A filler material for 6XXX series aluminum alloy and its welding process

Abstract

The present invention relates to a filler material for 6XXX series aluminum alloys and its welding process, belonging to the technical field of aluminum alloys. The elemental composition and its mass percentage of the filler material are as follows: Si 0.5% - 2.00%, Mg 0.80% - 2.00%, Cu 0.20% - 3.00%, Cr 0.20% - 0.50%, Mn 0.50% - 0.80%, Ti 0 - 0.10%, Zn 0.15% - 2.00%, Fe 0 - 0.15%, the balance being Al and other inevitable impurities, with a total impurity of 0 - 0.15%. This filler material has good weldability, promotes the precipitation strengthening mechanism, has the same strengthening element composition as the base metal of 6XXX series aluminum alloys, can be applied to the welding of 6XXX series aluminum alloys through various welding methods, reduces the dilution of strengthening elements in the weld, and can effectively improve the mechanical properties of the joint weld and the heat affected zone at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum alloys, and particularly relates to a filler material for 6XXX series aluminum alloys and its welding process. Background Art

[0002] With the in-depth development of lightweight in China, aluminum alloy, as a high-quality metal structural material, occupies an important position in the fields of aerospace, automobile manufacturing, shipbuilding, etc. due to its characteristics such as low density, high specific strength, corrosion resistance, and good processing performance. However, due to the high thermal conductivity, fast solidification rate, and high coefficient of thermal expansion of aluminum alloy, problems such as severe coarsening of the precipitated phases inside the welded joint occur, and these defects seriously deteriorate the mechanical properties of the joint. The heat-affected zone is the area where the softening of the welded joint is the most serious, and it is also the main reason for the deterioration of the mechanical properties of the entire weld structure. Because of the softening of the heat-affected zone, aluminum alloy is greatly restricted in industrial production. Therefore, improving the softening behavior of the joint and obtaining a weld with good mechanical properties is the direction that many scholars have been exploring.

[0003] Alloys of different system types have different types of welding wires, and for a specific type of alloy base material, the filler material plays a crucial role in the weld structure and properties. In industrial applications, secondary deformation treatment of the weld is rarely carried out. Therefore, for the research of welded joints, most efforts are focused on two aspects: the composition of the welding wire and the welding process.

[0004] At present, industrial aluminum alloy welding wires can be classified into pure Al welding wires, Al-Cu series welding wires, Al-Mn series welding wires, Al-Si series welding wires, and Al-Mg series welding wires according to chemical composition. Generally speaking, Al-Si series welding wires are used for welding 6XXX series aluminum alloys in industrial applications, Al-Cu series welding wires are used for welding 2XXX series aluminum alloys, and Al-Mg series welding wires are used for welding the remaining types of aluminum alloys. Due to the diversity of aluminum alloy types, it is extremely unreasonable to rigidly use Al-Mg series welding wires to weld many types of aluminum alloys, and it is also impossible to guarantee the microstructure and mechanical properties of the welded joint. Therefore, it is urgent to develop welding wires for corresponding system aluminum alloys in the field of aluminum alloy welding. At present, many researchers have carried out microalloying on existing welding wires to achieve the purpose of developing new welding wires. Patent CN118002980 A discloses an aluminum alloy welding wire, its preparation method and application for fusion welding of 6XXX series aluminum alloy extrusions. The composition of the aluminum alloy welding wire includes: 0-0.2% Si, 0-0.2% Fe, 0-0.05% Cu, 0.2-0.3% Mn, 5.8-6.8% Mg, 0-0.04% Ti, 0.1-0.12% Zr, 0.25-0.35% Sc, with the balance being Al and unavoidable impurities, each of the unavoidable impurities <0.05%, and the total impurities <0.15%. However, the improvement of the mechanical properties of the weld microstructure by this welding wire is still limited and cannot meet the requirements of industrial applications.

