CN102357734A - Method for connecting 2XXX and 7XXX heterogeneous aluminum alloy by laser filler wire - Google Patents

Abstract

The invention discloses a method for joining 2XXX and 7XXX dissimilar aluminum alloys by laser wire filler welding, which is applicable to the connection field of 2XXX and 7XXX series dissimilar aluminum alloys. In the present invention, two kinds of aluminum alloy plates to be welded are first assembled into a butt joint form, and by adjusting the positional relationship between the laser focus, the drop point of aluminum alloy welding wire and the butt joints of the two kinds of aluminum alloy plates, the laser beam, welding wire and The three aluminum alloy plates to be welded are in a reasonable relative position, and then adopt reasonable welding parameters such as laser power, welding speed and wire feeding speed, etc., and use AlCu or AlSi welding wire as filler material in the welding process to adjust the weld. ingredients to improve the performance of joints. The invention solves the problems of difficult connection of 2XXX and 7XXX series dissimilar aluminum alloys, softening of weld seam during fusion welding, and tendency of thermal cracking.

Description

A method for joining 2XXX and 7XXX dissimilar aluminum alloys by laser wire filler welding

Technical field:

The invention relates to a laser welding method for connecting 2XXX and 7XXX series dissimilar aluminum alloys through a filler wire, and is suitable for the connection field of 2XXX and 7XXX series dissimilar aluminum alloys.

technical background:

On the one hand, the manufacture of transportation vehicles must consider the requirements for performance, and on the other hand, the requirements for economy in the process of manufacturing and use must be considered. In order to achieve the above purpose, it is necessary to continuously reduce the weight of the vehicle under the condition of ensuring the performance of the vehicle. 2XXX and 7XXX aluminum alloys are two heat-treatable high-strength aluminum alloys, which are widely used in the aerospace field due to their low density and high specific strength. They are also substitute materials for modern high-speed trains, light vehicles and cars. Due to the wide application of the two aluminum alloys, it is inevitable that there will be a connection problem between the two. Traditionally, the connection method of aerospace aluminum alloys is mainly riveting, which increases the weight of the structure. 2XXX and 7XXX series of dissimilar aluminum alloys are mainly connected by bonding, but the bonding strength is low. Soldering is the preferred method to solve this problem.

Traditional welding methods have great limitations for welding aluminum alloys. Due to the large heat input of the arc welding method, the weld seam and the heat-affected zone of the 2XXX and 7XXX aluminum alloys will be severely softened during the welding process. Aluminum alloys are not recommended for arc welding. Friction stir welding has achieved good welding results in the welding of 2XXX, 6XXX, 7XXX series aluminum alloys and various aluminum alloys, but there are softening in the stirred zone, high forging pressure, high requirements for clamping, and difficulty in three-dimensional welding. The shortcomings of flexible processing and slow welding speed limit its application in many aspects. Although the quality of the weld seam obtained by vacuum electron beam welding is greatly improved compared with arc welding, it is difficult to be widely used due to the high cost, time-consuming and limited vacuum chamber space of vacuum electron beam welding.

Compared with traditional welding technology, laser welding technology has the advantages of controllable welding heat input, small heat-affected zone, fast welding speed, high welding efficiency, small welding deformation, and good beam accessibility, which is unmatched by other traditional heat sources. . In the process of laser deep penetration welding, due to the existence of deep penetration holes, laser welding has high energy density, fast heating and cooling speed, and narrow weld seam, making it a suitable method for aluminum alloy welding. Moreover, laser welding can perform complex flexible three-dimensional processing, is easy to realize automation, and has a wide range of commercial application prospects. Adding filler wire during the welding process not only stabilizes the welding process, but also plays a good role in bridging between the materials to be welded, which is beneficial to the connection between dissimilar metals, and can be effectively controlled by adjusting the welding wire composition. The composition of welded joints, inhibiting the generation of thermal cracks, and improving the performance of welded joints. These technical characteristics provide the possibility for the connection between 2XXX and 7XXX series dissimilar aluminum alloys.

