Aluminum / steel dissimilar metal and laser welding method thereof

Abstract

The invention discloses aluminum / steel dissimilar metal and a laser welding method thereof. The laser welding method comprises the steps that firstly, a proper groove is formed in an aluminum alloy base material, then the aluminum alloy and a steel base material are in butt joint and clamped, a coaxial powder feeding mode is adopted, composite powder is added into a welding area, and laser welding is conducted. According to the method, the weldability of the aluminum / steel dissimilar metal can be effectively improved, and the welding seam forming quality is improved. And by introducing alloy elements, the mutual reaction between aluminum and iron and aluminum elements in steel can be effectively inhibited while the welding seam structure is regulated and controlled, and the formation of Fe-Al intermetallic compounds is reduced, so that the tensile strength of a joint is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of dissimilar metal welding, and particularly relates to an aluminum / steel dissimilar metal and a laser welding method thereof. Background Art

[0002] Aluminum alloys and steels are two metal materials widely used in current industrial production, each having excellent properties. Aluminum alloys are widely favored due to their light weight, high strength, and good processing characteristics. As a basic industrial material with in-depth research and mature technology, steel has excellent mechanical properties such as high strength and good toughness, and also has good workability and weldability. In recent years, with the continuous development of technology, more and more industries have begun to integrate the advantages of aluminum alloys and steels to promote the optimization and upgrading of products. Especially in application scenarios requiring composite properties, the combination of dissimilar materials has become an effective technical route. In the field of automobile manufacturing, with the increasingly severe global energy supply problem and the continuous improvement of environmental protection requirements, energy conservation and emission reduction have become an important direction for promoting the development of the automobile industry. In order to reduce fuel consumption and improve the energy efficiency of automobiles, lightweight technology has become the focus of automotive industry research and production. To achieve lightweight and meet the mechanical properties and safety requirements of automobiles, using lightweight metals to replace traditional steel body structures has become an effective means.

[0003] The application of aluminum / steel welding in automobile manufacturing, especially in components such as body, frame, and chassis, can effectively achieve the balance between lightweight and strength. In order to reduce weight while maintaining the strength and safety of the body, automobile manufacturers are increasingly inclined to use connecting components of high-strength steel, aluminum alloys, and their dissimilar materials.

[0004] Although aluminum / steel welding has broad application prospects, its core challenge stems from the essential difference in crystal structures between aluminum and iron (the matrix element of steel) at room temperature: aluminum has an FCC structure, while iron has a BCC structure. The crystallographic differences result in significant differences in metallurgical compatibility and physical and chemical properties between the two. These differences lead to a series of welding problems, restricting the further application of aluminum / steel welding technology.

[0005] To improve the weld microstructure and enhance the performance of aluminum / steel welded joints, experts and scholars have carried out laser welding by adding an alloy element intermediate layer. The commonly used method is laser wire filling welding, but this method has disadvantages such as high heat input, difficult matching between the laser and the wire, and unstable welding quality, restricting its practical application. In contrast, laser powder filling welding has higher welding quality and better adaptability to complex shapes and special materials. Summary of the Invention

[0006] To overcome the deficiencies and drawbacks of the prior art, the primary objective of the present invention is to provide a laser welding method for dissimilar aluminum / steel metals. This laser welding method adds composite powder through a coaxial powder feeding method to improve the weld microstructure and enhance the mechanical properties of dissimilar aluminum / steel metals.

[0007] The second objective of the present invention is to provide a dissimilar aluminum / steel metal prepared by the above welding method.

[0008] The primary objective of the present invention adopts the following technical solutions:

[0009] A laser welding method for dissimilar aluminum / steel metals, comprising the following steps,

[0010] (1) Take an aluminum alloy base material and a steel base material, and open a groove on one side of the aluminum alloy base material;

[0011] (2) Prepare composite powder;

[0012] (3) Perform pre-welding pretreatment on the aluminum alloy base material and the steel base material respectively;

[0013] (4) Butt-joint and clamp the pre-treated aluminum alloy base material and steel base material in step (3);

[0014] (5) Add composite powder by means of coaxial powder feeding and perform laser welding on the aluminum alloy base material and steel base material to be welded.

