WO2024093247A1

WO2024093247A1 - Near-non-weld-thinning friction stir welding method for aluminum alloy sheet

Info

Publication number: WO2024093247A1
Application number: PCT/CN2023/100562
Authority: WO
Inventors: 李超; 王贺; 宋建岭; 杜岩峰; 钱伟; 刘含伟; 高文静; 马康; 赵彦广; 朱亚蓉; 肖宏; 赵英杰; 孙转平; 王宁; 张睿博; 刘旭; 邓利芬; 张鑫; 刘旺; 王馨梦
Original assignee: 天津航天长征火箭制造有限公司
Priority date: 2022-10-31
Filing date: 2023-06-16
Publication date: 2024-05-10
Also published as: CN115673523A

Abstract

Provided in the present invention is a near-non-weld-thinning friction stir welding method for an aluminum alloy sheet. The method comprises the following steps: controlling a thinning amount of a front side of a weld by means of a near-non-weld-thinning stir welding head; controlling a thinning amount of a back side of the weld by means of the near-non-weld-thinning stir welding head; and welding the weld by means of the near-non-weld-thinning stir welding head. The present invention has the beneficial effects that the present invention achieves the near-non-weld-thinning and near-zero-defect friction stir welding of an aluminum alloy sheet, thereby achieving the possibility of high-quality welding of sheet aerospace products, greatly improving the welding quality of products and reducing the welding deformation of the products, and the present invention has an important practical significance and great economic value for an engineering application of aerospace model products.

Description

A friction stir welding method for aluminum alloy thin plates with almost no thinning

Technical Field

The invention belongs to the technical field of rocket equipment, and in particular relates to a friction stir welding method for aluminum alloy thin plates with near-zero thinning.

Background technique

As an advanced solid-phase joining technology, friction stir welding technology has been widely used in shipbuilding, aerospace, rail transportation and other fields. Among the types of friction stir welding technologies that have been applied in engineering, single-shoulder friction stir welding technology has the largest application scale, which is mainly divided into single-shoulder conventional friction stir welding technology and single-shoulder retractable friction stir welding technology.

In the field of spacecraft manufacturing, the conventional single-shoulder friction stir welding technology uses a shoulder and a stirring needle integrated stirring head for welding open welds, such as the longitudinal seams of the barrel section of the launch vehicle tank and the longitudinal seams of the melon slices at the bottom of the tank. The single-shoulder retractable friction stir welding technology uses a shoulder and a stirring needle separated stirring head. During the welding process, the shoulder and the stirring needle are controlled separately, and the welding and retraction actions are carried out simultaneously, thereby filling the keyhole defects after the stirring needle welding and realizing the welding of closed annular seams, such as the annular seams at the bottom of the launch vehicle tank and the annular seams of the box assembly.

Disadvantages of the existing technology: During the current friction stir welding process, affected by the forging pressure of the stirring head shoulder, the plastic metal squeezed on the front of the weld will form flash and squeeze out of the weld area, resulting in a certain degree of material loss in the weld area, causing the front of the weld to be thinned, as shown in A1 in Figure 1. During the friction stir welding process, in order to prevent the stirring needle from being too long and piercing the pad, so that the pad material enters the weld and causes a dissimilar metal inclusion defect, the stirring needle length will be 0.15-0.25mm less than the actual product welding area thickness, but will form a shallow weak bonding defect on the back of the weld. In order to ensure the quality of the weld, the back of the weld needs to be polished to remove the weak bonding defect, resulting in a certain degree of thickness loss on the back of the weld, as shown in A2 in Figure 1.

A1 and A2 together cause the overall thinning of the weld, especially in the friction stir of thin aluminum alloy. During welding, the product is extremely sensitive to weld thinning. A large amount of thinning will seriously affect the weld forging force. At the same time, if the weld has defects exceeding the standard and requires repair welding, the repair welding will further aggravate the weld thinning, causing a vicious cycle of weld quality. Therefore, strictly controlling the thinning amount of A1 and A2 can greatly reduce the overall weld thinning and improve the weld quality.