[0005] Based on this, the present invention is proposed. Summary of the Invention

[0006] For this reason, the technical problem to be solved by the present invention is to overcome the problems in the prior art such as severe softening of the weld and heat affected zone of the welded joint of 6XXX series aluminum alloy, resulting in serious deterioration of the mechanical properties of the joint.

[0007] To solve the above technical problems, the present invention provides a filler material for 6XXX series aluminum alloy and its welding process. By multi-element composite solid solution strengthening the weld, and at the same time, the welding heat input required for this filler material is low, effectively reducing the softening of the welding heat affected zone, thereby achieving the coordinated improvement of the performance of the joint weld and heat affected zone.

[0008] The first object of the present invention is to provide a filler material for 6XXX series aluminum alloy. The element composition and mass percentage of the filler material for 6XXX series aluminum alloy are: Si 0.5%-2.00%, Mg 0.80%-2.00%, Cu 0.20%-3.00%, Cr 0.20%-0.50%, Mn 0.50%-0.80%, Ti 0-0.10%, Zn 0.15%-2.00%, Fe 0-0.15%, with the balance being Al and other unavoidable impurities, and the total impurities are 0-0.15%.

[0009] Furthermore, the elemental composition and its mass percentage of the filler material for 6XXX series aluminum alloy are as follows: Si 1.10 - 2.00%, Mg 0.80% - 2.00%, Cu 0.30% - 2.50%, Cr 0.20% - 0.40%, Mn 0.50% - 0.70%, Ti 0.02 - 0.08%, Zn 0.15% - 1.50%, Fe 0 - 0.15%, and the balance is Al and other inevitable impurities, with the total impurities being 0 - 0.15%.

[0010] In an embodiment of the present invention, the mass ratio of element Mg to element Zn is (1 - 6):1; the mass ratio of element Mg to element Cu is (1 - 3):1. In the alloy, in addition to the content of the main alloying elements affecting the precipitation phase behavior, properties, and microstructure, the ratio of the main alloying elements also affects the properties and microstructure of the alloy. When the total amount of alloying elements is constant, there will be obvious differences in the number of precipitation phases inside the alloys with different alloying element ratios, thus seriously affecting the mechanical properties of the alloy. Therefore, controlling the alloying element ratio plays an important role in regulating the material properties.

[0011] In an embodiment of the present invention, the form of the filler material for 6XXX series aluminum alloy is selected from one or more of powder, sheet, and wire.

[0012] In an embodiment of the present invention, the particle size of the powder is 10μm - 250μm, the thickness of the sheet is 50μm - 1000μm, and the diameter of the wire is 0.5mm - 3.2mm.

[0013] The second object of the present invention is to provide a welding process for 6XXX series aluminum alloy, including the following steps:

[0014] S1. Perform pre - welding aging treatment on the 6XXX series aluminum alloy base material;

[0015] S2. Fill the filler material between the welds formed by two 6XXX series aluminum alloy base materials and perform welding to obtain a welded joint; the filler material is the filler material for 6XXX series aluminum alloy as described above;

[0016] S3. Perform post - welding aging treatment on the welded joint.

[0017] In an embodiment of the present invention, in S1, the elemental composition and its mass percentage of the 6XXX series aluminum alloy base material are selected from one or more of the following three:

[0018] (1)Si 0.90%-1.00%, Mg 0.80%-0.90%, Cu 0.30%-0.40%, Cr 0.20%-0.25%, Mn 0.60%-0.65%, Ti 0.025%-0.03%, Zn 0-0.05%, Fe 0-0.15%, with the balance being Al and other inevitable impurities;

[0019] (2)Si 0.95%-1.10%, Mg 0.80%-0.90%, Cu 0.40%-0.50%, Cr 0.20%-0.30%, Mn 0.55%-0.65%, Ti 0.03%, Zn 0-0.05%, Fe 0-0.15%, with the balance being Al and other inevitable impurities;

[0020] (3)Si 1.10%-1.20%, Mg 0.90%-1.10%, Cu 0.55%-0.65%, Cr 0.20%-0.25%, Mn 0.60%-0.70%, Ti 0.03%, Zn 0.15%-0.25%, Fe 0-0.15%, with the balance being Al and other inevitable impurities.