[0015] Further, in step (1), the aluminum alloy base material is 6061 aluminum alloy, and the steel base material is 304 stainless steel. The present invention has no special restrictions on the specific components of 6061 aluminum alloy and 304 stainless steel, and common 304 stainless steel and 6061 aluminum alloy on the market can be used.

[0016] Further, the groove opened in step (1) is a single-sided groove, the groove angle is 15 - 25°, and the groove opening position is on the side of the butt joint surface of the aluminum alloy during the welding of the aluminum alloy base material and the steel base material.

[0017] Further, the groove angle is 20°.

[0018] Further, in step (2), the composite powder is obtained by uniformly mixing AlSi 15 Mg powder with a mass fraction of 85 - 90% and pure Ni powder with a mass fraction of 10 - 15%; the average particle size of the AlSi 15 Mg powder is 60 - 90 μm, and the average particle size of the pure Ni powder is 90 - 120 μm.

[0019] Further, the pretreatment step in step (3) is as follows: The aluminum alloy substrate and the steel substrate are respectively polished with sandpaper (180# to 2000#) to remove the oxide layer, then placed in an ultrasonic cleaner for oscillating washing for 30 minutes, and finally put into a dryer for drying, that is, the pretreatment is completed.

[0020] Further, the clamping method in step (4) is as follows: The aluminum alloy substrate and the steel substrate are combined in a butt joint form and clamped and fixed on a pure copper welding platform by a U-shaped fixture.

[0021] Further, in the laser welding process in step (5), the composite powder is added in a coaxial powder feeding manner, the powder feeding rate is 8 - 15 g / min, and the powder is fed in advance for 1 - 2 s before welding.

[0022] Further, the laser welding in step (5) is double-pass welding. The specific welding process parameters are as follows: the power is 1800 - 2000 W, the welding speed is 20 - 50 mm / s, the defocus amount is 0 mm, the flow rate of the front shielding gas is 8 - 12 L / min, and the flow rate of the back shielding gas is 5 - 8 L / min.

[0023] The second object of the present invention adopts the following technical solution:

[0024] A dissimilar aluminum / steel metal is prepared by the above laser welding method.

[0025] Further, the tensile strength of the dissimilar aluminum / steel metal is 120 - 150 Mpa.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] The present invention adopts a coaxial powder feeding method to add the composite powder into the welding area for laser welding. This method can effectively improve the weldability of dissimilar aluminum / steel metals, enhance the fluidity of the molten pool, and improve the weld forming quality. By introducing alloying elements, while regulating the weld microstructure, it can effectively inhibit the mutual reaction between aluminum and iron-aluminum elements in steel, reduce the formation of Fe-Al intermetallic compounds, and can also refine the weld grain structure, thereby improving the tensile strength of the joint.

[0028] The process of preparing and welding the composite powder of the present invention is simple and does not require expensive equipment and cumbersome processes. The double-pass welding adopted by the present invention has a better effect than single-pass welding. Double-pass welding fully melts the substrate and the powder, and the liquid metal flows more fully, which is conducive to the escape of gas and improves the weld forming. At the same time, the heat input of the two laser beams is more evenly distributed compared with the single high-power laser, which can reduce the welding stress and inhibit crack generation. Description of the Drawings

[0029] Figure 1Schematic diagram of the laser welding method for aluminum / steel dissimilar metals of the present invention;

[0030] Figure 2 Metallographic structure diagram of the aluminum / steel dissimilar metal prepared in Example 2 of the present invention;

[0031] Among them, aluminum alloy substrate - 1, coaxial powder feeding device - 2, laser beam - 3, composite powder - 4, groove - 5, steel substrate - 6. Specific embodiments

[0032] The present invention will be further described in detail below in conjunction with specific embodiments, but the implementation manners of the present invention are not limited thereto. The materials used in the examples of the present invention can all be obtained by purchasing commercially.

