defects or with minimized defects are disclosed. In some cases, the methods result in a FSW joint with layered intermetallic mixing and strong interlocking without forming a thicker (e.g., <2 μm) intermetallic layer at the interface.
The terms “invention,” “the invention,” “this invention” and “the present invention” used herein are intended to refer broadly to all of the subject matter of this patent application and the claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the patent claims below.
In this description, reference is made to alloys identified by aluminum industry designations, such as “series” or “6xxx.” For an understanding of the number designation system most commonly used in naming and identifying aluminum and its alloys, see “International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys” or “Registration Record of Aluminum Association Alloy Designations and Chemical Compositions Limits for Aluminum Alloys in the Form of Castings and Ingot,” both published by The Aluminum Association.
As used herein, the meaning of “a,” “an,” or “the” includes singular and plural references unless the context clearly dictates otherwise.
Disclosed is a tool for friction stir welding (FSW) two sheets, plates or other pieces of metal. In some cases, one or both of the metals is a thick gauge (e.g., about 5-10 mm) aluminum alloy, although in other cases one or both of the metals is not a thick gauge. In some cases, the second metal is a different metal, such as steel, copper, nickel or other metal. In some cases, the second metal has a different thickness than the first metal; in some cases, the second metal is thinner than the first metal. The first and second metals are friction stir welded to form a weld of any suitable configuration, including lap, edge, butt, T-butt, hem, T-edge, etc.
Pin 20 can have any suitable length 28. In some non-limiting examples, the length 28 of the pin 20 is between approximately 5 mm and approximately 11 mm, such as but not limited to between approximately 6 mm and approximately 9 mm or between approximately 5.9 mm and approximately 9.8 mm. Pin 20 includes a tip 30 that can be domed/curved. The dome shape of the tip 30 can help improve the life of the tool 10. The domed tip 30 can also increase the surface area and provide more contact with the metal work piece, which can result in an improved interlock between the metals being welded. Tip 30 can have any radius 32 (see
In some non-limiting examples, the ratio of the diameter 25 of the shoulder 24 to the length 28 of the pin 20 is increased from conventional tools. For example, the ratio of the diameter 25 to the length 28 may be greater than 2.5:1, such as but not limited to approximately 3:1 or approximately 3.5:1, which may reduce heat generated during FSW.
Pin 20 penetrates the first metal plate 110 by depth 150 and penetrates the second metal plate 120 by a depth 160. In some cases, depth 150 generally corresponds to the thickness of the first metal plate 110. In the example illustrated in
In some examples, as shown in
Tool 10 can be made of any suitable material such as steel. Two non-limiting examples of compositions of tool 10 are illustrated in Table 1 below, although any suitable material may be used.
As mentioned above, first and second metal plates 110, 120 can be any suitable material. In one example, first metal plate 110 is an aluminum alloy while second metal plate 120 is steel. Table 2 below lists two non-limiting examples of the composition of first metal plate 110, although any suitable aluminum alloy may be used, including any 2xxx, 5xxx, or 6xxx series aluminum alloy. As one non-limiting example, second metal plate 120 may be AISI 1018.
In some examples, clamping system 300 also includes end clamps 380 that secure the ends of the first and second metal plates 110 and 120 and, in some cases, the end stops 340. As with clamps 360, clamps 380 may be secured in any suitable way, including by bolting them to the fixture 310 by driving washer-fitted bolts 370 into the threaded holes 320. In some cases, end clamps 380 are not used. Utilizing a clamping system 300 with clamps 360 and/or clamps 380 helps secure the first and second metal plates 110 and 120 against the surface on which they are positioned, such as fixture surface 310. By preventing the first and second metal plates 110, 120 from lifting from the fixture surface 310, weld flash 400 as shown in
In some cases, the FSW system includes a heat sink or other heat transfer component, such as anvil 500 illustrated in
Also disclosed is a cooling system for controlling heat flow during FSW.
