Welding method for selective laser melting forming AlSi10Mg aluminum alloy structural part

Abstract

The invention relates to a welding method for a selective laser melting forming AlSi10Mg aluminum alloy structural part, belongs to the technical field of additive manufacturing and welding, and solves the problem that in the prior art, when the selective laser melting forming AlSi10Mg aluminum alloy structural part is welded, serious air hole defects exist in a welding joint due to internal residual hydrogen and an improper process. The method comprises the steps that S1, heat treatment is conducted, specifically, heat treatment is conducted on a to-be-welded selective laser melting forming AlSi10Mg aluminum alloy structural part before welding, the heat treatment temperature ranges from 220 DEG C to 260 DEG C, and the heat preservation time ranges from 6 h to 10 h; s2, cleaning is conducted, specifically, surface cleaning is conducted on the to-be-welded area of the structural part treated in the step S1; s3, assembling is conducted, specifically, the cleaned structural parts are assembled, and the assembling clearance is controlled to be not larger than 0.1 mm; and S4, welding is conducted, specifically, in the vacuum environment, the assembled to-be-welded joint is welded through electron beams, and electron beams are in a beam swing mode. And high-quality and low-porosity reliable connection of the AlSi10Mg aluminum alloy structural part formed by selective laser melting is achieved.

Description

Technical Field

[0001] This invention relates to the fields of additive manufacturing and welding technology, and in particular to a welding method for laser selective melting forming of AlSi10Mg aluminum alloy structural parts. Background Technology

[0002] With the increasing demand for lightweight, high-performance, and complex components in the aerospace field, selective laser melting (SLM) additive manufacturing technology has been widely adopted due to its ability to achieve integrated forming of materials and structures. AlSi10Mg aluminum alloy, with its excellent specific strength and casting properties, has become one of the commonly used material systems in SLM technology.

[0003] However, the layer-by-layer melting and solidification characteristic of SLM technology means that the formed AlSi10Mg components may contain pores and residual hydrogen. When these components require subsequent welding assembly, traditional welding methods are prone to inducing dense porosity defects in the weld. This is mainly because under the welding thermal cycle, the residual hydrogen inside the component will rapidly precipitate and accumulate. If the welding process is not properly controlled, the bubbles cannot escape from the molten pool in time, thus forming excessive porosity, which seriously damages the mechanical properties and reliability of the welded joint, making it unable to meet the high-quality standards required for structural components in the aerospace field.

[0004] Therefore, the problem of welding porosity in AlSi10Mg aluminum alloy structural parts formed by laser selective melting has become a key bottleneck restricting its further engineering application. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a welding method for laser selective melting forming AlSi10Mg aluminum alloy structural parts, in order to at least solve one of the problems in the prior art, namely, severe porosity defects in welded joints and insufficient mechanical properties and reliability caused by residual hydrogen inside the SLM formed components and improper welding processes.

[0006] On one hand, embodiments of the present invention provide a welding method for laser selective melting forming of AlSi10Mg aluminum alloy structural parts, comprising the following steps:

[0007] S1. Heat treatment: The AlSi10Mg aluminum alloy structural parts to be welded by selective laser melting are heat treated before welding. The heat treatment temperature is 220℃~260℃ and the holding time is 6h~10h.

[0008] S2. Cleaning: Clean the surface of the structural component to be welded area after step S1;

[0009] S3. Assembly: Assemble the cleaned structural components by butt joints, controlling the assembly gap to be ≤0.1mm, and the thickness of the joint to be welded to be 2mm~4mm;

[0010] S4. Welding: In a vacuum environment, an electron beam is used to weld the assembled head to be welded. The electron beam adopts a beam oscillation mode, in which the electron beam oscillates along a circular or elliptical trajectory in a plane perpendicular to the welding direction, with an oscillation frequency of 150Hz-250Hz.

[0011] Furthermore, in step S1, the heat treatment is carried out in an air atmosphere or a protective atmosphere.

