6xxx aluminum alloy sheet capable of reducing weld liquefaction cracks, and preparation method therefor and application thereof

Abstract

The present application provides a 6XXX aluminum alloy sheet capable of reducing weld liquefaction cracks, and a preparation method therefor and an application thereof. The aluminum alloy sheet is composed of the following components: Si: 0.4-0.8%, Fe: 0.1-0.35%, Mn: 0.08-0.2%, Mg: 0.45-0.9%, Cu: ≤0.2% (the total weight percentage of Mn and Cu being less than or equal to 0.2%), and the balance being Al and inevitable impurities. The preparation method comprises: sequentially carrying out casting, homogenization treatment, hot rough rolling, hot finish rolling and cold rolling on raw materials to obtain a cold-rolled sheet, carrying out heat preservation at 550-560°C for 20-30s, and then carrying out heat preservation at 60-70°C for 20-28 h. According to the present application, the specific ratio of aluminum alloy elements is controlled, and by incorporating a specific solution-aging treatment process, the produced 6XXX aluminum alloy sheet has good weldability, so that liquefaction cracks in weld lap joints can be effectively reduced, the weld strength is improved, and the mechanical properties of the joints are improved.

Description

6XXX aluminum alloy plate capable of reducing weld liquefaction cracks, preparation method thereof and application thereof

[0001] This application claims priority to Chinese patent application No. 202310723587.8, filed on June 16, 2023. This application incorporates the entire text of the aforementioned Chinese patent application. Technical Field

[0002] The present application relates to the technical field of aluminum alloys, and in particular to a 6XXX aluminum alloy plate capable of reducing weld liquefaction cracks, a preparation method thereof, and applications thereof. Background Art

[0003] 6XXX series aluminum alloys are heat-treatable and hardened aluminum alloys with medium strength, good formability, and excellent corrosion resistance. They are widely used in doors, roofs, and other areas of the automotive and rail transportation sectors, making them the preferred aluminum alloy for lightweighting. 6XXX aluminum alloys are generally enhanced through a "solution-aging" process. Connection methods for this series of materials include riveting, resistance spot welding, and arc welding. Arc welding, with its low cost and high degree of automation, is currently widely used in the automotive and rail transportation sectors.

[0004] 6XXX series aluminum alloys are weldable and frequently used in automotive exterior panels, typically assembled using arc lap welding. However, due to the alloy's inherent composition and processing characteristics, this material exhibits a certain degree of weld crack sensitivity. Under the influence of welding heat, the metal outside the weld fusion line can easily melt along the grain boundaries. Subsequent cooling and contraction can cause cracking in the liquefied layer along the grain boundaries, resulting in liquefaction cracks in the weld lap joint. Weld cracking is a serious defect in welded parts that can severely impact the performance of aluminum alloy welds. To ensure the quality of weld joints, this places higher demands on the aluminum alloy's material composition, processing technology, and welding process.

[0005] Summary of the Invention

[0006] The main purpose of this application is to provide a 6XXX aluminum alloy plate that can reduce weld liquefaction cracks, its preparation method and application, so as to solve the problem in the prior art that 6XXX aluminum alloy plates are prone to weld liquefaction cracks after welding.

[0007] In order to achieve the above object, according to one aspect of the present application, a method for preparing a 6XXX aluminum alloy plate capable of reducing weld liquefaction cracking is provided, wherein the aluminum alloy plate is composed of the following components by weight: Si 0.4-0.8%, Fe 0.1-0.35%, Mn 0.08-0.2%, Mg The invention relates to a 6XXX aluminum alloy plate having a content of 0.45-0.9%, Cu ≤ 0.2%, and a total weight percentage of Mn and Cu ≤ 0.2%, and the balance being Al and inevitable impurities, wherein each inevitable impurity is less than 0.05%, and the total impurities are less than 0.15%. The preparation method comprises the following steps: step S1, melting and casting the raw material of the 6XXX aluminum alloy plate to obtain an ingot; step S2, homogenizing the ingot to obtain a homogenized ingot; step S3, hot rough rolling the homogenized ingot to obtain a hot rough rolled plate, and then hot finish rolling the hot rough rolled plate to obtain a hot rolled plate; step S4, cold rolling the hot rolled plate to obtain a cold rolled plate; step S5, keeping the cold rolled plate at 550-560° C. for 20-30 seconds for solution treatment to obtain a solution plate; step S6, keeping the solution plate at 60-70° C. for 20-28 hours for aging treatment to obtain a 6XXX aluminum alloy plate.

