Preparation method of medium-thin plate AZ31B magnesium alloy high-toughness welded joint

Abstract

The invention provides a preparation method of a medium-thin plate AZ31B magnesium alloy high-toughness welding joint, and relates to the technical field of welding. The welding groove is in a Y shape, the groove angle of a welding joint is 60 degrees, the truncated edge size is 1.5 mm, the root gap is 0.5-1 mm, oil stain and oxidation film cleaning is carried out before welding, then assembling is carried out, single-face single-pass welding or single-face double-layer double-pass welding is carried out on an AZ31B test plate, and artificial aging treatment is carried out after welding. The preparation method of the medium-thin plate AZ31B magnesium alloy high-toughness welding joint overcomes the defects in the prior art, does not need a liner or back argon protection, is simple to operate, low in manufacturing cost and high in production efficiency, and can be suitable for welding production and manufacturing of various product structural forms.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and in particular to a method for preparing a medium-thin plate AZ31B magnesium alloy high-strength and toughness welded joint. Background Art

[0002] Energy conservation and emission reduction through lightweighting has become the focus of rail transit. Due to the advantages of magnesium alloy such as low density, high specific strength and specific stiffness, excellent damping and thermal conductivity, low price, and recyclability, it is currently the lightest alloy material and is very consistent with the development trend of lightweighting, energy conservation and emission reduction. It has broad application prospects in aerospace, automobile, rail and other fields.

[0003] However, magnesium alloy welding is very prone to hydrogen pores, slag inclusions, and microcracks formed by coarse structures. At high temperatures, magnesium oxide, magnesium nitride and other overheated structures are often formed, which greatly affects the welding quality. Many research institutes and universities at home and abroad have carried out magnesium alloy welding, and achieved satisfactory tensile properties of magnesium alloy welded joints through complex welding processes, but the bending properties of magnesium alloy welded joints are often unsatisfactory. Even if a larger bending diameter than the standard requirement is used, it still cannot be bent to 180° before cracking. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for preparing high-strength and toughness welded joints of medium and thin plates of AZ31B magnesium alloy, which does not require a gasket and back argon protection, is simple to operate, has a low manufacturing cost and high production efficiency, and can be applied to the welding production and manufacturing of various product structures.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0006] A method for preparing a high-strength and toughness welded joint of a medium-thin plate AZ31B magnesium alloy, wherein the weld groove is Y-shaped, the groove angle of the weld joint is 60°, the blunt edge size is 1.5 mm, and the root gap is 0.5-1 mm;

[0007] The method for preparing the welded joint comprises the following steps:

[0008] S1. Preparation before welding: Prepare AZ31B test plate according to the above groove requirements, clean the oil and oxide film within 30mm of the welding wire and weld and both sides, assemble the test plate according to the root gap, and fix the assembled test plate by spot welding.

[0009] S2. Welding: Single-sided single-pass welding or single-sided double-layer double-pass welding is adopted for AZ31B test plate, and the single-sided double-layer double-pass welding is divided into bottom welding and cover welding, that is, after the bottom welding, the welding black ash is cleaned up, and the cover welding is directly carried out without waiting for cooling;

[0010] S3. Artificial aging treatment: The welded joint is heated to 180-200℃ under argon protection and kept warm for 20-40min, then the pressure is increased to 2-4Mpa and the treatment is continued for 15-30min, then the pressure is increased to 6-10Mpa after the temperature is reduced to 100-120℃ and the treatment is continued for 20-30min, then the pressure is restored to normal pressure, and then immersed in 70-80℃ warm water and naturally cooled to normal temperature with the warm water.

[0011] Preferably, in step S1, a reverse deformation of 15-25° is prefabricated during spot welding and fixing.

[0012] Preferably, when the thickness of the AZ31B test plate is 3-4 mm, single-sided single-pass welding is adopted; when the thickness of the AZ31B test plate is 5-6 mm, single-sided double-layer double-pass welding is adopted.

