A heat treatment method for 6xxx series high-strength corrosion-resistant aluminum alloy and welded joint

Abstract

The invention discloses a heat treatment method for a 6xxx series high-strength corrosion-resistant aluminum alloy and a welded joint, belonging to the technical field of aluminum alloy heat treatment, wherein the specific chemical composition of the 6xxx series high-strength corrosion-resistant aluminum alloy includes: Si: 0.4-1.0%, Fe: ≤0.2%, Cu: 0.25-0.95%, Mn: 0.4-0.8%, Mg: 0.6-1.1%, Zr: 0.10-0.20%, Er: 0.10-0.20%, and the balance is Al and other inevitable impurity elements; then the 6xxx series high-strength corrosion-resistant aluminum alloy is subjected to heat treatment of the welded joint, and the specific process includes the following steps: S1: welding; S2: two-stage solution treatment; S3: quenching treatment; S4: aging treatment. By optimizing the heat treatment process, the strength of the welded joint of the 6xxx series aluminum alloy profile is effectively improved, and the welding coefficient (joint tensile strength / parent material tensile strength) of the joint obtained after heat treatment is ≥0.8, which provides a new idea for the engineering application of the 6xxx series high-strength corrosion-resistant aluminum alloy.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy heat treatment, and specifically relates to a heat treatment method for a 6xxx series high-strength corrosion-resistant aluminum alloy and a welded joint. Background Art

[0002] Driven by the development of my country's shipbuilding industry and marine engineering, aluminum alloy has become one of the main materials for shipbuilding. Aluminum alloy has the advantages of medium strength, good formability and processability, and its extruded profiles have been widely used. 6xxx series aluminum alloy is an aluminum alloy with magnesium and silicon as the main alloying elements and Mg2Si phase as the strengthening phase. It is a heat-treatable aluminum alloy. Generally, the strength of the material is ensured by extrusion-online quenching-aging treatment.

[0003] Welding is one of the most common engineering applications of aluminum alloy materials. Commonly used welding methods include fusion welding (TIG, MIG) and solid phase welding (friction stir welding). Affected by the welding heat input, the second phase in the heat-affected zone of the 6xxx series aluminum alloy welded joint aggregates and grows, showing an over-aging softening phenomenon, resulting in a significant decrease in the tensile strength of the joint, which has a serious impact on the normal service of the welded components. Therefore, a heat treatment method to improve the strength of 6 series aluminum alloy welded joints is urgently needed to promote the application of 6xxx series aluminum alloy materials on board ships.

[0004] After investigation, the relevant patents for heat treatment methods of 6xxx series aluminum alloy profile welding joints are as follows:

[0005] Invention patent CN104017979A "A heat treatment method for improving the performance of high-strength aluminum alloy friction stir welding joints" adopts a deep cryogenic treatment + low-temperature aging heat treatment method, which does not involve a solid solution heat treatment process for welded joints; patent CN108381117A "A heat-treatable strengthening aluminum alloy welding process" adopts a special welding cooling treatment method to achieve online direct solid solution quenching, and then improves the performance of the joint through artificial aging, without involving post-weld solid solution treatment. Due to the limited solid solution effect, the joint strength is not significantly improved; patent CN117512481A "A method for improving the strength of 6xxx series aluminum alloy profiles "Heat treatment method for strength and corrosion resistance of welded joints" The alloy composition is as follows: Si: 0.75~0.85%, Cu: 0.12~0.2%, Mn: 0.25~0.30%, Mg: 0.62~0.70%, Zr: 0.05~0.08%, Sc: 0.06~0.10%, Ti: 0.01~0.02, Fe: ≤0.13%, Zn: ≤0.12%, and the remainder is Al 6xxx series aluminum alloy. The heat treatment process of the welded joint prepared by MIG welding is low-temperature short-time annealing heat treatment after welding, the temperature is 320~340℃, and the insulation is 0.5~2h. This patent does not involve the solution treatment of new aluminum alloy profiles and welded joints; the base material of patent CN105349763B "A post-weld heat treatment method for high-strength aluminum alloy welded joints" is Al-Zn-Mg-Cu alloy, which belongs to the 7xxx series aluminum alloy, and has a different composition from the 6E21 series aluminum alloy, and its heat treatment process is also different.