[0008] Furthermore, the aluminum alloy is composed of the following components, by weight percentage: Si 0.7-0.8%, Fe 0.1-0.2%, Mn 0.08-0.15%, Mg 0.6-0.7%, Cu≤0.1%, and the total weight percentage of Mn and Cu ≤0.2%, and the balance is Al and unavoidable impurities, each unavoidable impurity is <0.05%, and the total impurities are <0.15%.

[0009] Furthermore, in step S1, the thickness of the ingot is 530-540 mm.

[0010] Furthermore, in step S2, the holding temperature of the homogenization treatment is 540-560° C., and the holding time is 8-10 hours.

[0011] Furthermore, in step S3, the starting rolling temperature of the hot rough rolling is 520-535° C.; and / or the pass reduction of the hot rough rolling is 20-30 mm; and / or the thickness of the hot rough rolled plate is 24-28 mm.

[0012] Furthermore, in step S3, the starting rolling temperature of hot finishing rolling is 510-520°C; and / or the finishing rolling temperature of hot finishing rolling is 260-270°C; and / or the pass reduction of hot finishing rolling is 5-6 mm; and / or the thickness of the hot rolled plate is 4-8 mm.

[0013] Furthermore, in step S4, the cold rolling reduction is 1 to 2 mm; and / or the thickness of the cold-rolled sheet is 1.0 to 1.5 mm.

[0014] According to another aspect of the present application, a 6XXX aluminum alloy plate capable of reducing weld liquefaction cracks is provided, which is obtained by the above-mentioned preparation method of the present application.

[0015] According to another aspect of the present application, a method for welding aluminum alloy is provided, using the above-mentioned 6XXX aluminum alloy plate of the present application as a base material and performing CMT+P welding with an ER5356 welding wire.

[0016] According to another aspect of the present application, a welded joint is provided, which is obtained using the welding method described above and has no liquefaction cracks.

[0017] The technical solution of the present application uses only a few simple additive elements and controls the specific ratio of aluminum alloy elements, especially controlling the total weight of Mn and Cu within a low range, to achieve improvements in 6XXX aluminum alloy sheet materials toward reducing weld liquefaction cracking. Combined with a specific "solution-aging" treatment process, the eutectic phase of the aluminum alloy can be completely dissolved back into the sheet, while eliminating the lamellar grain structure that grows during the rolling process of the original sheet, thereby effectively inhibiting the precipitation of low-melting-point MgSi (MgSiCu) eutectic phases between grain boundaries. When used for welding, the tendency of the molten zone of the joint to generate liquefaction cracks under welding heat input can be greatly reduced. The 6XXX aluminum alloy sheet of the present application does not contain rare metals, has a low cost, a simple preparation method, and can be processed and produced on conventional production lines. The produced 6XXX aluminum alloy sheet has good weldability, can effectively reduce liquefaction cracking in weld lap joints, improve weld strength, and enhance the mechanical properties of the joint, laying a foundation for the subsequent promotion and application of this material. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings that constitute part of this application are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation on this application. In the drawings:

[0019] FIG1 is a schematic diagram showing the dimensions of a tensile specimen according to Example 1 of the present application;

[0020] FIG2 shows macroscopic morphologies of welds according to Comparative Examples 1 to 3 and Examples 1 to 2 of the present application;

[0021] FIG3 shows a microstructure diagram and a composition analysis diagram of the partial melting zone of the weld according to Comparative Example 1; and

[0022] FIG4 shows a load-displacement curve of welds according to Comparative Examples 1 to 3 and Examples 1 to 2 of the present application. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] Explanation of terms:

[0025] CMT+P welding: Cold metal transfer+pulse, cold metal transfer welding+pulse welding.

