Ageing strengthening aluminum alloy plate strip for carrier gas brazing and preparation method of aging strengthening aluminum alloy plate strip

Abstract

The invention relates to an aging strengthening aluminum alloy plate strip for carrier gas brazing and a preparation method thereof.The aging strengthening aluminum alloy plate strip comprises a brazing layer, a core layer, a blocking layer A and a blocking layer B. The blocking layer A and the blocking layer B are located on the two sides of the core layer, and the core layer comprises, by mass, 0.8-1.3 wt% of Mg, 0.8-1.3 wt% of Si, 0.5-0.8 wt% of Cu, 0.2-0.5 wt% of Mn, 0.01-0.05 wt% of Ti and the balance Al and inevitable impurities; the thickness of the brazing layer accounts for 9%-11% of the total thickness of the plate strip, the thickness of the blocking layer A accounts for 6%-10% of the total thickness of the plate strip, the thickness of the blocking layer B accounts for 10%-14% of the total thickness of the plate strip, and the rest thickness is the core layer. Compared with a traditional material, the steel plate has higher pre-welding strength and post-welding strength, can adapt to various use environments, and is prolonged in service life. After being brazed, the product can be subjected to aging strengthening according to actual use requirements, different use strengths are obtained, and the product can be suitable for carrier gas brazing with low production cost, can be produced in a large scale and meets the use requirements of the current market.

Description

Technical Field

[0001] This application relates to the field of aluminum alloy materials, and in particular to an age-strengthened aluminum alloy sheet and strip for carrier gas brazing and a method for preparing the same. Background Technology

[0002] In the field of heat transfer, aluminum alloys are widely used in components such as air conditioner radiators due to their lightweight, high thermal conductivity, and ease of processing. Currently, the industry mainstream adopts bimetallic materials with 3-series aluminum alloy as the base and 4-series brazing layer on the surface. The base provides structural support, while the brazing layer melts during the brazing process to achieve the connection.

[0003] With the increasing demand for lightweight and high-performance equipment, the market is placing higher requirements on the strength, durability, and thinness of aluminum alloy materials. While traditional 3-series alloys can be strengthened by adding elements such as Cu and Mg, this often leads to decreased elongation and poorer formability. Specifically, the addition of Cu reduces corrosion resistance, while Mg is prone to volatilization and reaction with flux in the high-temperature environment of carrier gas brazing, severely affecting brazing quality. Although vacuum brazing can avoid the adverse effects of Mg, it suffers from high cost and low efficiency, making it difficult to meet the needs of large-scale production. Summary of the Invention

[0004] To improve the strength of aluminum alloy plates, this application provides an age-strengthened aluminum alloy plate and strip for carrier gas brazing and a method for preparing the same.

[0005] In a first aspect, this application provides an age-strengthened aluminum alloy sheet / strip for carrier gas brazing, which adopts the following technical solution: An age-strengthened aluminum alloy strip for carrier gas brazing includes a brazing layer, a core layer, and barrier layers A and B located on both sides of the core layer. The core layer comprises the following components by weight percentage: Mg: 0.8-1.3wt%, Si: 0.8-1.3wt%, Cu: 0.5-0.8wt%, Mn: 0.2-0.5wt%, Ti: 0.01-0.05wt%, balance being Al and unavoidable impurities; The thickness of the brazing layer accounts for 9-11% of the total thickness of the strip, the thickness of the barrier layer A accounts for 6-10% of the total thickness of the strip, the thickness of the barrier layer B accounts for 10-14% of the total thickness of the strip, and the remaining thickness is the core layer.

[0006] By adopting the above technical solution, the core layer is based on a modified alloy. Mg and Si form the strengthening phase Mg2Si, which provides the material with age-hardening potential, thus providing the core microstructure conditions for post-weld age-hardening. Cu is dissolved in the aluminum matrix to achieve solid solution strengthening, thereby improving the initial strength of the strip before welding. Mn and Ti work together to refine the grains of the core layer aluminum alloy and inhibit grain growth. While Cu and Mg improve strength, the strip's ductility is maintained. The barrier layers on both sides of the core layer form a dense protective layer, effectively blocking the volatilization of Mg under the high temperature of carrier gas brazing and reducing the reaction between Mg and flux. The brazing layer enhances the fusion connection effect during carrier gas brazing, enabling the strip to have both age-hardening potential and carrier gas brazing compatibility. The strip also has good initial strength, reserving sufficient microstructure space for different degrees of post-weld age-hardening.