[0012] Furthermore, in step S2, the surface cleaning includes grinding the area to be welded with a wind brush, scraping the area to be welded with a scraper until the metal luster is exposed, grinding the area to be welded with a wind brush again, and then wiping it with a silk cloth soaked in anhydrous ethanol.

[0013] Furthermore, the structural components cleaned in step S2 are then subjected to welding operations in step S4 within 4 hours.

[0014] Furthermore, in step S3, the assembly gap is ≤0.1; the assembly step difference is ≤0.15δ or 0.25, whichever is smaller, where δ is the thickness of the joint to be welded.

[0015] Furthermore, in step S3, the joint to be welded adopts a bottom-locking butt joint, with a bottom-locking width of 3mm to 5mm.

[0016] Furthermore, in step S4, when the trajectory is circular, the swing radius is 0.1mm to 0.5mm.

[0017] Furthermore, in step S4, the welding process parameters are: accelerating voltage 130kV~150kV, electron beam current 6mA~10mA, focusing current 1850mA~1950mA, and welding speed 6mm / s~12mm / s.

[0018] Furthermore, the welding operation in step S4 includes tack welding and formal welding, both of which employ the same beam oscillation mode.

[0019] Furthermore, after welding in step S4, the internal quality of the weld meets the requirements for Class I joints specified in the GJB1718A-2023 standard.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1) By subjecting the SLM-formed AlSi10Mg component to a specific low-temperature, long-term heat treatment (220-260℃, 6-10h) before welding, this invention can effectively promote the diffusion and escape of hydrogen atoms introduced during manufacturing and remaining inside the component, thereby fundamentally reducing the hydrogen source during welding.

[0022] 2) This invention employs a beam oscillation mode, particularly a closed-curve trajectory (such as a circle), in vacuum electron beam welding. This oscillation can effectively stir the molten pool electromagnetically, prolonging the molten pool's existence time. This not only facilitates the upward escape of existing bubbles in the molten pool but also breaks up larger bubbles, thus reducing the number and size of pores in the weld.

[0023] 3) This invention organically combines pre-weld dehydrogenation heat treatment, assembly precision control, and electron beam oscillation welding parameters to form a complete closed-loop process. These steps work together synergistically, ultimately achieving the high internal quality of the welded joint, meeting the requirements of Class I joints in the GJB1718A-2023 standard, thus broadening the application prospects of SLM-formed AlSi10Mg components.

[0024] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0025] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0026] Figure 1 This is a schematic diagram of the locking bottom butt joint form of the AlSi10Mg aluminum alloy structural component formed by laser selective melting in Embodiment 1 of the present invention;

[0027] Figure 2 This is a schematic diagram of the direct butt joint form of the AlSi10Mg aluminum alloy structural component formed by laser selective melting in Embodiment 2 of the present invention.

[0028] Figure 3 This is a schematic diagram of the beam oscillation trajectory used in electron beam welding in Embodiment 1 of the present invention (taking a circular trajectory as an example);

[0029] Figure 4 This is a flowchart of the welding method for laser selective melting forming of AlSi10Mg aluminum alloy structural parts according to the present invention. Detailed Implementation

[0030] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0031] This invention provides a welding method for laser selective melting forming AlSi10Mg aluminum alloy structural components, aiming to solve industry problems such as weld porosity, cracks, and decreased joint performance caused by residual hydrogen inside and improper traditional welding processes. This invention achieves high-quality, low-porosity connections of components by combining specific pre-weld heat treatment, strict pre-weld cleaning and assembly control, and optimized vacuum electron beam welding technology.

[0032] A specific embodiment of the present invention discloses a welding method for laser selective melting forming AlSi10Mg aluminum alloy structural parts, such as... Figure 4 As shown, it includes the following steps:

[0033] S1. Heat treatment: The AlSi10Mg aluminum alloy structural parts to be welded by selective laser melting are heat treated before welding. The heat treatment temperature is 220℃~260℃ and the holding time is 6h~10h.