[0033] In order to make the technical solutions provided by the present invention more concise, the following will be further described in detail in conjunction with the drawings and embodiments.

[0034] The laser welding method for aluminum / steel dissimilar metals in this embodiment includes the following steps,

[0035] (1) Open a groove on one side of the aluminum alloy substrate;

[0036] (2) Prepare composite powder;

[0037] (3) Perform pre - treatment before welding on the aluminum alloy substrate and the steel substrate respectively;

[0038] (4) Butt - clamp the aluminum alloy substrate and the steel substrate;

[0039] (5) Add composite powder by the method of coaxial powder feeding and perform laser welding on the aluminum alloy substrate and the steel substrate to be welded.

[0040] Furthermore, the aluminum alloy substrate is 6061 aluminum alloy; the steel substrate is 304 stainless steel. The present invention has no special restrictions on the specific components of 6061 aluminum alloy and 304 stainless steel, and common 304 stainless steel and 6061 aluminum alloy on the market can be used.

[0041] Furthermore, the groove opened in step (1) is a single - side groove, and the groove angle is 15 - 25°. The position where the groove is opened is on the butting surface side of the aluminum alloy during the welding of the aluminum alloy substrate and the steel substrate.

[0042] Furthermore, in step (2), the composite powder is obtained by uniformly mixing AlSi 15 Mg powder with a mass fraction of 85 - 90% and pure Ni powder with a mass fraction of 10 - 15%; the average particle size of the AlSi 15 Mg powder is 60 - 90 μm, and the average particle size of the pure Ni powder is 90 - 120 μm.

[0043] Further, the pretreatment step in step (3) is as follows: The aluminum alloy substrate and the steel substrate are respectively polished with sandpaper (180# to 2000#) to remove the oxide layer, then placed in an ultrasonic cleaner for oscillating washing for 30 minutes, and finally put into a dryer for drying, that is, the pretreatment is completed.

[0044] Further, the clamping method in step (4) is as follows: The aluminum alloy substrate and the steel substrate are combined in a butt joint form and clamped and fixed on a pure copper welding platform by a U-shaped fixture.

[0045] Further, in the laser welding process of step (5), the composite powder is added in a coaxial powder feeding manner, the powder feeding rate is 8 - 15 g / min, and the powder is fed in advance for 1 - 2 s before welding.

[0046] Further, the laser welding in step (5) is double-pass welding. The specific welding process parameters are as follows: the power is 1800 - 2000 W, the welding speed is 20 - 50 mm / s, the defocus amount is 0 mm, the flow rate of the front protective gas is 8 - 12 L / min, and the flow rate of the back protective gas is 5 - 8 L / min.

[0047] The following further describes the present invention in detail in conjunction with embodiments:

[0048] Example 1

[0049] The substrates used in this example are 6061 aluminum alloy with a size of 110 mm × 110 mm × 3 mm and 304 stainless steel with a size of 110 mm × 110 mm × 3 mm. After the 6061 aluminum alloy substrate is grooved, the above pretreatment is carried out, and then butt joint clamping is performed for coaxial powder feeding laser welding. The process parameters of the first pass of laser welding are as follows: the laser power is 1800 W, the welding speed is 50 mm / s, the defocus amount is 0 mm, the flow rate of the front protective gas is 10 L / min, and the flow rate of the back protective gas is 5 L / min. The process parameters of the second pass of laser welding are as follows: the laser power is 2000 W, the welding speed is 30 mm / s, the defocus amount is 0 mm, the flow rate of the front protective gas is 10 L / min, and the flow rate of the back protective gas is 5 L / min. The sample is subjected to a tensile test, and the tensile strength of the joint reaches 131 Mpa. In this example, the groove angle is 20°, and the composite powder is obtained by uniformly mixing AlSi 15 Mg powder with a mass fraction of 90% and pure Ni powder with a mass fraction of 10%; the average particle size of the AlSi 15 Mg powder is 80 μm, and the average particle size of the pure Ni powder is 100 μm. The composite powder is added in a coaxial powder feeding manner during the welding process, the powder feeding rate is 8 g / min, and the powder is fed in advance for 1 - 2 s before welding.

