High-strength weldable anti-fatigue aluminum alloy profile and preparation method and application thereof

Abstract

The invention belongs to the technical field of aluminum alloy, and particularly relates to a high-strength weldable anti-fatigue aluminum alloy profile and a preparation method and application thereof. Cu and Er are added into the alloy at the same time, the content range of the Cu element is strictly controlled to be larger than 0.2% and smaller than 0.5%, the content range of the Er element is strictly controlled to be 0.05-0.20%, the weight ratio of Cu to Er is further limited to be larger than 1 and smaller than or equal to 3, the casting process is improved on the basis of component design, and effective adding of Er and other components is ensured. Meanwhile, the standing time between quenching and aging is limited to be less than or equal to 12 hours, so that higher mechanical properties can be obtained. According to the aluminum alloy profile prepared through the method, through double improvement of components and the preparation method, the T5 state performance yield strength is larger than or equal to 365 MPa, the tensile strength is larger than or equal to 400 MPa, meanwhile, the welding coefficient of laser-arc hybrid welding is larger than or equal to 0.8, the fatigue strength is larger than or equal to 230 MPa (R =-0.2, Kt = 1, f = 10-200 Hz, and the cycle index is 1.0 * 107), and the comprehensive performance is comprehensively improved compared with traditional aluminum alloy materials such as 6082, 6061, 6063 and 6005.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloys, and specifically relates to a high-strength weldable fatigue-resistant aluminum alloy profile and a preparation method and application thereof. Background Art

[0002] In order to reduce energy consumption, save costs and achieve sustainable development, lightweight structure is one of the important development directions of the global manufacturing industry. Aluminum alloy is the most widely used type of non-ferrous metal structural material in industry. It has the advantages of high strength, light weight, good heat dissipation, good corrosion resistance, long service life, and easy recycling. It has been widely used in aviation, aerospace, automobile, machinery manufacturing, shipbuilding and chemical industries. Among them, Al-Mg-Si alloy, as a heat-treatable and strengthened aluminum alloy, has the advantages of good mechanical properties, good formability, and good corrosion resistance. It has been widely used in the fields of extruded profiles. In recent years, scholars have found in their research on adding Cu elements to the Al-Mg-Si alloy system that it can not only improve the peak aging mechanical properties of the alloy material, but also accelerate the aging hardening rate.

[0003] Welding is one of the main ways to connect aluminum alloys. Compared with other connection methods, it can simplify structural design, save man-hours and improve work efficiency. The use of automated robots can also reduce labor intensity. However, as one of the most effective ways to connect high-strength metal structures, welding still has some problems when applied to aluminum alloy materials. The most important problem is that aluminum alloys have fast thermal conductivity, and the welding process requires a high heat input. High heat will cause the material in the heat-affected zone to soften to varying degrees, thereby reducing the overall strength of the structural material. Since Al-Mg-Si alloy is a heat-treatable and strengthened aluminum alloy, this softening effect is more serious. The existence of the above welding problems seriously restricts the application of high-strength Al-Mg-Si alloy materials in welding structure scenarios.

[0004] Patent CN 105838943 B discloses an extrusion method of an Al-Mg-Si aluminum alloy and its profile. The patented alloy composition contains 0.07-0.35% Cr, but the Cr element significantly increases the quenching sensitivity of the alloy, thereby reducing the strength, which is not conducive to industrial production.

[0005] Patent CN 103045918A discloses a high welding strength Al-Mg-Si alloy and a method for preparing its profile. The disadvantage of the alloy described in the patent is that the mechanical properties need to be improved, and the price of the Sc element is relatively expensive, which is subject to certain restrictions in industrial production. Moreover, in terms of preparation technology, the patent adopts a single-stage homogenization process at 545-565°C, which cannot give full play to the role of rare earth elements.

[0006] Patent CN 115505796 A discloses a high-strength weldable A1-Si-Mg-Mn-Sc-Zr aluminum alloy profile and its preparation method. The patented alloy has a tensile strength of 338-341 MPa, a yield strength of 312-320 MPa, and a welding joint coefficient of about 0.7. Its comprehensive mechanical properties and welding joint coefficient need to be improved.

[0007] Patent CN 110760723 A discloses an aluminum-magnesium-silicon-erbium-zirconium alloy and a preparation process for improving high-temperature mechanical properties. The peak aging mechanical properties, aging hardening rate, and yield strength of the patented alloy need to be improved.

[0008] Patent CN 112941377 B discloses an Er-containing cast heat-resistant Al-Si-Cu-Mg alloy. The patented alloy belongs to a cast aluminum alloy. In terms of performance, the yield strength of the patented alloy is relatively low, only 231.5 to 315 MPa.