[0021] In an embodiment of the present invention, in S1, the initial form of the 6XXX series aluminum alloy base material is in the T0 state - T10 state.

[0022] T0: The state after solution treatment, followed by natural aging and then cold working.

[0023] T1: The state after cooling during the high-temperature forming process and then natural aging to a substantially stable state.

[0024] T2: The state after cooling during the high-temperature forming process, followed by cold working and then natural aging to a substantially stable state.

[0025] T3: The state after solution treatment, followed by cold working and then natural aging to a substantially stable state.

[0026] T4: The state after solution treatment and then natural aging to a substantially stable state.

[0027] T5: The state after cooling during the high-temperature forming process and then artificial aging.

[0028] T6: The state after solution treatment and then artificial aging.

[0029] T7: The state after over-aging after solution treatment.

[0030] T8: The state after solution treatment, followed by cold working and then artificial aging.

[0031] T9: Solution treatment followed by artificial aging and then cold working.

[0032] T10: Cooling during hot forming process, cold working, and then artificial aging.

[0033] In one embodiment of the present invention, in S1, the temperature of the pre-welding aging treatment is 140°C - 240°C, and the time is 1h - 4h; performing the pre-welding aging treatment under this condition can cause a large number of atomic clusters and GP zones to precipitate in the base material.

[0034] In one embodiment of the present invention, in S2, the welding process is selected from one or more of laser welding, electron beam welding, cold metal transfer welding, gas tungsten arc welding, gas metal arc welding, and friction stir welding.

[0035] In one embodiment of the present invention, in S2, the welding atmosphere is 99.99% argon.

[0036] In one embodiment of the present invention, in S3, the temperature of the post-welding aging treatment is 140°C - 240°C, and the time is 0.5h - 1.5h; performing the post-welding aging treatment under this condition can cause β and Q series strengthening phases to precipitate in the heat affected zone of the welded joint, and at the same time cause a large number of β, Q, and T series strengthening phases to precipitate in the weld; after the post-welding aging treatment is completed, air cool to 15°C - 35°C.

[0037] The technical solution of the present invention has the following advantages compared with the prior art:

[0038] (1) The filler material described in the present invention has a specific alloy composition ratio, and contains Mg, Zn, and Cu elements at the same time. After pre- and post-welding aging treatments, the Mg, Zn, Cu elements and Al, Si in the weld microstructure will interact with each other to form nano-scale precipitation phases such as β phase, Q phase, and T phase, and significantly increase the number density of the precipitation phases.

[0039] (2) The filler material described in the present invention has good weldability, which promotes the precipitation strengthening mechanism. Since the strengthening element composition of the filler material is the same as that of the 6XXX series aluminum alloy base material, it can be applied to the welding of 6XXX series aluminum alloys by various welding methods, reducing the dilution of the weld strengthening elements, and effectively improving the mechanical properties of both the joint weld and the heat affected zone at the same time, enabling the 6XXX series aluminum alloy to be widely used in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in combination with the drawings, where:

[0041] Figure 1SEM micrograph of the weld microstructure of the welded joints in Embodiments 1-3 of the present invention;

[0042] Figure 2 TEM micrograph of the weld microstructure of the welded joints in Embodiments 1-3 of the present invention;

[0043] Figure 3 SEM micrograph of the weld microstructure of the welded joints in Comparative Examples 1-9 of the present invention;

[0044] Figure 4 TEM micrograph of the weld microstructure of the welded joints in Comparative Examples 1-9 of the present invention. Detailed implementation manners

[0045] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. It should be understood that the specific embodiments are only used to explain the present invention, but the exemplified embodiments do not limit the present invention.