In some cases, one or both of first and second metal plates 110, 120 can be modified to have a reduced thickness area 700 as shown in
Also disclosed are methods and processes for FSW. In some cases, as described above, the FSW joins plates (or sheets and/or other pieces) of dissimilar metals and/or having different thicknesses. The process parameters disclosed herein provide a suitable weld between plates, including one or more thick plates (e.g., about 5 mm-about 10 mm), without jeopardizing the mechanical and/or corrosion properties of the plates 110, 120. As mentioned above, in some cases, first metal plate 110 may be a high strength 2xxx, 5xxx, or 6xxx aluminum alloy while the second plate 120 may be steel.
If desired, one or both of first and second metal plates 110, 120 may be prepared prior to FSW. For example, first and/or second metal plate 110, 120 may be cleaned by an abrasive pad and/or a solvent. In some non-limiting examples, an abrasive pad comprises metal, alloy, glass, diamond, polymer, natural sponge or the like. In some non-limiting examples, a solvent is organic. In some further non-limiting examples, a solvent acts as a degreaser. In some non-limiting examples, a solvent includes acetone, isopropanol, ethanol, methanol, hexanes, chloroform, chlorobenzene or the like.
Once the first and/or second metal plates 110, 120 are prepared, they are positioned with respect to one another. In one non-limiting example, the first metal plate 110 overlaps the second metal plate 120 by approximately 25 mm, although the plates may have any suitable overlap. Once the first and second metal plates 110, 120 have been positioned as desired, the plates 110, 120 are friction stir welded together using a FSW tool such as tool 10 described above. Any one or more of clamping system 300, heat sink 500, and cooling nozzles 600 may be employed during FSW.
In particular, a pin (such as pin 20) of the FSW tool (such as tool 10) is inserted into the first metal plate 110 at a plunge depth 150 (see
The tool 10 is further inserted into the second metal plate 120 to a suitable plunge depth 160 (see
Tables 3 and 4 below provide two non-limiting examples of suitable process parameters.
As discussed above, the method may optionally include positioning a heat sink, such as anvil 500, below the first and second metal plates 110, 120 prior to FSW. The method may additionally or alternatively include using a clamping system, such as clamping system 300, to secure the first and second metal plates 110, 120 relative to a fixation surface on which the first and second metal plates 110, 120 are positioned. As discussed above, the method may additionally or alternatively involve using a cooling system (such as one or more cooling nozzles 600) to cool the first and second metal plates 110, 120 as tool 10 traverses along the plates. Once the desired weld length is achieved, the tool 10 is removed from the first and second metal plates 110, 120.
Controlling one or more of the shoulder diameter 25 of the tool 10 (
An intermetallic zone between the first and second metal plates 110, 120 can be brittle and reduce weld strength. The disclosed process parameters result in a defect-free FSW joint or joint with minimized defects. The disclosed rotational speed and/or traverse speed of the tool 10 in combination with the disclosed plunge force and/or plunge depth helps alleviate or minimize shattering of one or both of first and second metal plates 110, 120 (particularly when second metal plate 120 is steel) in the nugget zone 920 for improved formability and corrosion resistance.
In some cases, the welded first and second metal plates 110 and 120 achieve approximately 60-70% of the strength of the non-welded metal with improved corrosion resistance without disturbing the non-welded metal microstructure.
Reference has been made in detail to various examples of the disclosed subject matter, one or more examples of which were set forth above. Each example was provided by way of explanation of the subject matter, not limitation thereof. In fact, those skilled in the art will understand that various modifications and variations may be made in the present subject matter without departing from the scope or spirit of the disclosure. For instance, features illustrated or described as part of one example may be used with another example to yield a still further example.
The following examples will serve to further illustrate the present invention without, at the same time, however, constituting any limitation thereof. On the contrary, it is to be clearly understood that resort may be had to various embodiments, modifications and equivalents thereof which, after reading the description herein, may suggest themselves to those skilled in the art without departing from the spirit of the invention.
