Method for improving welding performance of thick aluminum alloy plate

Abstract

A method for improving the welding performance of an aluminum alloy thick plate comprises the following steps that a Y-shaped groove is formed in an aluminum alloy plate, and the Y-shaped groove is provided with N steps; rectangular pulse wave TIG welding is adopted for conducting backing welding on the truncated edge of the bottom of the Y-shaped groove; carrying out cladding on the side part of the groove by adopting rectangular pulse wave TIG (Tungsten Inert Gas) welding; the groove is subjected to filling welding through direct current TIG welding, and after the step position of each step is completely covered, next filling welding is conducted; by adopting the welding method for welding the thick aluminum alloy plate and adopting a multi-pass welding mode, the effect of solid solution strengthening on a welding line of the last pass is achieved, a large amount of heat input at a time is dispersed into multiple times of input, the effect of reducing the peak temperature of a material is achieved, and therefore the strength and the ductility of a connector are further improved on the whole.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and in particular to a method for improving the welding performance of aluminum alloy thick plates. Background Art

[0002] Aluminum alloys have been increasingly widely used in aerospace, automotive and other fields due to their high strength, low density and low cost. With the increasing requirements for safety and energy conservation and emission reduction, the strength requirements of AlSiMg (Cu) aluminum alloys for automobiles are also getting higher and higher. In order to improve their strength, the content of one or more elements such as Si, Mg and Cu can be increased, with Si content above 0.7%wt, or even above 1.5%wt, Mg content above 0.8%, Mn content above 0.6%, and Cu content up to 1.%wt. Welding is an important method in aluminum alloy connection. Commonly used aluminum alloy welding methods include TIG welding, MIG welding, laser welding, stir friction welding, etc. Among them, TIG welding has been widely used due to its low cost and easy operation. 5 series welding wire is widely used in AlSiMg (Cu) aluminum alloy welding due to its high strength and toughness matching.

[0003] When using 5 series welding wire to perform TIG welding on AlSiMg (Cu) aluminum alloy, especially for thick plates, welding defects such as incomplete penetration and undercut are prone to occur, and the energy input is too high, resulting in low joint strength. In addition, the molten pool fuses the welding wire and the welded material, making the chemical composition of the molten pool extremely uneven, seriously affecting the stability of joint performance. Excessive alloying elements and alloying elements in the welding wire undergo eutectic reaction to produce coarse eutectic phases, seriously reducing joint performance. Studies have shown that the strength coefficient of AlSiMg (Cu) series aluminum alloy welded joints is only 0.5-0.6, and its elongation is usually less than 5%. In some studies, the elongation is below 3%, which seriously affects its use.

[0004] Therefore, there is an urgent need for a method to improve the welding performance of aluminum alloy thick plates to improve the welding strength and elongation of aluminum alloys. Summary of the invention

[0005] The purpose of the present invention is to provide a method for improving the welding performance of aluminum alloy thick plates, which solves the problems existing in the above-mentioned prior art.

[0006] A method for improving the welding performance of aluminum alloy thick plates comprises the following steps:

[0007] Step 1: Opening a Y-shaped groove on the aluminum alloy plate, wherein the Y-shaped groove has N steps;

[0008] Step 2: Use rectangular pulse wave TIG welding to perform base welding on the blunt edge of the bottom of the Y-shaped groove and cool it;

[0009] Step 3: Use rectangular pulse wave TIG welding to clad the side of the groove and cool it;

[0010] Step 4: Use DC TIG welding to fill the groove, cool it, and after each step is completely covered, proceed to the next filling weld.

[0011] Preferably, in step 2 and step 4, the weld metal completely covers the corresponding step area.

[0012] Preferably, after each welding is completed, the welding area is cooled to below 120° C. using liquid nitrogen before the next welding is performed.

[0013] Preferably, in step one, the thickness of the aluminum alloy plate is 6 to 15 mm. When the plate thickness is less than 9 mm, N=1, and 1 step + Y-shaped groove is opened; when the plate thickness is greater than 9 mm, N=2, and 2 steps + Y-shaped grooves are opened.

[0014] Preferably, the thickness of the blunt edge of the groove is 1 / 3 of the plate thickness and no more than 4 mm; the spacing of the blunt edges at the bottom of the groove is 0.5 to 2 mm; the step width is 2 to 4 mm, the groove angle is 20 to 50°, and the second groove angle is 5 to 10° smaller than the first groove angle.

[0015] Preferably, in step 2, the welding current amplitude is 90-110A, the welding speed is 0.5-1.5 mm / s, the blunt edge area is welded through once, and a cap weld is formed at the first step.