[0009] Patent CN 114058885 B discloses 6XXX series aluminum alloy sheet and its preparation method and welding method. The Cu content of the patent alloy is too high, and the welding performance of the alloy material is reduced. At the same time, the patent alloy composition contains Cr: 0.1-0.25%. The Cr element will significantly increase the quenching sensitivity of the alloy, thereby reducing the strength, which is not conducive to industrial production. In terms of performance, the yield strength and MIG welding coefficient in the patent embodiment need to be improved.

[0010] Patent CN117010787B discloses an aluminum alloy profile and its preparation method and application. The alloy achieves the purpose of comprehensive balance of strength, corrosion resistance and fatigue strength by adding Er and Zr in combination with a homogenization process system. However, the alloy does not control the ratio of Er and Cu elements, and the welding performance of the alloy is not described, and its fatigue strength still needs to be improved. Summary of the invention

[0011] In view of the problems existing in the prior art, the present invention provides a high-strength weldable fatigue-resistant aluminum alloy profile and a preparation method and application thereof. The present invention specifically includes the following contents:

[0012] In one aspect, the present invention provides a method for preparing a high-strength weldable fatigue-resistant aluminum alloy profile, comprising:

[0013] S1, prepare raw materials according to the following composition: the aluminum alloy profile includes the following components by weight percentage: 0.7%≤Si≤1.1%, Fe≤0.4%, 0.2%<Cu<0.5%, 0.3%<Mn≤0.8%, 0.7%<Mg≤1.1%, 0.05%≤Er≤0.2%, 0.05%≤Zr≤0.2%, unavoidable impurities≤0.15%, and the balance is Al; wherein the weight ratio of Cu to Er is 1<Cu / Er≤3;

[0014] S2, melting and casting: heating the aluminum ingot to melt, then adding other master alloys except erbium and magnesium, stirring and melting; then, adjusting the temperature to 770-790°C, adding the aluminum-erbium master alloy, stirring for 1-5 minutes and then keeping warm for 10-20 minutes, repeating the above stirring and keeping warm operation at least once; then, adjusting the temperature to 730-750°C, adding the magnesium ingot, stirring and melting to obtain an alloy melt; finally, casting to obtain an aluminum alloy ingot;

[0015] S3, soaking heating integrated heat treatment: heating the aluminum alloy ingot to 340-360°C, keeping the temperature for 8-12 hours; then continuing to heat to 550-560°C, keeping the temperature for 8-32 hours; then, cooling down to 480-550°C with the furnace and directly hot extruding;

[0016] S4, hot extrusion: control the mold temperature to 460-510°C, the temperature in the extrusion barrel to 390-450°C, and extrude the aluminum alloy ingot after the uniform heating and integrated heat treatment onto the upper mold;

[0017] S5, quenching: quench the extruded profile online, control the extrusion outlet quenching temperature to 480-550℃ and the exit quenching temperature to ≤85℃;

[0018] S6, stretching and straightening: stretching and straightening the quenched profile;

[0019] S7, artificial aging: control the parking time between quenching and artificial aging to ≤12h, adopt a single-stage aging system, the aging temperature is 160-200℃, and the time is 2-26h.

[0020] Furthermore, in step S2, the melting temperature of the aluminum ingot is 745-755°C; and / or, the stirring melting temperature of the other intermediate alloy is 700-750°C.

[0021] Furthermore, step S2 also includes sampling and analyzing the magnesium ingot after it is stirred and melted, adjusting the composition according to the analysis results, refining, slagging, and standing after the composition is qualified, and then adjusting the melt to 730-750°C to start casting.

[0022] Furthermore, the heating rate in step S3 is 30-50° C. / h.

[0023] Furthermore, in step S4, the extrusion rod speed is controlled to be 2-5 mm / s and the extrusion ratio is controlled to be 30-60.

[0024] Furthermore, the quenching method in step S5 is air cooling, water mist cooling or water cooling.

[0025] Furthermore, the stretching straightening amount in step S6 is controlled within a range of 0.5-2.0%.

[0026] The present invention also provides a high-strength weldable fatigue-resistant aluminum alloy profile prepared by the method of the present invention, wherein the laser-arc hybrid welding coefficient is ≥0.8; at R=-0.2, Kt=1, f=10-200Hz, and the number of cycles is 1.0×10 7 Under the test conditions, its fatigue strength is ≥230MPa.

[0027] Furthermore, its yield strength is ≥365MPa and its tensile strength is ≥400MPa.

[0028] In another aspect, the present invention further provides an application of the high-strength weldable fatigue-resistant aluminum alloy profile in the fields of automobiles, rail transportation, aerospace, shipbuilding and marine engineering, and construction.