Summary of the invention

In view of this, the present invention aims to provide a friction stir welding method for aluminum alloy thin plates with near-zero thinning to address the deficiencies of the prior art.

To achieve the above object, the technical solution of the present invention is achieved as follows:

A friction stir welding method for aluminum alloy thin plates with near-zero thinning comprises the following steps:

S1. Use a nearly non-thinning stirring head to control the thinning amount of the weld front;

S2. Use a nearly non-thinning stirring head to control the thinning amount on the back of the weld;

S3, use a nearly non-thinning stirring head to weld the weld;

The nearly non-thinning stirring head comprises a shaft shoulder and a stirring needle, and the shaft shoulder and the stirring needle are an integrally formed structure.

Furthermore, the method for controlling the amount of thinning of the back side of the weld in step S2 comprises the following steps:

A1. The back of the product weld is polished and smooth;

A2. Open a chamfer of C0.2~C0.5 on the back of the two pairs of product edges.

Furthermore, in the process of welding the weld with the nearly non-thinning stirring head in step S3, the plasticized metal material of the product flows circumferentially from the forward side to the backward side and then to the forward side under the rotating stirring action of the stirring needle and the shoulder. The plastic metal on the forward side flows out to form a cavity, and the metal on the backward side fills the cavity on the forward side under the action of the stirring head.

Furthermore, the process parameters of the nearly non-thinning stirring head in step S3 are: the stirring head inclination angle 1°～2°, stirring head rotation speed 300～600r/min, welding travel speed 100～250mm/min.

Furthermore, the structural curve of the shoulder is an Archimedean double helix structure, and the distribution angle of each spiral line of the Archimedean double helix structure is 180°.

Furthermore, the structural curve of the shoulder is an Archimedean triple helix structure, and the distribution angle of each spiral line of the Archimedean triple helix structure is 120°.

Furthermore, for products with a welding zone thickness of 2 to 4 mm, the structural parameters of the shoulder are:

The radius of the convex spherical surface is R50~R65mm, the shoulder diameter is Φ13~Φ16mm, the angle of the stirring head body on the shoulder side is 90°, the fillet of the transition zone between the shoulder and the stirring head body is R0.5~R1mm, the radius of the Archimedean spiral arc groove is R0.25~R0.4mm, and the radius of the spiral end point is 0.8~1mm smaller than the shoulder radius.

Furthermore, for products with a welding zone thickness of 2 to 4 mm, the structural parameters of the stirring needle are:

The stirring needle has a taper angle of 18 to 20°, a root diameter of Φ4 to Φ6mm, a root fillet of R0.8 to R1, three inclined surfaces are arranged on the stirring needle, and the three inclined surfaces are distributed at 120°. The height of the inclined surfaces is 2.5 to 3.5mm, the thread is a trapezoidal structure, the height of the trapezoidal thread is 0.25 to 0.35mm, the width of the thread root is 0.2 to 0.25mm, the taper angle is 60°, and the end point is 0 to 0.3mm higher than the inclined surface.

Compared with the prior art, the friction stir welding method for aluminum alloy thin plates with near-zero thinning described in the present invention has the following advantages:

The present invention discloses a method for stir friction welding of aluminum alloy thin plates with near-zero thinning. The present invention realizes stir friction welding of aluminum alloy thin plates with near-zero thinning and near-defects, makes high-quality welding of thin-plate aerospace products possible, greatly improves the welding quality of products, and reduces welding deformation of products. It has important practical significance and huge economic value for the engineering application of aerospace model products.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the attached figure:

FIG1 is a schematic diagram of a friction stir weld thinning state in the prior art according to an embodiment of the present invention;

FIG2 is a schematic diagram of a double helix structure of a stirring head with near-zero thinning according to an embodiment of the present invention;

FIG3 is a schematic diagram of a triple-helix structure of a stirring head with near-zero thinning according to an embodiment of the present invention;

FIG4 is a schematic cross-sectional view of a shaft shoulder of a stirring head with near-zero thinning according to an embodiment of the present invention;

