A fluorine-free activation welding process for brazing aluminum parts

Abstract

This invention relates to the field of aluminum and aluminum alloy welding technology, and discloses a fluorine-free activated welding process for brazing aluminum parts, which does not use fluoride flux, including the following steps: (1) mechanically grinding, ultrasonically cleaning and plasma activation treatment are performed on the welding area of ​​the aluminum part in sequence; (2) brazing base solder is laid on the welding area of ​​the aluminum part after step (1), the aluminum part is placed in a sealed cavity, argon gas is introduced for atmosphere replacement protection, and then high-frequency induction heating is used to melt the solder and form a metallurgical bond with the aluminum part substrate to complete the welding; (3) after welding, the solder is cooled to room temperature under the condition of maintaining argon atmosphere, and then ultrasonic cleaning and hot air drying are performed in sequence to obtain the welded joint. This invention uses plasma activation pretreatment to replace fluorine-containing flux, effectively breaking the dense oxide film on the surface of the aluminum part, and achieving good wetting and metallurgical bonding of the solder to the aluminum substrate without the use of fluoride, thus completely eliminating the risk of electrochemical pitting corrosion caused by residual fluoride ions.

Description

Technical Field

[0001] This invention relates to the field of aluminum and aluminum alloy welding technology, specifically to a fluorine-free activation welding process for brazing aluminum parts. Background Technology

[0002] Aluminum and aluminum alloys are widely used in fields with high requirements for lightweighting and precision, such as electronics, aerospace, and instrumentation, due to their low density, high specific strength, and excellent electrical and thermal conductivity. In these applications, low-temperature joining of aluminum components is often required. Brazing has become an important method for joining precision aluminum parts because of its low welding temperature, small heat input, and narrow heat-affected zone on the base material.

[0003] However, aluminum surfaces readily form dense and chemically stable aluminum oxide (Al₂O₃). This film, with its high melting point and non-wetting properties, severely hinders the spread and metallurgical bonding of the solder on the aluminum substrate. Traditional aluminum brazing processes generally rely on fluoride-containing fluxes, which utilize fluoride ions to... The reaction generates volatile or soluble products, thereby breaking down the oxide film; however, this method has significant drawbacks: First, fluoride residues are difficult to completely remove, and in humid or salt spray environments, they can easily cause electrochemical corrosion, leading to pitting corrosion at the joints and significantly reducing service life; Second, fluoride flux releases toxic and harmful gases (such as HF) during heating, endangering the health of operators and failing to meet environmental regulations such as RoHS; Third, traditional heating methods (such as resistance heating and hot air heating) have low temperature control precision and large thermal gradients, which can easily cause local overheating of aluminum parts, resulting in grain coarsening and decreased plasticity, making it difficult to meet the requirements of precision components for maintaining the properties of the base material.

[0004] Existing improvement technologies mostly focus on reducing fluoride content or optimizing heating equipment, failing to fundamentally eliminate the use of fluorides; some studies have attempted to use high-energy beam methods such as laser activation, but the equipment is expensive and the process is complex, making it difficult to achieve industrial-scale promotion.

[0005] Therefore, there is an urgent need to develop a new brazing process for aluminum parts that is environmentally friendly and safe, has controllable process, and can guarantee the overall performance of the joint, without the need for fluoride flux. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides a fluorine-free activated welding process for brazing aluminum parts. This process has advantages such as eliminating the need for fluoride flux, ensuring environmentally friendly and safe welding, eliminating the risk of corrosion at the joint, minimizing the heat-affected zone, and enhancing process controllability. It solves the problems of residual corrosion, environmental pollution, operational hazards, and unstable welding quality caused by the reliance on fluorine-containing fluxes in traditional aluminum brazing.

[0008] (II) Technical Solution

[0009] To achieve the above-mentioned objective of providing an environmentally friendly, reliable, and precision aluminum component connection fluorine-free brazing process, the present invention provides the following technical solution: a fluorine-free activated brazing process for aluminum components, which does not use fluoride flux, comprising the following steps:

[0010] (1) The welding area of ​​the aluminum parts is subjected to mechanical grinding, ultrasonic cleaning and plasma activation treatment in sequence;

[0011] (2) Lay brazing filler metal in the welding area of ​​the aluminum part after step (1), place the aluminum part in a sealed cavity, introduce argon gas for atmosphere replacement protection, and then use high frequency induction heating to melt the filler metal and form a metallurgical bond with the aluminum part substrate to complete the welding.