[0029] Beneficial effects of the present invention:

[0030] (1) Cu and Er are added to the alloy of the present invention at the same time, because Cu and Er have a beneficial effect on the Al-Mg-Si alloy system, and Cu has a beneficial effect on promoting the aging strengthening of the Al-Mg-Si alloy system; Er and Zr form submicron / nanoscale Al3(Zr x Er 1-x) composite precipitation phase, which directly leads to precipitation strengthening and inhibits recrystallization nucleation and grain growth during extrusion, promotes the precipitation of artificial aging phase, and achieves the purpose of comprehensive balance of strength, welding performance, and fatigue performance. However, at the same time, when Cu and Er elements are added to aluminum alloy at the same time, Er and Cu will react to form a low-melting point eutectic Al8Cu4Er phase, which is generally formed during melt crystallization. In addition to reducing the strength of the alloy itself, it can also weaken the beneficial effect of Cu elements in the alloy on promoting aging strengthening of the Al-Mg-Si alloy system. Therefore, the comprehensive performance of the alloy is reduced to a certain extent, so it is necessary to strictly control the addition amount of Cu and Er elements and the addition ratio between the two. Since the higher the Cu content, the greater the driving force for the formation of the Al8Cu4Er phase, but if the Cu content is too low, it is difficult to play its beneficial role in promoting the aging strengthening of the Al-Mg-Si alloy system. Therefore, the present invention strictly controls the Cu content range to 0.2% < Cu < 0.5%, the Er content range to 0.05-0.20%, and further limits the weight ratio of Cu to Er to 1 < Cu / Er ≤ 3. Thus, on the one hand, the formation trend of the Al8Cu4Er phase is suppressed to the maximum extent, and on the other hand, the beneficial effects of the Cu and Er elements on the Al-Mg-Si alloy system are played.

[0031] (2) The alloy elements of the ingot of the present invention are complex and the alloying degree is high. During the casting process, the ingot is subjected to cooling by cooling water, and the internal stress is large, which is easy to produce hot cracks. At the same time, because the alloy contains fine crystal elements such as Mn, Er, and Zr, the melt viscosity is large and the fluidity is poor, which is not conducive to the dehydrogenation and slag removal of the melt, so the tendency of looseness and slag inclusion is increased. In the alloy system of the present invention, microalloying elements Er and Zr are added in combination, among which the addition of Er element is relatively difficult. The present invention has determined through preliminary experimental research that after the aluminum ingot is charged into the furnace, the temperature is raised and melted, and the temperature is set to 750°C. The intermediate alloy (except erbium and magnesium ingots) is added at 700-750°C, and the Fe impurity content is strictly controlled, and the stirring and melting are carried out. Subsequently, the temperature is set to 780°C, and the aluminum-erbium intermediate alloy is added at 770-790°C. The aluminum-erbium intermediate alloy must not be exposed to the liquid surface. After adding, it is stirred for 1 minute and then kept warm for 15 minutes, and then stirred for the second time. After stirring for 1 minute, it is kept warm for 15 minutes. Then the temperature is set to 730-750℃, pure magnesium is added at 730-750℃, and the magnesium ingot is pressed into the aluminum liquid to melt. After the magnesium ingot is fully stirred and melted, sampling and analysis are carried out, and the composition is adjusted according to the analysis results. After the composition is qualified, refining, slag removal, and static, the melt is cast at 730-750℃ to ensure the effective addition of Er and Mg elements.

[0032] (3) According to literature reports, the law of the parking effect of Al-Mg-Si alloys is that for alloys with high Si and Mg contents, the longer the intermediate storage time, the lower the tensile strength and the higher the elongation, and the parking time should be shortened as much as possible; while for low-alloyed alloys, the intermediate parking time needs to be extended to meet the required mechanical properties, but the limit of alloying level also varies with different alloy systems. The present invention has found through research that the optimal parking time between quenching and aging of the aluminum alloy of the present invention is ≤12h, so that higher mechanical properties can be obtained.

[0033] (4) The traditional profile preparation process is to heat the ingot uniformly and then cool it to room temperature. Secondary heating and heat preservation are required before extrusion. This process route has high energy consumption and low production efficiency. The present invention adopts an integrated heat-averaging and heating process to homogenize the aluminum alloy ingot, and then directly hot extrude it after cooling it to the extrusion temperature with the furnace. There is no secondary heating and heat preservation process, which can save energy and improve production efficiency. At the same time, the present invention designs a two-stage homogenization process system. The first stage homogenization is realized, for example, Al3(Zr x Er 1-x ), the precipitation of dispersed phases such as Al6Mn, and the second level homogenization realizes the dissolution of soluble phases such as Mg2Si and Q phase, as well as the discontinuous morphological transformation of insoluble phases such as AlFeMnSi.