[0046] In the present invention, unless otherwise specified, the technical and scientific terms used in the present invention have the same meanings as those generally understood by those skilled in the technical field to which the present invention belongs.

[0047] In the present invention, unless otherwise specified, the term "and / or" includes any and all combinations of one or more of the related listed items.

[0048] In the present invention, unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods without special instructions, and the materials, reagents, etc. used can be obtained from commercial channels without special instructions.

[0049] Embodiment 1

[0050] The elemental composition and its mass percentage of the filler material for 6XXX series aluminum alloy in this embodiment are: Si 1.10%, Mg 0.90%, Cu 0.45%, Cr 0.30%, Mn 0.65%, Ti 0.05%, Zn 0.90%, Fe 0.10%, and the balance is Al and other unavoidable impurities, with the total impurities <0.15%.

[0051] The welding process specifically includes the following steps:

[0052] S1. Perform pre-weld aging treatment on the 6XXX series aluminum alloy base material at a temperature of 180 °C for 1 h. The elemental composition and its mass percentage of the base material are as follows: Si 1.10%, Mg 0.80%, Cu 0.40%, Cr 0.25%, Mn 0.55%, Ti 0.03%, Zn 0.05%, Fe 0.10%, and the balance is Al and other inevitable impurities. The initial state is T4 state.

[0053] S2. Fill the filler material between the welds formed by two 6XXX series aluminum alloy base materials and perform welding using pulsed cold metal transfer welding. The welding speed is 12 mm / s, the wire feeding speed is 5.8 m / min, the shielding gas flow rate is 30 L / min, the wire dry elongation is 12 mm, the filler material is a wire with a diameter of 1.2 mm, and the shielding gas is 99.99% argon.

[0054] S3. Perform post-weld aging treatment on the welded joint and then air-cool it to room temperature. Among them, the temperature of the post-weld aging treatment is 180 °C and the time is 1 h.

[0055] Example 2

[0056] The elemental composition and its mass percentage of the filler material for the 6XXX series aluminum alloy in this example are as follows: Si 1.10%, Mg 0.90%, Cu 0.45%, Cr 0.30%, Mn 0.65%, Ti 0.05%, Zn 0.30%, Fe 0.10%, and the balance is Al and other inevitable impurities, with the total impurities < 0.15%.

[0057] The welding process specifically includes the following steps:

[0058] S1. Perform pre-weld aging treatment on the 6XXX series aluminum alloy base material at a temperature of 180 °C for 1 h. The elemental composition and its mass percentage of the base material are as follows: Si 1.10%, Mg 0.80%, Cu 0.40%, Cr 0.25%, Mn 0.55%, Ti 0.03%, Zn 0.05%, Fe 0.10%, and the balance is Al and other inevitable impurities. The initial state is T4 state.

[0059] S2. Fill the filler material between the welds formed by two 6XXX series aluminum alloy base materials and perform welding using pulsed cold metal transfer welding. The welding speed is 12 mm / s, the wire feeding speed is 5.8 m / min, the shielding gas flow rate is 30 L / min, the wire dry elongation is 12 mm, the filler material is a wire with a diameter of 1.2 mm, and the shielding gas is 99.99% argon.

[0060] S3. Perform post-weld aging treatment on the welded joint and then air-cool it to room temperature. Among them, the temperature of the post-weld aging treatment is 180°C and the time is 1 h.

[0061] Example 3

[0062] The elemental composition and its mass percentage of the filler material for 6XXX series aluminum alloy in this example are: Si 1.10%, Mg 0.90%, Cu 0.45%, Cr 0.30%, Mn 0.65%, Ti 0.05%, Zn 0.15%, Fe 0.10%, and the balance is Al and other inevitable impurities, with the total impurities <0.15%.