[0012] (3) After welding, the welded joint is cooled to room temperature while maintaining an argon atmosphere, and then ultrasonic cleaning and hot air drying are performed in sequence to obtain the welded joint.

[0013] Preferably, the aluminum part is 1060 pure aluminum or 6061 aluminum alloy, and the welding gap is no more than 0.2mm.

[0014] Preferably, the mechanical grinding in step (1) uses 200-400 grit sandpaper to grind unidirectionally along the length of the aluminum base material, so that the surface roughness Ra of the welding area is 0.8-1.2μm.

[0015] Preferably, the plasma activation treatment in step (1) uses an argon-hydrogen mixed gas, wherein the volume ratio of argon to hydrogen is 8:1-10:1, the plasma power is 100-300W, the treatment time is 30-60s, and the plasma bombardment distance is 5-10mm.

[0016] Preferably, the solder base in step (2) is in powder or flake form, with a thickness of 0.1-0.3 mm; the solder base is selected from high-compatibility solder base or traditional solder, wherein the high-compatibility solder base contains 1.2%-1.5% lanthanum and cerium, 1.5%-2.5% silicon powder, 0.3%-0.4% copper powder, 0.3%-0.5% aluminum powder, and the balance is zinc; the traditional solder base contains 80%-85% aluminum, 5%-10% silicon, 0.5%-1% magnesium, and 5%-10% tin.

[0017] Preferably, the argon flow rate for argon atmosphere replacement in step (2) is 5-10 L / min, and the replacement time is 5-10 min, so that the oxygen content in the sealed cavity does not exceed 0.1%.

[0018] Preferably, the frequency of the high-frequency induction heating in step (2) is 200-400kHz, the heating rate is 5-8℃ / s, the heating temperature is 10-30℃ above the melting point of the solder, and the holding time is 10-15s.

[0019] Preferably, the cooling rate in step (3) is 2–5℃ / s; the ultrasonic cleaning time in step (1) is 5–8 min, and the ultrasonic cleaning time in step (3) is 5–10 min; both ultrasonic cleanings use anhydrous ethanol as the cleaning medium, the ultrasonic frequency is 20–40 kHz, and the power is 100–150 W.

[0020] Preferably, the temperature of the hot air drying in step (3) is 60–80°C and the drying time is 10 min.

[0021] (III) Beneficial Effects

[0022] Compared with the prior art, the present invention provides a fluorine-free activated brazing process for aluminum parts, which has the following beneficial effects:

[0023] 1. This invention effectively removes the dense oxide film on the surface of aluminum parts by replacing fluorine-containing flux with plasma activation pretreatment. This method achieves excellent wetting and metallurgical bonding of the solder to the aluminum substrate without the use of fluorides, completely eliminating the risk of electrochemical pitting corrosion caused by residual fluoride ions. Verified by a 5% NaCl salt spray test, the welded joint showed no rust or pitting, and its corrosion resistance was improved by more than 50% compared to traditional processes, significantly enhancing the reliability of the product in harsh environments such as the ocean and humid conditions.

[0024] 2. This invention utilizes a micro-nano-level rough surface formed by plasma activation to significantly increase the effective contact area between the solder and the aluminum base material. Combined with argon atmosphere protection throughout the process and high-frequency induction precise temperature control heating, it effectively suppresses oxidation regeneration and interface contamination, resulting in a solder spread rate of ≥95%, reducing the defect rate of incomplete soldering and missing soldering to below 0.1%, and achieving an overall welding qualification rate of 99.8%. It is especially suitable for precision aluminum parts with welding gaps ≤0.2mm, and can achieve 100% airtight connection, meeting the manufacturing requirements of high-sealing products such as sensor housings and electronic connectors.