[0026] As described in the background of this application, the prior art has the problem that 6XXX aluminum alloy plates are prone to weld liquefaction cracks after welding. In order to solve the above problem, in a typical embodiment of this application, a method for preparing a 6XXX aluminum alloy plate that can reduce weld liquefaction cracks is provided. The aluminum alloy plate is composed of the following components by weight: Si 0.4-0.8%, Fe 0.1-0.35%, Mn 0.08-0.2%, Mg The invention relates to a 6XXX aluminum alloy plate having a content of 0.45-0.9%, Cu ≤ 0.2%, and a total weight percentage of Mn and Cu ≤ 0.2%, and the balance being Al and inevitable impurities, wherein each inevitable impurity is less than 0.05%, and the total impurities are less than 0.15%. The preparation method comprises the following steps: step S1, melting and casting the raw material of the 6XXX aluminum alloy plate to obtain an ingot; step S2, homogenizing the ingot to obtain a homogenized ingot; step S3, hot rough rolling the homogenized ingot to obtain a hot rough rolled plate, and then hot finish rolling the hot rough rolled plate to obtain a hot rolled plate; step S4, cold rolling the hot rolled plate to obtain a cold rolled plate; step S5, keeping the cold rolled plate at 550-560° C. for 20-30 seconds for solution treatment to obtain a solution plate; step S6, keeping the solution plate at 60-70° C. for 20-28 hours for aging treatment to obtain a 6XXX aluminum alloy plate. Among them, unavoidable impurities include but are not limited to Ni, Cr, Zr, Ti, etc.

[0027] In the present application, the raw material of the 6XXX aluminum alloy plate is first melted and cast at 720-740°C to introduce various additive elements to obtain an ingot. The specific operation of this step is understandable to those skilled in the art based on the present application and will not be described in detail here. Secondly, the ingot is homogenized to achieve uniform distribution of elements and grains in the ingot structure. After obtaining the homogenized ingot, hot rough rolling and hot finish rolling are sequentially performed. Through two different hot rolling methods, a hot rolled plate with uniform structure and appropriate thickness is gradually obtained, and cold rolling is performed to achieve further precise control of the deformation process. Then the obtained cold rolled ingot is subjected to a heat treatment. After the plate is kept at 550-560°C for 20-30 seconds, it is cooled to room temperature and finally kept at 60-70°C for 20-28 hours for solution-aging treatment, so that the eutectic phase of the aluminum alloy is completely dissolved back into the plate, while eliminating the lamellar grain structure of the original plate that grows during the rolling process, thereby effectively inhibiting the precipitation of low-melting-point MgSi (MgSiCu) eutectic phases between grain boundaries. When used for welding, the tendency of the molten zone of the joint to generate liquefaction cracks under welding heat input can be greatly reduced, thereby obtaining the 6XXX aluminum alloy plate of the present application that can reduce weld liquefaction cracks.

[0028] This application uses only a few simple additive elements. By controlling the specific ratio of aluminum alloy elements, especially controlling the total weight of Mn and Cu within a relatively low range, the 6XXX aluminum alloy plate is improved in the direction of reducing weld liquefaction cracking. At the same time, combined with a specific preparation process, it can be processed and produced on a conventional production line. The produced 6XXX aluminum alloy plate has good weldability, especially when the CMT+P welding process is used with ER5356 welding wire to prepare weld joints, the tendency of liquefaction cracking in the weld lap joint can be effectively reduced, the weld strength can be improved, and the mechanical properties of the joint can be enhanced.