[0007] Secondly, this application provides a method for preparing age-strengthened aluminum alloy strips for carrier gas brazing, employing the following technical solution: A method for preparing age-strengthened aluminum alloy sheet and strip for carrier gas brazing includes the following steps: S1. Melting and casting: The materials of the brazing layer, core layer and barrier layer are melted and cast according to the proportions to obtain brazing layer ingot, core layer ingot and barrier layer ingot respectively. S2. Mill the brazing layer ingot, core layer ingot and barrier layer ingot respectively to obtain the milled brazing layer ingot, the milled core layer ingot and the milled barrier layer ingot. S3. Heat-treat the brazed layer ingot and the barrier layer ingot after milling, then hot-roll the heat-treated brazed layer ingot and the heat-treated barrier layer ingot respectively, shear and cool to obtain brazed layer skin and barrier layer skin. S4. Grind and clean the milled core layer ingot to obtain the treated core layer ingot. Stack the brazing layer skin, barrier layer skin, and treated core layer ingot in sequence and bundle them to obtain the composite ingot. S5. The composite ingot is heated and kept warm, and then hot rolled to obtain aluminum coil blanks. S6. The aluminum coil blank is rolled by a cold rolling mill. After rolling, cracks and burrs are removed. Finally, the coil is annealed in an annealing furnace, cooled and cut to obtain age-strengthened aluminum alloy sheet and strip for carrier gas brazing.

[0008] By adopting the above technical solution, the brazing layer and core layer are melted and cast separately and then milled, so that the surface of each layer of ingot is clean and the voids generated by interlayer composite are reduced. The brazing layer and the barrier layer are hot rolled in stages, so that the densification and thickness of the single layer ingot are precisely controlled. The overall hot rolling of the composite ingot promotes the atomic diffusion at the interface of the brazing layer, barrier layer and core layer, so that the layers are tightly bonded and the phenomenon of interlayer isolation during use is reduced. Subsequent cold rolling and annealing eliminates work hardening and releases internal stress, so that the strip has good plasticity and uniform structure.

[0009] Preferably, step S1, the melting and casting specifically includes the following steps: At a temperature of 760-780℃, add the corresponding alloy and stir for 20-30 minutes. Then, refine and degas at a temperature of 750-760℃ for 20-30 minutes until the hydrogen content of the liquid aluminum water is ≤0.15ml / 100gAl. Then, cast at a temperature of 670-700℃ with a casting speed of 30-50mm / min, a water flow of 2900-3000L / min, and a water temperature ≤30℃.

[0010] By adopting the above technical solution, melting and stirring at a temperature of 760-780℃ allows alloying elements to dissolve uniformly in the aluminum matrix, reducing the phenomenon of component segregation leading to uneven local properties. Refining and degassing at a temperature of 750-760℃ to a limited hydrogen content can effectively remove hydrogen and inclusions from the melt, reducing defects such as porosity and looseness in the ingot, thereby improving the density of the ingot and further improving the quality of the aluminum alloy plates and strips subsequently prepared.

[0011] Preferably, in step S3, the temperature of the brazing layer and the barrier layer after milling is 520-540℃ during the heat treatment, and the holding time is 10-14h.

[0012] By adopting the above technical solution, and optimizing the heating temperature and holding time within the above range, the brazing layer and barrier layer ingots can achieve complete recrystallization, thereby reducing the casting stress of the ingots, improving the plasticity and ductility of the ingots, reducing cracking and other phenomena in the subsequent hot rolling process, and ensuring uniform deformation and improved stability of the ingots in the subsequent hot rolling process.

[0013] Preferably, in step S3, the pressure during the hot rolling step is 900-1300t.

[0014] By adopting the above technical solution, and optimizing the pressure during hot rolling within the above range, the brazing layer and barrier layer ingots can achieve effective plastic deformation and densification under the synergistic effect of temperature. The ingots have uniform thickness and good density before and after hot rolling, and have good stability.

[0015] Preferably, in step S5, the temperature for heating and holding the composite ingot is 520-540℃, and the holding time is 10-14h.

[0016] By adopting the above technical solution, the heating and heat preservation time of the composite ingot is preferably within the above range, which makes the microstructure of each layer of the composite ingot fully softened and eliminates the local stress generated during stacking and bundling. For the Al-Si brazing layer, this treatment can promote the spheroidization and passivation of the coarse needle-like silicon phase. The plastic deformation of the brazing layer, barrier layer and core layer is coordinated and consistent during subsequent hot rolling, which reduces the interlayer delamination caused by the difference in deformation of each layer, and promotes atomic diffusion at the interlayer interface, thereby improving the interlayer bonding strength for subsequent hot rolling.

[0017] Preferably, in step S6, the rolling pressure during the cold rolling process is 500-700t.