[0034] (5) The yield strength of aluminum alloy extrusion profiles such as 6082, 6061, 6063, and 6005 in the T6 state is generally not higher than 300MPa, the fusion welding coefficient is about 0.65-0.7, and the fatigue strength is lower than 160MPa (same as the test conditions of the present invention). The aluminum alloy profiles prepared by the present invention have achieved a T5 state performance yield strength of ≥365MPa and a tensile strength of ≥400MPa through dual improvements in composition and preparation method. At the same time, the laser-arc hybrid welding coefficient is ≥0.8 and the fatigue strength is ≥230MPa (R=-0.2, K t =1, f = 10-200Hz, number of cycles 1.0×10 7 ), its comprehensive performance is comprehensively improved compared with traditional aluminum alloy materials such as 6082, 6061, 6063, and 6005. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the T5 state microstructure morphology of the aluminum alloy profile prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments shown below do not limit the invention content described in the claims. In addition, the entire contents of the structures represented by the following embodiments are not limited to those necessary as solutions to the invention described in the claims.

[0037] A method for preparing a high-strength weldable fatigue-resistant aluminum alloy profile, comprising:

[0038] (1) S1, preparing raw materials according to the following composition: the aluminum alloy profile comprises the following components by weight percentage: 0.7%≤Si≤1.1%, Fe≤0.4%, 0.2%<Cu<0.5%, 0.3%<Mn≤0.8%, 0.7%<Mg≤1.1%, 0.05%≤Er≤0.2%, 0.05%≤Zr≤0.2%, unavoidable impurities≤0.15%, and the balance is Al; wherein the weight ratio of Cu to Er is 1<Cu / Er≤3;

[0039] Cu and Er are added to the alloy of the present invention at the same time, because Cu and Er have a beneficial effect on the Al-Mg-Si alloy system, and Cu has a beneficial effect on promoting the aging strengthening of the Al-Mg-Si alloy system; Er and Zr form submicron / nanoscale Al3(Zr x Er 1-x ) composite precipitation phase, which directly leads to precipitation strengthening and inhibits recrystallization nucleation and grain growth during extrusion, promotes the precipitation of artificial aging phase, and achieves the purpose of comprehensive balance of strength, welding performance, and fatigue performance. However, at the same time, when Cu and Er elements are added to aluminum alloy at the same time, Er and Cu will react to form a low-melting point eutectic Al8Cu4Er phase, which is generally formed during melt crystallization. In addition to reducing the strength of the alloy itself, it can also weaken the beneficial effect of Cu elements in the alloy on promoting aging strengthening of the Al-Mg-Si alloy system. Therefore, the comprehensive performance of the alloy is reduced to a certain extent, so it is necessary to strictly control the addition amount of Cu and Er elements and the addition ratio between the two. Since the higher the Cu content, the greater the driving force for the formation of the Al8Cu4Er phase, but if the Cu content is too low, it is difficult to play its beneficial role in promoting the aging strengthening of the Al-Mg-Si alloy system. Therefore, the present invention strictly controls the Cu content range to 0.2% < Cu < 0.5%, the Er content range to 0.05-0.20%, and further limits the weight ratio of Cu to Er to 1 < Cu / Er ≤ 3. Thus, on the one hand, the formation trend of the Al8Cu4Er phase is suppressed to the maximum extent, and on the other hand, the beneficial effects of the Cu and Er elements on the Al-Mg-Si alloy system are played.

[0040] S2, the alloy elements of the ingot of the present invention are complex, the alloying degree is high, and it is subjected to cooling water quenching during the casting process, the internal stress is large, and hot cracks are easily generated. At the same time, because the alloy contains fine crystal elements such as Mn, Er, and Zr, the melt viscosity is large and the fluidity is poor, which is not conducive to the dehydrogenation and slag removal of the melt, so the tendency of looseness and slag inclusion is increased. In the alloy system of the present invention, microalloying elements Er and Zr are added in combination, among which the addition of Er element is relatively difficult. The present invention has determined the following melting and casting process through preliminary experimental research: the aluminum ingot raw material is heated and melted after charging the furnace, the temperature is set to 750°C, the intermediate alloy (except erbium and magnesium ingots) is added at 700-750°C, the Fe impurity content is strictly controlled, and the stirring and melting are carried out. Subsequently, the temperature is set to 780°C, and the aluminum-erbium intermediate alloy is added at 770-790°C. The aluminum-erbium intermediate alloy must not be exposed to the liquid surface. After adding, stir for 1min and keep warm for 15min, and then stir for the second time, stir for 1min and keep warm for 15min. Then the temperature is set to 730-750°C, pure magnesium is added at 730-750°C, and the magnesium ingot is pressed into the aluminum liquid to melt. After the magnesium ingot is fully stirred and melted, sampling and analysis are performed, and the composition is adjusted according to the analysis results. After the composition is qualified, refining, slag removal, and standing are performed, and the melt is cast at 730-750°C to obtain an aluminum alloy ingot. The melting and casting process of the present invention can ensure the effective addition of Er and Mg elements.