FIG5 is a schematic diagram of a double helix structure of a shaft shoulder of a stirring head with near-zero thinning according to an embodiment of the present invention;

FIG6 is a schematic diagram of a triple-helix structure of a shaft shoulder of a stirring head with near-zero thinning according to an embodiment of the present invention;

FIG7 is a schematic diagram of the structure of a stirring pin according to an embodiment of the present invention;

FIG8 is a schematic diagram of a cross-sectional structure of a stirring needle according to an embodiment of the present invention;

FIG9 is a schematic diagram of filling the forward side cavity during the friction stir welding process according to an embodiment of the present invention;

10 is a schematic diagram of the plastic metal flow state in the cross-sectional direction during the friction stir welding process according to an embodiment of the present invention;

FIG11 is a schematic diagram of the back chamfering of the butt joint edge before welding according to an embodiment of the present invention;

FIG. 12 is a schematic diagram of the overall method flow described in an embodiment of the present invention.

Detailed ways

It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate directions or positional relationships based on the figures. The orientation or positional relationship is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

As shown in FIGS. 1 to 12 , a friction stir welding method for aluminum alloy thin plates with near-zero thinning comprises the following steps:

S3, use a nearly non-thinning stirring head to weld the weld;

The nearly non-thinning stirring head comprises a shaft shoulder structure and a stirring needle structure, wherein the shaft shoulder structure and the stirring needle structure are an integrally formed structure, and both the shaft shoulder structure and the stirring needle structure are used for welding welds.

The present invention greatly reduces the thinning amount in the current single-shaft shoulder stir friction welding. By optimizing the design of the stirring head structure and chamfering the back of the workpiece to be welded before welding, the overall thinning amount of the weld is reduced by The thickness of the weld was reduced from 0.25 to 0.4 mm to 0.1 to 0.15 mm, and the weld qualification rate was increased to more than 95%, achieving near-zero-thinning and near-defective friction stir welding, improving the quality of the weld, and achieving the goal of qualified welding in one go.

Example 1

The idea of the present invention is:

1. Reduce or even eliminate the flash on the front of the weld, so that there is less or no loss of parent material on the front of the weld, thereby controlling the thinning amount on the front of the weld;

2. Under the premise of reducing the thinning amount of the weld front, ensure that there is sufficient forging pressure during welding to ensure the density of the weld, so as to ensure that the weld joint has good mechanical properties;

3. Under the premise of reducing the thinning amount of the weld front and ensuring the mechanical properties of the weld, improve the fluidity of the plastic metal during welding, strengthen the backfilling effect of the backward side of the stirring head on the forward side cavity, control the generation of weld defects from a mechanism point of view, and ensure the first-time welding pass rate of the weld;

4. Make full use of the fluidity of plastic metal in the vertical section direction to control the generation of weak bonding defects on the back side, thereby reducing the amount of grinding on the back side of the weld and controlling the amount of thinning on the back side of the weld.

Nearly non-thinning mixing head shoulder structure design:

In the present invention, the shoulder of the nearly non-thinning stirring head adopts the Archimedean spiral as the basic structural curve. In order to improve the convergence effect of the shoulder structure on the plastic metal and the stability of the welding process, an Archimedean double spiral or triple spiral structure is adopted. The distribution angle of each spiral line of the Archimedean double spiral is 180°, and the distribution angle of each spiral line of the Archimedean triple spiral is 120°, as shown in Figures 2 and 3.