An aluminum plate and a steel plate were friction stir welded using FSW tool 10 made with H13 steel. The aluminum plate and the steel plate were cleaned by scrubbing in acetone with an abrasive pad. The aluminum plate was an AA 5083 alloy with a thickness of 5.82 mm. The steel plate was an AISI 1018 alloy with a thickness of 2.0 mm. The process parameters for welds 1 and 2 are listed in Table 5.
Bar clamps were used to hold the aluminum plate and the steel plate in place. The FSW tool was made of AISI H13 steel (see Table 1). The hardness based on the Rockwell scale was 42 HRC (HRC denotes the metal was indented with a 120° spheroconical diamond with an axial load of 1.47 kN). The pin length of the tool was 5.94 mm, and the pin plunge depth 160 into the steel plate for weld #1 was 0.12 mm.
In weld #2, a local clamp was applied to prevent plate lifting, and the pin plunge depth was reduced to 0.07 mm. An air-bag system applied force to rollers adjacent to the FSW tool. Rollers held the work piece in place during the FSW process. Weld #2 was improved but some lifting occurred near the end of the plate, causing flash. The pin tip was worn further and pin length was reduced to 5.82 mm.
Tool 10 was used to friction stir weld an aluminum plate with a steel plate. As Example 1 demonstrated a problem employing a tool made of H13 tool steel in FSW of thicker gauge metals, a FSW tool of M42 tool steel (see Table 1) was used, as the composition provides high hardness. The aluminum plate was an AA 5083 alloy with a thickness of 5.82 mm. The steel plate was an AISI 1018 alloy with a thickness of 2.0 mm. The weld parameters employing the disclosed FSW tool are listed in Table 6.
Clamping system 300 using toe clamps 360 described above was applied (see
Weld #4 employed the same clamping system 300 with toe clamps 360 throughout the weld. The welded plates 110, 120 were allowed to passively cool to ambient temperature while remaining clamped. Weld #4 started with the pin 20 of the FSW tool 10 plunged 0.03 mm into the steel plate (plunge depth 160=−0.12 mm) and at halfway through, the weld plunge depth 160 increased by 0.03 mm (plunge depth 160=−0.25 mm). The welded aluminum and steel plates were left to fully cool in the fixture and loud popping and cracking sounds could be heard as the sample cooled. When removed from the fixture, the welded plates exhibited warping. The weld start and stop points de-bonded between the aluminum and steel plate, showing poor bonding.
Further development of the process for FSW thicker gauge metals is described herein. Three FSW trials were performed to explore the effect of (i) reducing the plunge depth of the pin 20 of the FSW tool 10 by reducing the thickness of the weld path, (ii) stressing the steel plate before FSW and (iii) pre-heating the steel plate before FSW. These modifications helped prevent weld flash and warping. A FSW tool 10 of M42 tool steel (see Table 1) was used. The aluminum plate was an AA 5083 alloy with a thickness of 5.82 mm. The steel plate was an AISI 1018 alloy with a thickness of 2.0 mm. The process parameters for the FSW are listed in Table 7.
Welding parameters for weld #5 are listed in Table 7.
Welding parameters for weld #6 are listed in Table 7. As shown in
Welding parameters for weld #7 are listed in Table 7. As shown in
Decreasing the plunge depth 160 of the pin 20 through plate thinning worked well for reducing the weld flash. Weld loads decreased. Neither pre-stressing nor preheating had an appreciable effect on warping reduction.
Further development of the process for FSW thicker gauge metals is described herein. Four FSW trials were performed to explore the effect of (i) reducing the tool rotational speed and (ii) forced-air cooling during FSW. These modifications helped prevent warping. A FSW tool 10 M42 tool steel (see Table 1) was used. The aluminum plate was an AA 5083 alloy with a thickness of 5.82 mm. The steel plate was an AISI 1018 alloy with a thickness of 2.0 mm. Clamping system 300 was employed applying side clamps 360 and end clamps 380 (see
Welding parameters for weld #8 are listed in Table 8. As shown in
Welding parameters for weld #9 are listed in Table 8. The plunge depth 160 of the pin 20 was increased by 0.1 mm compared to weld #8 to 0.15 mm. The weld surface was smooth and consistent with no flash. As the clamps 360, 380 were removed, the plates 110, 120 de-bonded from the weld exit to a distance 100 mm from the exit hole. The aluminum plate 110 shifted after de-bonding.