[0063] The welding process specifically includes the following steps:

[0064] S1. Perform pre-weld aging treatment on the 6XXX series aluminum alloy base material at a temperature of 180°C for 1 h. The elemental composition and its mass percentage of the base material are: Si 1.10%, Mg 0.80%, Cu 0.40%, Cr 0.25%, Mn 0.55%, Ti 0.03%, Zn 0.05%, Fe 0.10%, and the balance is Al and other inevitable impurities; the initial state is T4 state.

[0065] S2. Fill the filler material between the welds formed by two 6XXX series aluminum alloy base materials and perform welding using cold metal transfer welding with pulsed current. The welding speed is 12 mm / s, the wire feeding speed is 5.8 m / min, the shielding gas flow rate is 30 L / min, the wire dry elongation is 12 mm, the filler material is a wire with a diameter of 1.2 mm, and the shielding gas is argon with a purity of 99.99%.

[0066] S3. Perform post-weld aging treatment on the welded joint and then air-cool it to room temperature. Among them, the temperature of the post-weld aging treatment is 180°C and the time is 1 h.

[0067] Comparative Example 1

[0068] Basically the same as Example 1, the difference is that the mass percentages of the constituent elements of the filler material for 6XXX series aluminum alloy are different. The specific components are: Si 1.10%, Mg 0.10%, Cu 0.45%, Cr 0.30%, Mn 0.65%, Ti 0.05%, Zn 0.10%, Fe 0.10%, and the balance is Al and other inevitable impurities, with the total impurities <0.15%.

[0069] Comparative Example 2

[0070] Basically the same as Example 1, the difference is that the mass percentages of the constituent elements of the filler material of the 6XXX series aluminum alloy are different. The specific components are: Si 1.10%, Mg 0.20%, Cu 0.45%, Cr 0.30%, Mn 0.65%, Ti 0.05%, Zn 0.20%, Fe 0.10%, and the balance is Al and other inevitable impurities, with the total impurities <0.15%.

[0071] Comparative Example 3

[0072] Basically the same as Example 1, the difference is that the mass percentages of the constituent elements of the filler material of the 6XXX series aluminum alloy are different. The specific components are: Si 1.10%, Mg 0.30%, Cu 0.45%, Cr 0.30%, Mn 0.65%, Ti 0.05%, Zn 0.30%, Fe 0.10%, and the balance is Al and other inevitable impurities, with the total impurities <0.15%.

[0073] Comparative Example 4

[0074] Basically the same as Example 2, the difference is that the mass percentages of the constituent elements of the filler material of the 6XXX series aluminum alloy are different. The specific components are: Si 1.10%, Mg 0.30%, Cu 0.45%, Cr 0.30%, Mn 0.65%, Ti 0.05%, Zn 0.10%, Fe 0.10%, and the balance is Al and other inevitable impurities, with the total impurities <0.15%.

[0075] Comparative Example 5

[0076] Basically the same as Example 2, the difference is that the welding process is different, which specifically includes the following steps:

[0077] S1. The elemental composition and its mass percentage of the base material are: Si 1.10%, Mg 0.90%, Cu 0.45%, Cr 0.30%, Mn 0.65%, Ti 0.03%, Zn 0.05%, Fe 0.10%, and the balance is Al and other inevitable impurities; the initial state is T4 state;

[0078] S2. Fill the filler material between the welds formed by two 6XXX series aluminum alloy base materials and perform welding using pulsed cold metal transfer welding. The welding speed is 12 mm / s, the wire feeding speed is 5.8 m / min, the shielding gas flow rate is 30 L / min, the wire dry elongation is 12 mm, the filler material is a wire with a diameter of 1.2 mm, and the shielding gas is 99.99% argon;

[0079] S3. Perform post-weld aging treatment on the welded joint and then air cool it to room temperature; among them, the temperature of the post-weld aging treatment is 180 °C and the time is 1 h.