[0018] By adopting the above technical solution, the pressure of cold rolling is preferably within the above range, the ingot undergoes sufficient and uniform plastic deformation, effectively breaking the casting structure, refining the grains, improving the surface flatness and density of the strip, and preventing microcracks from forming in the strip due to excessive deformation. At the same time, it provides a basis for the uniformity of the structure after subsequent annealing, and avoids uneven thickness of the strip affecting subsequent brazing and use.

[0019] Preferably, in step S6, during the annealing process, the temperature of the roll material is controlled at 360-380℃, and the holding time is 3-5h.

[0020] By adopting the above technical solution, the temperature and time during the annealing process are preferably within the above range, which triggers a full recovery and recrystallization process, reduces cold rolling hardening, and allows the material to be processed to the O state, thus obtaining excellent formability. At the same time, the annealing temperature is lower than the temperature at which reinforcing phases such as Mg2Si dissolve in large quantities, which can retain some fine pre-precipitated atomic clusters and make the temperature inside and outside the coil uniform, thereby improving the internal stability.

[0021] Preferably, in step S6, the annealing process is carried out under a nitrogen protective atmosphere throughout.

[0022] By adopting the above technical solution, annealing is carried out under nitrogen conditions to prevent the residual cold rolling oil from combining with oxygen at high temperature and oxidizing to form yellow or black oil spots, which would affect the surface quality. The final product has good density and strength.

[0023] In summary, this application includes at least one of the following beneficial technical effects: By designing a modified alloy as the core layer, then composite barrier layers on both sides of the core layer, and attaching a brazing layer on the outside, and precisely controlling the ratio of each element in the core layer, the material has high strength potential and good formability. The barrier layer effectively inhibits the volatilization of Mg in the core layer during the carrier gas brazing process, so that the high-strength potential alloy can be stably applied to low-cost and high-efficiency carrier gas brazing. By first milling, heating, and hot rolling the brazing layer and barrier layer separately, then hot rolling them together with the core layer, and then cold rolling and annealing, the optimization of the structure of each layer and the diffusion of interface atoms are ensured, the interlayer is more solid, the risk of delamination is reduced, and finally high-quality strip is obtained. By precisely controlling a series of key process parameters such as the hydrogen content in the casting, the heating temperature and time at each stage, the hot rolling and cold rolling pressure, and the annealing atmosphere, the purity and density of the ingot are systematically improved, the hot working plasticity of the material is improved, the microstructure is refined, and the thickness accuracy and surface quality of the product are guaranteed. This ensures high consistency of the final aluminum alloy sheet and strip performance, high yield, and excellent brazing compatibility. Detailed Implementation

[0024] The present application will be further described in detail below with reference to the embodiments: Raw material description: All raw materials used in the examples are commercially available; Example 1

[0025] Prepare each raw material component according to the formula: Barrier layer: 3003 aluminum alloy; Core layer: Mg: 0.8wt%, Si: 0.8wt%, Cu: 0.5wt%, Mn: 0.2wt%, Ti: 0.01wt%, balance being unavoidable impurities and Al.

[0026] Brazing layer: 4343 aluminum alloy; Preparation of age-hardening aluminum alloy sheets and strips for carrier gas brazing: S1. The materials of the brazing layer, core layer and barrier layer are melted and cast separately according to the proportion. The melting and casting temperature is 760℃. After adding the corresponding intermediate alloy of each material, stir for 30 minutes. Then, refine and degas at 750℃ for 30 minutes until the hydrogen content of liquid aluminum water is ≤0.15ml / 100gAl. Cast the refined system at 670℃ with a casting speed of 50mm / min, a water flow rate of 2900L / min and a water temperature ≤30℃. After casting, saw off 150mm from the gate of the ingot to obtain the brazing layer ingot, the core layer ingot and the barrier layer ingot respectively. S2. Mill the surfaces of the brazing layer ingot, the core layer ingot, and the barrier layer ingot respectively. The milling amount of the two large surfaces of each ingot is 7.5mm / surface, resulting in a brazing layer ingot with a thickness of 380mm, a core layer ingot with a thickness of 365mm, and a barrier layer ingot with a thickness of 380mm after milling. S3. Heat-treat the milled brazed layer ingot and the milled barrier layer ingot at a temperature of 520℃ for 14 hours. Then remove them from the furnace and hot-roll the heat-treated brazed layer ingot and the heat-treated barrier layer ingot respectively. Roll the brazed layer ingot to 45mm and the barrier layer ingot to 42mm and 65mm respectively. Then cut them to the required length and store them for natural cooling to obtain brazed layer skin, barrier layer A skin and barrier layer B skin. S4. Grind the two large surfaces of the milled core layer ingot, clean it after grinding, and obtain the processed core layer ingot. Stack the brazing layer skin, barrier layer A skin, processed core layer ingot, and barrier layer B skin in sequence, and tie them with steel straps at both ends to obtain a four-layer composite ingot. S5. The composite ingot is heated to 520℃ and held for 14 hours. Then it is taken out of the furnace and rolled into an aluminum coil billet with a thickness of 6.5mm by a hot rolling mill with a hot rolling pressure of 900t. S6. The aluminum coil blank is cold rolled by a cold rolling mill at a pressure of 500t. The coil is rolled in passes of 6.5-4.2-2.8-1.9-1.3-1.0mm. After rolling, the edge cracks and burrs are removed by a rewinding and trimming machine. The width of each trimmed edge is 50mm. Finally, the coil is annealed to the O state in an annealing furnace at a temperature of 360℃ for 5 hours. Nitrogen protection is used throughout the annealing process. After exiting the furnace, the coil is naturally cooled to room temperature and then cut by a slitting machine to obtain age-strengthened aluminum alloy strips for carrier gas brazing.