[0006] In summary, there is no patent document in the prior art and patents that is similar to the new 6xxx series aluminum alloy proposed in the present invention: 6E21 high-strength and corrosion-resistant aluminum alloy profile, and its corresponding joint heat treatment process. Summary of the invention

[0007] In view of this, in order to solve the problems in the prior art that 6xxx series aluminum alloys have low strength and poor corrosion resistance, and the tensile strength of the joints is significantly reduced after welding, the present invention provides a 6xxx series high-strength and corrosion-resistant aluminum alloy and a heat treatment method for the welded joints, which can significantly improve the strength of the welded joints and provide technical support for the promotion and application of 6xxx series high-strength and corrosion-resistant aluminum alloys.

[0008] A 6xxx series high-strength corrosion-resistant aluminum alloy, wherein the chemical composition of the 6xxx series high-strength corrosion-resistant aluminum alloy comprises, by mass percentage, Si: 0.4-1.0%, Fe: ≤0.2%, Cu: 0.25-0.95%, Mn: 0.4-0.8%, Mg: 0.6-1.1%, Zr: 0.10-0.20%, Er: 0.10-0.20%, and the remainder is Al and other inevitable impurity elements.

[0009] Furthermore, the total content of impurity elements is ≤0.15%, wherein the content of a single impurity element is ≤0.05%.

[0010] Furthermore, the 6xxx series high-strength and corrosion-resistant aluminum alloy is a 6E21 aluminum alloy profile.

[0011] A heat treatment method for a 6xxx series high-strength corrosion-resistant aluminum alloy welded joint comprises the following steps:

[0012] S1: Welding: Using a 6xxx series high-strength and corrosion-resistant aluminum alloy as a weldment, welding it to obtain a 6xxx series high-strength and corrosion-resistant aluminum alloy welded joint, wherein the welding method is fusion welding or solid phase welding;

[0013] S2: Two-stage solid solution treatment: Put the welded 6E21 high-strength corrosion-resistant aluminum alloy welded joint into a heating furnace, and heat it up with the furnace to perform two-stage solid solution treatment; the first stage solid solution treatment: the temperature is 530~550℃, and the temperature is kept for 0.5~1h; the second stage solid solution treatment: the temperature is 565~575℃, and the temperature is kept for 0.5~1.5h;

[0014] S3: Quenching treatment: take out the welded joint after the solution treatment and immediately put it into the quenching medium for quenching treatment;

[0015] S4: Aging treatment: The welded joint after quenching treatment is placed in a heating furnace and subjected to aging treatment as the furnace heats up.

[0016] Furthermore, the fusion welding in step S1 is TIG welding or MIG welding, and the solid phase welding is stir friction welding.

[0017] Furthermore, in step S2, the heating rate of the first-stage solid solution is 10-20°C / min; the heating rate of the second-stage solid solution is 5-10°C / min.

[0018] Furthermore, the quenching medium in step S3 is tap water, wherein the water temperature of the tap water is room temperature.

[0019] Furthermore, the quenching transfer time of the quenching treatment in step S3 is ≤20s.

[0020] Furthermore, the aging treatment in step S4 includes the following steps: heating the quenched weld joint to 165-175°C at a heating rate of 10-20°C / min, and keeping the temperature for 6-10 hours.

[0021] Furthermore, the welding coefficient of the 6xxx series high-strength and corrosion-resistant aluminum alloy welded joint obtained after the heat treatment method is ≥0.8.