[0025] 3. This invention achieves rapid, uniform, and low-heat-input local heating through high-frequency induction heating, with the heating rate controlled at 5–8℃ / s and a small temperature gradient, effectively avoiding grain coarsening of aluminum parts due to local overheating; the microstructure of the weld heat-affected zone is stable, and the grain size of the base material is ≤20μm, which is more than 50% finer than the traditional resistance heating process, thus significantly preserving the original mechanical properties of the aluminum matrix and ensuring that the welded joint has excellent structural integrity.

[0026] 4. The welded joint obtained by the present invention not only has high forming quality, but also excellent mechanical properties: under fluorine-free and low heat damage conditions, the tensile strength retention rate of the joint is ≥90%, and the impact toughness is improved by 30% compared with the traditional fluoride fluxing process. It fully meets the dual requirements of precision instruments, electronic devices and other devices for lightweight and structural reliability, and expands the application scenarios of low temperature connection of aluminum parts in high-end manufacturing fields.

[0027] 5. The process of this invention is simple, environmentally friendly and efficient, with no emissions of toxic and harmful gases such as HF throughout the entire process, complying with international environmental regulations such as RoHS, and significantly improving the working environment. At the same time, the process is compatible with highly compatible brazing base solder and traditional brazing solder, has high heating efficiency, shortens the single-piece welding cycle by about 30%, and does not require expensive laser or vacuum equipment, only conventional sealed chambers and induction power supplies. The equipment modification cost is low, and it is easy to integrate into existing production lines, with good prospects for industrial promotion. Attached Figure Description

[0028] Figure 1 This is a flow chart of the fluorine-free activated welding process for brazing aluminum parts according to the present invention;

[0029] Figure 2 This is a detailed process flow diagram of the fluorine-free activated welding process for brazing aluminum parts according to the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] like Figure 1 and Figure 2 As shown, a fluorine-free activated brazing process for aluminum parts includes three core steps: pretreatment, welding, and post-treatment, as detailed below:

[0032] 1. Pretreatment: Plasma activation + surface cleaning

[0033] 1.1 Mechanical grinding: Select the aluminum parts to be welded (such as 1060 pure aluminum, 6061 aluminum alloy, commonly used grades, welding gap ≤0.2mm), and use 200-400 grit sandpaper to grind the surface of the welding area in one direction along the length of the base material to remove surface oil, dust and loose oxide scale. After grinding, the surface roughness is controlled at Ra=0.8-1.2μm.

[0034] 1.2 Ultrasonic cleaning: Place the polished aluminum parts in anhydrous ethanol for ultrasonic cleaning. The ultrasonic frequency is 20-40kHz, the power is 100-150W, and the cleaning time is 5-8 minutes to remove the metal debris and oil residue left after polishing. After cleaning, let it air dry at room temperature to ensure that the surface of the welding area is clean and free of impurities.

[0035] 1.3 Plasma Activation: The dried aluminum parts are placed in a plasma treatment device, and the process parameters are adjusted as follows: argon-hydrogen mixed gas (argon:hydrogen = 8-10:1, volume ratio), plasma power 100-300W, treatment time 30-60s, and plasma bombardment distance controlled at 5-10mm; the dense surface layer of the aluminum is peeled off through the physical bombardment of the plasma. Oxide film, while hydrogen plasma and residue The reduction reaction generates elemental aluminum and water vapor, further purifying the welding surface; plasma bombardment can form a micro-nano-level rough structure on the surface of aluminum parts, and the surface roughness is improved to Ra=1.5-3.0μm after treatment, increasing the contact area between the solder and the base material.

[0036] 2. Welding: Argon gas protection + high-frequency induction precision heating

[0037] 2.1 Solder application: The solder base material (such as high compatibility solder base material or traditional solder) is processed into powder or flakes and evenly applied to the welding area of ​​the aluminum part. The thickness of the solder application is adjusted according to the welding gap and controlled between 0.1-0.3 mm.

[0038] 2.2 Atmosphere Protection: Place the aluminum parts with solder laid on them into a sealed welding chamber, and introduce argon gas to replace the atmosphere. The argon gas flow rate is 5-10 L / min, and the replacement time is 5-10 min to ensure that the oxygen content in the chamber is ≤0.1% to avoid the solder and aluminum parts from oxidizing again during the welding process.

