Method for increasing weld penetration of cast aluminum alloy laser welding and reducing defects at same time

Abstract

The invention relates to the technical field of laser welding, in particular to a method for increasing the weld penetration of cast aluminum alloy laser welding and reducing defects at the same time, which comprises the following operation steps: carrying out alkaline and acid pickling on cast aluminum alloy, and then carrying out pulse anodic oxidation on the surface of a cast aluminum alloy sample by adopting a sulfuric acid method; a layer of oxidation film with uniform thickness and remarkable porous characteristic is generated on the surface of the cast aluminum alloy by utilizing the surface segregation phenomenon during forming of the cast aluminum alloy part; and after cleaning and drying, the cast aluminum alloy sample is subjected to laser welding, and meanwhile protective gas is sprayed out of a welding head. A layer of oxidation film can be generated on the surface of the cast aluminum through the anodic oxidation technology to improve the fusion depth, meanwhile, pulse anodic oxidation voltage vacancy is utilized, the oxidation hole structure of the anodic oxidation film is changed, the hole diameter is increased, and the oxygen element content and pores of an interface after welding are reduced. The method disclosed by the invention is simple and convenient to operate, reduces dyeing links and does not depend on expensive equipment.

Description

Technical Field

[0001] The invention relates to the technical field of laser welding, and in particular to a method for improving the penetration depth of a laser welding weld of a cast aluminum alloy while reducing defects. Background Art

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

[0003] 1. In the existing methods that use anodizing technology as the main means, in order to significantly increase the welding penetration, dyeing treatment is mostly performed after anodizing. The addition of dyeing treatment steps increases the process complexity and production cost, reduces efficiency, and is not conducive to large-scale industrial production. In addition, the dyeing treatment step needs to be adjusted according to different aluminum alloy grades and anodizing treatment processes, which limits the versatility.

[0004] 2. The existing anodizing technology fails to fully consider the effect of the porous structure of the anodized film on laser absorption, so the effect of using anodizing technology to improve laser absorption is limited. In addition, when using it to improve laser absorption, the existing technology does not take into account the defects such as inclusions and pores caused by the anodized film, and does not optimize the thickness and uniformity of the anodized film. Therefore, the existing technology needs to be improved. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems and provide a method for improving the penetration depth of the laser welding weld of cast aluminum alloy, while reducing defects such as oxygen content and porosity in the interface after welding.

[0006] The technical solution to achieve the purpose of the present invention is: a method for improving the penetration depth of laser welding of cast aluminum alloy and reducing the oxygen content and porosity of the interface after welding, comprising the following operating steps:

[0007] Step 1, using an alkaline solution to clean the surface of the cast aluminum alloy sample, and using a mixed acid solution to pickle the cast aluminum alloy sample;

[0008] Step 2, anodizing the surface of the cast aluminum alloy sample by sulfuric acid method and pulse voltage method, specifically: fix the cleaned cast aluminum alloy plate as an anode in an electrolytic cell, pour electrolyte into the electrolytic cell, the electrolyte is 8-12vt% sulfuric acid, the temperature is 23±2°C, apply pulse DC voltage, E1=20V, t1=50s; E2=0V, t2=50s; f=0.01Hz, current density 1A / dm 2 The oxidation time is 18 to 22 minutes to form an aluminum oxide film with a thickness of 3 to 5 μm.

[0009] By utilizing the surface segregation phenomenon during the forming of cast aluminum alloy parts, a layer of oxide film with uniform thickness is formed on the surface of the cast aluminum alloy without dyeing treatment. At the same time, the voltage is left idle during the pulse voltage method to dissolve the oxide pores on the surface of the oxide film and increase the pore size.

[0010] Step 3, cleaning the surface of the cast aluminum alloy sample after anodization again and performing a drying process;

[0011] Step 4, adjusting the welding parameters on the welding equipment to corresponding values;

[0012] Step 5, laser welding the cast aluminum alloy sample while spraying protective gas at the welding head.

[0013] In step 1 of the above technical solution, an ultrasonic cleaning machine and a 4-6 vt% sodium hydroxide solution are used to clean the cast aluminum alloy sample for 10-20 minutes to remove impurities such as oil, dust, etc. After cleaning, it is immersed in an acidic solution for pickling. The pickling uses a mixed acid of nitric acid-phosphoric acid-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 cannot be lower than 1.5, otherwise the aluminum base will be excessively corroded). Pickling can effectively remove oxides and impurities on the surface of the cast aluminum alloy sample.

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

[0015] In step 4 of the above technical solution, the laser equipment parameters are adjusted to corresponding values ​​according to the parameters of the cast 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 to 17 L / min.

[0017] The oxide film does not dissolve during the welding process. In the molten pool, this insoluble oxide film can easily absorb hydrogen from the atmosphere into the molten pool, thereby causing pores. The present invention prepares a suitable oxide film thickness and uses a protective gas to solve the gas problem caused by the residual oxide film in the molten pool. The actual measured porosity with and without the oxide film is similar, and there is no problem of pores.