[0041] S3, integrated heat treatment with equalizing heating: heat the aluminum alloy ingot to 340-360°C, and keep it warm for 8-12h; then continue to heat it to 550-560°C, with a heating rate of (30-50)°C / h, and keep it warm for 8-32h; then, cool it down to 480-550°C with the furnace and directly perform hot extrusion; the traditional profile preparation process is to heat the ingot uniformly and then cool it to room temperature, and then perform secondary heating and insulation before extrusion. This process route has high energy consumption and low production efficiency. The present invention adopts an integrated heat treatment and equalizing heating process to homogenize the aluminum alloy ingot, and then directly perform hot extrusion after cooling it down to the extrusion temperature with the furnace. There is no secondary heating, insulation and car skin process, which can save energy and improve production efficiency. The present invention designs a two-stage homogenization process system. The first stage homogenization is achieved, for example, Al3(Zr x Er 1-x ), the precipitation of dispersed phases such as Al6Mn, and the second level homogenization realizes the dissolution of soluble phases such as Mg2Si and Q phase, as well as the discontinuous morphological transformation of insoluble phases such as AlFeMnSi.

[0042] S4, hot extrusion: control the die temperature to 460-510°C, the temperature in the extrusion barrel to 390-450°C, the extrusion rod speed to 2-5 mm / s, the extrusion ratio to 30-60, and extrude the aluminum alloy ingot after the uniform heating and integrated heat treatment on the die;

[0043] S5, quenching: the extruded profile is quenched online, the quenching method is air cooling, water mist cooling or water cooling, and the extrusion outlet quenching temperature is controlled to be 480-550℃ and the outlet quenching temperature is ≤85℃;

[0044] S6, stretching and straightening: stretch and straighten the quenched profile, and the stretching and straightening amount is controlled at 0.5-2.0%.

[0045] S7, artificial aging: control the parking time between quenching and artificial aging to ≤12h, adopt a single-stage aging system, the aging temperature is 160-200℃, and the time is 2-26h. For Al-Mg-Si alloys with high Si and Mg contents, the longer the intermediate storage time, the lower the tensile strength and the higher the elongation, so the parking time should be shortened as much as possible; for low-alloyed alloys, the intermediate parking time needs to be extended to meet the required mechanical properties, but the boundaries of alloying height also vary with respect to different alloy systems, so the optimal parking time for different alloys needs to be adjusted according to the specific composition. The present invention has found through research that the optimal parking time between quenching and aging of the aluminum alloy of the present invention is ≤12h, so that higher mechanical properties can be obtained.

[0046] The high-strength weldable and fatigue-resistant aluminum alloy profile prepared by the method of the present invention has a laser-arc hybrid welding coefficient of ≥0.8; at R=-0.2, Kt=1, f=10-200Hz, and cycle number 1.0×10 7 Under the test conditions, its fatigue strength is ≥230MPa, while its yield strength is ≥365MPa and its tensile strength is ≥400MPa. The high-strength weldable fatigue-resistant aluminum alloy profile provided by the present invention improves the welding performance and fatigue strength while also comprehensively improving the mechanical properties of the aluminum alloy, which can meet the application requirements in the fields of automobiles, rail transportation, aerospace, ships and marine engineering, and construction.

[0047] Terminology explanation:

[0048] T5 state: refers to the state of being cooled by a high-temperature forming process and then artificially aged. It is suitable for products that are cooled by a high-temperature forming process and artificially aged without cold processing (straightening and leveling can be performed, but it does not affect the mechanical performance limit).

[0049] T6 state: refers to the state of artificial aging after solid solution heat treatment. It is suitable for products that are no longer cold-processed after solid solution heat treatment (straightening and leveling can be performed, but it does not affect the mechanical performance limit).