[0034] S2. Cleaning: Clean the surface of the structural component to be welded area after step S1;

[0035] S3. Assembly: Assemble the cleaned structural components by butt joints, controlling the assembly gap to be ≤0.1mm, and the thickness of the joint to be welded to be 2mm~4mm;

[0036] S4. Welding: In a vacuum environment, an electron beam is used to weld the assembled head to be welded. The electron beam adopts a beam oscillation mode, in which the electron beam oscillates along a circular or elliptical trajectory in a plane perpendicular to the welding direction, with an oscillation frequency of 150Hz to 250Hz.

[0037] Furthermore, in step S1, the heat treatment can be carried out in an air atmosphere or in a protective atmosphere (such as argon, nitrogen, etc.) to adapt to different production conditions and requirements.

[0038] Specifically, the core function of the heat treatment in step S1 is to remove hydrogen dissolved inside the part and to moderately regulate its non-equilibrium microstructure. SLM-formed AlSi10Mg has an extremely fast cooling rate, leading to supersaturated hydrogen solution in the molten aluminum, which is the main source of weld porosity.

[0039] By controlling the heat treatment temperature to 220℃~260℃ and the holding time to 6h~10h, sufficient diffusion kinetic energy can be provided for hydrogen atoms, allowing them to slowly migrate from the interior of the material to the surface and escape, thereby significantly reducing the risk of weld porosity from the source. If the temperature is too low or the time is too short, dehydrogenation will be incomplete; if the temperature is too high, it may cause over-aging, resulting in a significant loss of strength in the base material.

[0040] The low-temperature, long-term heat treatment method of this invention effectively removes hydrogen while better avoiding strength loss caused by material over-aging, achieving an optimal balance between hydrogen removal and retention of mechanical properties. Furthermore, this heat treatment also helps release some residual stress.

[0041] Furthermore, in step S2, the surface cleaning includes grinding the area to be welded using an air brush and scraping the area with a scraper to thoroughly remove any surface oxide film and other contaminants that may have formed after heat treatment, until the base metal is fully exposed and free of sharp corners or burrs. Subsequently, a cloth soaked in anhydrous ethanol is used for wiping to remove metal debris and oil residue generated during scraping. This combination of mechanical and chemical cleaning ensures a high degree of cleanliness on the surface to be welded.

[0042] In particular, scraping is superior to mechanical grinding because it can effectively prevent abrasive particles from embedding into the surface to be welded, thus introducing new sources of contamination.

[0043] It should be noted that, to avoid re-oxidation or contamination of the cleaned surface, the structural components cleaned in step S2 are placed in a clean environment and the subsequent welding operation in step S4 is performed within 4 hours. If this time limit is exceeded, the cleaning process must be repeated.

[0044] Furthermore, in step S3, strict requirements are placed on assembly precision to ensure the stability of the welding process and the quality of the weld formation. The assembly gap is ≤0.1, and the assembly step difference is ≤0.15δ or 0.25 (whichever is smaller), where δ is the thickness of the joint to be welded. This thickness range, along with the control of the gap and step difference, helps to ensure that the electron beam energy acts stably on the joint, which is an important prerequisite for obtaining a weld with uniform formation and consistent internal quality. Excessive gap or step difference will cause electron beam penetration and energy loss, easily resulting in defects such as undercut, incomplete penetration, or uneven formation.

[0045] Furthermore, in step S3, the joint to be welded adopts a lock-bottom butt joint with a lock-bottom width of 3mm to 5mm. This lock-bottom width range can provide effective positioning and molten pool support, prevent weld burn-through, while also taking into account assembly convenience and economy. For non-penetrating welds or joints with complex contours, a type I butt joint without a lock-bottom can also be used, but a copper or aluminum alloy gasket needs to be added to the back to support the molten pool.