[0013] Preferably, the process parameters for single-sided single-pass welding are: welding current 90-110A, welding voltage 13.1V, welding speed 16-24cm / min, 99.999% high-purity argon as shielding gas, and gas flow rate 9-13L / min.

[0014] Preferably, the process parameters of the base welding in the single-sided double-layer double-pass welding are: welding current 110-130A, welding voltage 13.6V, welding speed 18-26cm / min, gas flow rate 9-13L / min; the process parameters of the cover welding are: welding current 130-150A, welding voltage 14.1V, welding speed 14-21cm / min, gas flow rate 9-13L / min.

[0015] Preferably, the welding method in step S2 is manual argon tungsten arc welding with wire filling.

[0016] Preferably, the welding wire used in welding is an AZ31B magnesium alloy welding wire with a diameter of 3 mm.

[0017] The present invention provides a method for preparing a medium-thin plate AZ31B magnesium alloy high-strength and toughness welded joint, which has the advantages of:

[0018] (1) Due to the high thermal conductivity of magnesium alloy, a high welding current is required when welding magnesium alloy. However, magnesium alloy is easy to form low-melting eutectics with Cu and Al, and crystallization cracks are easy to form in the welded joint. When the temperature at the joint is too high, the low-melting point compounds in the joint structure will melt at the grain boundary to form cavities, or produce grain boundary oxidation, etc., and it is easy to cause the metal grains in the weld and near the weld to grow. Therefore, a higher welding speed is required to avoid excessive temperature at the joint. At the same time, it is necessary to ensure that the weld joint has sufficient high temperature residence time to promote the mutual diffusion of the chemical components of the weld metal and the parent metal to avoid segregation. In addition, the solubility of hydrogen in magnesium decreases with decreasing temperature, and the density of magnesium is smaller than that of aluminum, so the gas is less likely to escape, and pores are easy to form during the solidification process of the weld; and magnesium is extremely oxidizing, and it is easy to form an oxide film (MgO) during welding. MgO has a high melting point (2500℃) and a high density (3.2g / cm 3 ), which is easy to form inclusions in the weld and reduce the weld performance. At high temperatures, magnesium is also easy to combine with nitrogen in the air to form magnesium nitride, which deteriorates the joint performance. Therefore, argon (99.999%) is required to protect the front of the weld during welding to ensure the joint performance. The welded joint prepared by the present invention has excellent tensile properties and excellent bending properties. Even if a bending diameter smaller than the standard requirement is used for the bending test, no defects are generated after 180°.

[0019] (2) The present invention can obtain a high-strength and toughness welded joint of a medium-thin plate AZ31B magnesium alloy by simple manual wire-filling non-melting-electrode gas shielded welding (TIG) without using a liner and back argon protection. The tensile strength of 3mm is as high as 99.8%, and the tensile strength of 6mm is 99.2%. The 3mm and 6mm thick AZ31B magnesium alloy welding specimens are bent 180° without any defects under the condition that the pressure head diameter is 24mm and 48mm respectively. The method is simple to operate, low in manufacturing cost, high in production efficiency, and can be applied to the welding production and manufacturing of various product structures. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention is clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. 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.

[0021] Embodiment 1:

[0022] Preparation of welding joint:

[0023] The groove preparation of AZ31B magnesium alloy specimens with a thickness of 3 mm, a length of 300 mm, and a width of 150 mm was carried out, and the groove angle was 30° and the blunt edge size was 1.5 mm.

[0024] Then use an angle grinder to clean the oxide film on the groove surface and within 30mm from the center line of the groove. For assembly, the root gap is controlled at 1mm, and the gap at the arc start is slightly smaller than that at the arc end.

[0025] After assembly, the back of the specimen is spot welded and fixed. Due to the large welding deformation of magnesium alloy, a 15° reverse deformation is prefabricated.

[0026] Subsequently, welding was carried out using single-sided single-layer single-pass welding. The welding process parameters were: welding current 90A, welding voltage 13.1V, welding speed 16cm / min, 99.999% high-purity argon was used as the shielding gas, gas flow rate 9L / min, and the surface was cleaned with a wire brush.