[0027] The age-strengthened aluminum alloy strip structure used for carrier gas brazing consists of, from top to bottom: a brazing layer with a thickness of 9%, a barrier layer A with a thickness of 10%, a core layer with a thickness of 71%, and a barrier layer B with a thickness of 10%. Example 2

[0028] Prepare each raw material component according to the formula: Barrier layer: 3003 aluminum alloy; Core layer: Mg: 1.3wt%, Si: 1.3wt%, Cu: 0.8wt%, Mn: 0.5wt%, Ti: 0.05wt%, balance being unavoidable impurities and Al.

[0029] Brazing layer: 4045 aluminum alloy; Preparation of age-hardening aluminum alloy sheets and strips for carrier gas brazing: S1. The materials of the brazing layer, core layer and barrier layer are melted and cast separately according to the proportion. The melting and casting temperature is 780℃. After adding the corresponding intermediate alloy of each material, stir for 20 minutes. Then, refine and degas at 760℃ for 20 minutes until the hydrogen content of liquid aluminum water is ≤0.15ml / 100gAl. Cast the refined system at 700℃ with a casting speed of 30mm / min, a water flow rate of 3000L / min and a water temperature ≤30℃. After casting, saw off 200mm of the gate of the ingot to obtain the brazing layer ingot, the core layer ingot and the barrier layer ingot respectively. S2. Mill the surfaces of the brazing layer ingot, the core layer ingot, and the barrier layer ingot respectively. The milling amount of the two large surfaces of each ingot is 10mm / surface, to obtain a brazing layer ingot with a thickness of 390mm, a core layer ingot with a thickness of 375mm, and a barrier layer ingot with a thickness of 390mm after milling. S3. Heat the milled brazed layer ingot and the milled barrier layer ingot to a temperature of 540℃ and a holding time of 10h. Then remove them from the furnace and hot roll the heat-treated brazed layer ingot and the heat-treated barrier layer ingot respectively. Roll the brazed layer ingot to 50mm and the barrier layer ingot to 46mm and 70mm respectively. Then cut them to the required length and store them for natural cooling to obtain brazed layer skin, barrier layer A skin and barrier layer B skin. S4. Grind the two large surfaces of the milled core layer ingot, clean it after grinding, and obtain the processed core layer ingot. Stack the brazing layer skin, barrier layer A skin, processed core layer ingot, and barrier layer B skin in sequence, and tie them with steel straps at both ends to obtain a four-layer composite ingot. S5. The composite ingot is heated to 540℃ and held for 10 hours. Then it is taken out of the furnace and rolled into an aluminum coil billet with a thickness of 6.5mm by a hot rolling mill with a hot rolling pressure of 1300t. S6. The aluminum coil blank is cold rolled by a cold rolling mill at a pressure of 700t. The coil is rolled in passes of 6.5-4.2-2.8-1.9-1.3-1.0mm. After rolling, the edge cracks and burrs are removed by a rewinding and trimming machine. The width of each trimmed edge is 80mm. Finally, the coil is annealed to the O state in an annealing furnace at a temperature of 380℃ for 3 hours. Nitrogen protection is used throughout the annealing process. After exiting the furnace, the coil is naturally cooled to room temperature and then cut by a slitting machine to obtain age-strengthened aluminum alloy strips for carrier gas brazing.