In the laser deep penetration welding process, the laser power density exceeds the deep melting threshold of the material to produce deep penetration small holes, which will help the material absorb the laser. However, the small holes do not always exist stably. The stabilization phenomenon leads to the instability of the welding process, resulting in the deterioration of the weld shape. When laser welding aluminum alloy, due to the high evaporation pressure of Al, the laser welding process of aluminum alloy is generally unstable. Moreover, due to the large difference in the solubility of hydrogen in liquid aluminum alloys and solid aluminum alloys, hydrogen pores are easily formed in aluminum alloy welds. Unstable welding process and porosity are common problems in aluminum alloy welding. In addition to the characteristics of aluminum alloy welding, laser welding of 2XXX series alloys also needs to solve the problems of thermal cracks and weld softening; while 7XXX series aluminum alloys contain evaporative elements such as Mg and Zn with low boiling points in the alloys, laser welding will It leads to the instability of the small hole, the softening of the weld seam, and the deterioration of the welding quality. Therefore, the connection of 2XXX and 7XXX series dissimilar aluminum alloys is very difficult.

Adding filler wire in the laser welding process will reduce the temperature of the laser-material interaction zone and reduce the instability of the welding process. It can also adjust the composition of the weld metal, improve the tendency of hot cracking, and increase the strength of the weld. The invention will use the laser wire filling welding method to stabilize the welding process, solve the problems of hot cracks and pores in the laser welding process of 2XXX and 7XXX high-strength aluminum alloys, and then adjust the welding parameters such as the distance between the light wires, the wire feeding speed, and the beam offset. , to further stabilize the welding process, so as to realize the laser wire welding connection of 2XXX and 7XXX series dissimilar aluminum alloys.

Invention content:

In order to solve the above-mentioned problems existing in the welding of 2XXX and 7XXX dissimilar aluminum alloys, the present invention provides a laser wire-filling welding connection method for realizing 2XXX and 7XXX dissimilar aluminum alloys. This method uses a kilowatt-level laser as a heat source, and adds welding wire as a connecting metal during the laser welding process. On the one hand, the temperature in the interaction area between the laser and the material is reduced to stabilize the welding process. On the other hand, by adjusting the welding parameters such as the distance between the light wires, the wire feeding speed, and the beam offset, the welding process is further stabilized, which not only realizes the connection between the two aluminum alloys, but also solves the problems of hot cracks and pores, and improves the strength of the weld seam. reached a higher level.

Refer to Figures 1-3 for the technical solution of the present invention. The method for joining 2XXX and 7XXX series dissimilar aluminum alloys with laser wire filling is characterized in that: firstly, the surface of the materials to be welded is cleaned, and then the two kinds of aluminum alloy plates to be welded are assembled into a drawing The butt joint in the butt joint, (the requirements for the butt joint are higher during laser welding. The end faces to be welded are required to be straight, and the gap between the two end faces of the butt joint to be welded is less than 30% of the diameter of the laser focus.) Among them, the laser beam 3, The wire feeding nozzle 5 and the shielding gas nozzle 4 are fixed in the same plane, the wire feeding nozzle 5 and the shielding gas nozzle 4 are located on both sides of the laser beam 3 respectively, and the laser beam 3 is set at an incident angle (the angle between the laser beam 3 and the vertical direction is Incidence angle 12, between 0-15°) is incident on the surface of the steel plate, the angle between the aluminum alloy welding wire and the surface of the base metal 2024 1 (that is, the wire feeding angle 10) is between 45-60°, and the shielding gas nozzle The angle between the base metal 7075 2 surface (that is, the shielding gas angle 11) is between 45-55°; the distance between the aluminum alloy welding wire falling point and the laser focus is the distance between the light wire and the laser focus 13. The falling point of the aluminum alloy welding wire and the feeding point of the shielding gas are consistent, that is, the distance between the light wires is 0; the vertical distance from the laser focus to the butt aluminum alloy weld is the laser offset 14 (the offset is generally 0.2-0.7mm Between), in order to ensure the stability of the welding process of 2XXX and 7XXX series dissimilar aluminum alloys, generally the focus of the laser beam is located on the 2XXX aluminum alloy plate 1. In addition to ensuring the above parameters, it is necessary to adjust the laser power, welding speed and wire feeding speed to accurately control the welding heat input during the welding process, so as to realize the connection of 2XXX series and 7XXX series dissimilar aluminum alloys.