[0046] Specifically, step S4 is performed in a vacuum environment, preferably where the vacuum level of the electron beam welding machine chamber is no greater than 7 × 10⁻⁶. -2 Pa, the vacuum level in the electron beam gun chamber is no greater than 1×10 Pa. -3 A high-vacuum environment effectively prevents gas molecules from colliding and scattering with the electron beam, ensuring concentrated electron beam energy and preventing external gas from being entrained in the molten pool. This is a crucial environmental guarantee for achieving low-porosity welding.

[0047] Furthermore, in step S4, the beam oscillation mode is that the electron beam oscillates along a closed curve trajectory in a plane perpendicular to the welding direction, with an oscillation frequency of 150Hz to 250Hz. The closed curve trajectory can be circular, elliptical, or other suitable closed shape. When the closed curve trajectory is circular, the oscillation radius is 0.1mm to 0.5mm.

[0048] The beam oscillation generates an electromagnetic stirring effect on the weld pool. This stirring effect has the following effects: firstly, it can break up the bubbles that have formed in the weld pool, making them easier to float and escape; secondly, it can prolong the liquid residence time of the weld pool, while disturbing the dendrite growth front during the solidification process, thereby preventing bubbles from being captured by dendrites and effectively reducing the porosity in the weld.

[0049] In one feasible implementation, such as Figure 3 As shown, the closed curve trajectory is circular, resulting in the most uniform stirring effect.

[0050] In another feasible implementation, the closed curve trajectory is elliptical. By adjusting the major and minor axes of the ellipse, different stirring intensities can be applied in the longitudinal and transverse directions of the weld to adapt to different weld forming requirements.

[0051] Furthermore, in step S4, the welding process parameters are: accelerating voltage 130kV~150kV, electron beam current 6mA~10mA, focusing current 1850mA~1950mA, and welding speed 6mm / s~12mm / s.

[0052] Combining the above welding process parameters with the aforementioned beam oscillation parameters can work synergistically to suppress the porosity defects unique to AISi10Mg aluminum alloy welding by selective laser melting, while ensuring uniform weld formation and good fusion.

[0053] In this parameter combination, the accelerating voltage and electron beam current together determine the power level of the electron beam; the focusing current is used to control the beam spot size and energy density distribution; the welding speed and power together determine the line energy input; and the oscillation radius and frequency together regulate the stirring intensity and range of the molten pool.

[0054] Furthermore, the welding operation in step S4 includes tack welding and formal welding, both of which employ the same beam oscillation mode.

[0055] Specifically, tack welding can be performed first using the aforementioned welding process parameters or slightly smaller parameters to fix the relative position of the workpiece. Then, the formal welding can be performed using the aforementioned welding process parameters. Maintaining the same beam oscillation pattern throughout the welding process helps ensure the uniformity and consistency of the weld quality.

[0056] Furthermore, after welding in step S4, the weld is subjected to X-ray inspection, and the internal quality of the weld meets the requirements for Class I joints specified in GJB1718A-2023 standard.

[0057] The joints welded using the method of this invention exhibit excellent internal quality, as demonstrated by testing. Specifically, the porosity of the weld can be stably controlled below 0.5% (volume fraction); the room temperature tensile strength of the joint is not less than 80% of the strength of the laser selective melting formed AISi10Mg aluminum alloy base material. Furthermore, the joint has a dense metallographic structure, free from defects such as cracks and lack of fusion.

[0058] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best implementation of the invention and do not limit the scope of the invention in any way.

[0059] Example 1

[0060] A welding method for selective laser melting forming of AlSi10Mg aluminum alloy structural parts, the specific steps of which are as follows:

[0061] S1. Heat treatment: The AlSi10Mg aluminum alloy structural part to be welded by selective laser melting with a thickness of 3mm is placed in an air atmosphere and heat-treated at 240℃ for 8 hours.

[0062] S2. Cleaning: Use an air brush to grind the area to be welded, then use a scraper to scrape the area until the metal luster is exposed. Grind the area again with an air brush, then wipe it clean with a white silk cloth soaked in anhydrous ethanol. Place the cleaned parts in a clean environment and complete electron beam welding within 4 hours.

