A method of improving the weld penetration of laser welded cast aluminum alloy welds while reducing defects

Abstract

The present application relates to the technical field of laser welding, and particularly relates to a method for improving the penetration of laser welding of cast aluminum alloy and reducing defects, which has the following operation steps: the cast aluminum alloy is subjected to alkaline and acid pickling, and then the surface of the cast aluminum alloy sample is subjected to pulse anodic oxidation by using the sulfuric acid method; the surface segregation phenomenon during the forming of the cast aluminum alloy part is used to make the cast aluminum alloy surface generate an oxide film with uniform thickness and significant porous characteristics; the cast aluminum alloy sample is subjected to laser welding after cleaning and drying, and protective gas is sprayed from the welding head. The anodic oxidation process is used to generate an oxide film on the surface of the cast aluminum to improve the penetration, and the pulse anodic oxidation voltage is used to change the oxidation hole structure of the anodic oxide film, increase the pore size, and reduce the oxygen element content and the porosity of the interface after welding. The method is simple, convenient to operate, reduces the dyeing link, and does not depend on expensive equipment.

Description

Technical Field

[0001] This invention relates to the field of laser welding technology, and specifically to a method for increasing the penetration depth of laser welds in cast aluminum alloys while reducing defects. Background Technology

[0002] Cast aluminum alloys are widely used in aerospace, automotive manufacturing, and electronics industries due to their lightweight, high strength, and good corrosion resistance. However, during laser welding, the high reflectivity and thermal conductivity of cast aluminum alloys make it difficult to effectively absorb laser energy, resulting in insufficient penetration and unstable weld quality. This has become a major problem restricting the development of laser welding technology for aluminum alloys. Existing technologies improve laser absorption by heat treating the aluminum alloy surface, such as anodizing, but the following problems still exist:

[0003] 1. In existing methods that primarily utilize anodizing technology, dyeing is often performed after anodizing to significantly improve weld penetration. This additional dyeing step increases process complexity, production costs, and reduces efficiency, hindering large-scale industrial production. Furthermore, the dyeing step requires process adjustments for different aluminum alloy grades and anodizing processes, limiting its versatility.

[0004] 2. Existing anodizing techniques fail to fully consider the impact of the porous structure of the anodic oxide film on laser absorption, thus limiting the effectiveness of anodizing in improving laser absorption. Furthermore, existing techniques, when used to enhance laser absorption, do not take into account defects such as inclusions and porosity caused by the anodic oxide film, nor do they optimize the thickness and uniformity of the anodic oxide film. Therefore, existing techniques require further improvement. Summary of the Invention

[0005] The purpose of this invention is to provide a method for increasing the weld penetration depth of laser-welded cast aluminum alloys in order to solve the above-mentioned problems, while reducing defects such as oxygen content and porosity at the weld interface.

[0006] The technical solution to achieve the objective of this invention is: a method for increasing the weld penetration depth of laser-welded cast aluminum alloys while reducing the oxygen content and porosity at the weld interface, comprising the following steps:

[0007] Step 1: Clean the surface of the cast aluminum alloy sample with an alkaline solution and pickle the cast aluminum alloy sample with a mixed acid solution.

[0008] Step 2: Anodize the surface of the cast aluminum alloy sample using the sulfuric acid method and pulsed voltage method. Specifically, the cleaned cast aluminum alloy plate is fixed as the anode in an electrolytic cell. An electrolyte of 8-12 wt% sulfuric acid is poured into the cell, the temperature is 23±2℃, and a pulsed DC voltage is applied: E1 = 20V, t1 = 50s; E2 = 0V, t2 = 50s; f = 0.01Hz, current density 1A / dm³. 2 The oxidation time is 18–22 min, forming an aluminum oxide film with a thickness of 3–5 μm.

[0009] By utilizing the surface segregation phenomenon during the forming of cast aluminum alloy parts, a uniform oxide film is generated on the surface of the cast aluminum alloy without dyeing treatment. At the same time, the voltage idling during the pulse voltage method dissolves the oxide pores on the surface of the oxide film, thereby increasing the pore size.

[0010] Step 3: Clean the surface of the anodized cast aluminum alloy sample again and dry it.

[0011] Step 4: Adjust the welding parameters on the welding equipment to the corresponding values;

[0012] Step 5: Laser welding is performed on the cast aluminum alloy sample, while protective gas is sprayed out at the welding head.