[0027] The welded weld joint was heated to 180°C under argon protection for 40 minutes, then pressurized to 2Mpa for 30 minutes, cooled to 100°C and then pressurized to 10Mpa for 20 minutes, then restored to normal pressure and immersed in 70°C warm water, and naturally cooled to room temperature with the warm water.

[0028] After drying, the weld joint is subjected to penetrant and radiographic testing.

[0029] Embodiment 2:

[0030] Preparation of welding joint:

[0031] The groove preparation of AZ31B magnesium alloy specimens with a thickness of 3 mm, a length of 300 mm, and a width of 150 mm was carried out, and the groove angle was 30° and the blunt edge size was 1.5 mm.

[0032] Then use an angle grinder to clean the oxide film on the groove surface and within 30mm from the center line of the groove. For assembly, the root gap is controlled at 0.5mm, and the gap at the arc start is slightly smaller than that at the arc end.

[0033] After assembly, the back of the specimen is spot welded and fixed. Due to the large welding deformation of magnesium alloy, a 25° reverse deformation is prefabricated.

[0034] Subsequently, welding was carried out using single-sided single-layer single-pass welding. The welding process parameters were: welding current 110A, welding voltage 13.1V, welding speed 24cm / min, 99.999% high-purity argon was used as the shielding gas, gas flow rate 13L / min, and the surface was cleaned with a wire brush.

[0035] The welded weld joint was heated to 200°C under argon protection and kept warm for 20 minutes. The pressure was then increased to 4 MPa for 15 minutes. The welded weld joint was cooled to 120°C and then increased to 6 MPa for 30 minutes. The welded weld joint was restored to normal pressure and immersed in 80°C warm water and cooled naturally to normal temperature.

[0036] After drying, the weld joint is subjected to penetrant and radiographic testing.

[0037] Embodiment 3:

[0038] Preparation of welding joint:

[0039] The groove preparation of AZ31B magnesium alloy specimens with a thickness of 6 mm, a length of 300 mm, and a width of 150 mm was carried out, and the groove angle was 30° and the blunt edge size was 1.5 mm.

[0040] Then use an angle grinder to clean the oxide film on the groove surface and within 30mm from the center line of the groove. For assembly, the root gap is controlled within 0.5mm, and the gap at the arc start is slightly smaller than that at the arc end.

[0041] After assembly, the back of the specimen is spot welded and fixed. Due to the large welding deformation of magnesium alloy, a 15° reverse deformation is prefabricated.

[0042] Then, welding is carried out, using single-sided double-layer double-pass welding. Double-layer double-pass welding is divided into bottom welding and cover welding. After the bottom welding, the welding black ash is cleaned with a wire brush. There is no need to wait for cooling, and the cover welding is carried out directly. The bottom welding process parameters are: welding current 110A, welding voltage 13.6V, welding speed 18cm / min, gas flow 9L / min; cover welding process parameters are: welding current 130A, welding voltage 14.1V, welding speed 14cm / min, gas flow 9L / min. After welding, the surface black ash is cleaned with a wire brush.

[0043] The welded weld joint was heated to 180°C under argon protection for 40 minutes, then pressurized to 2Mpa for 30 minutes, cooled to 100°C and then pressurized to 10Mpa for 20 minutes, then restored to normal pressure and immersed in 70°C warm water, and naturally cooled to room temperature with the warm water.

[0044] After drying, the weld joint is subjected to penetrant and radiographic testing.

[0045] Embodiment 4:

[0046] Preparation of welding joint:

[0047] The groove preparation of AZ31B magnesium alloy specimens with a thickness of 6 mm, a length of 300 mm, and a width of 150 mm was carried out, and the groove angle was 30° and the blunt edge size was 1.5 mm.

[0048] Then use an angle grinder to clean the oxide film on the groove surface and within 30mm from the center line of the groove. For assembly, the root gap is controlled within 0.5mm, and the gap at the arc start is slightly smaller than that at the arc end.