[0050] Example 2

[0051] The base materials used in this embodiment are 6061 aluminum alloy with dimensions of 110mm×110mm×3mm and 304 stainless steel with dimensions of 110mm×110mm×3mm. After grooving the base materials, the above-mentioned pretreatment is carried out, and then butt joint clamping is performed for coaxial powder feeding laser welding. The process parameters of the first laser welding are as follows: laser power is 1900W, welding speed is 50mm / s, defocus amount is 0mm, the flow rate of the front protective gas is 10L / min, and the flow rate of the back protective gas is 5L / min. The process parameters of the second laser welding are: laser power is 2000W, welding speed is 30mm / s, defocus amount is 0mm, the flow rate of the front protective gas is 10L / min, and the flow rate of the back protective gas is 5L / min. The sample is subjected to a tensile test, and the tensile strength of the joint reaches 137Mpa. In this embodiment, the groove angle is 20°, and the composite powder is obtained by uniformly mixing AlSi 15 Mg powder with a mass fraction of 90% and pure Ni powder with a mass fraction of 10%; the AlSi 15 Mg powder has an average particle size of 80μm, and the pure Ni powder has an average particle size of 100μm. During the welding process, the composite powder is added in a coaxial powder feeding manner, and the powder feeding rate is 8g / min. The powder is fed in advance for 1 - 2s before welding.

[0052] Example 3

[0053] The base materials used in this embodiment are 6061 aluminum alloy with dimensions of 110mm×110mm×3mm and 304 stainless steel with dimensions of 110mm×110mm×3mm. After grooving the base materials, the above-mentioned pretreatment is carried out, and then butt joint clamping is performed for coaxial powder feeding laser welding. The process parameters of the first laser welding are as follows: laser power is 2000W, welding speed is 50mm / s, defocus amount is 0mm, the flow rate of the front protective gas is 10L / min, and the flow rate of the back protective gas is 5L / min. The process parameters of the second laser welding are: laser power is 2000W, welding speed is 30mm / s, defocus amount is 0mm, the flow rate of the front protective gas is 10L / min, and the flow rate of the back protective gas is 5L / min. The sample is subjected to a tensile test, and the tensile strength of the joint reaches 125Mpa. In this embodiment, the groove angle is 20°, and the composite powder is obtained by uniformly mixing AlSi 15 Mg powder with a mass fraction of 90% and pure Ni powder with a mass fraction of 10%; the AlSi 15 Mg powder has an average particle size of 80μm, and the pure Ni powder has an average particle size of 100μm. During the welding process, the composite powder is added in a coaxial powder feeding manner, and the powder feeding rate is 8g / min. The powder is fed in advance for 1 - 2s before welding.

[0054] Comparative Example 1

[0055] The base materials used in this embodiment are 6061 aluminum alloy with dimensions of 110 mm × 110 mm × 3 mm and 304 stainless steel with dimensions of 110 mm × 110 mm × 3 mm. The base materials are subjected to the above pretreatment, and then butt-clamped and directly laser welded. The process parameters for the first pass of laser welding are as follows: laser power is 1900 W, welding speed is 50 mm / s, defocus amount is 0 mm, the flow rate of the front protective gas is 10 L / min, and the flow rate of the back protective gas is 5 L / min. The process parameters for the second pass of laser welding are: laser power is 2000 W, welding speed is 30 mm / s, defocus amount is 0 mm, the flow rate of the front protective gas is 10 L / min, and the flow rate of the back protective gas is 5 L / min. The samples are subjected to a tensile test, and the tensile strength of the joint reaches 97 Mpa. In this comparative example, the groove angle is 20°, and the composite powder is obtained by uniformly mixing AlSi 15 Mg powder with a mass fraction of 90% and pure Ni powder with a mass fraction of 10%; the AlSi 15 The average particle size of the Mg powder is 80 μm, and the average particle size of the pure Ni powder is 100 μm. During the welding process, the composite powder is added in a coaxial powder feeding manner, the powder feeding rate is 8 g / min, and powder is fed in advance for 1 - 2 s before welding.