[0030] The age-strengthened aluminum alloy strip structure used for carrier gas brazing consists of, from top to bottom: a brazing layer with a thickness of 11%, a barrier layer A with a thickness of 6%, a core layer with a thickness of 69%, and a barrier layer B with a thickness of 14%. Example 3

[0031] Prepare each raw material component according to the formula: Barrier layer: 3003 aluminum alloy; Core layer: Mg: 1.05wt%, Si: 1.05wt%, Cu: 0.65wt%, Mn: 0.35wt%, Ti: 0.03wt%, balance being unavoidable impurities and Al.

[0032] Brazing layer: 4343 aluminum alloy; Preparation of age-hardening aluminum alloy sheets and strips for carrier gas brazing: S1. The materials of the brazing layer, core layer and barrier layer are melted and cast separately according to the proportion. The melting and casting temperature is 770℃. After adding the corresponding intermediate alloy of each material, stir for 25 minutes. Then, refine and degas at 755℃ for 25 minutes until the hydrogen content of liquid aluminum water is ≤0.15ml / 100gAl. Cast the refined system at 685℃ with a casting speed of 40mm / min, a water flow rate of 2950L / min and a water temperature ≤30℃. After casting, saw off 200mm of the gate of the ingot to obtain the brazing layer ingot, the core layer ingot and the barrier layer ingot respectively. S2. Mill the surfaces of the brazing layer ingot, the core layer ingot, and the barrier layer ingot respectively. The milling amount of the two large surfaces of each ingot is 8.75mm / surface, resulting in a brazing layer ingot with a thickness of 390mm, a core layer ingot with a thickness of 375mm, and a barrier layer ingot with a thickness of 390mm after milling. S3. Heat-treat the milled brazed layer ingot and the milled barrier layer ingot to a temperature of 530℃ and a holding time of 12h. Then remove them from the furnace and hot-roll the heat-treated brazed layer ingot and the heat-treated barrier layer ingot respectively. Roll the brazed layer ingot to 47.5mm and the barrier layer ingot to 44mm and 69mm respectively. Then cut them to the required length and store them for natural cooling to obtain brazed layer skin, barrier layer A skin and barrier layer B skin. S4. Grind the two large surfaces of the milled core layer ingot, clean it after grinding, and obtain the processed core layer ingot. Stack the brazing layer skin, barrier layer A skin, processed core layer ingot, and barrier layer B skin in sequence, and tie them with steel straps at both ends to obtain a four-layer composite ingot. S5. The composite ingot is heated to 530℃ and held for 12 hours. Then it is taken out of the furnace and rolled into an aluminum coil billet with a thickness of 6.5mm by a hot rolling mill with a hot rolling pressure of 1100t. S6. The aluminum coil blank is cold rolled by a cold rolling mill at a pressure of 600t. The coil is rolled in passes of 6.5-4.2-2.8-1.9-1.3-1.0mm. After rolling, the edge cracks and burrs are removed by a rewinding and trimming machine. The width of each trimmed edge is 65mm. Finally, the coil is annealed to the O state in an annealing furnace at a temperature of 370℃ for 4 hours. Nitrogen protection is used throughout the annealing process. After exiting the furnace, the coil is naturally cooled to room temperature and then cut by a slitting machine to obtain age-strengthened aluminum alloy strips for carrier gas brazing.

[0033] The age-strengthened aluminum alloy strip structure used for carrier gas brazing consists of, from top to bottom: a brazing layer with a thickness of 10%, a barrier layer A with a thickness of 8%, a core layer with a thickness of 70%, and a barrier layer B with a thickness of 12%. Example 4

[0034] Example 4 is based on Example 3. The difference between Example 4 and Example 3 is that the Si content in the core layer of Example 4 is 0.5wt%. Example 5

[0035] Example 5 is based on Example 3. The difference between Example 5 and Example 3 is that the Si content in the core layer of Example 5 is 1.6 wt%. Example 6

[0036] Example 6 is based on Example 3. The difference between Example 6 and Example 3 is that the Ti content in the core layer of Example 6 is 0.08 wt%. Example 7

[0037] Example 7 is based on Example 3. The difference between Example 7 and Example 3 is that the content of Mn in the core layer in Example 7 is 0.01wt%. Example 8

[0038] Example 8 is based on Example 3. The difference between Example 8 and Example 3 is that the content of Mn in the core layer in Example 8 is 0.8 wt%. Example 9

[0039] Example 9 is based on Example 3. The difference between Example 9 and Example 3 is that the melting temperature in step S1 of Example 8 is 730°C. Example 10

[0040] Example 10 is based on Example 3. The difference between Example 10 and Example 3 is that the melting temperature in step S1 of Example 10 is 810°C. Example 11

[0041] Example 11 is based on Example 3. The difference between Example 11 and Example 3 is that in step S1 of Example 11, the refining and degassing temperature is 720°C. Example 12