During the laser welding process, the laser 3 acts on the filler wire and the aluminum alloy plates (1 and 2) to be welded at the same time. Due to the high energy density of the laser, the welding wire melts in the interaction area between the laser and the material, and the aluminum alloy plate melts and Welding plasma 7 and deep penetration holes appear, and a large number of physical and chemical changes have taken place. With the movement of the laser, new deep penetration holes are continuously and stably formed, and the molten welding wire is continuously filled into the molten pool, while The temperature of the molten molten pool leaving the laser beam decreases continuously and solidifies to form a weld 6 . This process continues to achieve a metallurgical bond between the materials.

During the welding process, it is necessary to ensure that the feeding direction of the aluminum alloy welding wire is opposite to the welding direction 9, and helium is used as the shielding gas during the welding process. In the laser wire-filling joining method of dissimilar aluminum alloys, the laser light source can be any one of CO2, Nd:YAG, semiconductor or fiber laser, and the cross-sectional distribution of the beam needs to be a Gaussian distribution, and a laser with better beam quality.

The welding wire fed into the welding zone should be AlSi or AlCu welding wire with a diameter between 0.8-1.2mm.

The two kinds of aluminum alloy plates to be welded are 2XXX series and 7XXX series aluminum alloys respectively.

Basic principle of the present invention is:

When welding, the two aluminum alloy plates are assembled into a docking form. By adjusting the positional relationship between the laser focus, the falling point of the aluminum alloy welding wire and the butt joint of the two aluminum alloy plates, the laser beam, the welding wire and the welded aluminum The three alloy plates are in a reasonable relative position, and then adopt reasonable welding parameters such as laser power, welding speed and wire feeding speed, so that the molten AlSi or AlCu filler wire and the aluminum alloy plate form a joint with good transition.

When joining 2XXX series and 7XXX series dissimilar aluminum alloys by laser wire-filled welding, the surface of the material to be welded is first cleaned and assembled into a butt joint, wherein the laser beam 3, wire feeding nozzle 5 and shielding gas nozzle 4 are fixed in the same plane, and The nozzle 5 and the shielding gas nozzle 4 are respectively located on both sides of the laser beam 3, the incident angle 12 is between 0-15°, the laser beam 3 is incident on the surface of the material to be welded (1 and 2) at a certain incident angle 12, and the wire feed The angle 10 is between 45-60°, and the shielding gas angle 11 is between 45-55°. The above conditions are the basic conditions for laser wire-added welding. In order to ensure the stability of the process of laser welding 2XXX and 7XXX series dissimilar aluminum alloys, it is necessary to ensure that the distance between the light wires 13 is 0; the focus of the laser beam is located on the 2XXX aluminum alloy plate 1, and the laser offset 14 is between 0.2-0.7mm .

During the laser welding process, the laser 3 acts on the filler wire and the aluminum alloy plates (1 and 2) to be welded at the same time. Due to the high energy density of the laser, the welding wire melts in the interaction area, and the aluminum alloy plate melts and welding plasma appears 7. The deep melting hole has undergone a lot of physical and chemical changes. With the movement of the laser, the deep melting hole is continuously and stably formed, and the molten welding wire is continuously filled into the molten pool, and the liquid melted away from the laser beam The temperature of the pool keeps decreasing and solidifies into a weld 6.

When laser welding 2XXX and 7XXX series dissimilar aluminum alloys, the distance between the light wires needs to be 0mm. Because the contact position between the welding wire and the molten pool is exactly the point of action of the laser beam, the molten welding wire-droplet will have a smooth contact transition with the molten pool under the action of various forces in the interaction area between the laser and the material. . During the welding process, the molten pool remains basically stable, and a uniform weld shape can be obtained. When the distance between the light filaments is large, because most of the energy of the laser acts on the base metal, the energy on the base metal is too high, which increases the instability of the welding process and increases the probability of defects such as pits during the welding process.