[0063] S3. Assembly: According to Figure 1 As shown, the joint to be welded is assembled using a lock-bottom butt joint. The thickness of the joint to be welded is 3mm. If a lock-bottom butt joint is used, the lock bottom width should be 3mm. During assembly, the gap should be controlled at 0.1mm, and the step difference at 0.2mm.

[0064] S4. Welding: Vacuum electron beam welding is used. During welding, the electron beam follows a circular oscillation trajectory with an oscillation radius of 0.1 mm and a frequency of 200 Hz. The welding parameters are set as follows: accelerating voltage 140 kV, electron beam current 10 mA, focusing current 1850 mA, and welding speed 8 mm / s.

[0065] After welding, X-ray inspection was performed on the weld to assess its internal quality and thus evaluate the welding effect. The inspection results showed that the welded joint was well formed, with no defects such as undercut, cracks, or lack of fusion, and the internal quality of the weld met the requirements for Class I joints specified in GJB1718A-2023 standard.

[0066] Example 2

[0067] A welding method for selective laser melting forming of AlSi10Mg aluminum alloy structural parts, the specific steps of which are as follows:

[0068] S1. Heat treatment: The 2mm thick AlSi10Mg aluminum alloy structural part formed by laser selective melting is placed in an argon protective atmosphere and heat-treated at 260℃ for 6 hours.

[0069] S2. Cleaning: Use an air brush to grind the area to be welded, then use a scraper to scrape the area until the metal luster is exposed. Grind the area again with an air brush, then wipe it clean with a white silk cloth soaked in anhydrous ethanol. Place the cleaned parts in a clean environment and complete electron beam welding within 4 hours.

[0070] S3. Assembly: According to Figure 2 As shown, assembly is performed using a direct docking method, with the assembly gap controlled at 0.08mm and the step difference controlled at 0.1mm.

[0071] S4. Welding: Vacuum electron beam welding is used. During welding, the electron beam follows an elliptical oscillation trajectory with a major axis of 0.4 mm, a minor axis of 0.2 mm, and a frequency of 150 Hz. The welding parameters are set as follows: accelerating voltage 150 kV, electron beam current 10 mA, focusing current 1950 mA, and welding speed 12 mm / s.

[0072] Example 3

[0073] A welding method for selective laser melting forming of AlSi10Mg aluminum alloy structural parts, the specific steps of which are as follows:

[0074] S1. Heat treatment: The 4mm thick AlSi10Mg aluminum alloy structural part formed by laser selective melting is placed in an air atmosphere and heat-treated at 220℃ for 10 hours.

[0075] S2. Cleaning: Use an air brush to grind the area to be welded, then use a scraper to scrape the area until the metal luster is exposed. Grind the area again with an air brush, then wipe it clean with a white silk cloth soaked in anhydrous ethanol. Place the cleaned parts in a clean environment and complete electron beam welding within 4 hours.

[0076] S3. Assembly: The assembly is carried out by bottom locking and butt joint. The bottom locking width is 5mm, the assembly gap is controlled at 0.05mm, and the step difference is controlled at 0.15mm.

[0077] S4. Welding: Vacuum electron beam welding is used. During welding, the electron beam follows a circular oscillation trajectory with an oscillation radius of 0.3 mm and a frequency of 250 Hz. The welding parameters are set as follows: accelerating voltage 140 kV, electron beam current 8 mA, focusing current 1900 mA, and welding speed 9 mm / s.

[0078] Comparative Example 1

[0079] A welding method for laser selective melting forming of AlSi10Mg aluminum alloy structural parts is different from Example 1 only in that the pre-welding heat treatment step S1 is omitted, while the remaining steps and parameters are the same as in Example 1.