[0039] 2.3 High-frequency induction heating: Start the high-frequency induction heating equipment, adjust the heating frequency to 200-400kHz, control the heating rate to 5-8℃ / s, and raise the temperature to 10-30℃ above the melting point of the solder (e.g., 530-550℃). After the solder has completely melted and spread to cover the welding area, maintain the temperature for 10-15s to ensure that the solder and the aluminum substrate undergo a full metallurgical reaction to form a dense weld joint. High-frequency induction heating achieves synchronous heating of the base material and the solder through the principle of electromagnetic induction, with a small temperature gradient, which can effectively avoid local overheating of the aluminum parts.

[0040] 2.4 Cooling: After the heat preservation is completed, turn off the heating equipment, keep the argon atmosphere unchanged, and let the aluminum parts cool to room temperature with the furnace. The cooling rate should be controlled at 2-5℃ / s to reduce the residual stress of the joint.

[0041] 3. Post-processing: Ultrasonic cleaning + hot air drying

[0042] 3.1 Ultrasonic cleaning: After cooling, the aluminum parts are placed in anhydrous ethanol for ultrasonic cleaning. The ultrasonic frequency is 20-40kHz, the power is 100-150W, and the cleaning time is 5-10min to thoroughly remove trace amounts of welding slag and impurities adsorbed on the surface generated during the welding process.

[0043] 3.2 Hot air drying: Place the cleaned aluminum parts into a hot air drying oven, set the temperature to 60-80℃, and dry for 10 minutes to remove residual ethanol on the surface and avoid moisture residue causing joint corrosion; after drying, take out the aluminum parts to obtain fluorine-free activated welded aluminum joints.

[0044] Example 1

[0045] A fluorine-free activated brazing process for aluminum parts is applied to the welding of 6061 aluminum alloy sensor housings with a thickness of 1 mm and a welding gap of 0.1 mm. The specific steps are as follows:

[0046] Step 1. Pretreatment: The welding area was unidirectionally polished with 300-grit sandpaper and ultrasonically cleaned with anhydrous ethanol (frequency 30kHz, power 120W, time 6min); plasma activation parameters: argon-hydrogen mixed gas (9:1, volume ratio), power 200W, treatment time 45s, bombardment distance 8mm, and surface roughness Ra=2.2μm after treatment.

[0047] Step 2. Welding: Lay out the aforementioned high-compatibility brazing filler metal sheet (1.2%-1.5% lanthanum and cerium, 1.5%-2.5% silicon powder, 0.3%-0.4% copper powder, 0.3%-0.5% aluminum powder, with the balance being zinc), argon gas flow rate 8L / min, high-frequency induction heating frequency 300kHz, heating rate 6℃ / s, heating to 540℃, holding for 12s; cool with the furnace in an argon atmosphere at a cooling rate of 3℃ / s.

[0048] Step 3. Post-processing: Ultrasonic cleaning with anhydrous ethanol (frequency 30kHz, power 120W, time 8min), followed by hot air drying at 70℃ for 10min.

[0049] Test results: Solder spread rate 98%, welding qualification rate 100%; joint tensile strength 95MPa, grain size 15μm; no pitting corrosion after 600h of 5% NaCl salt spray test, and impact toughness improved by 32% compared with traditional process.

[0050] Example 2

[0051] A fluorine-free activation welding process for brazing aluminum components is applied to the welding of 1060 pure aluminum electronic connectors with a thickness of 0.5 mm and a welding gap of 0.2 mm. The specific steps are as follows:

[0052] Step 1. Pretreatment: The welding area was unidirectionally polished with 400-grit sandpaper and ultrasonically cleaned with anhydrous ethanol (frequency 25kHz, power 100W, time 5min); plasma activation parameters: argon-hydrogen mixed gas (8:1, volume ratio), power 150W, treatment time 35s, bombardment distance 6mm, and surface roughness Ra=1.8μm after treatment.

[0053] Step 2. Welding: Lay out traditional brazing solder powder (aluminum content 80%-85%, silicon content 5%-10%, magnesium content 0.5%-1%, tin content 5%-10%), argon flow rate 6L / min, high-frequency induction heating frequency 250kHz, heating rate 5℃ / s, heat up to 530℃, hold for 10s; cool with the furnace in argon atmosphere, cooling rate 2℃ / s.