[0016] Preferably, in step three, the welding amplitude current is 90-150A, the welding speed is 8-13mm / s, the thickness of the cladding weld is controlled within the melting depth of the base material of 1-2mm, the weld excess height is 0.5-1mm, ensuring that each bevel area is fully covered by welding, and the molten pool depth is 1-3mm.

[0017] Preferably, in step 4, the welding current is 150-300A, and the welding speed is 13-22mm / s.

[0018] Preferably, 99.99% pure argon gas is used for protection during welding, with a gas flow rate of 20 to 30 L / min.

[0019] Preferably, the pulse frequency is 0.5-2 Hz.

[0020] Preferably, the welding material is a high-strength AlSiMg (Cu) aluminum alloy, whose main alloy element content is 0.7% to 2% wtSi, 0.8% to 1.5% wtMg, 0.5% to 1.0% wtMn and 0.5% to 1.2% wtCu; the welding wire is ER5356 aluminum welding wire, and the welding wire diameter is 3 to 5 mm.

[0021] The present invention discloses the following technical effects: when welding AlSiMg (Cu) aluminum alloy, the softening degree of the heat-affected zone is affected by the peak temperature of the zone. When the peak temperature is 300-450°C, the strength is the lowest and the zone is relatively wide. Therefore, the liquid nitrogen cooling of the present invention, the special groove opening method in step one, the pulse TIG welding of the groove side at a higher welding speed in step three, and the DC TIG welding at a faster speed in step four can effectively reduce the heat input, reduce the welding peak temperature, reduce the over-aging width, and the irregular distribution of the softening zone between different passes, thereby achieving the purpose of reducing the softening effect, improving the joint strength and improving the elongation.

[0022] The present invention uses pulse TIG welding with a slower welding speed to form a cap weld during the blunt edge base welding, which effectively slows down the solidification rate of the molten pool and increases the pore escape time, thereby reducing welding residual stress and achieving the effect of further improving the joint strength.

[0023] The groove opening method and overlay welding in steps 1 and 3 of the present invention make the fusion line at the junction of the joint melting zone and the welded material form a stepped curve distribution, and the process adjustment of pulse TIG welding makes the grains of the molten pool near the fusion zone not grow horizontally and perpendicularly to the welding direction, but are arranged at a certain angle to both sides of the groove, which effectively slows down the crack growth rate;

[0024] After the cover welding in step 3, the present invention performs direct current TIG welding on the center area of ​​the groove in step 4. The cover weld plays a role in isolating the parent metal. After multiple passes of welding in steps 1, 2, and 3, the main component of the direct current TIG welding molten pool is the welding wire cladding metal, which reduces the fusion of elements such as Si in the joint structure, thereby reducing the precipitation of the eutectic phase in the cast structure of the fusion zone, giving full play to the strength characteristics of the welding wire cladding metal, and further improving the joint strength and elongation.

[0025] Research shows that the structure in the joint is a high-temperature cast-quenched structure. The multi-pass welding method has the effect of solid solution strengthening the weld of the previous pass, and disperses a large amount of heat input at one time into multiple inputs, which has the effect of reducing the peak temperature of the material, thereby further improving the joint strength and elongation as a whole. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0027] Figure 1: A schematic diagram of the first step of beveling in a method for improving the welding performance of aluminum alloy thick plates according to the present invention;

[0028] Figure 2 : Schematic diagram of step 2 of the base welding in a method for improving the welding performance of aluminum alloy thick plates of the present invention;

[0029] Figure 3 : Schematic diagram of cover welding in step three of a method for improving welding performance of aluminum alloy thick plates of the present invention;

[0030] Figure 4 : Schematic diagram of cover welding in step 4 of a method for improving welding performance of aluminum alloy thick plates of the present invention;

[0031] Specifically, 1. Second groove angle; 2. Blunt edge spacing; 3. Step width; 4. First groove angle. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] Embodiment 1:

[0035] A method for improving the welding performance of aluminum alloy thick plates, comprising:

[0036] Step 1: Welding a high-strength AlSiMg (Cu) aluminum alloy sheet with a thickness of 8 mm, the main alloying element content of which is 1.5% wtSi, 1.0% wtMg, 0.5% wtMn and 0.6% wtCu; opening a step + Y-shaped groove, the blunt edge thickness is 2 mm, the blunt edge spacing 2 is 0.5 mm, the step width 3 is 3 mm, and the groove angle is 45°; using 99.99% purity argon protection during welding, the gas flow rate is 25 L / min;

[0037] Step 2: Use rectangular pulse wave to perform TIG welding on the bottom blunt edge of the Y-shaped groove, with a welding current amplitude of 100A, a welding speed of 1mm / s, and a pulse frequency of 1.5HZ. The blunt edge area is welded through once, and a cap weld is formed at the first step, with the weld metal covering the step;

[0038] Step 3: Use rectangular pulse wave to perform TIG welding on the groove area, with a pulse frequency of 1.5HZ. The welding amplitude current is 100A, and the welding speed is 10mm / s, ensuring that each bevel area is fully covered by welding, and the molten pool depth is 2mm;

[0039] Step 4: Perform non-melting tungsten electrode DC argon arc welding to fill the groove, with a welding current of 200A and a welding speed of 15mm / s.

