Laser welding method for dual-phase steel and aluminum alloy with pre-set nano rare earth intermediate layer

Abstract

The present invention discloses a laser welding method for duplex steel and aluminum alloy with a pre-set nano rare earth intermediate layer, which belongs to the field of laser welding of dissimilar materials, including: fine grinding and cleaning the parts to be welded of the aluminum alloy plate and the duplex steel plate; uniformly mixing aluminum powder with nano-scale CeO2 powder, adding acetone to obtain a paste of Al-CeO2 powder; cutting a groove along the direction of the weld seam on the side where the aluminum alloy plate contacts the duplex steel plate, and pre-coating the paste of Al-CeO2 powder in the groove; installing a protective gas device and using argon gas for welding protection; step 5, clamping the aluminum alloy and duplex steel plate welding specimens to a universal welding fixture for laser welding. The method of the present invention solves the problem of cracks generated at the joint surface of steel-aluminum welding and the problem of pores generated by adding rare earth oxides to steel-aluminum welding, reduces the size and number of brittle intermetallic compounds at the interface, and improves the load capacity of the steel-aluminum laser welding joint.

Description

Technical Field

[0001] The invention relates to the technical field of laser welding of dissimilar materials, in particular to a laser welding method of dual-phase steel and aluminum alloy with a pre-set nano rare earth intermediate layer. Background Art

[0002] Duplex steel, due to its high strength, good toughness, and excellent collision energy absorption properties, has been widely used in the automotive, aerospace, and rail transportation industries, particularly in key areas such as frame structures, support reinforcements, and anti-collision components. Meanwhile, aluminum alloy, with its low density, high corrosion resistance, and excellent machinability, has become a key option for lightweight transportation, widely used in key components such as vehicle frames, engine hoods, aircraft fuselages, wings, skins, high-speed rail carriages, and door and window trim. With the further development of these advanced manufacturing technologies, stricter standards for welding accuracy, deformation control, and weld aesthetics have been established. Laser welding, as a precise, low-stress, high-strength welding method, is a key welding technology for improving the performance and quality of welds. This technology not only enhances the strength and lightweighting of these structures, but also plays a significant role in improving fuel economy and reducing emissions. It is one of the key technologies driving the development of advanced manufacturing towards greater efficiency and environmental friendliness.

[0003] However, the welding of duplex steel and aluminum alloys presents several major challenges. The significant difference in their thermophysical properties and the tendency for brittle intermetallic compounds to form in the weld at high temperatures are the main challenges. Numerous studies have demonstrated that, in the molten state, Fe and Al readily undergo metallurgical reactions to form Fe-Al intermetallic compounds, such as FeAl₃, Fe₃Al, and Fe₂Al₅. Calculation of the thermodynamic stability of each compound phase based on Gibbs free energy indicates that the intermetallic compounds that can be stable at the Fe / Al interface primarily consist of lamellar Fe₂Al₅ phases and acicular FeAl₃ phases concentrated in aluminum-rich regions. Areas of intermetallic compound concentration are prone to cracking, reducing joint performance and potentially leading to failure during service. Furthermore, the welding process is prone to spatter and the formation of pores within the weld. These factors contribute to poor joint mechanical properties and brittle fracture under stress.

[0004] Adding a third metal element to manipulate alloying metallurgy is an effective measure to improve joint quality. This metallurgical manipulation can generate a ductile interphase to replace some of the brittle Fe-Al compounds, reducing the intermetallic component (IMC) around the interface. The added metal element can also diffuse and dissolve between aluminum and steel, forming solid solutions or compounds. Furthermore, certain third elements can enhance the wetting and spreading of aluminum on the steel surface. These factors can improve the weld quality, reduce weld defects, and ultimately reduce joint brittleness and residual stress in the weld, ultimately enhancing the mechanical properties of duplex steel / aluminum alloy welds. Recent research has found that rare earth (RE) elements, with their large atomic radius and unique shell structure, facilitate metallurgical reactions with multiple elements. Furthermore, RE and RE oxides (REO) have purifying, microalloying, and modificatory properties. In steel-aluminum laser lap welding experiments, the addition of an Al-0.5% Ce interlayer to an Al-based Ce powder resulted in poor weld cross-section formability, with defects such as voids and cracks. Furthermore, the addition of an intermediate layer of powder locally increases the gap between the base metal and the weld metal, making it more susceptible to defects such as incomplete fusion and slag inclusions during welding, reducing the overall quality and stability of the welded joint. Laser welding requires even higher alignment and assembly accuracy, and the negative impact of directly adding an intermediate layer of powder on weld quality is even more severe. In summary, the current research on improving welding with the addition of rare earth elements or rare earth oxides, as well as the effects achieved, still leaves room for improvement and innovation. Summary of the Invention

[0005] The present invention aims to provide a laser welding method for duplex steel and aluminum alloys pre-incorporated with a nano-rare earth interlayer. This method addresses the current problems of pores within the weld and the formation of brittle Fe-Al intermetallic compounds at the weld interface during the welding of duplex steel and aluminum alloys. These intermetallic compounds primarily appear as large laths and needles, resulting in discontinuous weld metal matrix structure and, in turn, reduced mechanical properties of the weld metal. Furthermore, the brittle intermetallic compound phase is susceptible to cracking under external stress, reducing mechanical properties such as tensile strength, ductility, and impact toughness.