[0042] Example 12 is based on Example 3. The difference between Example 12 and Example 3 is that in step S1 of Example 12, the refining and degassing temperature is 780°C. Example 13

[0043] Example 13 is based on Example 3. The difference between Example 13 and Example 3 is that in step S1 of Example 13, the hydrogen content of the liquid aluminum water for refining and degassing is 18 ml / 100 g Al. Example 14

[0044] Example 14 is based on Example 3. The difference between Example 14 and Example 3 is that in step S1 of Example 14, the casting temperature is 650°C. Example 15

[0045] Example 15 is based on Example 3. The difference between Example 15 and Example 3 is that in step S1 of Example 15, the casting temperature is 720°C. Example 16

[0046] Example 16 is based on Example 3. The difference between Example 16 and Example 3 is that in step S3 of Example 16, the heat treatment temperature is 500°C. Example 17

[0047] Example 17 is based on Example 3. The difference between Example 17 and Example 3 is that in step S3 of Example 17, the temperature of the heat treatment is 560°C. Example 18

[0048] Example 18 is based on Example 3. The difference between Example 18 and Example 3 is that in step S5 of Example 18, the hot rolling pressure is 750t. Example 19

[0049] Example 19 is based on Example 3. The difference between Example 19 and Example 3 is that in step S5 of Example 19, the hot rolling pressure is 1450t. Example 20

[0050] Example 20 is based on Example 3. The difference between Example 20 and Example 3 is that in step S5 of Example 20, the temperature of the composite ingot heating and heat preservation treatment is 500°C. Example 21

[0051] Example 21 is based on Example 3. The difference between Example 21 and Example 3 is that in step S5 of Example 21, the temperature of the composite ingot heating and heat preservation treatment is 560°C. Example 22

[0052] Example 22 is based on Example 3. The difference between Example 22 and Example 3 is that in step S6 of Example 22, the cold rolling pressure is 400t. Example 23

[0053] Example 23 is based on Example 3. The difference between Example 23 and Example 3 is that in step S6 of Example 23, the cold rolling pressure is 800t. Example 24

[0054] Example 24 is based on Example 3. The difference between Example 24 and Example 3 is that in step S6 of Example 24, the annealing temperature is 330°C. Example 25

[0055] Example 25 is based on Example 3. The difference between Example 25 and Example 3 is that in step S6 of Example 25, the annealing temperature is 410°C.

[0056] Comparative Example 1 Comparative Example 1 is based on Example 3, but no Ti was added to the core layer of Comparative Example 1.

[0057] Comparative Example 2 Comparative Example 2 is based on Example 3, but no Mn was added to the core layer of Comparative Example 2.

[0058] Performance testing The following performance tests were performed on the samples from Examples 1-25 and Comparative Examples 1-2: (1) Density Using GB / T 5163-2018 as the testing reference, the density of the samples was tested. A block sample of 10mm×10mm×1.0mm was cut from the effective area of ​​the aluminum alloy strip. The sample surface was free of cracks, burrs, scratches and oxide scale. The edges of the sample were sanded until there were no sharp corners. After ultrasonic cleaning, the sample was dried to constant weight to ensure that there was no residual moisture or impurities on the sample surface. The actual density was determined by Archimedes' water displacement method. The density was calculated by combining the theoretical density of the core alloy. Each sample was tested 3 times and the average value was taken. The test results were filled in Table 1.

[0059] (2) Pre-welding strength Using GB / T 228.1-2021 as the testing reference, a 25mm × 6mm thin plate tensile specimen was cut. The electronic universal testing machine was adjusted to normal working condition, the test environment was set to 25℃, the tensile rate was 2mm / min, the testing machine was started, and the tensile test was carried out until the specimen broke. The maximum force (F0) displayed by the testing machine was recorded. The tensile strength was calculated according to the formula: R = F0 / S0 (S0 is the original cross-sectional area of ​​the gauge section of the specimen, S0 = gauge section width × plate thickness). Each specimen was tested 5 times, and the average value was taken as the final pre-weld strength result and filled in Table 1.

[0060] (3) Post-weld strength Using GB / T 13679-2008 as the testing reference, and in conjunction with GB / T 228.1-2021, the room temperature tensile strength of the brazed strip was determined. Each sample was tested 5 times, and the average value was recorded in Table 1.

[0061] Table 1 Performance test results of Examples 1-25 and Comparative Examples 1-2

[0062] As shown in Table 1, the density of Examples 1-3 is 99.2% or higher, the pre-weld strength is 174 MPa or higher, and the post-weld strength is 252 MPa or higher, indicating that the aluminum alloy strips prepared in this application have good density, pre-weld strength, and post-weld strength.