[0013] In step 1 of the above technical solution, the cast aluminum alloy sample is cleaned for 10-20 minutes using an ultrasonic cleaner and a 4-6 vt% sodium hydroxide solution to remove oil, dust and other impurities. After cleaning, it is immersed in an acidic solution for pickling. The pickling solution uses a mixed acid of nitric acid, phosphoric acid and hydrofluoric acid, with a hydrofluoric acid concentration of 1-2 vt, a nitric acid concentration of 18-22 vt, a phosphoric acid concentration of 38-42 vt, and a pH value controlled at 1.8-2.2 (Note: the pH value should not be lower than 1.5, otherwise the aluminum base will be excessively corroded). Pickling can effectively remove oxides and impurities from the surface of the cast aluminum alloy sample.

[0014] In step 3 of the above technical solution, the cast aluminum alloy sample is cleaned with an ultrasonic cleaner and distilled water for 10-20 minutes. After cleaning, it is placed in an oven with a preset temperature of 55-65℃ and dried at this temperature for 25-35 minutes.

[0015] In step 4 of the above technical solution, the parameters of the laser equipment are adjusted to the corresponding values ​​according to the parameters of the aluminum alloy sample to be welded.

[0016] In step 5 of the above technical solution, the protective gas is Ar, and the flow rate is 12-17 L / min.

[0017] The oxide film does not dissolve during the welding process. In the molten pool, this insoluble oxide film easily absorbs hydrogen from the atmosphere and enters the molten pool, resulting in porosity. However, the present invention can solve the gas problem caused by the residual oxide film in the molten pool by preparing a suitable oxide film thickness and using a protective gas. Actual measurements show that the porosity with oxide film and the porosity without oxide film are similar, and there is no porosity problem.

[0018] After adopting the above technical solution, the present invention has the following positive effects:

[0019] In this invention, the inherent properties of cast aluminum alloy materials, the porous nature of the oxide film after anodizing, and the presence of silicon particles in the oxide film are all factors that increase the welding depth.

[0020] This invention employs sulfuric acid anodizing, utilizing the surface segregation phenomenon during the forming of cast aluminum alloy parts to generate a silicon-particle oxide film on the surface of the cast aluminum alloy without any dyeing treatment. Simultaneously, by utilizing a voltage idler in the pulsed voltage method, the oxide film partially dissolves, increasing the number and size of surface oxide pores. This significantly increases the penetration depth of laser welding while reducing the total oxide content.

[0021] Furthermore, the addition of a protective gas during welding avoids direct contact between the metal and air, effectively inhibiting oxide formation and reducing porosity, thus further improving welding quality. The technical solution described in this invention features a simple experimental method and convenient operation, effectively increasing the depth of the weld pool and reducing defects such as oxides and porosity in the weld pool, thereby further improving the quality of the weld joint. Attached Figure Description

[0022] Figure 1 Comparison of the microstructure of the molten pool in (a) conventional laser welding without oxidation treatment, (b) welding using the method provided by this invention, and (c) welding with constant pressure anodizing treatment for high pressure die casting A357 aluminum alloy under the same process parameters (laser power 2 kW);

[0023] Figure 2 This is a schematic diagram of a pulse voltage.

[0024] Figure 3 To compare the anodic oxide film structure under two conditions: pulsed voltage (a) and constant voltage (b). Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0027] This invention provides a method for increasing the penetration depth of laser-welded cast aluminum alloys, comprising the following steps:

[0028] Step 1: Clean the surface of the cast aluminum alloy sample with an alkaline solution and pickle the cast aluminum alloy sample with a mixed acid solution.

[0029] Step 2: The surface of the cast aluminum alloy sample is anodized using the sulfuric acid method. By utilizing the surface segregation phenomenon during the forming of cast aluminum alloy parts, a uniform oxide film is generated on the surface of the cast aluminum alloy.

[0030] Step 3: Clean the surface of the anodized cast aluminum alloy sample again and dry it.

[0031] Step 4: Adjust the welding parameters on the welding equipment to the corresponding values;

[0032] Step 5: Laser welding is performed on the cast aluminum alloy sample, while protective gas is sprayed out at the welding head.