[0006] To achieve the above object, the present invention provides a laser welding method for duplex steel and aluminum alloy with a pre-set nano rare earth oxide intermediate layer, which specifically comprises the following steps:

[0007] Step 1: Use 400-grit sandpaper to fine-grind the areas to be welded on the aluminum alloy plate and the duplex steel plate, then use an ultrasonic cleaner to clean the areas to be welded on the aluminum alloy plate and the duplex steel plate, and then dry them to remove surface oxides and oil stains on the areas to be welded;

[0008] Step 2: Evenly mix nano-scale CeO2 (cerium oxide) powder and aluminum powder, define the rare earth element addition content by the mass fraction of CeO2 powder in the total powder, use a powder ball mill to ensure that the CeO2 powder and aluminum powder are evenly distributed, and add acetone to make the mixed powder into a paste form to obtain a paste-like Al-CeO2 powder;

[0009] Step 3: Cut a groove along the weld seam on the side where the aluminum alloy plate contacts the duplex steel plate. The groove has a width of less than or equal to 0.3 mm and a depth of less than 0.3 mm. Pre-apply Al-CeO2 paste powder inside the groove of the aluminum base material. The Al-CeO2 paste powder applied inside the groove of the aluminum alloy plate is the intermediate layer powder added between the aluminum and steel layers.

[0010] Step 4: Install the protective gas device and use argon gas for welding protection;

[0011] Step 5: Clamp the aluminum alloy plate and duplex steel plate welding specimens onto a universal welding fixture, overlap the duplex steel plate on top and the aluminum alloy plate on the bottom, and offset the laser head 10° in the welding direction; laser welding is performed after the acetone in the intermediate layer powder evaporates.

[0012] Preferably, in the above-mentioned laser welding method of dual-phase steel and aluminum alloy with a pre-set nano rare earth oxide intermediate layer, the dimensions of the aluminum alloy plate and the dual-phase steel plate are both 100 mm in length, 50 mm in width and 1 mm in thickness.

[0013] Preferably, in the above-mentioned laser welding method for dual-phase steel and aluminum alloy with a pre-set nano rare earth oxide intermediate layer, the diameter of the CeO2 powder in step 2 is about 80 nm, and the diameter of the aluminum powder is about 100 μm.

[0014] Preferably, in the above-mentioned laser welding method of dual-phase steel and aluminum alloy with a pre-formed nano rare earth oxide intermediate layer, the mass fraction of CeO2 powder is 80-100%.

[0015] Preferably, in the above-mentioned laser welding method of dual-phase steel and aluminum alloy with a pre-set nano rare earth oxide intermediate layer, the coating amount of the intermediate layer powder in step 3 is 30-40 mg / cm 2 .

[0016] Preferably, in the above-mentioned laser welding method for dual-phase steel and aluminum alloy with a pre-set nano rare earth oxide intermediate layer, the purity of the protective gas argon in step 4 is 99.999%, and the gas flow rate is 20 L / min.

[0017] Preferably, in the above-mentioned laser welding method of duplex steel and aluminum alloy with a pre-set nano rare earth oxide intermediate layer, the duplex steel plate is overlapped on the top and the aluminum alloy plate is overlapped on the bottom in step 5, and the overlapping length of the two is 10 mm.

[0018] Preferably, in the above-mentioned laser welding method for duplex steel and aluminum alloy with a pre-set nano rare earth oxide intermediate layer, the laser welding in step five adopts the laser keyhole welding mode of the IPG YLS-4000 equipment, with a laser wavelength of 1065±5nm, a focal length of 400mm, and a laser defocus of 0mm.

[0019] The above method utilizes an Al / Fe overlap joint, prefabricating a groove on the Al side and placing an Al / CeO2 mixed powder inside the groove. This structure innovatively addresses the issues of overlap gaps in the Al / Fe overlap joint caused by the volume of added powder, as well as powder loss caused by the added powder being partially squeezed out of the weld area under the pressure of the welding fixture. This method allows for sufficient addition of the mixed powder to the weld pool while ensuring both powder addition and precise weldment, avoiding welding defects such as slag inclusion and lack of fusion, and improving weld formation.