In order to ensure the stability of the welding process, when laser welding 2XXX and 7XXX series dissimilar aluminum alloys, the focus of the laser beam is generally not located at the center of the weld, but on the 2XXX aluminum alloy plate, and the distance from the center of the weld is The displacement is generally between 0.2-0.7. Because the main problems of laser welding 2XXX series alloys are thermal cracks and pores, the welding process is relatively stable. In order to stabilize the welding process, the position of the laser focus is shifted on the 2XXX series alloys. If the offset is too large, the solidification center of the weld metal deviates seriously from the center of the weld, and the solidified metal cannot cover the ports of the 7XXX series, resulting in a decline in weld quality. If the focus of the laser beam is located at the center of the weld or shifted toward the 7XXX series, the instability of the laser welding process for 7XXX series aluminum alloys will affect the joining quality of 2XXX and 7XXX series dissimilar aluminum alloys.

In addition to the above parameters, the laser power, welding speed and wire feeding speed need to be adjusted during the welding process to accurately control the welding heat input and realize the connection of 2XXX series and 7XXX series dissimilar aluminum alloys. The working gas used in the welding process is helium, and the feeding direction of the working gas is consistent with the welding direction.

The welding process of laser wire adding is a fusion welding process. The weld seam has undergone a melting and rapid solidification process, resulting in changes in the structure and strengthening phase of the weld seam. Under the action of high temperature, some easily evaporated metal elements are lost, and the welding heat-affected zone Under the action of heat, the structure and strengthening phase will also change, resulting in the difference between the weld performance and the base metal. Adding Al-Si and Al-Cu welding wire in the welding process can not only supplement the lost evaporable elements in the weld, but also generate strengthening phases such as θ(Al ₂ Cu) phase, Mg2S, etc., thereby improving the weld joints. Mechanical behavior.

Description of drawings

Figure 1 is a schematic diagram of the laser wire filler welding to connect 2XXX and 7XXX dissimilar aluminum alloys

Figure 2 is a cross-sectional view of 2XXX and 7XXX dissimilar aluminum alloys connected by laser wire filler welding

Figure 3 Schematic diagram of laser offset

Figure 4 shows the morphology (a) and cross-section (b) of the welding seam of 2XXX and 7XXX dissimilar aluminum alloys welded by laser filler wire

Figure 5 is the tensile curve of the weld seam filled with 2319 welding wire

Figure 6 is the tensile curve of the weld seam filled with 4043 welding wire

Figure 7 shows the fracture characteristics of welds filled with 2319 and 4043 welding wires

Figure 8 is the fracture morphology of the weld filled with 2319 welding wire

Figure 9 shows the fracture morphology of the weld filled with 4043 welding wire

In the figure, 1-2XXX base metal; 2-7XXX base metal; 3-laser beam; 4-shielding gas nozzle; 5-wire feed nozzle; 6-weld seam; 7-welding plasma; 8-welding direction; 9- Welding small hole; 10-wire feed angle; 11-shielding gas angle; 12-incidence angle; 13-wire spacing; 14-laser offset;

Detailed ways:

Method 1:

When using AlCu welding wire with a diameter of 1.2mm (the wire grade is 2319) as the filler material to weld and connect 2024 and 7075 dissimilar aluminum alloys, first clean the surfaces of the materials to be welded 2024 and 7075, and assemble them into a butt joint as shown in Figure 1, where the laser beam 3 , the wire feeding nozzle 5 and the shielding gas nozzle 4 are fixed in the same plane, and the wire feeding nozzle 5 and the shielding gas nozzle 4 are respectively located on both sides of the laser beam 3 (the wire feeding angle and the shielding gas angle are 45° and 55° respectively), The laser beam 3 is incident on the surface of the material to be welded (1 and 2) at an incident angle of 12 (10°), the distance between the filaments 13 is 0, the focus of the laser beam is located on the 2XXX aluminum alloy plate 1, and the laser offset 14 is 0.5 mm, the parameters of laser welding are laser power 3500W, welding speed 4m/min, wire feeding speed 3.5m/min, and laser wire welding is performed under the above conditions. The obtained weld and cross-sectional images are shown in Fig. 4.