[0056] Comparative Example 2

[0057] The base materials used in this embodiment are 6061 aluminum alloy with dimensions of 110 mm × 110 mm × 3 mm and 304 stainless steel with dimensions of 110 mm × 110 mm × 3 mm. After grooving the base materials, the above pretreatment is carried out, and then butt-clamped and coaxial powder feeding laser welding is carried out. Only a single pass of laser welding is performed. The process parameters of laser welding are: laser power is 1900 W, welding speed is 50 mm / s, defocus amount is 0 mm, the flow rate of the front protective gas is 10 L / min, and the flow rate of the back protective gas is 5 L / min. The joint formation is poor, and there is an obvious depression at the top of the joint. The samples are subjected to a tensile test, and the tensile strength of the joint is only 78 Mpa. In this comparative example, the groove angle is 20°, and the composite powder is obtained by uniformly mixing AlSi 15 Mg powder with a mass fraction of 90% and pure Ni powder with a mass fraction of 10%; the AlSi 15 The average particle size of the Mg powder is 80 μm, and the average particle size of the pure Ni powder is 100 μm. During the welding process, the composite powder is added in a coaxial powder feeding manner, the powder feeding rate is 8 g / min, and powder is fed in advance for 1 - 2 s before welding.

[0058] Comparative Example 3

[0059] The base materials used in this embodiment are 6061 aluminum alloy with dimensions of 110 mm × 110 mm × 3 mm and 304 stainless steel with dimensions of 110 mm × 110 mm × 3 mm. After grooving the base materials, the above-mentioned pretreatment is carried out, and then butt clamping is performed for coaxial powder feeding laser welding. The powder used is only AlSi 15 Mg process parameters for the first pass of laser welding: laser power is 1900 W, welding speed is 50 mm / s, defocus amount is 0 mm, front shielding gas flow rate is 10 L / min, and back shielding gas flow rate is 5 L / min. Process parameters for the second pass of laser welding: laser power is 2000 W, welding speed is 30 mm / s, defocus amount is 0 mm, front shielding gas flow rate is 10 L / min, and back shielding gas flow rate is 5 L / min. The sample is subjected to a tensile test, and the tensile strength of the joint reaches 112 Mpa. In this comparative example, the groove angle is 20°, and the composite powder is obtained by uniformly mixing 90% by mass of AlSi 15 Mg powder and 10% by mass of pure Ni powder; the average particle size of the AlSi 15 Mg powder is 80 μm, and the average particle size of the pure Ni powder is 100 μm. During the welding process, the composite powder is added in a coaxial powder feeding manner, the powder feeding rate is 8 g / min, and powder is fed in advance for 1 - 2 s before welding.

[0060] Comparative Example 4

[0061] The base materials used in this embodiment are 6061 aluminum alloy with dimensions of 110 mm × 110 mm × 3 mm and 304 stainless steel with dimensions of 110 mm × 110 mm × 3 mm. After grooving the base materials, the above-mentioned pretreatment is carried out, and then butt clamping is performed for coaxial powder feeding laser welding. The powder used is a mixture of 90% by mass of AlSi 10 and 10% of pure Ni powder. Process parameters for the first pass of laser welding: laser power is 1900 W, welding speed is 50 mm / s, defocus amount is 0 mm, front shielding gas flow rate is 10 L / min, and back shielding gas flow rate is 5 L / min. Process parameters for the second pass of laser welding: laser power is 2000 W, welding speed is 30 mm / s, defocus amount is 0 mm, front shielding gas flow rate is 10 L / min, and back shielding gas flow rate is 5 L / min. The sample is subjected to a tensile test, and the tensile strength of the joint reaches 120 Mpa. In this comparative example, the groove angle is 20°, and the composite powder is obtained by uniformly mixing 90% by mass of AlSi 15 Mg powder and 10% by mass of pure Ni powder; the average particle size of the AlSi 15 Mg powder is 80 μm, and the average particle size of the pure Ni powder is 100 μm. During the welding process, the composite powder is added in a coaxial powder feeding manner, the powder feeding rate is 8 g / min, and powder is fed in advance for 1 - 2 s before welding.