[0033] In step 1 of the above technical solution, the cast aluminum alloy sample is cleaned for 15 minutes using an ultrasonic cleaner and a 5 VT% sodium hydroxide solution to remove oil, dust and other impurities. After cleaning, it is immersed in an acidic solution for pickling. The pickling solution uses a mixed acid of nitric acid, phosphoric acid and hydrofluoric acid, with a hydrofluoric acid concentration of 1.5 VT, a nitric acid concentration of 20 VT, a phosphoric acid concentration of 40 VT, and a pH value controlled at around 2 (the pH value should not be lower than 1.5, otherwise the aluminum base will be excessively corroded). Pickling can effectively remove oxides and impurities from the surface of the cast aluminum alloy sample.

[0034] In step 2 of the above technical solution, the sulfuric acid concentration is 10 wt%, the temperature is 23 ± 2℃, the voltage is a pulse voltage (E1 = 20V, t1 = 50s; E2 = 0V, t2 = 50s; f = 0.01Hz), and the current density is 1A / dm³. 2Oxidation time: 20 min.

[0035] In step 3 of the above technical solution, the cast aluminum alloy sample is cleaned with an ultrasonic cleaner and distilled water for 15 minutes. After cleaning, it is placed in an oven with a preset temperature of 60°C and dried at this temperature for 30 minutes.

[0036] In step 4 of the above technical solution, the parameters of the laser equipment are adjusted to the corresponding values ​​according to the parameters of the aluminum alloy sample to be welded.

[0037] In step 5 of the above technical solution, the protective gas is Ar, and the flow rate is 15 L / min.

[0038] Example 1

[0039] The above method is used to weld A356 and A357 cast aluminum alloy plates. The specific operation steps are as follows:

[0040] (1) Clean the surface of the cast aluminum alloy plate using an ultrasonic cleaner with a 5 vt% sodium hydroxide solution as the cleaning agent. The cleaning time is set to 15 minutes to ensure thorough cleaning. After ultrasonic cleaning, the cast aluminum alloy plate is immersed in an acidic solution for pickling. The pickling solution uses a mixed acid of nitric acid, phosphoric acid, and hydrofluoric acid with a hydrofluoric acid concentration of 1.5 vt, a nitric acid concentration of 20 vt, and a phosphoric acid concentration of 40 vt. The pH value is controlled at around 2 (the pH value should not be lower than 1.5, otherwise the aluminum base will be over-corroded). Pickling can effectively remove oxides and impurities from the surface of the cast aluminum alloy sample and prevent poor oxidation effect during the anodizing process.

[0041] (2) The cast aluminum alloy plate was anodized using the sulfuric acid method. The treated cast aluminum alloy plate was fixed as the anode in an electrolytic cell. An electrolyte of 10 wt% sulfuric acid was poured into the electrolytic cell, and the temperature was 23 ± 2℃ to ensure the stability of the anodizing process and the quality of the oxide film. The cathode material was a titanium mesh. A pulsed DC voltage (E1 = 20V, t1 = 50s; E2 = 0V, t2 = 50s; f = 0.01Hz) and a current density of 1A / dm³ were applied. 2 An oxidation reaction was initiated on the surface of the aluminum plate over a period of 20 minutes. During this electrochemical process, aluminum atoms on the surface of the aluminum plate reacted with oxygen atoms in the electrolyte to form an aluminum oxide film. The thickness of the oxide film was measured to be approximately 5 μm.

[0042] (3) The surface of the anodized cast aluminum alloy plate is cleaned again using an ultrasonic cleaner with distilled water as the cleaning agent. The cleaning time is set to 15 minutes to ensure thorough cleaning. After ultrasonic cleaning, the cast aluminum alloy plate is placed in an oven at a preset temperature of 60°C for 30 minutes to ensure that there is no residual moisture on the surface of the cast aluminum alloy plate, preventing defects such as porosity caused by moisture during laser welding.

[0043] (4) Debug the laser equipment, set the laser power to 3kw, the welding speed to 4m / min, the defocusing amount to 0mm, and the spot diameter to 0.4mm.

[0044] (5) After drying, the cast aluminum alloy plate is fixed with a clamp and laser welding is performed. During the welding process, a protective gas is added. The protective gas is Ar and the flow rate is 15L / min. Its main function is to isolate oxygen in the air and prevent the cast aluminum alloy in the molten pool from undergoing oxidation reaction at high temperature, which can effectively reduce the generation of porosity.

[0045] The following table shows the weld depth, weld porosity, and oxygen content at the weld interface after laser welding in Example 1:

[0046]

[0047] Example 2

[0048] The difference between Example 2 and Example 1 is that the A356 and A357 aluminum alloy plates were not anodized before laser welding; other conditions were the same as in Example 1.