Method 2:

When using AlCu welding wire with a diameter of 1.2mm (the wire grade is 2319) as the filler material to weld and connect 2024 and 7075 dissimilar aluminum alloys, first clean the surfaces of the materials to be welded 2024 and 7075, and assemble them into a butt joint as shown in Figure 1, where the laser beam 3 , the wire feeding nozzle 5 and the shielding gas nozzle 4 are fixed in the same plane, and the wire feeding nozzle 5 and the shielding gas nozzle 4 are respectively located on both sides of the laser beam 3 (the wire feeding angle and the shielding gas angle are 45° and 55° respectively), The laser beam 3 is incident on the surface of the material to be welded (1 and 2) at an incident angle of 12 (10°), the distance between the filaments 13 is 0, the focus of the laser beam is located on the 2XXX aluminum alloy plate 1, and the laser offset 14 is 0.5 mm, the parameters of laser welding are laser power 3500W, welding speed 4m/min, wire feeding speed 3.5m/min, and laser wire welding is performed under the above conditions.

The above weldments are processed into tensile samples, the average tensile strength of the weld using 2319 welding wire is 339.5MPa, and the average tensile strength of the weld using 4043 welding wire is 308.6. The tensile curves of welding seams using 2319 and 4043 welding wires are very similar, and Figures 5 and 6 are the tensile curves of the two welding wires respectively. The laser welding seam is narrow. In this experiment, the width of the weld seam is less than 2mm, and the heat-affected zone is also very small. The weld seam and the materials outside the heat-affected zone maintain the good strength and toughness of the original base metal. Therefore, it is difficult to reflect the elongation of the weld part on the tensile curve.

There is a big difference in the fracture positions of the two groups. The top view of the weld using 2319 welding wire (Fig. 7a) shows that the weld fracture is neat, and the upper half of the fracture occurs near the fusion zone or heat-affected zone from the weld cross-sectional view (Fig. 7b). , is basically located at the head of the T-shaped weld joint, and the fracture in the middle and lower part of the weld occurs in the center of the weld, and such a fracture runs through the entire weld fracture. The weld using 4043 welding wire is extremely irregular in the top view (Fig. 7ac). The fracture in the weld section (Fig. 7d) obliquely penetrates the entire weld section. A weld fracture similar to that of 2319 welding wire is formed at the line.

Figure 8 is the topography of the tensile fracture of the weld filled with 2319 welding wire. Dimples with obvious ductile fracture characteristics are distributed in some areas, and ridge-shaped fractures produced in the cleavage fracture mode can be seen in some areas, so this is a kind of Fracture where ductile fracture and cleavage fracture modes are mixed.

The tensile fracture morphology of the weld filled with 4043 welding wire is shown in Figure 9. The fracture is distributed with dimples of relatively uniform size, which is a fracture formed by ductile fracture.

Claims (2)

1. a laser fills silk and connects the method for 2XXX and 7XXX series heterogeneity aluminum alloy, and it is characterized in that: material surface to be welded at first is assembled into banjo fixing butt jointing with two kinds of aluminium alloy plates to be welded after cleaning; Wherein laser beam, wire feed nozzle are fixed in the same plane with the protection gas jets, and the wire feed nozzle lays respectively at the both sides of laser beam with protecting gas jets, and laser beam incident is to surface of steel plate, and incidence angle is the angle of laser beam and vertical direction, between 0-15 °; Angle between aluminium alloy welding wire and the mother metal surface is the wire feed angle, between 45-60 °; Angle between protection gas jets and the mother metal surface is protection air horn degree, between 45-55 °;

The fall spacing of silk point and laser spot of aluminium alloy welding wire is the chevilled silk spacing, guarantee during welding that laser spot is put with the silk that falls of aluminium alloy welding wire and protective gas send into consistently, promptly the chevilled silk spacing is 0; Laser spot is that the laser side-play amount is between 0.2-0.7mm to the vertical range of butt joint aluminium alloy weld seam; The focus of laser beam is positioned on the 2XXX aluminium alloy plate 1;

The scope that in the process of welding, also need regulate laser power is 3.0-3.5kW, and the scope of speed of welding is 3.0-5.0m/min, and the scope of wire feed rate is 2.5-4.0m/min; Welding process need guarantee aluminium alloy welding wire send into direction and welding direction is opposite, welding process adopts helium to do protective gas; The welding wire of sending into the weld zone is AlSi or AlCu welding wire, and diameter is between 0.8-1.2mm.

2. according to the said method of claim 1, it is characterized in that: LASER Light Source is CO ₂, Nd:YAG or optical-fiber laser any one.

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