[0022] Compared with the prior art, this application has the following beneficial effects:

[0023] The present invention provides a method for heat treatment of a 6xxx series high-strength and corrosion-resistant aluminum alloy and a welded joint. According to the rare earth erbium micro-alloying characteristics of the 6xxx series aluminum alloy, the heat treatment process is optimized to effectively improve the strength of the welded joint of the 6xxx series aluminum alloy profile. The welding coefficient (joint tensile strength / parent material tensile strength) of the welded joint obtained after the heat treatment is ≥0.8, which provides a new idea for the engineering application of the 6xxx series high-strength and corrosion-resistant aluminum alloy. DETAILED DESCRIPTION

[0024] At present, aluminum alloys are affected by welding heat input during the welding process, which will cause the second phase in the heat-affected zone of the weld joint to grow and show over-aging softening phenomenon, thereby causing a significant decrease in the tensile strength of the weld joint, which has a serious impact on the normal service of the welded components.

[0025] Based on the above problems, the present invention proposes a heat treatment method for a 6xxx series high-strength and corrosion-resistant aluminum alloy profile welded joint. The method involves the chemical composition of a new 6xxx series aluminum alloy profile and the heat treatment process of the welded joint.

[0026] A 6xxx series high-strength corrosion-resistant aluminum alloy profile, preferably an Al-Mg-Si-Zr-Er aluminum alloy. Its chemical composition (by mass percentage) includes: Si: 0.4-1.0%, Fe: ≤0.2%, Cu: 0.25-0.95%, Mn: 0.4-0.8%, Mg: 0.6-1.1%, Zr: 0.10-0.20%, Er: 0.10-0.20%, and the balance is Al and other unavoidable impurity elements; wherein the total content of impurity elements is ≤0.15%, and the content of a single impurity element is ≤0.05%.

[0027] The 6xxx series high-strength and corrosion-resistant aluminum alloy in the present invention is specifically a 6E21 aluminum alloy profile. According to the "Method for Representing Deformed Aluminum and Aluminum Alloy Grades", 6 represents the 6 series aluminum alloy, E represents the modification of the aluminum alloy with the rare earth element Er, and 21 represents the specific number of the alloy in the 6xxx series.

[0028] The various elements in the 6E21 aluminum alloy profile of the present invention exist in synergy and work together to make it have high strength and good corrosion resistance, meet the requirements for ship use, and affect the subsequent heat treatment process.

[0029] The Er element exists in Mg-containing Al alloys in three main forms: solid solution in the Al matrix; forming a primary Al3Er phase or distributed at the grain boundary in the form of a eutectic compound; precipitating in the crystal in the form of fine Al3Er; specifically, in the 6E21 aluminum alloy profile of the present invention, except for a small portion of the Er element solid solution in the matrix to form a supersaturated solid solution, most of the Er element gathers at the solid-liquid interface front, aggravating the composition fluctuation near the solid-liquid interface and increasing the composition supercooling at the solid-liquid interface front, prompting a large amount of primary Al3Er phase to be directly precipitated in the melt, playing a good role in heterogeneous nucleation, thereby refining the grains; at the same time, the primary Al3Er phase has a superlattice structure (L 12 ), has the characteristics of low density, high strength, and high melting point. It is not easy to dissolve back during heat treatment and can be coherent with the matrix (coherence can maximize the strengthening effect of the dispersed phase).

[0030] When Er and Si elements exist at the same time, grain refinement, elongation and heat resistance of 6E21 aluminum alloy are improved; in addition, the composite addition of Cu, Er and Si elements can also improve the thermal stability of Al alloy: specifically, Cu, Mg and Si atoms are segregated at the interface of Al matrix, which can regulate the mismatch between atoms at the interface, reduce the interface mismatch stress, and reduce the interface energy, thereby improving the thermal stability of the alloy; at the same time, by adding Mn elements, the formation of brittle phases containing Fe and other elements that are not conducive to the toughness of the alloy is regulated, and Al5Mn5 phase is formed, which increases the corrosion resistance and improves the plasticity.