[0080] Comparative Example 6

[0081] Basically the same as Example 2, except that the welding process is different, specifically including the following steps:

[0082] S1. Perform pre-weld aging treatment on the 6XXX series aluminum alloy base material at a temperature of 180°C for 1 hour; the elemental composition and its mass percentage of the base material are: Si 1.10%, Mg 0.90%, Cu 0.45%, Cr 0.30%, Mn 0.65%, Ti 0.05%, Zn 0.30%, Fe 0.10%, and the balance is Al and other inevitable impurities; the initial state is T4 state;

[0083] S2. Fill the filler material between the welds formed by two 6XXX series aluminum alloy base materials and perform welding using cold metal transfer welding with pulse addition. The welding speed is 12 mm / s, the wire feeding speed is 5.8 m / min, the shielding gas flow rate is 30 L / min, the wire dry elongation is 12 mm, the filler material is a wire with a diameter of 1.2 mm, and the shielding gas is 99.99% argon.

[0084] Comparative Example 7

[0085] Basically the same as Example 3, except that the mass percentages of the constituent elements of the filler material for the 6XXX series aluminum alloy are different. The specific components are: Si 1.10%, Mg 0.30%, Cu 0.45%, Cr 0.30%, Mn 0.65%, Ti 0.05%, Zn 0.05%, Fe 0.10%, and the balance is Al and other inevitable impurities, with the total impurities < 0.15%.

[0086] Comparative Example 8

[0087] Basically the same as Example 3, except that the mass percentages of the constituent elements of the filler material for the 6XXX series aluminum alloy are different. The specific components are: Si 1.10%, Mg 0.60%, Cu 0.45%, Cr 0.30%, Mn 0.65%, Ti 0.05%, Zn 0.10%, Fe 0.10%, and the balance is Al and other inevitable impurities, with the total impurities < 0.15%.

[0088] Comparative Example 9

[0089] Basically the same as Example 3, except that the welding process is different, specifically including the following steps:

[0090] S1. Perform pre-weld aging treatment on the 6XXX series aluminum alloy base material at a temperature of 120 °C for 1 h. The elemental composition and its mass percentage of the base material are as follows: Si 1.10%, Mg 0.90%, Cu 0.45%, Cr 0.30%, Mn 0.65%, Ti 0.05%, Zn 0.15%, Fe 0.10%, and the balance is Al and other inevitable impurities. The initial state is T4 state.

[0091] S2. Fill the filler material between the welds formed by two 6XXX series aluminum alloy base materials and perform welding using cold metal transfer welding with pulsed current. The welding speed is 12 mm / s, the wire feeding speed is 5.8 m / min, the shielding gas flow rate is 30 L / min, the wire dry elongation is 12 mm, the filler material is a wire with a diameter of 1.2 mm, and the shielding gas is 99.99% argon.

[0092] S3. Perform post-weld aging treatment on the welded joint and then air-cool it to room temperature. Among them, the temperature of the post-weld aging treatment is 180 °C and the time is 1 h.

[0093] Test Example 1

[0094] Perform SEM and TEM characterization on the welded joints obtained in Examples 1-3 and Comparative Examples 1-9. The results are as Figures 1-4 shown.

[0095] It can be seen from Figures 1-2 that there are submicron-sized dispersed phases (α-Al(FeMnCr)Si phases) with relatively large sizes in the heat-affected zone of the welded joints in Examples 1-3. These precipitates can effectively pin dislocations and, as non-uniform nucleation cores for grains, effectively refine the grains. Since the contents of Mn, Cr, and Fe elements are the same in Examples 1-3, the number density of the dispersed phases is roughly the same, and the contribution value to the strength of the heat-affected zone of the welded joints is the same. However, due to the decrease in the content of Zn element in Examples 2-3, the number density of the internal nano-sized precipitates is lower than that in Example 1.