[0040] After welding is completed, use liquid nitrogen to cool the welding area to below 120℃ before proceeding to the next welding.

[0041] The welding wire used is 5356.

[0042] Embodiment 2:

[0043] A method for improving the welding performance of aluminum alloy thick plates, comprising:

[0044] Step 1: Weld 8mm thick high-strength AlSiMg (Cu) aluminum alloy sheet, the main alloying element content of which is 1.1% wtSi, 0.8% wtMg, 0.5% wtMn. Open 1 step + Y-shaped groove, the blunt edge thickness is 2mm, the blunt edge spacing 2 is 0.5mm, the step width 3 is 3mm, and the groove angle is 45°. Use 99.99% pure argon protection during welding, and the gas flow rate is 25L / min;

[0045] Step 2: Use rectangular pulse wave to perform TIG welding on the bottom blunt edge of the Y-shaped groove, with a welding current amplitude of 100A, a welding speed of 1.5mm / s, and a pulse frequency of 1.5HZ. The blunt edge area is welded through once, and a cap weld is formed at the first step, with the weld metal covering the step;

[0046] Step 3: Use rectangular pulse wave to perform TIG welding on the groove area, with a pulse frequency of 1.5HZ. The welding amplitude current is 100A, and the welding speed is 10mm / s, ensuring that each bevel area is fully covered by welding, and the molten pool depth is 2mm;

[0047] Step 4: Perform non-melting tungsten electrode DC argon arc welding to fill the groove, with a welding current of 200A and a welding speed of 15mm / s.

[0048] After welding is completed, use liquid nitrogen to cool the welding area to below 120℃ before proceeding to the next welding.

[0049] The welding wire used is 5356.

[0050] Embodiment 3:

[0051] A method for improving the welding performance of aluminum alloy thick plates, comprising:

[0052] Step 1: Weld a 14mm thick high-strength AlSiMg (Cu) aluminum alloy sheet with main alloying elements of 1.5% wtSi, 1.0% wtMg, 0.5% wtMn and 0.6% wtCu. Open 2 steps + Y-shaped grooves, the blunt edge thickness is 3mm, the blunt edge spacing 2 is 0.5mm, the step width 3 is 3mm, the first groove angle 4 is 35°, and the second groove angle 1 is 30°. Use 99.99% pure argon protection during welding, and the gas flow rate is 25L / min;

[0053] Step 2: Use rectangular pulse wave to perform TIG welding on the bottom blunt edge of the Y-shaped groove, with a welding current amplitude of 100A, a welding speed of 1mm / s, and a pulse frequency of 1.5HZ. The blunt edge area is welded through once, and a cap weld is formed at the first step, with the weld metal covering the step;

[0054] Step 3: Use rectangular pulse wave to perform TIG welding on the groove area, with a pulse frequency of 1.5HZ. The welding amplitude current is 100A, and the welding speed is 10mm / s, ensuring that each bevel area is fully covered by welding, and the molten pool depth is 2mm;

[0055] Step 4: Perform non-melting tungsten electrode DC argon arc welding to fill the groove, with a welding current of 250A and a welding speed of 15mm / s.

[0056] After welding is completed, use liquid nitrogen to cool the welding area to below 120℃ before proceeding to the next welding.

[0057] The welding wire used is 5356.

[0058] Comparative Example 1:

[0059] The implementation process is the same as that of Example 1, except that the groove is V-shaped, has no steps, the blunt edge thickness is 3 mm, and there is no opening cover welding described in step 2.

[0060] Comparative Example 2:

[0061] The implementation process is the same as that of Example 2. The thickness of the material to be welded is 6 mm. There is no liquid nitrogen cooling, no groove opening, no base welding, and the welding is completed in one time.

[0062] Comparative Example 3:

[0063] The implementation process is the same as that of Example 1, except that DC TIG welding is used, the welding current of the base welding is 150A, the welding current of step three is 170A, and the welding current of step three is 250A.

[0064] Comparative Example 4

[0065] The AlSiMg(Cu) aluminum alloy sheet used in Example 1 was directly subjected to a tensile test.

[0066] Comparative Example 5

[0067] The AlSiMg(Cu) aluminum alloy sheet used in Example 2 was directly subjected to a tensile test.