[0029] In a preferred embodiment, the aluminum alloy comprises the following composition, by weight: Si 0.7-0.8%, Fe 0.1-0.2%, Mn 0.08-0.15%, Mg 0.6-0.7%, Cu ≤ 0.1%, with the combined weight percentage of Mn and Cu ≤ 0.2%, and the balance consisting of Al and unavoidable impurities, with each unavoidable impurity less than 0.05% and the total impurities less than 0.15%. 6XXX aluminum alloys with this composition exhibit improved weld strength and a lower tendency to liquefaction cracking.

[0030] In order to further increase the compatibility of the above-mentioned aluminum alloy of the present application with conventional production lines, thereby making it easier to prepare the aluminum alloy plate of the present application, in a preferred embodiment, in step S1, the thickness of the ingot is 530 to 540 mm.

[0031] Homogenization treatment can dissolve non-equilibrium low-melting eutectic structure and promote uniform distribution of elements. In a preferred embodiment, in step S2, the holding temperature of the homogenization treatment is 540-560°C and the holding time is 8-10 hours. The above-mentioned homogenization process can make the element particles further evenly dispersed and precipitated, which is beneficial to control the grain structure in the subsequent rolling process, thereby further improving the strength of the aluminum alloy. The strength of the weld obtained after welding is higher, which can further reduce the tendency of liquefaction cracks to appear in the weld.

[0032] Hot rough rolling can utilize a higher starting temperature and a larger pass reduction to rapidly hot-roll the ingot to near the target thickness, accelerating the deformation process. In a preferred embodiment, in step S3, the starting temperature for hot rough rolling is 520-535°C; and / or the pass reduction for hot rough rolling is 20-30 mm; and / or the thickness of the hot rough rolled plate is 24-28 mm. This hot rough rolling process can shorten production time while further improving the element distribution and grain size distribution of the plate, thereby further reducing the tendency of liquefaction cracking in welded joints during aluminum alloy welding.

[0033] Accordingly, in order to further improve the hot working performance and forming performance of the plate during hot rolling, thereby further improving the weld strength and reducing its tendency to liquefaction cracks, in a preferred embodiment, in step S3, the starting rolling temperature of hot finishing rolling is 510-520°C; and / or the finishing temperature of hot finishing rolling is 260-270°C; and / or the pass reduction of hot finishing rolling is 5-6 mm; and / or the thickness of the hot rolled plate is 4-8 mm.

[0034] In a preferred embodiment, in step S4, the cold rolling pass reduction is 1 to 2 mm; and / or the thickness of the cold-rolled plate is 1.0 to 1.5 mm, thereby further improving the welding performance of the aluminum alloy, refining the grains, improving the material itself and the weld strength during welding, and further reducing the tendency of liquefaction cracks to occur in the weld joint.

[0035] In another typical embodiment of the present application, a 6XXX aluminum alloy plate capable of reducing weld liquefaction cracks is provided, which is obtained by the above-mentioned preparation method of the present application.

[0036] In another typical embodiment of the present application, a method for welding an aluminum alloy is provided, wherein the aforementioned 6XXX aluminum alloy plate is used as the base material and is welded to an ER5356 welding wire for CMT+P welding. The CMT+P welding process parameters may be conventional parameters in the art and may be adjusted based on the actual material preparation conditions. These parameters are readily understood by those skilled in the art and are not further elaborated here.

[0037] In another typical embodiment of the present application, a welding joint is provided, which is obtained using the welding method described above. The welding joint has no liquefaction cracks, and the weld strength and reliability are greatly improved.

[0038] Typically, but not limited to, 6XXX aluminum alloy plate comprises the following composition: Si 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8% or a range consisting of any two of them; Fe 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35% or a range consisting of any two of them; Mn 0.08%, 0.09%, 0.1%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2% or a range consisting of any two of them; Mg The present invention relates to an alloy of aluminum and magnesium, wherein the weight percentage of the alloy is 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9% or a range consisting of any two of them; the weight percentage of Cu is 0%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4% or a range consisting of any two of them; the weight percentage of the total Mn and Cu is 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2% or a range consisting of any two of them; the balance is Al and unavoidable impurities, each unavoidable impurity is less than 0.05%, and the total impurities is less than 0.15%.

