A friction stir welding method using lateral inclination

Abstract

The present invention discloses a friction stir welding method using a lateral inclination angle, wherein a stirring needle and a shoulder are coaxially arranged, and the axial direction of the stirring needle and the shoulder is inclined to the rear of the forward direction relative to the normal direction of the plate surface to be welded, and the angle between the axial direction of the stirring needle and the shoulder and the normal direction is β, and is characterized in that the axial direction of the stirring needle and the shoulder is also inclined to the forward side relative to the normal direction, and the angle between the axial direction of the stirring needle and the shoulder and the normal direction is α. In the friction stir welding of the present invention, after the stirring head is inclined to the rear of the forward direction and to the forward side at the same time, the position of the shoulder part pressed into the metal surface coincides with the position of defects such as the friction stir welding tunnel hole and furrow, thereby increasing the hydrostatic pressure at the defect, so that the defect is closed under the action of pressure, thereby improving the quality of the welded joint.

Description

Technical Field

[0001] The invention relates to a friction stir welding method using a lateral inclination angle, and belongs to the technical field of friction stir welding. Background Art

[0002] Friction stir welding technology uses the friction between a high-speed rotating welding tool (stirring head) and the workpiece to generate heat, which increases the local temperature of the welded material and softens it, thereby achieving large shear deformation; under the stirring action of the welding tool, the interface of the welded workpiece is drawn into the interior of the metal, and the newly generated interface is welded under the pressure of the welding tool and the action of van der Waals force to form a welding structure.

[0003] The process parameters of friction stir welding include the rotation speed of the stirring head, the welding travel speed, the axial downward pressure of the stirring head during welding, and the angle (inclination) between the rotation axis of the stirring head and the normal of the welding surface.

[0004] Adopting a certain angle (inclination) between the stirring head rotation axis L and the welding surface normal N is beneficial to increasing friction heat and increasing the fluidity of the metal during stirring welding; at the same time, the inclined stirring head shoulder extends below the surface of the welding area, providing a larger downward pressure on the back side of the welding area, so that the metal in the welding area can be filled under a larger hydrostatic pressure condition, and a better welding effect can be obtained.

[0005] Figure 1 This is a schematic diagram of conventional friction stir welding. The stirring head 1 and the shoulder 2 move in the forward direction A (weld direction) while rotating. At the same time, the self-rotation axis of the stirring head and the normal of the plate (workpiece) to be welded have an angle β, which is formed by the stirring head and the shoulder tilting to the rear side of the forward direction A. The welding effect is best when the angle β is 2-4 degrees. If there is no backward tilted angle β, the heat generation during friction stir welding will be reduced, and the welding quality and welding effect will deteriorate.

[0006] At present, the stirring head is tilted to the rear, and this placement method of the stirring head can usually meet the welding requirements. However, a large number of studies (existing documents 1-4) show that defects such as tunnel holes and furrows produced by friction stir welding occur at the position of the stirring needle on the forward side. The inventors also found similar situations during the study of friction stir welding of aluminum alloys, such as Figure 2-Figure 5 shown. Figure 2 The tunnel-type hole defect of the friction stir welding joint is shown. Figure 3 Shows typical plowing defects in friction stir welding. Figure 4 The tunnel hole defect of the friction stir welding of cast A356 aluminum alloy T6 is shown. Figure 5 The tunnel hole defect of AA6061T6 plate in friction stir welding is shown. Figure 3 , Figure 4 , Figure 5 As shown in the figure, defects such as tunnel holes and furrows are located on the advancing side and deviate from the center line of the weld by a radius of the stirring needle. Figure 1 As shown, the forward side and the backward side are located on both sides of the forward direction A of the stirring needle. The metal in the forward side area moves in the forward direction A under the stirring action of the stirring needle, and the metal in the backward side area moves in the opposite direction of the forward direction A under the stirring action of the stirring needle. Since defects such as tunnel holes and furrows exist on the forward side, after the stirring head is tilted to the rear of the forward direction A, the position of the deepest shoulder part pressed into the metal surface does not coincide with the position of defects such as tunnel holes and furrows in the friction stir welding, resulting in the inability to further improve the welding quality. Therefore, how to reduce the possibility of defects such as tunnel holes and furrows is the key to improving the quality of friction stir welding.

[0007] Existing literature 1. Rajiv Sharan Mishra, Partha Sarathi De, Nilesh Kumar: FrictionStir Welding and Processing, Springer Cham Heidelberg, New York Dordrecht London, 2014;

[0008] Existing literature 2. Stephen Leon.J1*,Bharathiraja.G1 and Jayakumar.V:IOPconference series:Materials Science and Engineering 954(2020)012007,doi:10.1088 / 1757-899X / 954 / 1 / 012007;

[0009] Existing literature 3. Noor Zaman Khan, Arshad Noor Siddiquee, Zahid A. Khan, Suha K. Shihab, Journal of Alloys and Compounds 648 (2015) 360e367;

[0010] Existing literature 4. Panel Y. G. Kima H. ​​Fujiib T. Tsumurab T. Komazakic K. Nakata, Materials Science and Engineering A, Volume 415, Issues 1–2, 15 January 2006, Pages 250-254. Summary of the invention

[0011] In order to overcome the problems existing in the prior art, the present invention provides a stir friction welding method using a lateral inclination angle to reduce the possibility of defects such as tunnel holes and furrows in stir friction welding. The specific technical solution is as follows.