[0031] The 6E21 aluminum alloy of the present invention further contains Zr element, wherein the Zr element is mainly concentrated near the interface between the Al3Er precipitation phase and the matrix, and at the same temperature, the diffusion rate of Zr in the Al matrix is ​​less than that of Er, forming an Al3 (Er, Zr) phase with a core-shell structure, and the synergistic effect of the Er element and the Zr element improves the thermal stability of the alloy, and also contributes to the increase of the alloy hardness to a certain extent; and the Zr element also inhibits the precipitation of Er in the 6E21 aluminum alloy at a lower aging temperature; at a higher aging temperature, the inhibited Er element and the Zr element precipitate synergistically, and the alloy presents an aging peak value far higher than that of the existing 6XXX series aluminum alloy, which can maintain its aging strengthening for a longer time.

[0032] At present, fusion welding is mostly used in the welding process of marine aluminum alloys: common fusion welding includes TIG welding and MIG welding. Affected by the welding heat input, the joint strength loss is relatively serious. At the same time, the post-weld heat treatment process generally directly adopts a single-stage solid solution and aging process, and does not fully consider the impact of the low melting point in the welded joint on the solid solution process and the joint performance, making it difficult to fully explore the strength potential of the alloy welded joint.

[0033] Using a 6xxx series high-strength and corrosion-resistant aluminum alloy as a weldment, welding it to obtain a 6xxx series high-strength and corrosion-resistant aluminum alloy welded joint, wherein the welding method is fusion welding or solid phase welding;

[0034] Based on this, the present invention performs melting welding (TIG welding and MIG welding) and solid phase welding (friction stir welding) on ​​6xxx series high-strength and corrosion-resistant aluminum alloy base materials, wherein TIG welding and MIG welding are both existing technologies and will not be elaborated here; friction stir welding is a solid phase connection technology, during which the material is always in a thermoplastic state and will not melt, and the welding heat input is low.

[0035] Specifically, friction stir welding includes the following steps:

[0036] S11: Preparation phase: The 6xxx series aluminum alloy weldment to be welded is firmly fixed on the working platform to ensure the stability of the welding process.

[0037] S12: Rotation and insertion stage: The stirring head rotates at high speed and inserts the stirring needle into the joint of the 6xxx series aluminum alloy weldment until the shoulder of the stirring head is in close contact with the surface of the 6xxx series aluminum alloy weldment.

[0038] During this process, the friction between the stirring needle and the surrounding 6xxx series aluminum alloy base material generates heat, which increases the temperature of the material at the joint and softens it.

[0039] S13: Welding stage: The stirring head rotates and moves relative to the 6xxx series aluminum alloy weldment along the joint, causing strong plastic deformation of the material in front of the stirring head.

[0040] As the stirring head moves forward, the highly plastically deformed material at the front is squeezed to the back of the stirring head to form a dense solid-phase connection joint.

[0041] S14: Ending stage: After welding is completed, the stirring head leaves the 6xxx series aluminum alloy weldment, completing the entire friction stir welding process.

[0042] Friction stir welding has the characteristics of few welding defects, small welding deformation, high welding coefficient, etc. In the present invention, the tensile strength of the friction stir welding joint (241MPa) is 23MPa higher than the tensile strength of the MIG welding joint (218MPa). After heat treatment, the strength of the joint is also higher than that of the fusion welding joint.

[0043] In order to eliminate the softening zone of the joint, the present invention proposes a heat treatment process for the welded joint, which mainly includes the following steps:

[0044] S1: Two-stage solid solution treatment: Place the above-mentioned new 6xxx aluminum alloy welded joint into a heating furnace with blast, and heat it up with the furnace to perform a first-stage solid solution treatment on the welded joint: heat it to 530~550℃ at a heating rate of 10~20℃ / min, and keep it warm for 0.5~1h. Then perform a second-stage solid solution treatment: heat it to 565~575℃ at a heating rate of 5~10℃ / min, and keep it warm for 0.5~1.5h.

[0045] The double-stage solution heats the alloy to a certain temperature to dissolve the second phase into the matrix to the maximum extent, thereby improving the strength and hardness of the alloy. The key to this process is to choose the right temperature to ensure that the second phase can be fully dissolved while avoiding overheating and overburning of the aluminum alloy; different aluminum alloys have different requirements for the specific solution temperature range, and the solution temperature of most aluminum alloys is usually between 470 and 525 ° C.