The end face of the shaft shoulder of the nearly non-thinning stirring head adopts a convex spherical structure, which can increase the forging pressure of the stirring head during welding, ensuring that the weld has sufficient weld density while reducing the amount of thinning, thereby improving the mechanical properties of the weld. For aluminum alloy sheets with a thickness of 2 to 4 mm in the welding area, the shaft shoulder structure follows the following design:

The radius of the convex spherical surface is R50～R65mm, the diameter of the shaft shoulder is Φ13～Φ16mm, and the main stirring head on the shaft shoulder side is The body angle is 90°, the fillet of the transition zone between the shaft shoulder and the main body of the stirring head is R0.5-R1mm, and the radius of the Archimedean spiral arc groove is R0.25-R0.4mm, as shown in Figure 4. Influenced by the strong aggregation characteristics of the Archimedean spiral structure, the radius of the spiral end point is 0.8-1mm smaller than the shoulder radius, which can improve the edge morphology on both sides of the weld and make the transition between the weld and the base material smooth, as shown in Figures 5 and 6.

Nearly non-thinning stirring head stirring needle structure design:

For aluminum alloy sheets with a thickness of 2 to 4 mm in the welding zone, the stirring needle structure follows the following design:

The stirring needle has a taper angle of 18-20°, a root diameter of Φ4-Φ6mm, a root fillet of R0.8-R1, three inclined planes are machined on the stirring needle, distributed at 120°, and the height of the inclined plane is 2.5-3.5mm. The thread adopts a trapezoidal structure, which can effectively enhance the structural strength of the stirring needle compared with the current triangular thread. The height of the trapezoidal thread is 0.25-0.35mm, the root width of the thread is 0.2-0.25mm, and the taper angle is 60°. At the end of the thread processing, the tool gradually withdraws within 1/4 of a circle, and the end point is 0-0.3mm higher than the inclined plane, as shown in Figures 7 and 8. This structure can greatly improve the structural strength and reliability of the stirring head, and can meet the continuous and uninterrupted welding of at least 16m long ring welds.

Nearly zero-thinning friction stir welding process scope:

As shown in Figure 9, during the friction stir welding process, the plasticized metal material flows from the forward side to the backward side and then to the forward side in an annular direction under the rotating stirring action of the stirring needle and the shaft shoulder. The plastic metal on the forward side flows out to form a cavity. The metal on the backward side fills the forward side cavity under the action of the stirring head to maintain the consistency of the tissue density in the weld. The entire welding process is a dynamic balance process of tissue flow. The unreasonable structure of the stirring head and the process parameters will break the dynamic balance of the welding process and lead to the generation of internal defects in the weld.

Through a large number of process tests and verifications, for aluminum-lithium alloy materials, near-zero thinning stirring head welding is adopted. The process range is: stirring head inclination angle 1°~2°, stirring head rotation speed 300~600r/min, welding travel speed 100~250mm/min, which can obtain weld joints with beautiful shape, dense structure, excellent mechanical properties and weld front thinning less than 0.1mm.

Control of back thinning amount in friction stir welding with near-zero thinning:

The thinning of the back of the weld is mainly caused by the grinding and cleaning of weak bonding defects. Controlling the weak bonding defects can control the amount of grinding on the back of the weld, and controlling the amount of grinding can control the amount of thinning on the back of the weld. The flow direction of the plastic metal on the weld cross section during the stir friction welding process is shown in Figure 10. Under the action of the stirring needle thread, the plastic metal tends to flow to the back of the weld. Therefore, increasing the mixing degree of the plastic metal in the gap range of 0.15 to 0.25 mm between the end face of the stirring needle and the back pad can effectively control the generation of weak bonding defects.

The control method is: before welding the product, open a chamfer of C0.2 to C0.5 on the back of the two butt edges, as shown in Figure 11. During the welding process, the plastic metal in the weld will be fully filled and mixed in the chamfer, which can effectively control the generation of weak bonding defects. Through experimental verification, the number of weak bonding defects on the back of the weld is reduced to 10 to 20% before optimization. The back of the weld only needs to be polished and smooth, and the thinning amount can be controlled within 0.05mm.

Purpose of the present invention: (1) The present invention develops a thin plate aluminum alloy near-zero thinning stirring head, designs the stirring head shaft shoulder and stirring needle structure, and adopts the stirring head to effectively control the thinning amount of the weld front side;

(2) The present invention adopts a method of chamfering the back side of the product to be welded, which effectively controls the generation of weak bonding defects in the weld, and further controls the amount of grinding on the back side of the weld and the amount of thinning of the weld.