[0012] A friction stir welding method using a lateral inclination angle, wherein a stirring needle and a shaft shoulder are coaxially arranged, the axial direction of the stirring needle and the shaft shoulder is inclined rearwardly of the forward direction relative to the normal direction of the plate surface to be welded, and the angle between the axial direction of the stirring needle and the shaft shoulder and the normal direction is β, characterized in that the axial direction of the stirring needle and the shaft shoulder is also inclined toward the forward side relative to the normal direction, and the angle between the axial direction of the stirring needle and the shaft shoulder and the normal direction is α.

[0013] Furthermore, the angle β is greater than 0 degrees and less than or equal to 4 degrees.

[0014] Furthermore, the angle α is greater than 0 degrees and less than or equal to 10 degrees.

[0015] Furthermore, the diameter of the shoulder is D, the stirring needle is conical, the maximum diameter is d', the minimum diameter is d", and the angle α satisfies:

[0016] At this time, the lowest point of the shoulder can be better made to fall on the edge of the stirring needle contour.

[0017] Friction stir welding technology uses the friction between a high-speed rotating welding tool (stirring head) and the workpiece to generate heat, which increases the local temperature of the welded material and softens it, thereby achieving large shear deformation; under the stirring action of the welding tool, the interface of the welded workpiece is drawn into the interior of the metal, and the newly generated interface is welded under the pressure of the welding tool and the action of van der Waals force to form a welding structure.

[0018] During the friction stir welding process, the metal flow law is as follows: the stirring head (including the shoulder and the stirring needle) is rotating, driving the metal to rotate around the stirring head. At the same time, when the stirring needle moves forward, it will cut a groove similar to the outline of the stirring needle on the welding path of the metal plate. Driven by the stirring head, the metal on the forward side moves forward, and under the constraints of the shoulder and the front metal, it rotates to the backward side with the stirring head; the metal on the backward side is driven by the stirring head and pushed by the metal rotating from the forward side, and flows to the gap left behind the stirring needle and fills the gap. When the welding speed is slow, the gap left behind the stirring needle per unit time is small, and more metal is brought in under the condition of fast rotation speed, so the gap will be well filled with metal. But when the rotation speed is slow and the welding speed is fast, the gap left behind the stirring needle is large, and less metal is brought in under the condition of rotation, so the gap will form insufficient welding defects from metal flow. The macroscopic picture of the tunnel hole (Wormholes or tunnel hole) is as follows Figure 5; The macroscopic picture of the furrow (Surface lack of filling) is as follows Figure 3 , Figure 3 The middle furrow is located at the contour edge of the stirring pin on the advancing side.

[0019] In all current research and welding engineering practices, the stirring head is tilted toward the rear (opposite to the forward direction of the stirring needle). There are no reports or engineering practices on the stirring head tilting toward the rear and the forward side at the same time.

[0020] When the stirring head is tilted backward, during the friction stir welding process, the farthest end of the gap formed by the forward stirring needle and the metal is at the edge of the contour of the stirring needle on the forward side, which is half the diameter of the stirring needle away from the center line; and the deepest downward pressure of the shoulder is in the middle of the weld. In this way, there is a very large position deviation between the highest hydrostatic pressure in the welding area and the location of the tunnel hole and the furrow. At the same time, after the metal flows through the area with the highest hydrostatic pressure and continues to move forward to the area with low hydrostatic pressure, the flow rate will slow down significantly, and the location of the defect generation on the forward side is as follows: Figure 6 As shown in the white dotted line position, the result is that the metal is not easy to fill the tunnel holes and furrows; defects such as tunnel holes and furrows are formed due to insufficient metal flow.

[0021] like Figure 7 As shown, when the stirring head of the present invention is tilted toward the rear and the forward side at the same time, during the friction stir welding process, the downward pressure of the shoulder will be closer to the farthest end of the gap filling, that is, located at the edge of the contour of the stirring needle on the forward side, so that the highest hydrostatic pressure in the welding area is at the location of the tunnel hole and the furrow. At the same time, the metal flow will not experience a stage where the hydrostatic pressure decreases from high to low, and there will be no tunnel hole and furrow defects formed due to insufficient metal flow, which is more conducive to eliminating the tunnel hole and furrow defects formed due to insufficient metal flow. Fig. 9 shown.

[0022] according to Fig. 9 It can be seen that when the diameter of the shoulder is D, the maximum diameter of the conical stirring needle is d', and the minimum diameter is d", in order to make the lowest point of the stirring head shoulder fall on the edge of the stirring needle contour, the angle α tilted toward the forward side should satisfy:

[0023]

[0024] In practice, the angle α inclined toward the advancing side can be determined as the optimal value through experiments to obtain the best welding effect.