[0054] Step 3. Post-processing: Ultrasonic cleaning with anhydrous ethanol (frequency 25kHz, power 100W, time 6min), followed by hot air drying at 65℃ for 10min.

[0055] Test results: Solder spread rate 96%, welding qualification rate 99.9%; joint tensile strength 82MPa, grain size 18μm; no pitting corrosion after 550h of 5% NaCl salt spray test, and impact toughness improved by 28% compared with traditional process.

[0056] Example 3

[0057] A fluorine-free activated brazing process for aluminum parts is applied to the welding of 6061 aluminum alloy instrument brackets with a thickness of 2mm and a welding gap of 0.15mm. The specific steps are as follows:

[0058] Step 1. Pretreatment: The welding area was unidirectionally polished with 200-grit sandpaper and ultrasonically cleaned with anhydrous ethanol (frequency 20kHz, power 150W, time 8min); plasma activation parameters: argon-hydrogen mixed gas (10:1, volume ratio), power 300W, treatment time 60s, bombardment distance 10mm, and surface roughness Ra=3.0μm after treatment.

[0059] Step 2. Welding: Lay out the aforementioned high-compatibility brazing filler metal sheet (1.2%-1.5% lanthanum and cerium, 1.5%-2.5% silicon powder, 0.3%-0.4% copper powder, 0.3%-0.5% aluminum powder, with the balance being zinc), argon gas flow rate 10 L / min, high-frequency induction heating frequency 400 kHz, heating rate 8℃ / s, heating to 550℃, holding for 15s; cool with the furnace in an argon atmosphere at a cooling rate of 5℃ / s.

[0060] Step 3. Post-processing: Ultrasonic cleaning with anhydrous ethanol (frequency 20kHz, power 150W, time 10min), followed by hot air drying at 80℃ for 10min.

[0061] Test results: Solder spread rate 99%, welding qualification rate 100%; joint tensile strength 102MPa, grain size 12μm; no pitting corrosion after 680h of 5% NaCl salt spray test, and impact toughness improved by 35% compared with traditional process.

[0062] Example 4

[0063] A fluorine-free activated brazing process for aluminum parts is applied to the brazing of 1060 pure aluminum precision terminals with a thickness of 0.8 mm and a welding gap of 0.08 mm. The specific steps are as follows:

[0064] Step 1. Pretreatment: The welding area was unidirectionally polished with 400-grit sandpaper and ultrasonically cleaned with anhydrous ethanol (frequency 40kHz, power 100W, time 5min); Plasma activation parameters: argon-hydrogen mixed gas (8:1, volume ratio), power 100W, treatment time 30s, bombardment distance 5mm, and surface roughness Ra=1.5μm after treatment.

[0065] Step 2. Welding: Lay out traditional brazing solder powder (aluminum content 80%-85%, silicon content 5%-10%, magnesium content 0.5%-1%, tin content 5%-10%), argon flow rate 5L / min, high-frequency induction heating frequency 200kHz, heating rate 5℃ / s, heat up to 530℃, hold for 10s; cool with the furnace in argon atmosphere, cooling rate 2℃ / s.

[0066] Step 3. Post-processing: Ultrasonic cleaning with anhydrous ethanol (frequency 40kHz, power 100W, time 5min), followed by hot air drying at 60℃ for 10min.

[0067] Test results: Solder spread rate 95%, welding qualification rate 99.8%; joint tensile strength 80MPa, grain size 16μm; no pitting corrosion after 520h of 5% NaCl salt spray test, and impact toughness improved by 25% compared with traditional process.

[0068] Comparative Example 1

[0069] The same 6061 aluminum alloy sensor housing as in Example 1 was welded using a traditional fluoride flux brazing process. The specific steps were as follows: after grinding and cleaning, fluoride flux was applied, and the same high-compatibility brazing base solder as in Example 1 was laid. The temperature was then resistively heated to 540°C and held for 12 seconds. After cooling, the residual flux was removed by washing with water.

[0070] Test results: Solder spread rate 90%, welding qualification rate 92%; joint tensile strength 75MPa, grain size 35μm; obvious pitting corrosion appeared after 300h of 5% NaCl salt spray test, and the impact toughness decreased by 30% compared with Example 1.