[0050] Example 1

[0051] A method for preparing a high-strength weldable fatigue-resistant aluminum alloy profile:

[0052] The raw materials of aluminum alloy are mixed and melted according to the composition ratio. After the aluminum ingot is loaded into the furnace, the temperature is raised and melted. The temperature is set to 750℃. The intermediate alloy (except erbium and magnesium ingots) is added at 730℃. The Fe impurity content is strictly controlled and stirred and melted. Then the temperature is set to 780℃, and the aluminum-erbium intermediate alloy is added at 780℃. The aluminum-erbium intermediate alloy must not be exposed to the liquid surface. After adding, stir for 1 minute and keep warm for 15 minutes. Stir for the second time, stir for 1 minute and keep warm for 15 minutes. Then the temperature is set to 740℃, and pure magnesium is added at 740℃. The magnesium ingot is pressed into the aluminum liquid to melt. After the magnesium ingot is fully stirred and melted, it is sampled and analyzed, and the composition is adjusted according to the analysis results. After the composition is qualified, the aluminum alloy ingot is refined, slag-stripped, and allowed to stand, and the melt is cast at 740°C to obtain an aluminum alloy ingot; the aluminum alloy ingot is homogenized, and the double-stage homogenization heat treatment process is 350°C×11h+555°C×16h, air cooling, and a heating rate of 40°C / h, and then the temperature is reduced to an extrusion temperature of 525°C with the furnace for hot extrusion; the heating temperature of the mold in the heating furnace is controlled at 475°C; the heating temperature of the extrusion barrel is controlled at 420°C; then the upper mold is extruded, the extrusion rod speed is controlled at 2.3mm / s, and the extrusion ratio is controlled at 33.3; the quenching temperature at the profile extrusion outlet is controlled at 520°C, and the quenching method is selected to be water-cooled, and the quenching temperature is 50°C; the tensile straightening amount of the profile is controlled at 1%; a single-stage aging system is adopted, the aging temperature is 170°C, and the time is 12h; the time between online quenching and artificial aging is 2h. The performance of the profile was evaluated after being stored at room temperature for 24 hours. The yield strength was 367MPa, the laser-arc hybrid welding coefficient was ≥0.82 (laser melting welding), and the fatigue strength was ≥230MPa (R=-0.2, K t =1, f = 10-200Hz, number of cycles 1.0×10 7 ). The aluminum alloy composition is shown in Table 1, the process parameters are shown in Table 2, the performance evaluation results are shown in Table 3, and the microstructure of the alloy profile T5 is shown in Table Figure 1 .

[0053] Embodiment 2-10

[0054] The difference between Examples 2 to 10 and Example 1 is that the aluminum alloy composition and process parameters are different. The aluminum alloy composition is shown in Table 1, the process parameters are shown in Table 2, and the performance evaluation results are shown in Table 3.

[0055] Comparative Examples 1-11

[0056] The difference between Comparative Examples 1 to 11 and Example 1 is that the aluminum alloy compositions and process parameters are different. The aluminum alloy compositions are shown in Table 1, the process parameters are shown in Table 2, and the performance evaluation results are shown in Table 3.

[0057] Table 1 Alloy composition of the present invention and comparative examples

[0058]

[0059] Table 2 Preparation process parameters of the present invention and comparative examples

[0060]

[0061]

[0062] Table 3 Performance of alloys in the embodiments of the present invention and comparative examples

[0063]

[0064]

[0065] Description: Fatigue strength test conditions: R = -0.2, K t =1, f = 10-200Hz, number of cycles 1.0×10 7 .

[0066] Laser-arc hybrid welding parameters: power 5.5kW, welding speed 0.10m / s, wire feeding speed 9m / min, defocus -3mm, wire distance 3mm.

[0067] It can be seen from the above that the alloy compositions of Comparative Examples 1 to 4 are greatly different from those of the present invention, and the process parameters of Comparative Examples 5 to 11 are greatly different from those of the present invention.

[0068] In Comparative Example 1, the content of Si and Mg elements is low, Si and Mg elements are dissolved back during homogenization and solid solution, and the content of β" strengthening phase precipitated during aging is lower than that of Examples 1-10, so that the strength and fatigue properties of the alloy material are lower than those of Examples 1-10, and there is no obvious effect on the welding coefficient.

[0069] The Cu content in Comparative Example 2 is relatively low, which weakens the beneficial effect of the Cu element in the alloy on promoting aging strengthening of the Al-Mg-Si alloy system, resulting in a decrease in the strength and fatigue properties of the alloy material.

[0070] The high Cu content in Comparative Example 3 will produce a large amount of Al8Cu4Er harmful phase, which weakens the beneficial effect of Cu in the alloy on promoting aging strengthening of the Al-Mg-Si alloy system, and reduces the comprehensive performance of the alloy to a certain extent. At the same time, with the increase of Cu content, the Al2Cu eutectic phase in the weld zone increases, which reduces the strength of the weld zone and the welding coefficient of the alloy material.

[0071] When the Mn content in Comparative Example 4 is too much, the strengthening effect of the Si element will be reduced, resulting in intracrystalline segregation, a reduction in the dispersed precipitate phase, and a coarse-grained structure in the extruded product, which reduces the strength and fatigue properties of the alloy material and the welding coefficient.