[0039] Typically but not limitatively, in step S1 , the thickness of the ingot is 530 mm, 532 mm, 534 mm, 536 mm, 538 mm, 540 mm, or a range consisting of any two of these values.

[0040] Typically but not limitatively, in step S2, the holding temperature for homogenization treatment is 540°C, 542°C, 546°C, 548°C, 550°C, 552°C, 554°C, 556°C, 558°C, 560°C or a range consisting of any two of them; the holding time is 8h, 8.5h, 9h, 9.5h, 10h or a range consisting of any two of them.

[0041] Typically but not limitatively, in step S3, the starting rolling temperature of the hot rough rolling is 520°C, 522°C, 524°C, 526°C, 528°C, 530°C, 532°C, 535°C or a range consisting of any two of them; the pass reduction is 20mm, 22mm, 24mm, 26mm, 28mm, 30mm or a range consisting of any two of them; the thickness of the hot rough rolled plate is 24mm, 25mm, 26mm, 27mm, 28mm or a range consisting of any two of them.

[0042] Typically but not limitatively, in step S3, the start rolling temperature of hot finishing rolling is 510°C, 512°C, 514°C, 516°C, 518°C, 520°C or a range consisting of any two of them; the finishing temperature is 260°C, 262°C, 264°C, 268°C, 270°C or a range consisting of any two of them; the pass reduction is 5mm, 5.2mm, 5.4mm, 5.6mm, 5.8mm, 6mm or a range consisting of any two of them; the thickness of the hot rolled plate is 4mm, 5mm, 6mm, 7mm, 8mm or a range consisting of any two of them.

[0043] Typically but not limitatively, in step S4, the cold rolling pass reduction is 1 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2 mm or a range consisting of any two of them; the thickness of the cold-rolled sheet is 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm or a range consisting of any two of them.

[0044] Typically but not limitatively, in step S5, the temperature of the solution treatment is 550°C, 551°C, 552°C, 553°C, 554°C, 555°C, 556°C, 557°C, 558°C, 559°C, 560°C or a range consisting of any two of them; the holding time is 20s, 21s, 22s, 23s, 24s, 25s, 26s, 27s, 28s, 29s, 30s or a range consisting of any two of them.

[0045] Typically, but not limitatively, in step S6, the aging treatment temperature is 60° C., 61° C., 62° C., 63° C., 64° C., 65° C., 66° C., 67° C., 68° C., 69° C., 70° C., or a range consisting of any two thereof; and the holding time is 20 h, 21 h, 22 h, 23 h, 24 h, 25 h, 26 h, 27 h, 28 h, or a range consisting of any two thereof.

[0046] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0047] Example 1

[0048] The alloy composition of the 6XXX aluminum alloy plate of Example 1 is shown in Table 1.

[0049] Step S1, melting and casting the raw material of 6XXX aluminum alloy plate at 720° C. according to Table 1 to obtain an ingot with a thickness of 535 mm;

[0050] Step S2, heating the ingot to 550° C., keeping the temperature for 9 hours, and performing a homogenization treatment to obtain a homogenized ingot;

[0051] Step S3: The homogenized ingot is subjected to hot rough rolling at a starting rolling temperature of 525° C. and a pass reduction of 25 mm to obtain a hot rough rolled plate with a thickness of 26 mm; the hot rough rolled plate is then subjected to hot finish rolling at a starting rolling temperature of 515° C., a finishing rolling temperature of 265° C., and a pass reduction of 5.5 mm to obtain a hot rolled plate with a thickness of 6 mm;

[0052] Step S4, cold rolling the hot-rolled plate with a reduction of 1.5 mm per pass to obtain a cold-rolled plate with a thickness of 1.5 mm;

[0053] Step S5, heating the cold-rolled sheet to 555° C., keeping the temperature for 25 seconds, and cooling to room temperature to perform a solution treatment to obtain a solution-treated sheet;

[0054] Step S6: keeping the solutionized plate at 66° C. for 24 hours for aging treatment to obtain a 6XXX aluminum alloy plate.