[0063] The core layer Si content in Examples 4 and 5 deviates. When the Si content is too low, it is difficult to form a sufficient amount of Mg2Si strengthening phase, which weakens the aging strengthening potential of the material and reduces the strength after brazing. When the Si content is too high, too much Si will form a coarse silicon phase, which affects the stability of the material.

[0064] Example 6: The Ti content in the core layer is too high. Excessive Ti will form coarse and brittle TiAl3 phase particles, which will become the origin of cracks during rolling, impairing the rollability and ductility of the plate and reducing the stability of the system.

[0065] The content of Mn in the core layer of Examples 7 and 8 deviates. When Mn is insufficient, the effect of grain refinement and inhibition of recrystallization is weak. During hot rolling and annealing, the grains are prone to grow, the material strength decreases, and the uniformity of the structure deteriorates. When Mn is excessive, coarse Mn-containing dispersed phases are formed, which affects the ductility, interferes with the precipitation of Mg2Si, and reduces the stability.

[0066] The melting and casting temperatures in Examples 9 and 10 deviated. When the melting and casting temperature was too low, the alloying elements could not be fully dissolved and diffused, resulting in poor melt fluidity and reduced uniformity of each component, which led to a decrease in the density and uniformity of the prepared ingot. When the melting and casting temperature was too high, the melt was oxidized and burned off, and the ingot contained porosity and inclusions, resulting in a decrease in product quality.

[0067] The refining and degassing temperatures in Examples 11 and 12 differed. When the refining temperature was too low, the melt viscosity was too high, making it difficult for the refining gas to float and reducing the degassing effect. When the refining temperature was too high, the melt oxidized and Mg was damaged, which changed the actual composition of the core layer and affected the product quality.

[0068] In Example 13, the liquid aluminum water used for refining and degassing had an excessively high hydrogen content. This high hydrogen content precipitated during casting solidification, forming more micropores and reducing the quality of the ingot.

[0069] The casting temperatures in Examples 14 and 15 deviated. When the casting temperature was too low, the fluidity of the melt decreased sharply, resulting in defects such as cold shuts and incomplete pouring during the casting process. The ingot was also shrinkage-prone and had poor density. When the casting temperature was too high, solidification was slow, the grains were coarse, and the tendency for hot cracking increased, resulting in a decrease in the quality of the prepared product.

[0070] The heating temperatures in step S3 of Examples 16 and 17 deviate from each other. When the heating temperature is too low, the non-equilibrium eutectic phase and dendritic segregation in the ingot are difficult to dissolve and diffuse fully, resulting in incomplete homogenization of the microstructure and a decrease in interlayer bonding strength. When the heating temperature is too high, the plasticity of the material is damaged, and cracking occurs in the subsequent rolling process.

[0071] In Examples 18 and 19, the pressure deviates during hot rolling. When the hot rolling pressure is insufficient, it is difficult to achieve sufficient plastic deformation of the ingot to break up the coarse casting structure, resulting in poor densification and the presence of unwelded micropores inside the plate. When the hot rolling pressure is too high, although the deformation is sufficient, it will lead to local overheating, a decrease in system quality, and a decrease in stability.

[0072] In Examples 20 and 21, the heating and heat preservation temperatures in step S5 deviate. When the temperature is too low, the metal layers are difficult to soften sufficiently, the atomic diffusion dynamics at the interface are insufficient, the bonding strength of the hot-rolled composite layers decreases, and interlayer separation occurs subsequently. When the temperature is too high, the brazing layer structure is damaged, and the diffusion of Mg elements from the core layer to the surface is aggravated, weakening the barrier layer effect.

[0073] In Examples 22 and 23, the cold rolling pressure deviates in step S6. When the cold rolling pressure is too low, the introduced deformation energy storage step results in insufficient recrystallization of the O-state material after subsequent annealing, leading to coarse grains and insufficient nucleation sites for subsequent aging, thus affecting the aging strengthening effect. When the cold rolling pressure is too high, the work hardening is too severe, resulting in decreased plasticity and poor formability.

[0074] In step S6 of Examples 24 and 25, the annealing temperature deviates. When the annealing temperature is too low, it is difficult to complete recrystallization, the cold rolling hardening is not fully eliminated, the material does not reach the true O state, the formability is poor, and the product has low aging strengthening efficiency. When the annealing temperature is too high, it is close to the temperature at which the strengthening phases such as Mg2Si are significantly dissolved, which consumes the aging strengthening potential.

[0075] In Comparative Example 1, no Ti was added to the core layer, resulting in a significant decrease in grain refinement. The as-cast grains were coarse, which also had an adverse effect on the plastic deformation of the material, reduced formability, affected the stability of the microstructure, and decreased overall performance.