[0046] The 6xxx series aluminum alloy welded joint profile of the present invention was tested by DSC, and it was found that it had a low melting point second phase at about 550°C. Specifically, the second phase was mainly a Cu-containing phase. Therefore, a solid solution treatment was first performed at 530~550°C to promote the dissolution of the low melting point second phase in the matrix and prevent the material from being overburned due to direct high-temperature solid solution treatment.

[0047] Then heat it to 565~575℃ at a heating rate of 5~10℃ / min and keep it for 0.5~1.5h. Due to the enrichment of rare earth element Er at the front, the alloy components are supercooled, and different multi-element alloy phases have different melting points; at the same time, the third phases such as Al3Er, Al3Zr and Al (Er, Zr) have good thermal stability and require a higher solid solution temperature. The temperature is raised to 565~575℃. At this time, the undissolved third phases such as Al3Er, Al3Zr and Al (Er, Zr) in the weld joint continue to dissolve back into the matrix. In addition, the presence of the third phase can effectively inhibit the growth of recrystallized grains and increase the recrystallization starting temperature. Therefore, the strengthening caused by the dissolution of the third phase in the secondary solid solution and the softening caused by recrystallization are balanced.

[0048] The temperature of the secondary solid solution is controlled below 575°C to prevent the heating temperature from being too high, which will cause the low-melting-point eutectic in the alloy to melt and cause overburning, which will significantly reduce the mechanical properties of the alloy.

[0049] S2: Quenching treatment: Take out the welded joint after solution treatment and immediately perform quenching treatment. The quenching medium is tap water, the water temperature is room temperature, and the quenching transfer time is ≤20s.

[0050] After the solution treatment, quenching is performed immediately, i.e., rapid cooling, to fix the supersaturated state of the second phase, the third phase and other multi-element alloy phases in the aluminum matrix. This is because during the rapid cooling process, the second phase and the third phase and other multi-element alloy phases do not have time to precipitate, thus maintaining a high concentration state in the Al matrix, creating conditions for subsequent aging treatment.

[0051] S3: Aging treatment: The welded joint after solution quenching treatment is subjected to aging heat treatment, and the temperature is raised with the furnace, heated to 165~175℃ at a heating rate of 10~20℃ / min, and kept warm for 6~10h.

[0052] The 6xxx series high-strength corrosion-resistant aluminum alloy of the present invention can precipitate nano-scale dispersed particles under the process of two-stage solid solution combined with artificial aging treatment, greatly improving the strengthening effect. The presence of the Er-containing third phase Al3Er, Al (Er, Zr) and other multi-element alloy phases increases the nucleation particles, making the second phase (Al-Mg phase) more dispersed, thereby improving the aging strength of the alloy; at the same time, Er and Zr also have a synergistic strengthening effect. When Er and Zr are added in combination, Al3Er will nucleate first, and other elements will nucleate and grow with it as the core. The Al (Er, Zr) phase formed by aging in the A1 alloy is rich in Er in the center and rich in Zr in the outer layer. At this time, the stability of the third phase after aging strengthening is greatly improved, and the strength of its ternary alloy phase is also greatly improved compared to the strength of binary alloy phases such as Al3Er and Al3Zr.

[0053] Example 1

[0054] (1) This embodiment provides a 6xxx series high-strength and corrosion-resistant aluminum alloy profile, specifically a 6E21 aluminum alloy profile, which is composed of the following components (in mass percentage):

[0055] Si: 0.87%, Fe: 0.15%, Cu: 0.82%, Mn: 0.49%, Mg: 0.89%, Zr: 0.11%, Er: 0.14%, the balance is Al and other inevitable impurity elements;

[0056] The tensile strength of the extruded profile is 405MPa, the yield strength is 383MPa, and the elongation is 14%; the exfoliation corrosion grade is PB.

[0057] (2) After friction stir welding, the tensile strength of the aluminum alloy joint is 241 MPa.