[0055] In step S7, the prepared 6XXX aluminum alloy plate is used as the base material and CMT+P welding is performed with the ER5356 welding wire. The welding parameters are: wire feeding speed 4.4 m / min, welding speed 72 cm / min, shielding gas 99.99% argon, and shielding gas flow rate 12 L / min.

[0056] Example 2

[0057] The alloy composition of the 6XXX aluminum alloy plate of Example 2 is shown in Table 1.

[0058] Step S1, melting and casting the raw material of 6XXX aluminum alloy plate at 720° C. according to Table 1 to obtain an ingot with a thickness of 535 mm;

[0059] Step S2, heating the ingot to 555° C., keeping the temperature for 9.5 hours, and performing a homogenization treatment to obtain a homogenized ingot;

[0060] Step S3: The homogenized ingot is subjected to hot rough rolling at a starting rolling temperature of 530° C. and a pass reduction of 25 mm to obtain a hot rough rolled plate with a thickness of 26 mm; the hot rough rolled plate is then subjected to hot finish rolling at a starting rolling temperature of 513° C., a finishing rolling temperature of 263° C., and a pass reduction of 5.5 mm to obtain a hot rolled plate with a thickness of 6 mm;

[0061] Step S4, cold rolling the hot-rolled plate with a reduction of 1.5 mm per pass to obtain a cold-rolled plate with a thickness of 1.5 mm;

[0062] Step S5, heating the cold-rolled sheet to 558° C., keeping the temperature for 25 seconds, and cooling to room temperature for solution treatment to obtain a solution-treated sheet;

[0063] Step S6: keeping the solutionized plate at 65° C. for 24 hours for aging treatment to obtain a 6XXX aluminum alloy plate.

[0064] In step S7, the prepared 6XXX aluminum alloy plate is used as the base material and CMT+P welding is performed with the ER5356 welding wire. The welding parameters are 4.4 m / min, the welding speed is 72 cm / min, the shielding gas is 99.99% argon, and the shielding gas flow rate is 12 L / min.

[0065] Examples 3 to 6

[0066] The difference between Examples 3 to 6 and Example 1 is that the alloy composition of the 6XXX aluminum alloy plate is different, see Table 1 for details.

[0067] Example 7

[0068] The difference between Example 7 and Example 1 is that in step S2, the holding temperature of the homogenization treatment is 540° C. and the holding time is 10 h.

[0069] Example 8

[0070] The difference between Example 8 and Example 1 is that in step S2, the holding temperature of the homogenization treatment is 560° C. and the holding time is 8 hours.

[0071] Example 9

[0072] Example 9 differs from Example 1 in that, in step S3, the starting temperature for hot rough rolling is 520°C, the reduction per pass is 20 mm, and the thickness of the hot rough rolled sheet is 28 mm; the starting temperature for hot finish rolling is 510°C, the finishing temperature is 260°C, the reduction per pass is 5 mm, and the thickness of the hot rolled sheet is 8 mm. In step S4, the reduction per pass for cold rolling is 1 mm.

[0073] Example 10

[0074] Example 10 differs from Example 1 in that, in step S3, the start rolling temperature of the hot rough rolling is 535°C, the pass reduction is 30 mm, and the thickness of the hot rough rolled plate is 24 mm; the start rolling temperature of the hot finish rolling is 520°C, the finishing temperature is 270°C, and the pass reduction is 6 mm; the thickness of the hot rolled plate is 4 mm. In step S4, the pass reduction of the cold rolling is 2 mm.

[0075] Example 11

[0076] The difference between Example 11 and Example 1 is that in step S5, the temperature of the solution treatment is 550° C. and the holding time is 30 s.

[0077] Example 12

[0078] The difference between Example 12 and Example 1 is that in step S5, the temperature of the solution treatment is 560° C. and the holding time is 20 s.