[0049] The following table shows the welding depth, weld porosity, and oxygen content of the weld interface after laser welding in Example 2:

[0050]

[0051] Example 3

[0052] The difference between Example 3 and Example 1 is that the A356 and A357 aluminum alloy plates are subjected to a constant voltage E = 20V during anodizing; other conditions are the same as in Example 1.

[0053] Specific step (2) is as follows: The cast aluminum alloy plate is anodized using the sulfuric acid method. The treated cast aluminum alloy plate is fixed as the anode in an electrolytic cell. An electrolyte of 10 wt% sulfuric acid is poured into the electrolytic cell, and the temperature is 23 ± 2℃ to ensure the stability of the anodizing process and the quality of the oxide film. The cathode material is a titanium mesh. A constant voltage E = 20V and a current density of 1A / dm³ are applied. 2This process causes an oxidation reaction on the surface of the aluminum plate. In this electrochemical process, aluminum atoms on the surface of the aluminum plate react with oxygen atoms in the electrolyte to form an aluminum oxide film. The thickness of the oxide film was measured to be approximately 5 μm.

[0054] The following table shows the welding depth, weld porosity, and oxygen content of the weld interface after laser welding in Example 3:

[0055]

[0056] Example 4

[0057] The difference between Example 4 and Example 1 is that no protective gas is added when laser welding A356 and A357 aluminum alloy plates.

[0058]

[0059] Example 5

[0060] The difference between Example 5 and Example 1 is that the oxidation time for A356 and A357 aluminum alloy plates is 30 minutes and the oxide film thickness is about 10 μm.

[0061]

[0062] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for increasing the penetration depth of laser-welded cast aluminum alloys while reducing defects, characterized in that, The operation steps are as follows: Step 1: Clean the surface of the cast aluminum alloy sample with an alkaline solution, and then pickle the cast aluminum alloy sample with a mixed acid solution. In Step 1, use an ultrasonic cleaner to clean the sample, using a 4-6 vt% sodium hydroxide solution as the cleaning agent, and clean the cast aluminum alloy sample for 10-20 minutes. After cleaning, immerse the sample in a mixed acid solution for pickling. The mixed acid solution is a mixture of nitric acid, phosphoric acid, and hydrofluoric acid, with a hydrofluoric acid concentration of 1-2 vt, a nitric acid concentration of 18-22 vt, a phosphoric acid concentration of 38-42 vt, and a pH value controlled at 1.8-2.

2. Step 2: The surface of the cleaned cast aluminum alloy sample is anodized using sulfuric acid to form a uniform oxide film. The cleaned cast aluminum alloy sample is then fixed as the anode in an electrolytic cell. An electrolyte of 8-12 wt% sulfuric acid is poured into the cell, the temperature is 23±2℃, and a pulsed DC voltage is applied: E1=20V, t1=50s; E2=0V, t2=50s; f=0.01Hz, current density 1A / dm³. 2 Oxidation forms an aluminum oxide film; Step 3: Clean the surface of the anodized cast aluminum alloy sample again and dry it. Step 4: Adjust the welding parameters on the welding equipment; perform laser welding on the cast aluminum alloy sample, and simultaneously spray protective gas from the welding head to increase the penetration depth of the laser weld on the cast aluminum alloy.

2. The method for increasing the penetration depth of laser-welded cast aluminum alloys and reducing defects according to claim 1, characterized in that: In step 2, the thickness of the alumina film is 4~6μm.

3. The method for increasing the penetration depth of laser-welded cast aluminum alloys and reducing defects according to claim 1, characterized in that: In step 3, the cast aluminum alloy sample is cleaned with an ultrasonic cleaner and distilled water for 10-20 minutes. After cleaning, it is placed in an oven with a preset temperature of 55-65℃ and kept at this temperature to dry.

4. The method for increasing the penetration depth of laser-welded cast aluminum alloys and reducing defects according to claim 1, characterized in that: In step 4, the parameters of the laser equipment are adjusted to the corresponding values ​​according to the parameters of the cast aluminum alloy sample to be welded.

5. The method for increasing the penetration depth of laser-welded cast aluminum alloys and reducing defects according to claim 1, characterized in that: In step 4, the protective gas is Ar, and the flow rate is 12~17 L / min.

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