[0071] Comparative Example 2

[0072] The same 6061 aluminum alloy sensor housing as in Example 1 was welded using a plasma-free argon-protected high-frequency induction welding process. The specific steps were as follows: after grinding and cleaning, the same high-compatibility brazing filler metal as in Example 1 was directly applied, and the remaining welding and post-processing parameters were the same as in Example 1.

[0073] Test results: Solder spread rate 65%, cold solder joint rate 15%; joint tensile strength 58MPa, grain size 16μm; no pitting corrosion in 5% NaCl salt spray test for 400h, but the joint sealing performance was not up to standard due to cold solder joint.

[0074] Comparative Example 3

[0075] The same 6061 aluminum alloy instrument bracket as in Example 3 was welded using a plasma activation + air atmosphere high-frequency induction heating process. The specific steps were as follows: the pretreatment plasma activation parameters were the same as in Example 3, no argon gas protection was used during welding, and the other parameters were the same as in Example 3.

[0076] Test results: Solder spread rate 72%, cold solder joint rate 8%; joint tensile strength 65MPa, grain size 14μm; local oxidation and corrosion occurred after 280h of 5% NaCl salt spray test, and the sealing performance did not meet the standard.

[0077] Comparative Example 4

[0078] Using a fluoride flux + high-frequency induction heating process, 1060 pure aluminum precision terminals of the same specifications as in Example 4 were welded. The specific steps were as follows: after grinding and cleaning, fluoride flux was applied, no plasma activation was performed, and the same traditional solder as in Example 4 was laid. The high-frequency induction heating parameters under argon protection were the same as in Example 4.

[0079] Test results: Solder spread rate 94%, welding qualification rate 98.5%; joint tensile strength 78MPa, grain size 17μm; after 250h of 5% NaCl salt spray test, obvious pitting corrosion appeared in the joint, and flux residue caused the insulation performance of the terminal to decrease by 20%.

[0080] As can be seen from the performance test results of Examples 1-4 and Comparative Examples 1-4 above, the fluorine-free activated welding process for aluminum brazing described in this invention has significant technical advantages and performance improvement effects compared with traditional fluorine-containing flux processes and non-optimized fluorine-free processes.

[0081] In terms of welding quality, the solder spreading rate of Examples 1-4 was ≥95%, with a maximum of 99%, and the welding qualification rate was consistently above 99.8%. Moreover, 100% sealing welding could be achieved for precision aluminum parts with welding gaps ≤0.2mm. Comparative Example 1 used a traditional fluoride flux + resistance heating process, with a solder spreading rate of only 90% and a welding qualification rate of 92%. Comparative Example 2 lacked a plasma activation step, resulting in a solder spreading rate that dropped directly to 65%, a false weld rate as high as 15%, and a complete failure to meet sealing performance standards. Comparative Example 3 eliminated the argon protective atmosphere, causing secondary oxidation of the solder and aluminum parts during the welding process, resulting in a spreading rate of only 72% and obvious oxidation and corrosion defects at the joint.

[0082] Analysis of the mechanical properties of the joints and the microstructure of the base material shows that the tensile strength of the welded joints in Examples 1-4 is ≥80MPa, with a maximum of 102MPa. Furthermore, the high-frequency induction precise temperature control keeps the grain size of the aluminum base material in the welding area at 12-18μm, which is more than 50% finer than the grain size of the traditional resistance heating process. In Comparative Example 1, due to local overheating of resistance heating, the grain size of the base material coarsens to 35μm, and the tensile strength of the joint is only 75MPa, with a significant decrease in impact toughness. Although Comparative Example 4 uses high-frequency induction heating, it relies on fluoride flux and has no plasma activation, resulting in a joint tensile strength of only 78MPa, failing to leverage the performance-enhancing effect of precise temperature control.