[0058] (3) After solution quenching treatment at 540℃×1h+570℃×1h and aging heat treatment at 170℃×8h, the tensile strength of the welded joint of the aluminum alloy profile is increased to 353MPa, and the welding coefficient is 0.866.

[0059] Example 2

[0060] (1) This embodiment provides a 6xxx series high-strength and corrosion-resistant aluminum alloy profile, specifically a 6E21 aluminum alloy profile, which is composed of the following components (in mass percentage):

[0061] Si: 0.46%, Fe: 0.17%, Cu: 0.30%, Mn: 0.55%, Mg: 1.01%, Zr: 0.12%, Er: 0.13%, the balance is Al and other inevitable impurity elements;

[0062] The tensile strength of the extruded profile is 399MPa, the yield strength is 381MPa, and the elongation is 13%; the exfoliation corrosion grade is PB.

[0063] (2) After TIG welding of aluminum alloy profiles, the tensile strength of the joint is 201MPa.

[0064] (3) After solution quenching treatment at 530℃×0.5h+575℃×1.5h and aging heat treatment at 170℃×10h, the tensile strength of the welded joint of the aluminum alloy profile is increased to 322MPa, and the welding coefficient is 0.807.

[0065] Example 3

[0066] (1) This embodiment provides a 6xxx series high-strength and corrosion-resistant aluminum alloy profile, specifically a 6E21 aluminum alloy profile, which is composed of the following components (in mass percentage):

[0067] Si: 0.96%, Fe: 0.19%, Cu: 0.33%, Mn: 0.57%, Mg: 0.84%, Zr: 0.14%, Er: 0.12%, and the balance is Al and other inevitable impurity elements.

[0068] The tensile strength of the extruded profile is 408MPa, the yield strength is 386MPa, and the elongation is 15%; the exfoliation corrosion grade is PA grade.

[0069] (2) After MIG welding of aluminum alloy profiles, the tensile strength of the joint is 218MPa.

[0070] (3) After solution quenching treatment at 550℃×1h+565℃×0.5h and aging heat treatment at 170℃×6h, the tensile strength of the welded joint of the aluminum alloy profile is increased to 333MPa, and the welding coefficient is 0.816.

[0071] Example 4

[0072] (1) This embodiment provides a 6xxx series high-strength and corrosion-resistant aluminum alloy profile, specifically a 6E21 aluminum alloy profile, which is composed of the following components (in mass percentage):

[0073] Si: 0.63%, Fe: 0.06%, Cu: 0.46%, Mn: 0.44%, Mg: 0.69%, Zr: 0.10%, Er: 0.12%. The tensile strength of the extruded profile is 402MPa, the yield strength is 379MPa, and the elongation is 13%; the exfoliation corrosion grade is PB.

[0074] (2) After MIG welding of aluminum alloy profiles, the tensile strength of the joint is 214MPa.

[0075] (3) After solution quenching treatment at 540℃×0.5h+570℃×1h and aging heat treatment at 170℃×8h, the tensile strength of the welded joint of the aluminum alloy profile is increased to 326MPa, and the welding coefficient is 0.811.

[0076] In summary, regardless of whether Examples 1 to 4 are fusion welding or solid phase welding, after the heat treatment method of the present invention: two-stage solid solution and aging treatment, the tensile strength of the welded joints is significantly improved, and the welding coefficient is greater than 0.8, overcoming the softening phenomenon of the welded joints during the welding process.

[0077] Comparative Examples 1 to 3

[0078] The materials and components of the profiles in Comparative Examples 1 to 3 are different from those in Example 1, but the welding method, solution treatment and aging treatment are the same as those in Example 1.

[0079] Comparative Example 1 provides an aluminum alloy profile composed of the following components (mass percentage): Si: 0.73%, Fe: 0.04%, Cu: 0.48%, Mn: 0.42%, Mg: 0.80%, and the balance is Al and other unavoidable impurity elements; the extruded profile has a tensile strength of 368 MPa, a yield strength of 334 MPa, and an elongation of 10%; and the exfoliation corrosion grade is PB.