[0049] After assembly, the back of the specimen is spot welded and fixed. Due to the large welding deformation of magnesium alloy, a 15° reverse deformation is prefabricated.

[0050] Then, welding is carried out, using single-sided double-layer double-pass welding. Double-layer double-pass welding is divided into bottom welding and cover welding. After the bottom welding, the welding black ash is cleaned with a wire brush. There is no need to wait for cooling, and the cover welding is carried out directly. The bottom welding process parameters are: welding current 130A, welding voltage 13.6V, welding speed 26cm / min, gas flow 13L / min; cover welding process parameters are: welding current 150A, welding voltage 14.1V, welding speed 21cm / min, gas flow 13L / min. After welding, the surface black ash is cleaned with a wire brush.

[0051] The welded weld joint was heated to 200°C under argon protection and kept warm for 20 minutes. The pressure was then increased to 4 MPa for 15 minutes. The welded weld joint was cooled to 120°C and then increased to 6 MPa for 30 minutes. The welded weld joint was restored to normal pressure and immersed in 80°C warm water and cooled naturally to normal temperature.

[0052] After drying, the weld joint is subjected to penetrant and radiographic testing.

[0053] Comparative Example 1:

[0054] Preparation of welding joint:

[0055] The groove preparation of AZ31B magnesium alloy specimens with a thickness of 3 mm, a length of 300 mm, and a width of 150 mm was carried out, and the groove angle was 30° and the blunt edge size was 1.5 mm.

[0056] Then use an angle grinder to clean the oxide film on the groove surface and within 30mm from the center line of the groove. For assembly, the root gap is controlled at 1mm, and the gap at the arc start is slightly smaller than that at the arc end.

[0057] After assembly, the back of the specimen is spot welded and fixed. Due to the large welding deformation of magnesium alloy, a 15° reverse deformation is prefabricated.

[0058] Subsequently, welding was carried out using single-sided single-layer single-pass welding. The welding process parameters were: welding current 90A, welding voltage 13.1V, welding speed 16cm / min, 99.999% high-purity argon was used as the shielding gas, gas flow rate 9L / min, and the surface was cleaned with a wire brush to obtain the weld joint for penetration and X-ray inspection.

[0059] Comparative Example 2:

[0060] The groove preparation of AZ31B magnesium alloy specimens with a thickness of 6 mm, a length of 300 mm, and a width of 150 mm was carried out, and the groove angle was 30° and the blunt edge size was 1.5 mm.

[0061] Then use an angle grinder to clean the oxide film on the groove surface and within 30mm from the center line of the groove. For assembly, the root gap is controlled within 0.5mm, and the gap at the arc start is slightly smaller than that at the arc end.

[0062] After assembly, the back of the specimen is spot welded and fixed. Due to the large welding deformation of magnesium alloy, a 15° reverse deformation is prefabricated.

[0063] Then, welding is carried out, using single-sided double-layer double-pass welding. Double-layer double-pass welding is divided into bottom welding and cover welding. After the bottom welding, the welding black ash is cleaned with a wire brush. There is no need to wait for cooling, and the cover welding is directly carried out. The bottom welding process parameters are: welding current 110A, welding voltage 13.6V, welding speed 18cm / min, gas flow 9L / min; cover welding process parameters are: welding current 130A, welding voltage 14.1V, welding speed 14cm / min, gas flow 9L / min. After welding, the surface black ash is cleaned with a wire brush, and the welding joint is obtained for penetration and radiographic detection.

[0064] Detection:

[0065] 1. After the welding joints prepared in the above Examples 1-4 and Comparative Examples 1-2 were tested and qualified, each group was subjected to tensile, bending tests and metallographic tests according to standards ISO4136, ISO5173-2023 and ISO17639-2022, respectively. The formula of the metallographic sample etching solution was 33% HNO3 + 67% H2O, and the etching time was 8S. The specific test results are shown in Table 1 below:

[0066] Table 1

[0067]

[0068] It can be seen from the above table that the welded joints prepared in Examples 1-4 have good tensile strength, tensile strength and joint strength coefficient, and the overall quality is high.