Advantages of the present invention: The present invention realizes nearly zero-thinning and nearly zero-defect stir friction welding of thin-plate aluminum alloy, makes high-quality welding of thin-plate aerospace products possible, greatly improves the welding quality of products, and reduces the welding deformation of products. It has important practical significance and huge economic value for the engineering application of aerospace model products.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

A friction stir welding method for aluminum alloy thin plates with near-zero thinning, characterized in that it comprises the following steps:

S1. Use a nearly non-thinning stirring head to control the thinning amount of the weld front;

S2. Use a nearly non-thinning stirring head to control the thinning amount on the back of the weld;

S3, use a nearly non-thinning stirring head to weld the weld;

The nearly non-thinning stirring head comprises a shaft shoulder and a stirring needle, and the shaft shoulder and the stirring needle are an integrally formed structure.
The friction stir welding method for aluminum alloy thin plate with near-zero thinning according to claim 1 is characterized in that the method for controlling the thinning amount of the back side of the weld in step S2 comprises the following steps:

A1. The back of the product weld is polished and smooth;

A2. Open a chamfer of C0.2~C0.5 on the back of the two pairs of product edges.
According to the near-zero-thinning friction stir welding method for aluminum alloy thin plates as described in claim 1, it is characterized in that: in the near-zero-thinning stirring head in step S3, during the welding process of the weld, the plasticized metal material of the product flows annularly from the forward side to the backward side and then to the forward side under the rotating stirring action of the stirring needle and the shaft shoulder, and the plasticized metal on the forward side flows out to form a cavity, and the metal on the backward side fills the cavity on the forward side under the action of the stirring head.
According to the near-zero-thinning stir friction welding method for aluminum alloy thin plates as described in claim 1, it is characterized in that the process parameters of the near-zero-thinning stirring head in step S3 are: stirring head inclination angle 1°~2°, stirring head rotation speed 300~600r/min, welding travel speed 100~250mm/min.
The friction stir welding method for aluminum alloy thin plate with near-zero thinning according to claim 1 is characterized in that the structural curve of the shoulder is an Archimedean double helix structure, and the distribution angle of each spiral line of the Archimedean double helix structure is 180°.
According to the friction stir welding method for aluminum alloy thin plates with near-zero thinning as described in claim 1, it is characterized in that the structural curve of the shoulder is an Archimedean triple helix structure, and the distribution angle of each spiral line of the Archimedean triple helix structure is 120°.
According to the friction stir welding method for aluminum alloy thin plate with near-zero thinning as claimed in claim 5 or 6, it is characterized in that the structural parameters of the shoulder are:

The radius of the convex spherical surface is R50~R65mm, the shoulder diameter is Φ13~Φ16mm, the angle of the stirring head body on the shoulder side is 90°, the fillet of the transition zone between the shoulder and the stirring head body is R0.5~R1mm, the radius of the Archimedean spiral arc groove is R0.25~R0.4mm, and the radius of the spiral end point is 0.8~1mm smaller than the shoulder radius.
The friction stir welding method for aluminum alloy thin plate with near-zero thinning according to claim 7 is characterized in that the structural parameters of the stirring needle are:

The stirring needle has a taper angle of 18 to 20°, a root diameter of Φ4 to Φ6mm, a root fillet of R0.8 to R1, three inclined surfaces are arranged on the stirring needle, and the three inclined surfaces are distributed at 120°. The height of the inclined surfaces is 2.5 to 3.5mm, the thread is a trapezoidal structure, the height of the trapezoidal thread is 0.25 to 0.35mm, the width of the thread root is 0.2 to 0.25mm, the taper angle is 60°, and the end point is 0 to 0.3mm higher than the inclined surface.
According to the nearly non-thinning friction stir welding method for aluminum alloy thin plates as described in claim 8, it is characterized in that the structural parameters of the shoulder and the structural parameters of the stirring needle are both set for products with a welding zone thickness of 2 to 4 mm.