[0020] Adding nano-scale rare earth element Ce can also promote the absorption of laser energy by the weld metal of laser welding, so that the molten pool can last longer, the gas escape time window is longer, and the viscosity of the molten metal in the molten pool can be reduced. The gas in the molten pool can escape upward faster, so that there are basically no pores in the weld after the molten metal solidifies.

[0021] The addition of nano-sized rare earth element Ce reduced weld defects around the fusion line. This is primarily due to the CeO₂ inhibiting the interdiffusion of Al and Fe, significantly suppressing their metallurgical reactions at the interface, reducing the formation of brittle Fe-Al intermetallic compounds, and lowering crack sensitivity at the weld interface. Furthermore, the Fe-Ce and Al-Ce microstructures generated by Ce at the weld interface exhibit superior toughness, making the weld less susceptible to crack formation. These two effects also significantly improved the mechanical properties of the weld joint. With the addition of the rare earth element, the maximum load on the weld increased from 2460.71 N (without CeO₂) to 2683.20 N, and the average linear load of the joint increased from 60.47 N / mm to 89.61 N / mm. With the addition of 100% CeO₂ powder, the fracture pattern of the joint changed from brittle fracture to mixed fracture, with dimples appearing at the fracture surface, indicating improved joint toughness.

[0022] Therefore, the laser welding method of the dual-phase steel and aluminum alloy using the above-mentioned structure with a pre-prepared rare earth oxide intermediate layer has the following beneficial effects:

[0023] (1) Improve weld formation performance and optimize process window: Adding nano rare earth elements can reduce pores around the fusion line, effectively increase the weld penetration and width, and enhance the bonding strength between the weld and the base material. This is mainly because the addition of rare earth elements can promote the absorption rate of laser energy by the material to be welded, causing more metal to melt and increase the weld penetration and width. At the same time, the solidification time of the molten pool is increased, and the gas has sufficient time to escape, effectively avoiding the formation of pores.

[0024] On the other hand, since the addition of nano rare earth oxides can promote the material's absorption of lasers, it can lower the temperature threshold required for welding and complete welding at a lower laser power density, thereby achieving the beneficial effects of reducing the heat-affected zone, reducing welding deformation and residual stress, increasing welding speed, and improving production efficiency.

[0025] (2) Fully utilizing the powder filling effect: Compared to directly applying powder to the parent metal of the Al / Fe overlap structure, the present invention prefabricates grooves on the Al side and fills the grooves with rare earth oxide intermediate layer powder. This eliminates the additional assembly gap in the overlap structure caused by the volume of the metal oxide powder, effectively avoiding defects such as lack of fusion and slag inclusion, and improving weld formation. At the same time, it solves the problem of metal oxide powder being partially squeezed out of the welding area under the pressure of the welding fixture, thereby avoiding problems such as inaccurate effective powder usage and powder waste.

[0026] (3) Reduce the formation of brittle intermetallic compounds: Adding Ce can hinder the mutual diffusion of Fe and Al to form metallurgical bonds, thus avoiding the formation of Fe-Al phases at the boundary of the fusion zone, which are brittle, hard, and prone to crack initiation and expansion. This promotes the improvement of the mechanical properties of the weld. Nano-scale CeO2 powder, due to its extremely small particle size and large specific surface area, has higher surface activity and is more evenly distributed in the molten pool, further enhancing the above effect.

[0027] (4) Improve weld structure and refine grains: Nano-scale CeO2 powder has higher surface activity for melt reaction. The Ce element in it easily reacts with Fe, Al and other elements in the weld to form fine and dispersed Fe-Ce and Al-Ce second phase particles, providing more heterogeneous nucleation sites for the grains and promoting grain refinement.

[0028] (5) Improve mechanical properties: Since the generated nanoscale Ce phase can effectively hinder the movement of dislocations, it promotes the entanglement of dislocations to form dislocation cells that accumulate around the grain boundaries, thereby strengthening the weld performance and improving the shear strength.

[0029] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1This is a schematic diagram of the laser welding principle of dual-phase steel and aluminum alloy with a pre-set rare earth oxide intermediate layer according to the present invention;

[0031] Figure 2 A structural diagram of the dual-phase steel and aluminum alloy loaded onto a welding fixture according to the present invention;

[0032] Figure 3 Cross-sectional images of welds of the duplex steel and aluminum alloy of the present invention with different mass fractions of pre-set rare earth oxide intermediate layers added; (a) is a cross-sectional image of a weld without the addition of Al-CeO2 intermediate layer powder; (b) is a cross-sectional image of a weld with the addition of Al-10% CeO2 intermediate layer powder; (c) is a cross-sectional image of a weld with the addition of Al-30% CeO2 intermediate layer powder; (d) is a cross-sectional image of a weld with the addition of Al-60% CeO2 intermediate layer powder; and (e) is a cross-sectional image of a weld with the addition of Al-100% CeO2 intermediate layer powder.