[0062] From the data of the above embodiments and comparative examples, in the laser welding of dissimilar aluminum / steel metals by adding composite powder through the coaxial powder feeding method, the present invention can effectively improve the weld microstructure. The addition of Ni / Si elements in the composite powder can generate ductile phases of Al-Ni and Fe-Si-Al, inhibit the formation of hard and brittle Fe-Al intermetallic compounds in the weld, reduce the tendency of brittle fracture of the joint. The Si element can also improve the fluidity of the molten pool and refine the grain size in the weld area. The addition of Mg element can reduce the burn loss of the base material, and the addition of composite powder effectively improves the mechanical properties of the joint.

[0063] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A laser welding method for aluminum / steel dissimilar metals, characterized in that, It includes the following steps: (1) Take an aluminum alloy substrate and a steel substrate, and open a groove on one side of the aluminum alloy substrate; (2) Prepare composite powder; (3) Perform pre-treatment before welding on the aluminum alloy substrate and the steel substrate respectively; (4) Butt-clamp the pre-treated aluminum alloy substrate and steel substrate in step (3); (5) Add composite powder by means of coaxial powder feeding and perform laser welding on the aluminum alloy substrate and steel substrate to be welded.

2. The aluminum / steel dissimilar metal laser welding method according to claim 1, characterized in that, In step (1), the aluminum alloy substrate is 6061 aluminum alloy, and the steel substrate is 304 stainless steel.

3. The aluminum / steel dissimilar metal laser welding method according to claim 1, characterized in that In step (1), the groove opened is a single-sided groove, the groove angle is 15 - 25°, and the groove opening position is on the side of the butt joint surface of the aluminum alloy when the aluminum alloy substrate and the steel substrate are welded.

4. The aluminum / steel dissimilar metal laser welding method according to claim 1, characterized in that, The composite powder described in step (2) is obtained by uniformly mixing AlSi 15 Mg powder with a mass fraction of 85-90% and pure Ni powder with a mass fraction of 10-15%; the average particle size of the AlSi 15 Mg powder is 60-90 μm, and the average particle size of the pure Ni powder is 90-120 μm.

5. The aluminum / steel dissimilar metal laser welding method according to claim 1, characterized in that, The pre-treatment steps in step (3) are: polish the aluminum alloy substrate and the steel substrate with sandpaper to remove the oxide layer, then place them in an ultrasonic cleaner and oscillate and wash for 30 min, and finally put them into a dryer for drying, that is, the pre-treatment is completed.

6. The laser welding method for aluminum / steel dissimilar metals according to claim 1, characterized in that, The clamping method in step (4) is: combine the aluminum alloy substrate and the steel substrate in a butt joint form, and clamp and fix them on a pure copper welding platform through a U-shaped clamp.

7. The aluminum / steel dissimilar metal laser welding method according to claim 1, characterized in that, In step (5), during the laser welding process, composite powder is added in a coaxial powder feeding manner, the powder feeding rate is 8 - 15 g / min, and powder is fed in advance for 1 - 2 s before welding.

8. The aluminum / steel dissimilar metal laser welding method according to claim 1, characterized in that, The laser welding in step (5) is double-pass welding. The specific welding process parameters are: the power is 1800 - 2000 W, the welding speed is 20 - 50 mm / s, the defocus amount is 0 mm, the front shielding gas flow rate is 8 - 12 L / min, and the back shielding gas flow rate is 5 - 8 L / min.

9. An aluminum / steel dissimilar metal, characterized in that, Prepared according to the laser welding method described in any one of claims 1 to 8.

10. The aluminum / steel dissimilar metal according to claim 9, characterized in that, The tensile strength of the aluminum / steel dissimilar metal is 120 - 150 Mpa.

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