[0079] Example 13

[0080] The difference between Example 13 and Example 1 is that in step S6, the aging treatment temperature is 60° C. and the holding time is 28 h.

[0081] Example 14

[0082] The difference between Example 14 and Example 1 is that in step S6, the aging treatment temperature is 70° C. and the holding time is 20 h.

[0083] Comparative Example 1

[0084] The difference between Comparative Example 1 and Example 1 is that in step S5, the temperature of the solution treatment is 500° C. and the holding time is 10 s.

[0085] Comparative Example 2

[0086] The difference between Comparative Example 2 and Example 1 is that the alloy composition of the 6XXX aluminum alloy plate is different, see Table 1 for details.

[0087] Comparative Example 3

[0088] The difference between Comparative Example 3 and Example 1 is that the alloy composition of the 6XXX aluminum alloy plate is different, as shown in Table 1. In step S5, the temperature of the solution treatment is 600° C. and the holding time is 60 seconds.

[0089] Material testing:

[0090] With reference to GB / T 3246.1-2012 Microstructure Test Method for Wrought Aluminum and Aluminum Alloy Products, the microstructures of the welded joints of the above-described embodiments and comparative examples were observed and analyzed for composition. The welded samples were subjected to tensile property testing, with the dimensions of the tensile specimens shown in FIG1 . The weld load-displacement characteristics were also measured, and the results are shown in Table 1.

[0091] The weld macromorphology of Comparative Examples 1 to 3 and Examples 1 to 2 is shown in Figure 2. 2a in Figure 2 is the weld macromorphology of Comparative Example 1, 2b in Figure 2 is the weld macromorphology of Comparative Example 2, 2c in Figure 2 is the weld macromorphology of Comparative Example 3, 2d in Figure 2 is the weld macromorphology of Example 1, and 2e in Figure 2 is the weld macromorphology of Example 2. As shown in Figure 2, the comparative example has obvious liquefaction cracks in the partial melting zone of the weld (near the fusion coil exit portion), while no liquefaction cracks are found in the corresponding position in the example.

[0092] Figure 3 shows the microstructure and composition analysis of the partially melted zone of the weld in Comparative Example 1. As shown in Figure 3, liquefaction cracks in the partially melted zone of the comparative weld are distributed and propagated along grain boundaries. The grains in the region where liquefaction cracks occur are relatively coarse, and the precipitated phases between the grain boundaries are primarily MgSi (MgSiCu) eutectic phases. During the welding process, the material is subjected to uneven thermal cycling, resulting in residual stress distribution. The coarse grains in the partially melted zone and the eutectic phases between the grain boundaries become the weakest areas of the entire joint, leading to liquefaction cracks in the welded joint.

[0093] The weld load-displacement curves for Comparative Examples 1 to 3 and Examples 1 to 2 are shown in Figure 4. Figure 4a is the weld load-displacement curve for Comparative Example 1, Figure 4b is the weld load-displacement curve for Comparative Example 2, Figure 4c is the weld load-displacement curve for Comparative Example 3, Figure 4d is the weld load-displacement curve for Example 1, and Figure 4e is the weld load-displacement curve for Example 2. As shown in Figure 4, the breaking loads of the joints in the examples are generally higher than those in the comparative examples, indicating that eliminating liquefaction cracks helps improve the mechanical properties of the joints.

[0094] Table 1

[0095] As can be seen from the above, compared with the comparative examples, the embodiments of the present application use only a few simple additive elements. By controlling the specific aluminum alloy element ratio, especially controlling the total weight of Mn and Cu within a lower range, the 6XXX aluminum alloy plate is improved in the direction of reducing weld liquefaction cracking. At the same time, combined with a specific "solution-aging" treatment process, the eutectic phase of the aluminum alloy can be completely dissolved back into the plate, while eliminating the lamellar grain structure that grows during the rolling process of the original plate, thereby effectively inhibiting the precipitation of low-melting-point MgSi (MgSiCu) eutectic phases between grain boundaries. When used for welding, it can greatly reduce the tendency of the joint part of the molten zone to produce liquefaction cracks under welding heat input. The 6XXX aluminum alloy plate of the present application does not contain rare metals, has a low cost, a simple preparation method, and can be processed and produced on a conventional production line. The produced 6XXX aluminum alloy plate has good weldability, can effectively reduce weld lap joint liquefaction cracking, improve weld strength, and enhance the mechanical properties of the joint. In addition, it can be seen that when all process parameters are within the preferred range of the present application, the comprehensive performance of the material is better.