[0080] Comparative Example 2 provides an Er-containing aluminum alloy profile, consisting of the following components (mass percentage): Si: 0.68%, Fe: 0.09%, Cu: 0.42%, Mn: 0.40%, Mg: 0.80%, Er: 0.13%, and the balance is Al and other unavoidable impurity elements; the extruded profile has a tensile strength of 380 MPa, a yield strength of 354 MPa, and an elongation of 13%; the exfoliation corrosion grade is PB.

[0081] Comparative Example 3 provides a Zr-containing aluminum alloy profile, consisting of the following components (mass percentage): Si: 0.64%, Fe: 0.13%, Cu: 0.38%, Mn: 0.42%, Mg: 0.83%, Zr: 0.16%, and the remainder is Al and other inevitable impurity elements; the extruded profile has a tensile strength of 376 MPa, a yield strength of 345 MPa, and an elongation of 13%; the exfoliation corrosion grade is PB.

[0082] Comparative Examples 4-5

[0083] The welding method of Comparative Examples 4-5 is different from that of Example 1, and the profile material and composition, solution treatment and aging treatment are the same as those of Example 1.

[0084] After TIG welding of the 6E21 aluminum alloy profile obtained in Comparative Example 4, the tensile strength of the joint is 224 MPa.

[0085] After MIG welding of the 6E21 aluminum alloy profile obtained in Comparative Example 5, the tensile strength of the joint is 233 MPa.

[0086] Comparative Examples 6-7

[0087] The solid solution treatment of Comparative Examples 6-7 is different from that of Example 1. A single-stage solid solution treatment is adopted. The profile material and composition, welding method and aging treatment are the same as those of Example 1.

[0088] The 6E21 aluminum alloy welded joint obtained in Comparative Example 6 was subjected to solution quenching treatment at 540°C for 2h;

[0089] The 6E21 aluminum alloy welded joint obtained in Comparative Example 7 was subjected to solution quenching treatment at 570°C for 2h;

[0090] Comparative Examples 8 to 9

[0091] The solution treatment of Comparative Examples 8-9 is different from that of Example 1, wherein the temperatures of the primary solution treatment and the secondary solution treatment are different from those of Example 1; the profile material and composition, welding method and aging treatment are the same as those of Example 1.

[0092] The 6E21 aluminum alloy welded joint obtained in Comparative Example 8 was subjected to solution quenching treatment at 520°C × 1h + 555°C × 1h;

[0093] The 6E21 aluminum alloy welded joint obtained in Comparative Example 9 was subjected to solution quenching treatment at 560°C × 1h + 585°C × 1h;

[0094] Table 1 Heat treatment parameters and experimental results of samples of Example 1 and Comparative Examples 1 to 9

[0095]

[0096] As shown in the above table, by comparing different experimental parameters and experimental results, Comparative Examples 1 to 3 can show that the Er element and Zr element in the 6xxx series aluminum alloy can enhance the strength and corrosion resistance of the aluminum alloy, and the Er element and the Zr element have a composite synergistic effect. Compared with aluminum alloys that do not contain Er and Zr elements or contain a single Er element or Zr element, aluminum alloys that contain Er and Zr elements at the same time have better tensile strength and welding coefficient after heat treatment due to the presence of multi-element alloy phases such as Al3Er, Al3Zr, and Al (Er, Zr).

[0097] Comparative Examples 4 to 5 show that the strength of the welded joints obtained by fusion welding, i.e., MIG welding or TIG welding, is less than the strength of the welded joints after friction stir welding. This is because friction stir welding has the characteristics of fewer welding defects, smaller welding deformation, and higher welding coefficient. After heat treatment, the joint strength is also higher than that of the fusion welded joint, indicating that friction stir welding is more compatible with the heat treatment method of the welded joint.