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

[0019] In the present invention, the welding depth is increased by utilizing the characteristics of the cast aluminum alloy material itself, the porous characteristics of the oxide film after anodization, and the oxide film containing silicon particles in the oxide film.

[0020] The present invention adopts sulfuric acid anodizing and utilizes the surface segregation phenomenon during the forming of cast aluminum alloy parts to form a layer of silicon particle oxide film on the surface of the cast aluminum alloy without dyeing treatment. At the same time, the voltage is left idle in the pulse voltage method to dissolve part of the oxide film, increase the number of surface oxide pores and enlarge the pore diameter, significantly increase the penetration depth of laser welding, and reduce the total oxide content.

[0021] In addition, adding shielding gas during the welding process avoids direct contact between metal and air, which not only effectively inhibits the generation of oxides, but also reduces the generation of pores, further improving the welding quality. The technical solution described in the present invention has a simple experimental method and convenient operation, can effectively increase the depth of the welding pool, and reduce defects such as oxides and pores in the molten pool, further improving the quality of the welded joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 For high pressure die casting A357 aluminum alloy, under the same process parameter conditions (laser power 2kw), (a) conventional laser welding without oxidation treatment, (b) welding using the method provided by the present invention, and (c) welding using constant pressure anodizing treatment. Microstructure comparison diagram of the molten pool area;

[0023] Figure 2 Schematic diagram of pulse voltage.

[0024] Figure 3 Comparison of the structure of anodized films under pulse voltage (a) and constant voltage (b). DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The present invention provides a method for improving the penetration depth of a cast aluminum alloy laser welding weld, which comprises the following operating steps:

[0028] Step 1, using an alkaline solution to clean the surface of the cast aluminum alloy sample, and using a mixed acid solution to pickle the cast aluminum alloy sample;

[0029] Step 2, anodizing the surface of the cast aluminum alloy sample by sulfuric acid method, utilizing the surface segregation phenomenon during the forming of the cast aluminum alloy parts to form an oxide film with uniform thickness on the surface of the cast aluminum alloy;

[0030] Step 3, cleaning the surface of the cast aluminum alloy sample after anodization again and performing a drying process;

[0031] Step 4, adjusting the welding parameters on the welding equipment to corresponding values;

[0032] Step 5, laser welding the cast aluminum alloy sample while spraying protective gas 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 5vt% sodium hydroxide solution to remove impurities such as oil, dust, etc. After cleaning, it is immersed in an acidic solution for pickling. The pickling uses a mixed acid of nitric acid-phosphoric acid-hydrofluoric acid, with a hydrofluoric acid concentration of 1.5vt%, a nitric acid concentration of 20vt%, a phosphoric acid concentration of 40vt%, and a pH value controlled at around 2 (the pH value cannot be lower than 1.5, otherwise the aluminum base will be excessively corroded). Pickling can effectively remove oxides and impurities on the surface of the cast aluminum alloy sample.

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

[0035] In step 3 of the above technical solution, the cast aluminum alloy sample is cleaned for 15 minutes using an ultrasonic cleaner and distilled water. 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 laser equipment parameters are adjusted to corresponding values ​​according to the parameters of the cast 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 cleaning machine, using 5vt% sodium hydroxide solution as a cleaning agent, and setting the cleaning time to 15min to ensure adequate cleaning. After ultrasonic cleaning, the cast aluminum alloy plate is immersed in an acid solution for pickling. The pickling is carried out using a mixed acid of nitric acid, phosphoric acid, and hydrofluoric acid, with a hydrofluoric acid concentration of 1.5vt%, a nitric acid concentration of 20vt%, a phosphoric acid concentration of 40vt%, and a pH value of about 2 (the pH value cannot be lower than 1.5, otherwise the aluminum base will be over-corroded). Pickling can effectively remove oxides and impurities on the surface of the cast aluminum alloy sample, and prevent poor oxidation during anodizing.

[0041] (2) The cast aluminum alloy plate was anodized by sulfuric acid method. The treated cast aluminum alloy plate was fixed as the anode in the electrolytic cell. The electrolyte was poured into the electrolytic cell. The electrolyte was 10vt% sulfuric acid and the temperature was 23±2°C to ensure the stability of the anodization process and the quality of the oxide film. The cathode material was titanium mesh. A pulsed DC voltage (E1=20V, t1=50s; E2=0V, t2=50s; f=0.01Hz) was applied with a current density of 1A / dm 2 , so that the surface of the aluminum plate undergoes oxidation reaction, and the oxidation time is 20 minutes. In this electrochemical process, the aluminum atoms on the surface of the aluminum plate react with the oxygen atoms in the electrolyte to form an aluminum oxide film. The thickness of the oxide film is measured to be about 5μm.