[0096] It can be seen from Figures 3-4It can be seen that in Comparative Examples 1-9, submicron-scale dispersed phase α-Al(FeMnCr)Si phase is generated inside the heat-affected zone. Since the contents of Mn, Cr, and Fe elements are the same, the number density of the dispersed phase is roughly the same, and the contribution value to the strength of the heat-affected zone of the welded joint is roughly the same. However, due to the decrease in the contents of Mg and Zn elements in Comparative Examples 1-4 and Comparative Examples 7-8, the number density of nanoscale precipitated phases inside the heat-affected zone decreases under the same processing technology. In Comparative Example 5, the heat-affected zone of the welded joint was not subjected to pre-weld aging treatment, resulting in slow development of the precipitated phases inside before welding and reducing the number density of subsequent precipitated phases. In Comparative Example 6, post-weld aging treatment was not carried out, resulting in a decrease in the number of nanoscale precipitated phases inside. In Comparative Example 9, the heat-affected zone of the welded joint was subjected to pre-weld aging at 120 °C / 1 h. Due to the low temperature and short time, it also led to slow development of the precipitated phases inside before welding, and finally reduced the number density of subsequent precipitated phases.

[0097] Test Example 2

[0098] The welded joints obtained from Examples 1-3 and Comparative Examples 1-9 were subjected to room-temperature tensile tests. The tests were carried out with reference to the standards of "GB / T 2651-2023 Destructive tests on welds in metallic materials - Transverse tensile test" and "GB / T 228 - Metallic materials - Tensile testing at ambient temperature". The results are shown in Table 1:

[0099] Table 1

[0100]

[0101] As can be seen from Table 1, the welded joints obtained with the filler materials and welding processes of the examples have excellent tensile strength, yield strength, and elongation.

[0102] By comparing the results of Example 1 and Comparative Examples 1-3, Example 2 and Comparative Example 4, and Example 3 and Comparative Examples 7-8, it can be seen that when the Mg / Zn ratio remains unchanged, the decrease in the contents of Mg and Zn elements leads to a decrease in the number of submicron-scale dispersed phases and nanoscale precipitated phases inside the heat-affected zone of the welded joint. According to the Orowan strengthening mechanism, the dispersed phase and the precipitated phase are the main factors determining the strength of the heat-affected zone. On the premise of keeping the Mg / Zn ratio constant, appropriately increasing the contents of Mg and Zn elements is beneficial to increasing the number density of the dispersed phase and the precipitated phase in the heat-affected zone, thereby improving its mechanical properties.

[0103] Comparing the results of Example 2 and Comparative Example 5, it can be seen that under the condition of the same Mg / Zn ratio and the same contents of Mg and Zn elements, the mechanical properties of the heat affected zone of the specimen without pre-weld aging are lower than those of the specimen with pre-weld aging. This is because the specimen without pre-weld aging (T4 state specimen) has been in a very early aging stage. In this stage, the number of precipitates in the alloy is very small, mainly a small amount of GP zones. After the action of the welding thermal cycle, the internal precipitates develop into strengthening phases, and the strengthening phases grow into Q phases after post-weld heat treatment. For the alloy with pre-weld aging treatment at 180°C / 1 h, the alloy with pre-weld aging treatment is in a relatively high level of under-aging stage, and a large number of GP zones appear inside the alloy, and at the same time, part of them are transformed into strengthening phase particles. After the action of the welding thermal cycle, the GP zones develop into β″ phases and Q′ phases, and the number density of nano-phases is relatively higher.

[0104] Comparing the results of Example 2 and Comparative Example 6, it can be seen that under the condition of the same Mg / Zn ratio and the same contents of Mg and Zn elements, the mechanical properties of the heat affected zone of the welded joint without post-weld aging are lower than those of the heat affected zone with post-weld aging. This is because after the action of the welding thermal cycle, the specimen undergoes Ostwald ripening behavior, the internal fine nano-phases dissolve, resulting in a decrease in the number of nano-phases, while the larger-sized nano-phases coarsen and grow, gradually developing into equilibrium phases, and the strengthening ability is further reduced. In the specimen after post-weld heat treatment, the internal strengthening phases grow into Q phases, but there will also be fine-sized GP zones and metastable phases formed, thereby increasing the number density of the precipitated phases and improving the mechanical properties.