[0080] Comparative Example 2

[0081] A welding method for selective laser melting to form AlSi10Mg aluminum alloy structural parts differs from Example 1 only in that the electron beam welding in step S4 does not use beam oscillation, but instead performs linear welding. The remaining steps and parameters are the same as in Example 1.

[0082] Characterization results and analysis

[0083] The welded joints of the above-described embodiments and comparative examples were characterized by X-ray inspection and porosity statistics, and the results are shown in Table 1 below.

[0084] Table 1. Comparison of weld porosity and mechanical properties

[0085]

[0086]

[0087] As shown in Table 1, in Examples 1-3 using the complete technical solution of this invention, the weld porosity was controlled at an extremely low level (<0.5%), the tensile strength reached more than 80% of the base material, and all met the GJB1718A-2023 Class I joint standard. In contrast, Comparative Example 1, due to the lack of pre-weld dehydrogenation treatment, had a significantly excessive weld porosity and severely degraded mechanical properties; Comparative Example 2, although heat-treated, did not employ a beam-flow oscillating stirring molten pool, resulting in poor porosity escape conditions and still a high porosity, failing to meet performance standards.

[0088] In summary, this invention successfully solves the industry problem of high-quality welding of SLM-formed AlSi10Mg aluminum alloys through the synergistic effect of low-temperature long-time dehydrogenation heat treatment and vacuum electron beam closed-track oscillating welding, providing a reliable technical guarantee for the expanded application of this type of advanced manufacturing material in high-end fields such as aerospace.

[0089] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A welding method for laser selective melting forming of AlSi10Mg aluminum alloy structural parts, characterized in that, Includes the following steps: S1. Heat treatment: The AlSi10Mg aluminum alloy structural parts to be welded by selective laser melting are heat treated before welding. The heat treatment temperature is 220℃~260℃ and the holding time is 6h~10h. S2. Cleaning: Clean the surface of the structural component to be welded area after step S1; S3. Assembly: Assemble the cleaned structural components by butt joints, controlling the assembly gap to be ≤0.1mm, and the thickness of the joint to be welded to be 2mm~4mm; S4. Welding: In a vacuum environment, an electron beam is used to weld the assembled head to be welded. The electron beam adopts a beam oscillation mode, in which the electron beam oscillates along a circular or elliptical trajectory in a plane perpendicular to the welding direction, with an oscillation frequency of 150Hz-250Hz.

2. The welding method according to claim 1, characterized in that, In step S1, the heat treatment is carried out in an air atmosphere or a protective atmosphere.

3. The welding method according to claim 1, characterized in that, In step S2, the surface cleaning includes grinding the area to be welded with an air brush, scraping the area to be welded with a scraper until the metal luster is exposed, grinding the area to be welded with an air brush again, and then wiping it with a silk cloth soaked in anhydrous ethanol.

4. The welding method according to claim 3, characterized in that, The structural components cleaned in step S2 are then welded in step S4 within 4 hours.

5. The welding method according to claim 1, characterized in that, In step S3, the assembly gap is ≤0.1; the assembly step difference is ≤0.15δ or 0.25, whichever is smaller, where δ is the thickness of the joint to be welded.

6. The welding method according to claim 1 or 5, characterized in that, In step S3, the joint to be welded adopts a bottom-locking butt joint, with a bottom-locking width of 3mm to 5mm.

7. The welding method according to claim 1, characterized in that, In step S4, when the trajectory is circular, the swing radius is 0.1mm to 0.5mm.

8. The welding method according to claim 1 or 7, characterized in that, In step S4, the welding process parameters are: accelerating voltage 130kV~150kV, electron beam current 6mA~10mA, focusing current 1850mA~1950mA, and welding speed 6mm / s~12mm / s.

9. The welding method according to claim 1, characterized in that, The welding operation in step S4 includes tack welding and formal welding, both of which use the same beam oscillation mode.

10. The welding method according to claim 1, characterized in that, After welding in step S4, the internal quality of the weld meets the requirements for Class I joints specified in GJB1718A-2023 standard.

Images