[0072] In Comparative Example 5, the Er and Zr content is low, and the Al3 (Zr x Er 1-x ) content is lower than that of Examples 1 to 10, Al3(Zr x Er 1-x ) precipitation strengthening and inhibiting recrystallization nucleation and grain growth during extrusion, which weakens the effect of promoting phase precipitation during artificial aging, resulting in a decrease in the strength and fatigue properties of the alloy material and a decrease in the welding coefficient.

[0073] Through preliminary experimental research, it was found that it is difficult to effectively add Er element in the melting and casting process. It is most suitable to add Al-Er master alloy in the melting and casting process at a higher melt temperature and a smaller window of 770-790°C. In Example 6, the Al-Er master alloy addition temperature in the melting and casting process is too low, and Er element cannot be effectively added. Al3(Zr x Er 1-x ) effect is weakened, which causes the strength and fatigue properties of the alloy material to decrease and the welding coefficient to decrease.

[0074] In Comparative Example 7, the first-stage homogenization time is short, and the Al3(Zr x Er 1-x ), the Al6Mn content is lower than that of Examples 1 to 10, which reduces the strength and fatigue properties of the alloy material and the welding coefficient.

[0075] The process route of the present invention is online quenching, and sufficient solid solution is achieved during the extrusion process. In comparative example 8, the extrusion temperature is relatively low, the temperature of the alloy material is relatively low during the entire extrusion process, the quenching temperature is relatively low, and the degree of solid solution is relatively poor, which reduces the strength and fatigue properties of the alloy material. At the same time, the undissolved Mg2Si particles are not conducive to welding, which also reduces the welding coefficient of the alloy material.

[0076] The extrusion process will generate a large amount of heat energy. The faster the extrusion speed, the higher the temperature of the profile during the extrusion process. The extrusion speed of the profile in Example 9 is relatively low, the temperature of the profile during the extrusion process is relatively low, and the degree of solid solution is poor, which reduces the strength and fatigue properties of the alloy material. At the same time, the undissolved Mg2Si is not conducive to welding, which also reduces the welding coefficient of the alloy material.

[0077] In Comparative Example 10, the time between online quenching and artificial aging of the profile is relatively long. Unfavorable clusters are precipitated during the natural aging process, which weakens the degree of solid solution. In the subsequent aging process, the precipitation kinetics weakens, and the precipitation strengthening effect weakens, which reduces the strength and fatigue properties of the alloy material. However, the degree of solid solution is relatively sufficient, the size of the unfavorable clusters is small, and there is no obvious effect on the welding coefficient.

[0078] In comparative example 11, the aging temperature of the profile is low, and the precipitation strengthening effect is weakened, resulting in a decrease in the strength and fatigue properties of the alloy material. However, the degree of solid solution is relatively sufficient, and there are no residual Mg2Si particles, which has no significant effect on the welding coefficient.

[0079] In comparison, the embodiments of the present invention match the refined alloy composition design of the composite microalloying high solute content 6xxx with the precise processing technology, so that it can take into account the requirements of yield strength, welding performance and fatigue strength. Through the solid solution of Si and Mg elements, the precipitation strengthening phase β" can fully play its role without a large amount of excess Mg and Si. The addition of a small amount of Cu element promotes the formation of β" phase during the aging process and improves the aging hardening performance. The present invention strictly controls the Cu element content range of 0.2-0.5% and the Er element content range of 0.05-0.20%. On the one hand, it suppresses the formation trend of Al8Cu4Er phase, and on the other hand, it exerts the beneficial effects of Cu and Er elements on the Al-Mg-Si alloy system. An appropriate amount of Mn element can inhibit the recrystallization process, significantly refine the recrystallized grains at the end of the recrystallization stage, and also contributes to the improvement of the relative strength of the dispersion strengthening formed by Mn. Composite addition of microalloying elements Er and Zr forms submicron / nanoscale Al3(Zr) during the homogenization process. x Er 1-x ) composite precipitate phase, which directly leads to precipitation strengthening and inhibits recrystallization nucleation and grain growth during extrusion, promotes the precipitation of artificial aging phase, and achieves the purpose of comprehensive balance of strength, welding and fatigue properties.