[0105] Comparing the results of Example 3 and Comparative Example 9, it can be seen that under the condition of the same Mg / Zn ratio and the same contents of Mg and Zn elements, the mechanical properties of the heat affected zone of the welded joint with pre-weld aging at 120°C / 1 h are lower than those of the heat affected zone with pre-weld aging at 180°C / 1 h. This is because the pre-weld aging temperature is relatively low, resulting in a relatively low number density of nano-phases in the heat affected zone.

[0106] Obviously, the above examples are only for clearly illustrating the examples and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A welding process for 6XXX series aluminum alloy, characterized in that, It includes the following steps: S1. Perform pre-welding aging treatment on the 6XXX series aluminum alloy base material; the temperature of the pre-welding aging treatment is 140°C - 240°C, and the time is 1h - 4h; S2. Fill the filler material between the welds formed by two 6XXX series aluminum alloy base materials and perform welding to obtain a welded joint; the element composition and its mass percentage of the filler material are: Si 0.5% - 2.00%, Mg 0.80% - 2.00%, Cu 0.20% - 3.00%, Cr 0.20% - 0.50%, Mn 0.50% - 0.80%, Ti 0 - 0.10%, Zn 0.15% - 2.00%, Fe 0 - 0.15%, and the balance is Al and other inevitable impurities, with a total impurity of 0 - 0.15%; S3. Perform post-welding aging treatment on the welded joint; the temperature of the post-welding aging treatment is 140°C - 240°C, and the time is 0.5h - 1.5h; after the post-welding aging treatment is completed, air-cool to 15°C - 35°C.

2. The welding process of the 6XXX series aluminum alloy according to claim 1, characterized in that, In S2, the mass ratio of element Mg to element Zn is (1 - 6):1; the mass ratio of element Mg to element Cu is (1 - 3):

1.

3. The welding process of the 6XXX series aluminum alloy according to claim 1, characterized in that, In S2, the form of the filler material is selected from one or more of powder, sheet, and wire.

4. The welding process of the 6XXX series aluminum alloy according to claim 3, characterized in that, The particle size of the powder is 10μm - 250μm, the thickness of the sheet is 50μm - 1000μm, and the diameter of the wire is 0.5mm - 3.2mm.

5. The welding process of the 6XXX series aluminum alloy according to claim 1, characterized in that, In S1, the element composition and its mass percentage of the 6XXX series aluminum alloy base material are selected from one or more of the following three: (1) Si 0.90% - 1.00%, Mg 0.80% - 0.90%, Cu 0.30% - 0.40%, Cr 0.20% - 0.25%, Mn 0.60% - 0.65%, Ti 0.025% - 0.03%, Zn 0 - 0.05%, Fe 0 - 0.15%, and the balance is Al and other inevitable impurities; (2) Si 0.95% - 1.10%, Mg 0.80% - 0.90%, Cu 0.40% - 0.50%, Cr 0.20% - 0.30%, Mn 0.55% - 0.65%, Ti 0.03%, Zn 0 - 0.05%, Fe 0 - 0.15%, and the balance is Al and other inevitable impurities; (3) Si 1.10% - 1.20%, Mg 0.90% - 1.10%, Cu 0.55% - 0.65%, Cr 0.20% - 0.25%, Mn 0.60% - 0.70%, Ti 0.03%, Zn 0.15% - 0.25%, Fe 0 - 0.15%, and the balance is Al and other inevitable impurities.

6. The welding process of the 6XXX series aluminum alloy according to claim 1, characterized in that, In S1, the initial form of the 6XXX series aluminum alloy base material is T0 state - T10 state.

7. The welding process of the 6XXX series aluminum alloy according to claim 1, characterized in that, In S2, the welding process is selected from one or more of laser welding, electron beam welding, cold metal transfer welding, tungsten inert gas welding, metal inert gas welding, and friction stir welding.

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