Welding parameters for weld #10 are listed in Table 8. The pin plunge depth 160 into the steel plate was 0.15 mm. The weld surface was smooth and consistent with no flash. As the clamps 360, 380 were removed, the plates remained bonded, but a series of ticking sounds were emitted from the joint line.
Welding parameters for weld #11 are listed in Table 8. A forced air cooling jet, such as nozzle 600 shown in
Welds #8 and 9 generated the most heat, which may have contributed to the low bond strength. Weld #10, which had a slightly lower heat generation, remained bonded but with suspected local separation. Weld #11 employed forced air cooling and remained bonded with no suspected bondline separation. Increasing the cooling rate of the weld exhibited reduced warping.
Further development of the process for FSW thicker gauge metals is described herein. Four FSW trials were performed to explore the effect of (i) pre-stressing the steel work piece, (ii) cooling with forced air, (iii) cooling with water mist, (iv) lowering the tool rotational speed and (v) increasing the traverse speed during FSW. The modifications prevented warping and steel debris found within the aluminum plate. A FSW tool 10 of M42 tool steel (see Table 1) was used. The aluminum plate was an AA 5083 alloy with a thickness of 5.82 mm. The steel plate was an AISI 1018 alloy with a thickness of 2.0 mm. Clamping system 300 was employed applying side clamps 360 and end clamps 380 (see
Welding parameters for weld #12 are listed in Table 9. The pin plunge depth 160 into the steel plate was 0.15 mm. The steel plate was pre-stressed (see
Welding parameters for weld #13 are listed in Table 9. The pin plunge depth 160 into the steel plate was 0.15 mm. Four water mist cooling nozzles (such as nozzles 600 shown in
Welding parameters for weld #14 are listed in Table 9. The pin plunge depth 160 into the steel plate was 0.15 mm. No cooling was applied for weld #14. The weld surface was smooth and consistent with no flash. The weld completed without incident. As the clamps 360, 380 were removed, no popping or cracking sounds were emitted.
Welding parameters for weld #15 are listed in Table 9. The pin plunge depth 160 into the steel plate was 0.15 mm. No cooling was applied for weld #14. The weld surface was smooth and consistent with no flash. The weld completed without incident and no popping or cracking sounds were noted upon removal of the clamps 360, 380 and removal from the fixture.
De-bonding occurred when the most heat was generated, internal stresses were greater for weld #12 with the pre-stressed steel plate, and the effective pin tip plunge depth 160 was increased. The increased cooling rate caused by the presence of the water mist behind the FSW tool 10 was extremely effective at reducing the warping caused by the welding process.
Further development of the process for FSW thicker gauge metals is described herein. Two FSW trials were performed to explore the effect of (i) combining findings from previous trials and (ii) employing a copper anvil 500 as a heat sink during FSW. The modifications prevented warping of the aluminum plate and the steel plate. A FSW tool of M42 tool steel (see Table 1) was used. The aluminum plate was an AA 5083 alloy with a thickness of 5.82 mm. The steel plate was an AISI 1018 alloy with a thickness of 2.0 mm. The process parameters are listed in Table 10.
The parameters for weld #16 are listed in Table 10. The pin plunge depth 160 into the steel plate was reduced by 0.07 mm to a depth of 0.08 mm compared to weld #15. The weld surface was smooth and consistent with no flash. The weld completed without incident, although light popping sounds were noted while cooling in the fixture.