[0098] Comparative Examples 6 to 7 show that regardless of whether at 540°C or 570°C, the strength and welding coefficient of the welded joint obtained after single-stage solution treatment are less than those of the double-stage solution treatment. Therefore, the single-stage solution treatment of the present invention has limitations. A single solution temperature will cause the residual third phase inside the 6E21 aluminum alloy welded joint to be unable to be completely dissolved in the matrix. At the same time, the low-melting-point second phase will be overburned, both of which will reduce the tensile strength of the welded joint.

[0099] Comparative Examples 8 to 9 show that appropriate temperatures for the primary and secondary solid solutions are required in the two-stage solid solution treatment. It is not feasible to have a primary or secondary solid solution temperature that is too high or too low. Too high a temperature will cause the low-melting point phase to be overburned, reducing the tensile strength of the welded joint; too low a temperature will cause the second phase, the third phase and other multi-element alloy phases to be unable to fully dissolve, reducing the tensile strength of the welded joint.

[0100] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A heat treatment method for a 6xxx series high-strength and corrosion-resistant aluminum alloy welded joint, characterized in that: The heat treatment method comprises: S1: Welding: Using a 6xxx series high-strength corrosion-resistant aluminum alloy as a weldment, welding it to obtain a 6xxx series high-strength corrosion-resistant aluminum alloy welded joint, wherein the welding method is fusion welding or solid phase welding; the 6xxx series high-strength corrosion-resistant aluminum alloy has a chemical composition, by mass percentage, of Si: 0.4-1.0%, Fe: ≤0.2%, Cu: 0.25-0.95%, Mn: 0.4-0.8%, Mg: 0.6-1.1%, Zr: 0.10-0.20%, Er: 0.10-0.20%, and the remainder is Al and other unavoidable impurity elements; S2: Two-stage solid solution treatment: Place the welded 6xxx series high-strength corrosion-resistant aluminum alloy welded joint into a heating furnace, and heat it up with the furnace to perform two-stage solid solution treatment; the first stage solid solution treatment: temperature is 530~550℃, and the temperature is kept for 0.5~1h; the second stage solid solution treatment: temperature is 565~575℃, and the temperature is kept for 0.5~1.5h; The first-level solid solution allows the second phase to dissolve into the matrix to improve the strength and hardness of the alloy; the second-level solid solution allows the undissolved third phase in the weld joint to dissolve back into the matrix to inhibit the growth of recrystallized grains and increase the recrystallization starting temperature; the second phase is mainly a Cu-containing phase, and the third phase includes Al3Er, Al3Zr and Al (Er, Zr); S3: Quenching treatment: take out the welded joint after the solution treatment and immediately put it into the quenching medium for quenching treatment; S4: Aging treatment: The welded joint after quenching treatment is placed in a heating furnace and subjected to aging treatment as the furnace heats up.

2. The heat treatment method according to claim 1, characterized in that The total content of impurity elements is ≤0.15%, of which the content of a single impurity element is ≤0.05%.

3. The heat treatment method according to claim 1, characterized in that The 6xxx series high-strength and corrosion-resistant aluminum alloy is a 6E21 aluminum alloy profile.

4. The heat treatment method according to claim 1, characterized in that: The fusion welding in step S1 is TIG welding or MIG welding, and the solid phase welding is friction stir welding.

5. The heat treatment method according to claim 1, characterized in that: In step S2, the heating rate of the first-stage solid solution is 10-20°C / min; the heating rate of the second-stage solid solution is 5-10°C / min.

6. The heat treatment method according to claim 1, characterized in that: The quenching medium in step S3 is tap water, wherein the water temperature of the tap water is room temperature.

7. The heat treatment method according to claim 1, characterized in that: The quenching transfer time of the quenching treatment in step S3 is ≤20s.

8. The heat treatment method according to claim 1, characterized in that: The aging treatment in step S4 includes the following steps: heating the quenched weld joint to 165-175°C at a heating rate of 10-20°C / min and keeping the temperature for 6-10 hours.

9. The heat treatment method according to claim 1, characterized in that: The welding coefficient of the 6xxx series high-strength and corrosion-resistant aluminum alloy welded joint obtained after heat treatment is ≥0.8.

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