[0033] Figure 4 (a) is the weld morphology without Ce addition; (b) is a local enlarged view of the weld boundary; (c) is the Fe element surface scan in Figure (b); (d) is the Al element surface scan in Figure (b); (e) is the intermetallic compound morphology at the bottom of the weld; (f) is a local enlarged view of Figure (e);

[0034] Figure 5 (a) is the weld morphology with 100% Ce addition; (b) is a local magnified view of the weld boundary; (c) is a local magnified view of (b); the rest are surface scans of Ce, Fe, and Al elements, where the diffusion of the three elements can be observed;

[0035] Figure 6 (a) is the fracture morphology of the weld without adding Ce; (b) is a local enlarged view of Figure (a); (c) is the fracture morphology of the weld; (d) is a local enlarged view of Figure (c);

[0036] Figure 7 (a) is a fracture morphology of a weld with 100% mass fraction of Ce added; (b) is a region with dimple morphology in a fracture morphology of a weld with 100% mass fraction of Ce added; (c) is a partial enlarged view of (b);

[0037] Figure 8 Graph showing the hardness variation trends of welds made of the duplex steel and aluminum alloy of the present invention with different mass fractions of a pre-added rare earth oxide interlayer added; (a) shows the horizontal hardness variation of the steel-side weld; (b) shows the horizontal hardness variation of the aluminum-side weld; and (c) shows the longitudinal hardness variation of the weld.

[0038] Figure 9A graph showing the shear performance variation trend of welds with different mass fractions of pre-set rare earth oxide intermediate layers added to the dual-phase steel and aluminum alloy of the present invention.

[0039] Reference numerals: 1. aluminum alloy plate; 2. duplex steel plate; 3. intermediate layer powder; 4. backing plate; 5. laser welding equipment. DETAILED DESCRIPTION

[0040] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] The terms used in the embodiments of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The singular forms "a," "an," "the," and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, and unless the context clearly indicates otherwise, "a plurality" generally includes at least two.

[0042] It should also be noted that the terms "include," "comprises," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a product or device comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such product or device. In the absence of further limitations, an element defined by the phrase "comprises a..." does not exclude the presence of other identical elements in the product or device comprising the element.

[0043] Example 1

[0044] The aluminum alloy plate 1 and the duplex steel plate 2 were finely ground at the locations to be welded using 400-grit sandpaper. The locations to be welded were then cleaned using an ultrasonic cleaner and then dried to remove surface oxides and oil stains. The dimensions of the aluminum alloy plate 1 and the duplex steel plate 2 were both 100 mm long, 50 mm wide, and 1 mm thick.

[0045] Aluminum powder was uniformly mixed with CeO2 powder having a diameter of 80 nm, wherein the CeO2 powder accounted for 10% of the total powder mass. A powder ball mill was used to ensure uniform distribution of the powder. Acetone was added to make the mixed powder into a paste form to obtain a paste-like Al-CeO2 powder.

[0046] On the side where the aluminum alloy plate 1 contacts the dual-phase steel plate 2, a groove is cut along the direction of the weld seam. The width of the groove is less than or equal to 0.3 mm and the depth is less than 0.3 mm. Al-CeO2 paste powder is pre-coated inside the groove of the aluminum base material. The Al-CeO2 paste powder coated in the groove of the aluminum alloy plate is the intermediate layer powder 3 added between the aluminum and steel layers. The coating amount of the intermediate layer powder 3 is 35 mg / cm 2 ;

[0047] Install a protective gas device and use argon for welding protection. The purity of argon is 99.999% and the gas flow rate is 20L / min.

[0048] The aluminum alloy plate 1 and the duplex steel plate 2 welding specimens are clamped on a universal welding fixture. A pad 4 is set if necessary. The duplex steel plate is overlapped on the upper side and the aluminum alloy plate is overlapped on the lower side. The overlap length of the two is 10 mm. The laser head is offset 10° in the welding direction. After the acetone in the intermediate layer powder is volatilized, laser welding is performed. The laser welding equipment 5 adopts the laser keyhole welding mode of the IPGYLS-4000 equipment. The laser wavelength is 1065±5 nm, the focal length is 400 mm, and the laser defocus is 0 mm. The laser power is 1800 W. The cross-sectional image of the weld after welding is completed is as follows: Figure 3 (b) shown.