The weld parameters for weld #17 are listed in Table 10. All conditions are identical to weld #16, including the plunge depth 160. The weld surface was smooth and consistent with no flash. The weld completed without incident and no popping or cracking sounds were noted during cooling or upon removal from the fixture.
Slight plastic deformation of the copper anvil 500 occurred after welding for both welds #16-17. Some differences were noted between the welds despite the attempts to maintain identical welding conditions. For example, there was slightly more advancing side material build-up on weld #16, more distortion on weld #16 and a possible wormhole on weld #17.
Further development of the process for FSW thicker gauge metals is described herein. Two FSW trials were performed to explore butt welding aluminum alloy and steel plates using FSW. A FSW tool 10 of M42 tool steel (see Table 1) was used. The aluminum plate was an AA 5083 alloy with a thickness of 5.82 mm. The steel plate was an AISI 1018 alloy with a thickness of 2.0 mm. The process parameters are listed in Table 11.
The parameters for weld #18 are listed in Table 11. The reference point for the tool position was the outside edge of the steel plate 120.
The parameters for weld #19 are listed in Table 11. The reference point for the tool position was the outside edge of the steel plate 120. The weld surface contained a line at the joint interface throughout the length of the weld. The exit hole contains a wormhole type of indication. Tool tilt for this weld was 2°. Despite changes to the tool programming, the tool was plunged about 0.7 mm too far into the steel plate (target was 0.2 mm).
Warping, grain structure, hardness, tensile strength and corrosion resistance of the FSW bonded pieces were analyzed for select weld trials.
Warping results are presented in Table 12. The amount of warping was measured by placing the welded bond in reference to a flat surface.
The grain structure of some of the samples after FSW is presented in
Corrosion resistance of the welded joints was tested according to the ASTM B117 standard. Welded workpieces were exposed to a salt spray for 500 hours. The joints were tested in as received (Bare/without coating) and painted conditions. Cathoguard 500 (supplied by BASF) was applied using the electrocoat (e-coat) method. Before e-coating, the samples were subjected to Zn phosphating with target coat weight of 2.5-3.0 g/m2. After 500 hours of testing, the samples were assessed based on the residual mechanical strength by tensile testing and corrosion morphology assessment by metallographic cross section. For comparison purposes, the unexposed bare and painted samples were subjected to tensile testing as well.
As-welded samples were not subjected to the corrosion test for comparison. Exemplary bare samples were bonded to steel and subjected to the corrosion test. Exemplary coated samples were bonded to steel and coated as described above. For both alloys, corrosion tested samples demonstrated slight decreases in bond strength compared to a non-corroded aluminum-steel FSW sample.
Also evident is no intergranular corrosion demonstrating the FSW joint can resist intergranular corrosion.
The alloys and methods described herein can be used in automotive and transportation applications, such as commercial vehicle, aircraft, ship building, automotive or railway applications, or other applications. For example, the alloys could be used for chassis, cross-member, and intra-chassis components (encompassing, but not limited to, all components between the two C channels in a commercial vehicle chassis) to achieve strength, serving as a full or partial replacement of high-strength steels. In certain examples, the alloys can be used in O, F, T4, T6x, or T8x tempers. In certain aspects, the alloys are used with a stiffener or insert to provide additional strength.
In certain aspects, the alloys and methods can be used to prepare motor vehicle body part products. For example, the disclosed alloys and methods can be used to prepare automobile body parts, such as bumper beams, side beams, roof beams, cross beams, pillar reinforcements (e.g., A-pillars, B-pillars, and C-pillars), inner panels, side panels, floor panels, tunnels, structure panels, reinforcement panels, inner hoods, or trunk lid panels. The disclosed aluminum alloys and methods can also be used in aircraft, ship building or railway vehicle applications, to prepare, for example, external and internal panels. In certain aspects, the disclosed alloys can be used for other applications, such as automotive battery plates/shates and wiring chases.
The present application claims the benefit of U.S. Provisional Patent Application No. 62/377,721 filed Aug. 22, 2016, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62377721 | Aug 2016 | US |