[0083] Judging from the corrosion resistance performance, Examples 1-4, due to the complete elimination of fluoride flux and the avoidance of oxidation through plasma activation and argon protection, all had a corrosion resistance time of ≥520h in the 5% NaCl salt spray test, with the longest reaching 680h, and no pitting or rusting phenomena on the surface. Comparative Examples 1 and 4, due to residual fluoride ions, had a salt spray corrosion resistance time of only 300h and 250h respectively, and obvious pitting pits appeared on the surface of the joints. Comparative Example 4 also had a 20% decrease in the insulation performance of the terminal due to flux residue. Comparative Example 3, due to oxidation caused by welding in an air atmosphere, had a salt spray corrosion resistance time of only 280h, and the joint had oxidation and rust defects.

[0084] In summary, this invention, through a combined process design of plasma activation pretreatment, argon atmosphere protection, and high-frequency induction precise heating, achieves simultaneous improvement in solder spreading performance, joint mechanical properties, and corrosion resistance under the premise of complete fluorine-free operation. This is significantly superior to traditional processes and non-optimized fluorine-free processes, demonstrating outstanding creativity and practicality.

[0085] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0086] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A fluorine-free activated brazing process for aluminum parts, characterized in that: The steps to avoid using fluoride flux include: (1) The welding area of ​​the aluminum parts is subjected to mechanical grinding, ultrasonic cleaning and plasma activation treatment in sequence; (2) Lay brazing filler metal in the welding area of ​​the aluminum part after step (1), place the aluminum part in a sealed cavity, introduce argon gas for atmosphere replacement protection, and then use high frequency induction heating to melt the filler metal and form a metallurgical bond with the aluminum part substrate to complete the welding. (3) After welding, the welded joint is cooled to room temperature while maintaining an argon atmosphere, and then ultrasonic cleaning and hot air drying are performed in sequence to obtain the welded joint.

2. The fluorine-free activated welding process for brazing aluminum parts according to claim 1, characterized in that: The aluminum parts are made of 1060 pure aluminum or 6061 aluminum alloy, and the welding gap is no more than 0.2mm.

3. The fluorine-free activation welding process for brazing aluminum parts according to claim 1, characterized in that: In step (1), the mechanical grinding is performed by grinding 200-400 grit sandpaper along the length of the aluminum base material in one direction, so that the surface roughness Ra of the welding area is 0.8-1.2μm.

4. The fluorine-free activation welding process for brazing aluminum parts according to claim 1, characterized in that: The plasma activation treatment in step (1) uses an argon-hydrogen mixed gas, wherein the volume ratio of argon to hydrogen is 8:1-10:1, the plasma power is 100-300W, the treatment time is 30-60s, and the plasma bombardment distance is 5-10mm.

5. The fluorine-free activation welding process for brazing aluminum parts according to claim 1, characterized in that: The solder base mentioned in step (2) is in powder or flake form, with a thickness of 0.1-0.3 mm. The solder base is selected from high compatibility solder base or traditional solder. The high compatibility solder base contains 1.2%-1.5% lanthanum and cerium, 1.5%-2.5% silicon powder, 0.3%-0.4% copper powder, 0.3%-0.5% aluminum powder, and the balance is zinc. The traditional solder base contains 80%-85% aluminum, 5%-10% silicon, 0.5%-1% magnesium, and 5%-10% tin.

6. The fluorine-free activation welding process for brazing aluminum parts according to claim 1, characterized in that: In step (2), the argon flow rate for argon atmosphere replacement is 5-10 L / min, and the replacement time is 5-10 min, so that the oxygen content in the sealed cavity does not exceed 0.1%.

7. The fluorine-free activated welding process for brazing aluminum parts according to claim 1, characterized in that: The frequency of the high-frequency induction heating in step (2) is 200-400kHz, the heating rate is 5-8℃ / s, the heating temperature is 10-30℃ above the melting point of the solder, and the holding time is 10-15s.

8. The fluorine-free activated welding process for brazing aluminum parts according to claim 1, characterized in that: The cooling rate in step (3) is 2–5℃ / s; the ultrasonic cleaning time in step (1) is 5–8 min, and the ultrasonic cleaning time in step (3) is 5–10 min; anhydrous ethanol is used as the cleaning medium for both ultrasonic cleanings, the ultrasonic frequency is 20–40 kHz, and the power is 100–150 W.

9. The fluorine-free activation welding process for brazing aluminum parts according to claim 1, characterized in that: The temperature of the hot air drying in step (3) is 60–80℃ and the drying time is 10 min.

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