[0049] Example 2

[0050] The aluminum alloy plate 1 and the duplex steel plate 2 were finely ground at the locations to be welded using 400-grit sandpaper. The locations to be welded were then cleaned using an ultrasonic cleaner and then dried to remove surface oxides and oil stains. The dimensions of the aluminum alloy plate 1 and the duplex steel plate 2 were both 100 mm long, 50 mm wide, and 1 mm thick.

[0051] Aluminum powder was uniformly mixed with CeO2 powder having a diameter of 80 nm, wherein the CeO2 powder accounted for 30% of the total powder mass. A powder ball mill was used to ensure uniform distribution of the powder. Acetone was added to make the mixed powder into a paste form to obtain a paste-like Al-CeO2 powder.

[0052] On the side where the aluminum alloy plate 1 contacts the dual-phase steel plate 2, a groove is cut along the direction of the weld seam. The width of the groove is less than or equal to 0.3 mm and the depth is less than 0.3 mm. Al-CeO2 paste powder is pre-coated inside the groove of the aluminum base material. The Al-CeO2 paste powder coated in the groove of the aluminum alloy plate is the intermediate layer powder 3 added between the aluminum and steel layers. The coating amount of the intermediate layer powder 3 is 35 mg / cm 2 ;

[0053] Install a protective gas device and use argon for welding protection. The purity of argon is 99.999% and the gas flow rate is 20L / min.

[0054] The aluminum alloy plate 1 and the duplex steel plate 2 welding specimens are clamped on a universal welding fixture. A pad 4 is set if necessary. The duplex steel plate is overlapped on the upper side and the aluminum alloy plate is overlapped on the lower side. The overlap length of the two is 10 mm. The laser head is offset 10° in the welding direction. After the acetone in the intermediate layer powder is volatilized, laser welding is performed. The laser welding equipment 5 adopts the laser keyhole welding mode of the IPGYLS-4000 equipment. The laser wavelength is 1065±5 nm, the focal length is 400 mm, and the laser defocus is 0 mm. The laser power is 1800 W. The cross-sectional image of the weld after welding is completed is as follows: Figure 3 (c) shown.

[0055] Example 3

[0056] The aluminum alloy plate 1 and the duplex steel plate 2 were finely ground at the locations to be welded using 400-grit sandpaper. The locations to be welded were then cleaned using an ultrasonic cleaner and then dried to remove surface oxides and oil stains. The dimensions of the aluminum alloy plate 1 and the duplex steel plate 2 were both 100 mm long, 50 mm wide, and 1 mm thick.

[0057] Aluminum powder was uniformly mixed with CeO2 powder having a diameter of 80 nm, wherein the CeO2 powder accounted for 60% of the total powder mass. A powder ball mill was used to ensure uniform distribution of the powder. Acetone was added to make the mixed powder into a paste form to obtain a paste-like Al-CeO2 powder.

[0058] On the side where the aluminum alloy plate 1 contacts the dual-phase steel plate 2, a groove is cut along the direction of the weld seam. The width of the groove is less than or equal to 0.3 mm and the depth is less than 0.3 mm. Al-CeO2 paste powder is pre-coated inside the groove of the aluminum base material. The Al-CeO2 paste powder coated in the groove of the aluminum alloy plate is the intermediate layer powder 3 added between the aluminum and steel layers. The coating amount of the intermediate layer powder 3 is 35 mg / cm 2 ;

[0059] Install a protective gas device and use argon for welding protection. The purity of argon is 99.999% and the gas flow rate is 20L / min.

[0060] The aluminum alloy plate 1 and the duplex steel plate 2 welding specimens are clamped on a universal welding fixture. A pad 4 is set if necessary. The duplex steel plate is overlapped on the upper side and the aluminum alloy plate is overlapped on the lower side. The overlap length of the two is 10 mm. The laser head is offset 10° in the welding direction. After the acetone in the intermediate layer powder is volatilized, laser welding is performed. The laser welding equipment 5 adopts the laser keyhole welding mode of the IPGYLS-4000 equipment. The laser wavelength is 1065±5 nm, the focal length is 400 mm, and the laser defocus is 0 mm. The laser power is 1800 W. The cross-sectional image of the weld after welding is completed is as follows: Figure 3 (d) shown.

[0061] Example 4

[0062] The aluminum alloy plate 1 and the duplex steel plate 2 were finely ground at the locations to be welded using 400-grit sandpaper. The locations to be welded were then cleaned using an ultrasonic cleaner and then dried to remove surface oxides and oil stains. The dimensions of the aluminum alloy plate 1 and the duplex steel plate 2 were both 100 mm long, 50 mm wide, and 1 mm thick.