[0076] In Comparative Example 2, no Mn was added to the core layer. During annealing, the material underwent complete recrystallization and grain growth, making it difficult to obtain a stable microstructure with fine structure and a large number of substructures. This weakened the matrix strength and affected the microstructure stability of the material at the high temperature of brazing, resulting in a decline in product quality.

[0077] This specific embodiment is merely an explanation of this application and is not intended to limit it. Based on the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of this application. The technical scope of this application is not limited to the contents of the specification but must be determined according to the scope of the claims.

Claims

1. An age-hardening aluminum alloy sheet / strip for carrier gas brazing, characterized in that: The core layer comprises a brazing layer, a core layer, and barrier layers A and B located on both sides of the core layer. By mass percentage, the core layer comprises the following components: Mg: 0.8-1.3wt%, Si: 0.8-1.3wt%, Cu: 0.5-0.8wt%, Mn: 0.2-0.5wt%, Ti: 0.01-0.05wt%, balance being Al and unavoidable impurities; The thickness of the brazing layer accounts for 9-11% of the total thickness of the strip, the thickness of the barrier layer A accounts for 6-10% of the total thickness of the strip, the thickness of the barrier layer B accounts for 10-14% of the total thickness of the strip, and the remaining thickness is the core layer.

2. A method for preparing age-strengthened aluminum alloy strips and plates for use in the carrier gas brazing process described in claim 1, characterized in that: Includes the following steps: S1. Melting and casting: The materials of the brazing layer, core layer and barrier layer are melted and cast according to the proportions to obtain brazing layer ingot, core layer ingot and barrier layer ingot respectively. S2. Mill the brazing layer ingot, core layer ingot and barrier layer ingot respectively to obtain the milled brazing layer ingot, the milled core layer ingot and the milled barrier layer ingot. S3. Heat-treat the brazed layer ingot and the barrier layer ingot after milling, then hot-roll the heat-treated brazed layer ingot and the heat-treated barrier layer ingot respectively, shear and cool to obtain brazed layer skin material, barrier layer A skin material and barrier layer B skin material. S4. Grind and clean the milled core layer ingot to obtain the treated core layer ingot. Stack the brazing layer skin, barrier layer A skin, treated core layer ingot, and barrier layer B skin in sequence and bundle them to obtain the composite ingot. S5. The composite ingot is heated and kept warm, and then hot rolled to obtain aluminum coil blanks. S6. The aluminum coil blank is rolled by a cold rolling mill. After rolling, cracks and burrs are removed. Finally, the coil is annealed in an annealing furnace, cooled and cut to obtain age-strengthened aluminum alloy sheet and strip for carrier gas brazing.

3. The method for preparing age-strengthened aluminum alloy strips for carrier gas brazing according to claim 2, characterized in that: In step S1, the melting and casting specifically includes the following steps: At a temperature of 760-780℃, add the corresponding alloy and stir for 20-30 minutes. Then, refine and degas at a temperature of 750-760℃ for 20-30 minutes until the hydrogen content of the liquid aluminum water is ≤0.15ml / 100gAl. Then, cast at a temperature of 670-700℃ with a casting speed of 30-50mm / min, a water flow of 2900-3000L / min, and a water temperature ≤30℃.

4. The method for preparing an age-strengthened aluminum alloy sheet / strip for carrier gas brazing according to claim 2, characterized in that: In step S3, the temperature of the brazing layer and the barrier layer after milling is 520-540℃ during the heat treatment, and the holding time is 10-14h.

5. The method for preparing age-strengthened aluminum alloy strips for carrier gas brazing according to claim 2, characterized in that: In step S5, the hot rolling pressure is 900-1300t.

6. The method for preparing an age-strengthened aluminum alloy sheet / strip for carrier gas brazing according to claim 2, characterized in that: In step S5, the temperature for heating and holding the composite ingot is 520-540℃, and the holding time is 10-14h.

7. The method for preparing an age-strengthened aluminum alloy sheet / strip for carrier gas brazing according to claim 2, characterized in that: In step S6, the rolling pressure during the cold rolling process is 500-700t.

8. The method for preparing an age-strengthened aluminum alloy sheet / strip for carrier gas brazing according to claim 2, characterized in that: In step S6, during the annealing process, the temperature of the coil is controlled at 360-380℃, and the holding time is 3-5h.

9. A method for preparing age-strengthened aluminum alloy strips for carrier gas brazing according to claim 2, characterized in that: In step S6, the annealing process is carried out under a nitrogen protective atmosphere throughout.

Images