[0042] (3) The surface of the cast aluminum alloy plate after anodizing is cleaned again by using an ultrasonic cleaning machine, using distilled water as a cleaning agent, and setting the cleaning time to 15 minutes to ensure sufficient cleaning. After the ultrasonic cleaning is completed, the cast aluminum alloy plate is placed in an oven with a preset temperature of 60°C for drying for 30 minutes to ensure that there is no residual moisture on the surface of the cast aluminum alloy plate to prevent defects such as pores caused by moisture during laser welding.

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

[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 with a flow rate of 15 L / min. Its main function is to isolate the 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 pores.

[0045] The welding depth, welding interface porosity and welding interface oxygen content after laser welding of Example 1 are shown in the following table:

[0046]

[0047] Example 2

[0048] Compared with Example 1, Example 2 differs in that: the A356 and A357 aluminum alloy plates are not anodized before laser welding; other conditions are the same as those of Example 1.

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

[0050]

[0051] Example 3

[0052] Compared with Example 1, Example 3 differs in that: when the A356 and A357 aluminum alloy plates are subjected to anodizing treatment, a constant voltage E=20V is used; other conditions are the same as those in Example 1.

[0053] The specific step (2) is: anodize the cast aluminum alloy plate using sulfuric acid method, fix the treated cast aluminum alloy plate as anode in the electrolytic cell, pour electrolyte into the electrolytic cell, the electrolyte is 10vt% sulfuric acid, the temperature is 23±2℃, to ensure the stability of the anodizing process and the quality of the oxide film, the cathode material is titanium mesh. Apply a constant voltage E=20V, current density 1A / dm 2, causing an oxidation reaction on the surface of the aluminum plate. In this electrochemical process, the aluminum atoms on the surface of the aluminum plate react with the oxygen atoms in the electrolyte to form an aluminum oxide film. The thickness of the oxide film was measured to be about 5μm.

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

[0055]

[0056] Example 4

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

[0058]

[0059] Example 5

[0060] Compared with Example 1, Example 5 differs in that when the A356 and A357 aluminum alloy plates are anodized, the oxidation time is 30 minutes and the oxide film thickness is about 10 μm.

[0061]

[0062] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is 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 in the protection scope of the present invention.

Claims

1. A method for increasing the weld penetration of cast aluminum alloy laser welding while reducing defects, characterized in that: The steps are as follows: Step 1, using an alkaline solution to clean the surface of the cast aluminum alloy sample, and then using a mixed acid solution to pickle the cast aluminum alloy sample; Step 2, anodizing the surface of the cast aluminum alloy sample after cleaning by sulfuric acid method, so that a layer of oxide film with uniform thickness is formed on the surface of the cast aluminum alloy; Step 3, cleaning the surface of the cast aluminum alloy sample after anodization again and performing a drying process; Step 4, adjusting the welding parameters on the welding equipment; performing laser welding on the cast aluminum alloy sample, spraying a protective gas at the welding head during laser welding, and increasing the penetration depth of the laser welding weld of the cast aluminum alloy.

2. The method for increasing the weld penetration of cast aluminum alloy laser welding and reducing defects according to claim 1, characterized in that: In step 1, the cast aluminum alloy sample is cleaned for 10 to 20 minutes using an ultrasonic cleaning machine and a 4 to 6 vt% sodium hydroxide solution. After cleaning, it is immersed in an acidic solution for pickling. The pickling uses a mixed acid of nitric acid, phosphoric acid and hydrofluoric acid, with a hydrofluoric acid concentration of 1 to 2 vt%, a nitric acid concentration of 18 to 22 vt%, a phosphoric acid concentration of 38 to 42 vt%, and a pH value controlled at 1.8 to 2.

2.

3. The method for increasing the weld penetration of cast aluminum alloy laser welding and reducing defects according to claim 1, characterized in that: In step 2, the cleaned cast aluminum alloy plate is fixed as an anode in an electrolytic cell, an electrolyte is poured into the electrolytic cell, the electrolyte is 8-12vt% sulfuric acid, the temperature is 23±2°C, a pulsed DC voltage is applied, E1=20V, t1=50s; E2=0V, t2=50s; f=0.01Hz, current density 1A / dm 2 , oxidized to form an aluminum oxide film.

4. The method for increasing the weld penetration of cast aluminum alloy laser welding and reducing defects according to claim 1, characterized in that: In step 2, the thickness of the aluminum oxide film is 4 to 6 μm.

5. The method for increasing the weld penetration of cast aluminum alloy laser welding and reducing defects according to claim 1, characterized in that: In step 3, the cast aluminum alloy sample is cleaned for 10 to 20 minutes using an ultrasonic cleaner and distilled water. After cleaning, the sample is placed in an oven with a preset temperature of 55 to 65° C. and dried at this temperature.

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

7. The method for increasing the weld penetration of cast aluminum alloy laser welding and reducing defects according to claim 1, characterized in that: In step 5, the protective gas is Ar, and the flow rate is 12 to 17 L / min.

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