[0063] Take CeO2 powder with a diameter of 80nm, do not mix it with aluminum powder, and the CeO2 powder content is 100%. Add acetone to make the mixed powder into a paste form to obtain a paste-like Al-CeO2 powder;

[0064] On the side where the aluminum alloy plate 1 contacts the dual-phase steel plate 2, a groove is cut along the direction of the weld seam. The width of the groove is less than or equal to 0.3 mm and the depth is less than 0.3 mm. Al-CeO2 paste powder is pre-coated inside the groove of the aluminum base material. The Al-CeO2 paste powder coated in the groove of the aluminum alloy plate is the intermediate layer powder 3 added between the aluminum and steel layers. The coating amount of the intermediate layer powder 3 is 35 mg / cm 2 ;

[0065] Install a protective gas device and use argon for welding protection. The purity of argon is 99.999% and the gas flow rate is 20L / min.

[0066] The aluminum alloy plate 1 and the duplex steel plate 2 welding specimens are clamped on a universal welding fixture. A pad 4 is set if necessary. The duplex steel plate is overlapped on the upper side and the aluminum alloy plate is overlapped on the lower side. The overlap length of the two is 10 mm. The laser head is offset 10° in the welding direction. After the acetone in the intermediate layer powder is volatilized, laser welding is performed. The laser welding equipment 5 adopts the laser keyhole welding mode of the IPGYLS-4000 equipment. The laser wavelength is 1065±5 nm, the focal length is 400 mm, and the laser defocus is 0 mm. The laser power is 1800 W. The cross-sectional image of the weld after welding is completed is as follows: Figure 3 (e) shown.

[0067] See Figure 5 As shown, Figure 5 (b) is a local enlarged view of the welding boundary, where the shallowest part is CeO2.

[0068] Comparative Example 1

[0069] The aluminum alloy plate and the duplex steel plate were finely ground at the welded parts using 400-grit sandpaper, and then cleaned with an ultrasonic cleaner and then dried to remove surface oxides and oil stains. The dimensions of the aluminum alloy plate and the duplex steel plate were both 100 mm long, 50 mm wide, and 1 mm thick.

[0070] Install a protective gas device and use argon for welding protection. The purity of argon is 99.999% and the gas flow rate is 20L / min.

[0071] The aluminum alloy plate and the duplex steel plate welding specimens were clamped on a universal welding fixture, and the laser head was offset 10° in the welding direction. Laser welding was performed after the acetone in the intermediate layer powder volatilized. The laser welding adopted the laser keyhole welding mode of the IPG YLS-4000 equipment. The laser wavelength was 1065±5nm, the focal length was 400mm, and the laser defocus was 0mm. The laser power was 1800W. The cross-sectional image of the weld after welding was as follows: Figure 3 As shown in (a).

[0072] See Figure 4 As shown in the figure, the situation of the welding part when no Ce is added is observed. Figure 4 (b) is a local magnified image of the weld boundary, where the intermetallic compounds and cracks in the intermetallic compound layer can be clearly observed; Figure 4 (c) and Figure 4 (d) Figure 4 The Fe and Al elemental scans in (b) show the diffusion of the two elements. The lighter-colored areas indicate the presence of the intermetallic layer, which contains a variety of Fe-Al compounds. The parameters were 1800W at 140cm / min. The elemental scans provided demonstrate elemental diffusion, allowing the general trend to be determined by the abundance or absence of color. Compared to Comparative Example 1, where no CeO2 was added, Example 4 shows a decrease in Fe diffusion on the aluminum side and Al diffusion in the weld. This indicates that the presence of the added intermediate rare earth oxide hinders mutual diffusion and inhibits metallurgical reactions between the two elements.

[0073] Comparative Example 2

[0074] The aluminum alloy plate and the duplex steel plate were finely ground at the welded parts using 400-grit sandpaper, and then cleaned with an ultrasonic cleaner and then dried to remove surface oxides and oil stains. The dimensions of the aluminum alloy plate and the duplex steel plate were both 100 mm long, 50 mm wide, and 1 mm thick.

[0075] On the side where the aluminum alloy plate 1 contacts the dual-phase steel plate 2, a paste-like Al-CeO2 powder is pre-coated on the area to be welded of the aluminum base material without making a groove, wherein the CeO2 powder in the paste-like Al-CeO2 powder accounts for 100% of the total powder mass;

[0076] Install a protective gas device and use argon for welding protection. The purity of argon is 99.999% and the gas flow rate is 20L / min.

[0077] The aluminum alloy plate and duplex steel plate welding specimens were clamped on a universal welding fixture, and the laser head was offset 10° in the welding direction. Laser welding was performed after the acetone in the intermediate layer powder volatilized. The laser welding adopted the laser keyhole welding mode of the IPG YLS-4000 equipment, with a laser wavelength of 1065±5nm, a focal length of 400mm, a laser defocus of 0mm, and a laser power of 1800W.