[0025] By adopting the above-mentioned technical scheme, the stirring head (including the stirring needle and the shoulder) is tilted toward the rear of the forward direction and toward the forward side at the same time. The position of the shoulder part pressed into the metal surface coincides with the position of defects such as the stir friction welding tunnel hole and furrow, thereby increasing the hydrostatic pressure at the defect and closing the defect under the action of pressure, thereby improving the quality of the welded joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of existing friction stir welding;

[0027] Figure 2 This is a photo of a tunnel-type hole defect in a friction stir welded joint;

[0028] Figure 3 This is a photo of a typical plowing defect in friction stir welding;

[0029] Figure 4 It is a microscopic magnified photo of the tunnel hole defect of the cast A356 aluminum alloy T6 heat-treated plate after the existing stir friction welding;

[0030] Figure 5 This is a microscopic magnified photo of the tunnel hole defect of AA6061T6 plate after the existing friction stir welding;

[0031] Figure 6 It is a simulation diagram of medium effect strain distribution of AA6061 plate using existing friction stir welding;

[0032] Figure 7 is a schematic diagram of friction stir welding of the present invention, Figure 7 (a) is the front view, Figure 7 (b) is a top view, Figure 7 (c) is a side view,

[0033] Figure 8 It is a simulation diagram of medium effect strain distribution of AA6061 plate by friction stir welding of the present invention;

[0034] Fig. 9 It is a schematic diagram of the geometric relationship of the friction stir welding of the present invention;

[0035] Fig.10 It is a microscopic magnified photograph of the tunnel hole defect of the cast A356 aluminum alloy T6 heat-treated plate after the stir friction welding of the present invention;

[0036] Fig.11 This is a microscopic magnified photograph of the tunnel hole defect of the AA6061T6 plate after the stir friction welding of the present invention.

[0037] In the figure: stirring head 1, shaft shoulder 2, forward direction A, forward side F, backward side B. DETAILED DESCRIPTION

[0038] Example 1

[0039] Cast A356 aluminum alloy T6 heat-treated plate, tensile strength 250MPa, elongation 8%; the stirring head has a shoulder diameter of 18mm, a stirring needle length of 5.5mm, a stirring needle root diameter of 7mm, and a stirring needle tip diameter of 3mm. When the stirring head is tilted 2° to the rear after welding, the metallographic photo is as follows Figure 4 As shown in the figure, there are obvious hole defects, the tensile strength of the weld is 200MPa, and the elongation is 6%. When the patented method is used, the stirring head is tilted 2° to the rear and 4° to the forward side, and the position of the shoulder part pressed into the metal surface coincides with the position of the friction stir welding tunnel hole, furrow and other defects. The metallographic photo after welding is shown in the figure below. Fig.10 As shown, the defects caused by insufficient metal flow are significantly reduced, the weld tensile strength is 230MPa, and the elongation is 8%.

[0040] Example 2

[0041] 6061 aluminum alloy T6 heat-treated rolled plate, tensile strength 280MPa, elongation 12%; the stirring head has a shoulder diameter of 18mm, a stirring needle length of 5.5mm, a stirring needle root diameter of 7mm, and a stirring needle tip diameter of 3mm. When the stirring head is tilted 2° to the rear, the metallographic photo is as follows: Figure 5 As shown in the figure, there are obvious hole defects, the tensile strength of the weld is 210MPa, and the elongation is 8%. When the patented method is used, the stirring head is tilted 2° to the rear and 4° to the forward side, and the position of the shoulder part pressed into the metal surface coincides with the position of the friction stir welding tunnel hole, furrow and other defects. The metallographic photo after welding is as follows Fig.11 As shown, the defects caused by insufficient metal flow are significantly reduced, the weld tensile strength is 240MPa, and the elongation is 10%.

[0042] In addition, when the stirring head is tilted less than 4° to the rear and less than 10° to the forward side, better defect control can be observed compared with the traditional stir friction welding method.

[0043] The embodiments of the present invention are described above in conjunction with the accompanying drawings. In the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention is not limited to the above-mentioned specific implementations, which are merely illustrative and not restrictive. Under the enlightenment of the present invention, those skilled in the art can also make many forms without departing from the scope of protection of the present invention and the claims, all of which belong to the protection scope of the present invention.

Claims

1. A friction stir welding method using a lateral inclination angle, wherein the stirring needle and the shaft shoulder are coaxially arranged, the axial direction of the stirring needle and the shaft shoulder is inclined backward in the forward direction relative to the normal direction of the plate surface to be welded, and the angle between the axial direction of the stirring needle and the shaft shoulder and the normal direction is β, characterized in that: The axial direction of the stirring needle and the shaft shoulder is also inclined toward the forward side relative to the normal direction, and the angle between the axial direction of the stirring needle and the shaft shoulder and the normal direction is α; The diameter of the shoulder is D, the stirring needle is conical, its maximum diameter is d', its minimum diameter is d", and the angle α satisfies: 。 2. A friction stir welding method using a lateral inclination angle according to claim 1, characterized in that: The angle β is greater than 0 degrees and less than or equal to 4 degrees.

3. The friction stir welding method using a lateral inclination angle according to claim 1, characterized in that: The angle α is greater than 0 degrees and less than or equal to 10 degrees.

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