[0068] The alloy was subjected to tensile testing and the results are shown in the following table:

[0069] Case Tensile strength / MPa Elongation / % Example 1 262 6.5 Example 2 226 7.1 Example 3 252 7.0 Comparative Example 1 223 4.2 Comparative Example 2 171 4.9 Comparative Example 3 225 3.8 Comparative Example 4 378 15 Comparative Example 5 309 10

[0070] The results show that the experimental results of Examples 1 and 3 show that, through the method described in the present invention, the tensile strength of the alloy welded joint described in Example 1 reaches 262MPa and 252MPa, the welding coefficient reaches more than 0.65, and the elongation reaches more than 6.5%. The strength of the aluminum alloy welded in Example 2 reaches 226MPa, the welding coefficient reaches 0.69, and the elongation reaches 7.1%. Comparative Example 1 has no covering welding, which reduces the number of welding passes, has a high heat input, and the molten welding wire is directly fused with the parent material. Its composition is relatively complex and uneven, and a coarse eutectic phase is precipitated, which cannot play the role of isolating the parent metal, and fails to form the effect of solid solution treatment of the covering weld by the filling weld. The stepless design makes it impossible to make the grains of the molten pool attached to the fusion zone grow horizontally and perpendicular to the welding direction, so that its performance and elongation are ultimately low. In Comparative Example 2, the fracture position occurs in the affected area, and the joint strength is low because the heat input of the one-time penetration is high, and the heat-affected zone has a more serious over-aging. Comparative Example 3 also has an excessively large welding current, and direct current replaces the alternating current described in steps two and three of the method of the present invention, resulting in a higher overall heat input and a greater depth of the covering weld described in step three, causing the groove step to be melted as a whole, increasing the crack propagation rate, and ultimately resulting in lower performance and elongation.

[0071] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for improving the welding performance of aluminum alloy thick plates, characterized in that: The following steps are involved: Step 1: Opening a Y-shaped groove on the aluminum alloy plate, wherein the Y-shaped groove has N steps; Step 2: Use rectangular pulse wave TIG welding to perform base welding on the blunt edge of the bottom of the Y-shaped groove and cool it; Step 3: Use rectangular pulse wave TIG welding to clad the side of the groove and cool it; Step 4: Use DC TIG welding to fill the groove and cool it.

2. The method for improving the welding performance of aluminum alloy thick plates according to claim 1, characterized in that: In step 1, the thickness of the aluminum alloy plate is 6 to 15 mm. When the plate thickness is less than 9 mm, N=1, and 1 step + Y-shaped groove is opened; when the plate thickness is greater than 9 mm, N=2, and 2 steps + Y-shaped grooves are opened.

3. The method for improving the welding performance of aluminum alloy thick plates according to claim 2, characterized in that: The thickness of the blunt edge of the groove is 1 / 3 of the plate thickness and is not greater than 4 mm; the spacing of the blunt edges at the bottom of the groove is 0.5 to 2 mm; the step width is 2 to 4 mm, the groove angle is 20 to 50°, and the second groove angle is 5 to 10° smaller than the first groove angle.

4. A method for improving the welding performance of aluminum alloy thick plates according to claim 1, characterized in that: In the step 2, the welding current amplitude is 90-110A, the welding speed is 0.5-1.5 mm / s, the blunt edge area is welded through once, and a cap weld is formed at the first step.

5. The method for improving the welding performance of aluminum alloy thick plates according to claim 1, characterized in that: In step three, the welding amplitude current is 90-150A, the welding speed is 8-13mm / s, the cladding weld thickness is controlled within the base material melting depth of 1-2mm, the weld excess height is 0.5-1mm, each bevel area is fully covered by welding, and the molten pool depth is 1-3mm.

6. The method for improving the welding performance of aluminum alloy thick plates according to claim 1, characterized in that: In step 4, the welding current is 150-300A, and the welding speed is 13-22mm / s.

7. A method for improving the welding performance of aluminum alloy thick plates according to claim 1, characterized in that: During welding, 99.99% pure argon gas protection is used with a gas flow rate of 20 to 30 L / min.

8. A method for improving the welding performance of aluminum alloy thick plates according to claim 1, characterized in that: The pulse frequency is 0.5~2HZ.

9. A method for improving the welding performance of aluminum alloy thick plates according to claim 1, characterized in that: The welding wire is ER5356 aluminum welding wire with a diameter of 3 to 5 mm.

10. The method for improving the welding performance of aluminum alloy thick plates according to claim 1, characterized in that: After welding is completed, use liquid nitrogen to cool the welding area to below 120℃ before proceeding to the next welding.

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