[0078] The welding process parameters of the above-mentioned Examples 1-4 and Comparative Examples 1-2 are shown in Table 1.

[0079] Table 1 Welding process parameters of Examples 1-4 and Comparative Examples 1-4

[0080]

[0081] After welding, cross-sections of the specimens were cut using a wire-cut machine, and then standard metallographic specimens were mounted, ground, and polished. The average hardness of the weld zone was measured. Finally, the steel and aluminum sides were etched using NitAl etchant (4% HNO3, 96% C2H5OH) and Kalé reagent (2ml HF, 3ml HCl, 5ml HNO3, 190ml H2O), respectively, to observe the grain microstructure. Optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to observe the morphology and microstructure of the welds.

[0082] After testing, it was found that Figure 8As shown in the figure, when the mass fraction of CeO2 added at the sample interface is 100%, the average hardness of the fusion zone of the steel side weld is 421.41HV, which is higher than the hardness of the samples with 10% addition and no addition. Since the metallurgical reaction between Fe and Al is easy to occur at the edge of the weld, a brittle intermetallic compound phase with higher hardness is generated at the boundary. Therefore, a sharp increase in hardness is easy to occur at the junction of the aluminum side weld and the aluminum base material. At the same time, the average hardness of the weld area of ​​the sample with 100% CeO2 addition is 432.43HV, which is 16.39% higher than the hardness of the sample without addition. At the same time, the hardness value in the vertical weld direction is significantly higher than the hardness of the welds with other addition amounts, and a sharp increase in the hardness of the weld at the bottom of the molten pool is observed. And refer to Figure 9 As shown, it can be seen that the shear performance of the weld is enhanced when 100% CeO2 is added compared with that without CeO2.

[0083] Duplex steel is primarily composed of ferrite, a matrix, and martensite, present in islands. Under the action of the laser, the metal in the weld zone absorbs heat and becomes molten metal, which rapidly cools to form α-Fe ferrite. Under the influence of high temperatures, Ce atoms, acting as solute atoms, dissolve in the α-Fe. The large size of Ce atoms leads to a high degree of lattice distortion, increasing dislocation resistance and thus strengthening the weld through solid solution.

[0084] Because the solid solubility of Ce in α-Fe at high temperatures is only 0.4 wt%, the added Ce atoms in the weld exist in a very small amount as a solid solution in the α-Fe. A high-mass fraction of rare earth oxide CeO2 is added to the weld as an intermediate metal powder. Under the influence of Marangoni convection, it is evenly distributed in the weld area and metallurgically bonds with molten Fe and Al atoms to form nanoscale second-phase particles such as Fe-Ce and Ce-Al. This increases the alloy's undercooling while providing a large number of heterogeneous nucleation sites for grain nucleation, thereby refining the weld grains. Simultaneously, the eutectic structure formed during solidification aggregates at grain boundaries, reducing the ferrite interfacial energy, hindering grain growth, and resulting in a fine grain size. Furthermore, the presence of a large number of high-density dislocations in the weld creates an ultrafine eutectic structure that hinders dislocation movement, causing dislocations to entangle and accumulate, forming dislocation walls within the crystal.

[0085] From the above, it can be seen that adding a high-mass fraction of rare earth oxide CeO2 as an intermediate layer metal powder into the weld can increase the average hardness of the weld area, refine the weld grains, inhibit the occurrence of cracks in the weld area and cause weld fracture, and can improve the weld formation.

[0086] Therefore, the present invention employs the aforementioned structure for laser welding duplex steel and aluminum alloys with a pre-installed nano-rare earth interlayer. This method employs an Al / Fe overlap joint, pre-forms a groove on the Al side, and places an Al / CeO2 mixed powder. This innovative structure addresses the issues of overlap joints, where the added powder is partially squeezed out of the weld area under the pressure of welding fixtures, and where the added powder leads to overlap gaps in Al / Fe overlap joints. This method allows for the sufficient addition of the mixed powder to the weld pool, while simultaneously ensuring both powder addition and precise assembly of the weldment. This improves weld formation, and the addition of rare earth elements reduces porosity around the weld fusion line.

[0087] CeO2 can promote the welding material to absorb more laser energy, thereby increasing the molten metal in the weld, and with the increase of the added amount, the weld width and depth increase, and the weld size increases; the size of the Fe-Al intermetallic compound decreases, and the CeO2 element added into the weld as an intermediate layer reacts metallurgically with some Al atoms diffused into the weld in the molten pool, forming an Al-Ce phase intermetallic compound at the weld boundary, and a small amount of CeO2 powder added into the weld is distributed in a band at the bonding surface, inhibiting the metallurgical bonding of Fe and Al atoms, thereby reducing the size of the Fe-Al intermetallic compound generated in the weld.