[0069] 2. Bending performance test: According to the standard, the bending diameter of a 6mm thick weld joint is 79mm, and the bending diameter of a 3mm thick weld joint is 39mm. In the following experiments, a bending diameter of 24mm was used for testing the 3mm weld joints prepared in Experimental Group 1-2 and Comparative Example 1 (the sample size was 6×20mm), and a bending diameter of 48mm was used for testing the 6mm weld joints prepared in Examples 3-4 and Comparative Example 2 (the sample size was 3×20mm); the qualified standard is that no cracks larger than 3mm can appear in any direction of the sample, and the smaller the bending diameter, the more difficult it is to pass the test, and the better the performance of the weld joint.

[0070] Table 2: 3mm welding joint bending performance test

[0071]

[0072]

[0073] Table 3: 6mm welding joint bending performance test

[0074]

[0075]

[0076] It can be seen from the above table that the samples prepared in Examples 1-2 and Examples 3-4 have better anti-bending effects.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a medium-thin plate AZ31B magnesium alloy high-strength and toughness welded joint, characterized in that: The welding groove is Y-shaped, and the groove angle of the weld joint is 60°, the blunt edge size is 1.5mm, and the root gap is 0.5-1mm; The method for preparing the welded joint comprises the following steps: S1. Preparation before welding: Prepare AZ31B test plate according to the above groove requirements, clean the oil and oxide film within 30mm of the welding wire and weld and both sides, assemble the test plate according to the root gap, and fix the assembled test plate by spot welding. S2. Welding: Single-sided single-pass welding or single-sided double-layer double-pass welding is adopted for AZ31B test plate, and the single-sided double-layer double-pass welding is divided into bottom welding and cover welding, that is, after the bottom welding, the welding black ash is cleaned up, and the cover welding is directly carried out without waiting for cooling; S3. Artificial aging treatment: The welded joint is heated to 180-200℃ under argon protection and kept warm for 20-40min, then the pressure is increased to 2-4Mpa and the treatment is continued for 15-30min, then the pressure is increased to 6-10Mpa after the temperature is reduced to 100-120℃ and the treatment is continued for 20-30min, then the pressure is restored to normal pressure, and then immersed in 70-80℃ warm water and naturally cooled to normal temperature with the warm water.

2. The method for preparing a medium-thin plate AZ31B magnesium alloy high-toughness welded joint according to claim 1, characterized in that: In the step S1, a reverse deformation of 15-25° is prefabricated during the spot welding and fixing.

3. The method for preparing a medium-thin plate AZ31B magnesium alloy high-toughness welded joint according to claim 1, characterized in that: When the thickness of the AZ31B test plate is 3-4mm, single-sided single-pass welding is adopted; when the thickness of the AZ31B test plate is 5-6mm, single-sided double-layer double-pass welding is adopted.

4. The method for preparing a medium-thin plate AZ31B magnesium alloy high-toughness welded joint according to claim 1, characterized in that: The process parameters for single-sided single-pass welding are: welding current 90-110A, welding voltage 13.1V, welding speed 16-24cm / min, 99.999% high-purity argon is used as shielding gas, and gas flow rate is 9-13L / min.

5. The method for preparing a medium-thin plate AZ31B magnesium alloy high-toughness welded joint according to claim 1, characterized in that: The process parameters of the base welding in the single-sided double-layer double-pass welding are: welding current 110-130A, welding voltage 13.6V, welding speed 18-26cm / min, gas flow 9-13L / min; the process parameters of the cap welding are: welding current 130-150A, welding voltage 14.1V, welding speed 14-21cm / min, gas flow 9-13L / min.

6. The method for preparing a medium-thin plate AZ31B magnesium alloy high-toughness welded joint according to claim 1, characterized in that: The welding method in step S2 is manual argon tungsten arc welding with wire filling.

7. The method for preparing a medium-thin plate AZ31B magnesium alloy high-toughness welded joint according to claim 1, characterized in that: The welding wire used is AZ31B magnesium alloy welding wire with a diameter of 3 mm.

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