[0080] The present invention controls the melting and casting process to add Al-Er master alloy at 770-790℃ and stirs twice. After each stirring for 1 minute, keep the temperature for 15 minutes, but the liquid surface must not be exposed to ensure the effective addition of Er element. The aluminum alloy ingot is homogenized by using an integrated process of uniform heating, and then the temperature is lowered to the extrusion temperature for hot extrusion. A two-stage homogenization process system is designed. The first stage homogenization is realized, for example, Al3(Zr x Er 1-x ), the precipitation of dispersed phases such as Al6Mn, and the second-level homogenization realizes the dissolution of soluble phases such as Mg2Si and Q phase, as well as the discontinuous morphology transformation of insoluble phases such as AlFeMnSi. By increasing the ingot heating temperature, the extrusion speed, and the quenching temperature, a high-temperature and high-speed extrusion process can be achieved, thereby achieving a more sufficient solid solution effect. Shorten the parking time between online quenching and artificial aging to promote the effect of artificial aging. Use a reasonable aging process to achieve the peak strength of the alloy material.

[0081] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a high-strength weldable fatigue-resistant aluminum alloy profile, characterized in that: include: S1, prepare raw materials according to the following composition: the aluminum alloy profile includes the following components by weight percentage: 0.7%≤Si≤1.1%, Fe≤0.4%, 0.2%<Cu<0.5%, 0.3%<Mn≤0.8%, 0.7%<Mg≤1.1%, 0.05%≤Er≤0.2%, 0.05%≤Zr≤0.2%, unavoidable impurities≤0.15%, and the balance is Al; wherein the weight ratio of Cu to Er is 1<Cu / Er≤3; S2, melting and casting: heating the aluminum ingot to melt, then adding other master alloys except erbium and magnesium, stirring and melting; then, adjusting the temperature to 770-790°C, adding the aluminum-erbium master alloy, stirring for 1-5 minutes and then keeping warm for 10-20 minutes, repeating the above stirring and keeping warm operation at least once; then, adjusting the temperature to 730-750°C, adding the magnesium ingot, stirring and melting to obtain an alloy melt; finally, casting to obtain an aluminum alloy ingot; S3, soaking heating integrated heat treatment: heating the aluminum alloy ingot to 340-360°C, keeping the temperature for 8-12 hours; then continuing to heat to 550-560°C, keeping the temperature for 8-32 hours; then, cooling down to 480-550°C with the furnace and directly hot extruding; S4, hot extrusion: control the mold temperature to 460-510°C, the temperature in the extrusion barrel to 390-450°C, and extrude the aluminum alloy ingot after the uniform heating and integrated heat treatment onto the upper mold; S5, quenching: quench the extruded profile online, control the extrusion outlet quenching temperature to 480-550℃ and the exit quenching temperature to ≤85℃; S6, stretching and straightening: stretching and straightening the quenched profile; S7, artificial aging: control the parking time between quenching and artificial aging to ≤12h, adopt a single-stage aging system, the aging temperature is 160-200℃, and the time is 2-26h.

2. The method for preparing a high-strength weldable fatigue-resistant aluminum alloy profile according to claim 1, characterized in that: In step S2, the aluminum ingot is melted at a temperature of 745-755°C; and / or, the other intermediate alloy is stirred and melted at a temperature of 700-750°C.

3. The method for preparing a high-strength weldable fatigue-resistant aluminum alloy profile according to claim 1, characterized in that: Step S2 also includes sampling and analyzing the magnesium ingot after it is stirred and melted, adjusting the composition according to the analysis results, refining, slagging, and standing after the composition is qualified, and then adjusting the melt to 730-750°C to start casting.

4. The method for preparing a high-strength weldable fatigue-resistant aluminum alloy profile according to claim 1, characterized in that: The heating rate in step S3 is 30-50°C / h.

5. The method for preparing a high-strength weldable fatigue-resistant aluminum alloy profile according to claim 1, characterized in that: Step S4 controls the extrusion rod speed to 2-5 mm / s and the extrusion ratio to 30-60.

6. The method for preparing a high-strength weldable fatigue-resistant aluminum alloy profile according to claim 1, characterized in that: The quenching method in step S5 is air cooling, water mist cooling or water cooling.

7. The method for preparing a high-strength weldable fatigue-resistant aluminum alloy profile according to claim 1, characterized in that: The stretching straightening amount in step S6 is controlled within a range of 0.5-2.0%.

8. A high-strength weldable fatigue-resistant aluminum alloy profile prepared by the method according to any one of claims 1 to 7, characterized in that: The laser-arc hybrid welding coefficient is ≥0.8; at R = -0.2, K t =1, f = 10-200Hz, number of cycles 1.0×10 7 Under the test conditions, its fatigue strength is ≥230MPa.

9. The high-strength weldable fatigue-resistant aluminum alloy profile according to claim 8, characterized in that: Its yield strength is ≥365MPa and its tensile strength is ≥400MPa.

10. Application of the high-strength weldable fatigue-resistant aluminum alloy profile according to any one of claims 8 or 9 in the fields of automobiles, rail transportation, aerospace, shipbuilding and marine engineering, and construction.

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