[0096] The foregoing description is merely a preferred embodiment of the present application and is not intended to limit the present application. Persons skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for preparing a 6XXX aluminum alloy sheet capable of reducing weld liquefaction cracks, characterized in that: The aluminum alloy plate is composed of the following components by weight percentage: Si 0.4-0.8%, Fe 0.1-0.35%, Mn 0.08-0.2%, Mg 0.45-0.9%, Cu≤0.2%, and the total weight percentage of Mn and Cu is ≤0.2%, and the balance is Al and inevitable impurities, each of the inevitable impurities is <0.05%, and the total impurities are <0.15%; the preparation method comprises the following steps: Step S1, melting and casting the raw material of the 6XXX aluminum alloy plate to obtain an ingot; Step S2, homogenizing the ingot to obtain a homogenized ingot; Step S3, performing hot rough rolling on the homogenized ingot to obtain a hot rough rolled plate, and then performing hot finish rolling on the hot rough rolled plate to obtain a hot rolled plate; Step S4, cold rolling the hot-rolled sheet to obtain a cold-rolled sheet; Step S5, keeping the cold-rolled sheet at 550-560° C. for 20-30 seconds to perform a solid solution treatment to obtain a solid solution sheet; Step S6, keeping the solution-treated plate at 60-70° C. for 20-28 hours for aging treatment to obtain the 6XXX aluminum alloy plate.

2. The preparation method according to claim 1, characterized in that: The aluminum alloy is composed of the following components by weight: Si 0.7-0.8%, Fe 0.1-0.2%, Mn 0.08-0.15%, Mg 0.6-0.7%, Cu≤0.1%, and the total weight percentage of Mn and Cu ≤0.2%, and the balance is Al and inevitable impurities, each of the inevitable impurities is <0.05%, and the total impurities are <0.15%.

3. The preparation method according to claim 1 or 2, characterized in that: In the step S1, the thickness of the ingot is 530-540 mm.

4. The preparation method according to claim 1 or 2, characterized in that: In the step S2, the holding temperature of the homogenization treatment is 540-560° C., and the holding time is 8-10 hours.

5. The preparation method according to claim 1 or 2, characterized in that: In the step S3, the starting rolling temperature of the hot rough rolling is 520-535° C.; and / or the pass reduction of the hot rough rolling is 20-30 mm; and / or the thickness of the hot rough rolled plate is 24-28 mm.

6. The preparation method according to claim 1 or 2, characterized in that: In step S3, the starting temperature of the hot finishing rolling is 510-520°C; and / or the final rolling temperature of the hot finishing rolling is 260-270°C; and / or the pass reduction of the hot finishing rolling is 5-6 mm; and / or the thickness of the hot rolled plate is 4-8 mm.

7. The preparation method according to claim 1 or 2, characterized in that: In the step S4, the cold rolling reduction is 1-2 mm per pass; and / or the thickness of the cold rolled sheet is 1.0-1.5 mm.

8. A 6XXX aluminum alloy sheet capable of reducing weld liquefaction cracks, characterized in that: Obtained by the preparation method according to any one of claims 1 to 7.

9. A method for welding aluminum alloy, characterized in that: The 6XXX aluminum alloy plate described in claim 8 is used as the base material and CMT+P welding is performed with the ER5356 welding wire.

10. A welding joint, characterized in that: The welding method according to claim 9 is used to obtain the welded joint, and the welded joint has no liquefaction cracks.

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