[0088] The increase in the mass percentage of CeO2 added can make the grains at the weld boundary on the steel side present an ellipsoidal equiaxed crystal morphology and refine the grains. The maximum load of the joint with 100% CeO2 powder added increased from 2460.71N to 2683.20N, and the linear load of the joint reached 89.61N / mm. After adding rare earth elements, the fracture mode of the joint changed from brittle fracture to mixed fracture. Tough dimples appeared at the fracture of the joint with 100% CeO2 powder added, and the surface joint toughness was improved. Figure 6 and Figure 7 As shown, Figure 6 and Figure 7 By comparison, Figure 6 (c) is the weld fracture morphology, showing a cleavage platform, similar to a step; Figure 7 (a) is the fracture morphology of the weld with 100% mass fraction of Ce added. The crack is clearly visible. This part is a typical feature of brittle fracture - the crack extends along the grain boundary, and the grains are "rock candy-like"; Figure 7 (b) is a diagram of the area with dimple morphology in the fracture morphology of the weld with 100% mass fraction of Ce added; by comparison, it can be seen that the fracture morphology after adding Ce has the typical characteristics of both brittle fracture and ductile fracture, and the fracture mode of the fracture is a mixed fracture mode.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A laser welding method for dual-phase steel and aluminum alloy with a pre-set nano rare earth intermediate layer, characterized in that: The specific steps include: Step 1: Use 400-grit sandpaper to fine-grind the areas to be welded on the aluminum alloy plate and the duplex steel plate, then use an ultrasonic cleaner to clean the areas to be welded on the aluminum alloy plate and the duplex steel plate, and then dry them to remove surface oxides and oil stains on the areas to be welded; Step 2: Evenly mix nano-scale CeO2 powder and aluminum powder, define the rare earth element addition content by the mass fraction of CeO2 powder in the total powder, use a powder ball mill to ensure that the CeO2 powder and aluminum powder are evenly distributed, and add acetone to make the mixed powder into a paste form to obtain a paste-like Al-CeO2 powder; Step 3: Cut a groove along the weld seam on the side where the aluminum alloy plate contacts the duplex steel plate. The groove has a width of less than or equal to 0.3 mm and a depth of less than 0.3 mm. Pre-apply Al-CeO2 paste powder inside the groove of the aluminum base material. The Al-CeO2 paste powder applied inside the groove of the aluminum alloy plate is the intermediate layer powder added between the aluminum and steel layers. Step 4: Install the protective gas device and use argon gas for welding protection; Step 5: Clamp the aluminum alloy plate and duplex steel plate welding specimens onto a universal welding fixture, overlap the duplex steel plate on top and the aluminum alloy plate on the bottom, and offset the laser head 10° in the welding direction; laser welding is performed after the acetone in the intermediate layer powder evaporates.

2. The laser welding method for dual-phase steel and aluminum alloy with a pre-installed nano rare earth intermediate layer according to claim 1, characterized in that: The dimensions of the aluminum alloy plate and the dual-phase steel plate are both 100 mm in length, 50 mm in width and 1 mm in thickness.

3. The laser welding method for dual-phase steel and aluminum alloy with a pre-installed nano rare earth intermediate layer according to claim 2, characterized in that: In the step 2, the diameter of the CeO2 powder is 80 nm, and the diameter of the aluminum powder is 100 μm.

4. The laser welding method for dual-phase steel and aluminum alloy with a pre-installed nano rare earth intermediate layer according to claim 3, characterized in that: The mass fraction of CeO2 powder in the step 2 is 80-100%.

5. The laser welding method for dual-phase steel and aluminum alloy with a pre-installed nano rare earth intermediate layer according to claim 4, characterized in that: The coating amount of the intermediate layer powder in step 3 is 30-40 mg / cm 2 .

6. The laser welding method of dual-phase steel and aluminum alloy with a pre-installed nano rare earth intermediate layer according to claim 5, characterized in that: In the step 4, the purity of the protective gas argon is 99.999%, and the gas flow rate is 20 L / min.

7. The laser welding method of dual-phase steel and aluminum alloy with a pre-installed nano rare earth intermediate layer according to claim 6, characterized in that: In the step 5, the duplex steel plate is overlapped on the top and the aluminum alloy plate is overlapped on the bottom, and the overlapping length of the two is 10 mm.

8. The laser welding method of dual-phase steel and aluminum alloy with a pre-installed nano rare earth intermediate layer according to claim 7, characterized in that: The laser welding in step 5 adopts the laser keyhole welding mode of IPG YLS-4000 equipment, with a laser wavelength of 1065±5nm, a focal length of 400mm, and a laser defocus of 0mm.

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