Method for improving corrosion resistance and mechanical properties of 3103 aluminum alloy

Abstract

The present application relates to a kind of method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy, belong to aluminum alloy technical field, to solve the technical problems that the corrosion resistance, mechanical properties and stability of the 3103 aluminum alloy prepared by existing method cannot be considered simultaneously.The method of the present application adds Sm in raw material to carry out melt modification treatment, rare earth Sm forms dispersed AlMnFeSm intermetallic compound, refines α-Al grain, breaks continuous flake Fe / Mn-rich harmful second phase, blocks the corrosion channel of grain boundary, relies on fine-grain strengthening+second phase strengthening to simultaneously improve strength, plasticity and corrosion resistance.Simultaneously, semi-continuous casting process is used, and stage variable-speed casting is used to greatly improve the compactness and uniformity of casting blank, the quality of casting blank is stable, suitable for large-scale continuous industrial production, and the qualified rate of finished product is high, finally the corrosion resistance and mechanical properties of 3103 aluminum alloy are improved.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, and in particular to a method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy. Background Technology

[0002] 3103 aluminum alloy belongs to the aluminum-manganese series of rust-resistant aluminum alloys. It possesses excellent formability, weldability, and moderate corrosion resistance, and its cost is controllable. It is widely used in automotive air conditioning pipes, refrigeration heat exchange profiles, outdoor corrosion-resistant aluminum components, and marine freshwater transportation pipes, making it a core and commonly used aluminum material in civil heat exchange and lightweight corrosion-resistant structural applications. With the rapid upgrading of the new energy vehicle, high-end refrigeration equipment, and lightweight shipbuilding industries, the comprehensive performance requirements of downstream components for 3103 aluminum alloy are continuously increasing. These requirements not only demand excellent plasticity and weldability but also stringent requirements for corrosion resistance, microstructure uniformity, and mechanical stability.

[0003] The existing traditional 3103 aluminum alloy manufacturing process has many technical problems, which seriously restrict the high-end application of the material. First, in the conventional aluminum-manganese alloy smelting process, Mn element is prone to local compositional segregation, and coarse, unevenly distributed primary Al6Mn intermetallic phases are easily formed in the melt. At the same time, Fe and Si impurities are easily enriched to form continuous lamellar iron-rich phases and coarse inclusions, resulting in uneven ingot structure and coarse grains. This directly leads to processing defects such as cracks, peeling, and dimensional deviations during subsequent extrusion and rolling. Second, traditional refining processes mostly use conventional sodium salt refining agents and single-blowing refining mode, which easily introduces harmful impurities such as Na and Ca. These impurities are enriched at grain boundaries, significantly reducing the aluminum alloy's resistance to stress corrosion and pitting corrosion. At the same time, conventional refining cannot effectively remove fine Mn inclusions and dissolved hydrogen, resulting in insufficient melt cleanliness and internal defects such as porosity, gas holes, and microcracks in the ingot. Furthermore, traditional 3103 aluminum alloys lack a precise melt homogenization, gradient purification, and constant temperature casting control system. The parameters for melt stirring, slag removal, filtration, and casting processes are coarse, which easily leads to problems such as secondary oxidation of rare earth elements (when added in small amounts during conventional modification processes), agglomeration of second-phase particles, and increased segregation during ingot solidification. The final product has problems such as poor corrosion resistance, large dispersion of mechanical properties, and insufficient long-term service stability, making it difficult to meet the long-term service requirements of high-end refrigeration, automotive corrosion-resistant components, and lightweight marine parts. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy, addressing the technical problem that existing methods cannot simultaneously achieve good corrosion resistance, mechanical properties, and stability in 3103 aluminum alloy.

[0005] In a first aspect, the present invention provides a method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy, comprising the following steps: S1: According to the chemical composition of the raw materials: select high-purity aluminum ingots, Al-10Mn master alloy, Al-20Si master alloy, Al-10Zr master alloy, Al-5Ti master alloy, Al-10Cr master alloy, and Al-10Sm master alloy. S2: High-purity aluminum ingots, Al-10Mn master alloy, Al-20Si master alloy, Al-10Zr master alloy, Al-5Ti master alloy and Al-10Cr master alloy are heated and melted, and after cooling, Al-10Sm master alloy is added, stirred and modified to obtain a melt. S3: The melt is subjected to argon rotary blowing refining, slag removal and impurity removal in sequence to obtain a high-purity melt; S4: The high-purity melt is transported to a semi-continuous casting crystallizer and cast using stepped variable speed casting to obtain aluminum alloy casting rods; S5: The aluminum alloy casting rod is subjected to high-temperature homogenization treatment, air-cooled to room temperature, and then hot-extruded at low temperature to obtain 3103 aluminum alloy with improved corrosion resistance and mechanical properties.

[0006] Furthermore, the chemical composition of the 3103 aluminum alloy by mass percentage is as follows: Mn 0.60~0.90%, Si 0.10~0.18%, Fe 0.10~0.20%, Cu≤0.05%, Mg≤0.05%, Cr 0.05~0.15%, Zn≤0.05%, Ti 0.05~0.10%, Zr 0.05~0.12%, Sm 0.09~0.28%, single impurity ≤0.02%, total impurities ≤0.10%, balance Al.

[0007] Furthermore, in S2, the temperature for heating and melting is 740~760℃, the temperature for cooling is 710~730℃, and the time for deterioration is 10~20min.

[0008] Furthermore, in S3, the argon flow rate in the argon rotary jet refining process is 7-10 L / min, the rotor speed is 350-500 r / min, and the refining time is 18-22 min.

[0009] Furthermore, in S4, the high-purity melt is precisely temperature-controlled at 710~720℃, and the melt is transported to the semi-continuous casting crystallizer under fully enclosed and heat-preserving conditions.

[0010] Furthermore, in S4, the stepped variable speed casting includes first low-speed buffer casting, then steady-state high-speed forming, and finally low-speed steady flow finishing.

[0011] Furthermore, the low-speed buffer casting speed is 20–40 mm / min, the steady-state high-speed forming speed is 50–100 mm / min, and the low-speed steady-flow finishing speed is 10–25 mm / min.

[0012] Furthermore, in S5, the high-temperature homogenization treatment involves heating to a temperature of 580-620°C at a heating rate of 3-5°C / min and holding at that temperature for 8-10 hours.

[0013] Furthermore, in S5, the low-temperature hot extrusion molding includes: reheating the cast rod to 400~440℃ and holding it at that temperature for 1~2 hours, while simultaneously preheating the extrusion cylinder to 400~410℃ for extrusion molding.

[0014] Furthermore, the extrusion ratio is 10~40, and the extrusion speed is 0.3~1.2 m / min.

[0015] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. The method of this invention involves adding Sm to the raw materials for melt modification treatment. The rare earth Sm forms a dispersed AlMnFeSm intermetallic compound, refining α-Al grains, breaking up continuous flaky Fe / Mn-rich harmful second phases, and blocking grain boundary corrosion channels. Strength, plasticity, and corrosion resistance are simultaneously improved through grain refinement strengthening and second phase strengthening. Simultaneously, a semi-continuous casting process with staged variable-speed casting significantly improves the density and microstructure uniformity of the cast billet, ensuring stable billet quality, adaptability to large-scale continuous industrial production, and a high finished product qualification rate. High-temperature homogenization treatment effectively eliminates casting dendrite segregation, promotes uniform precipitation of rare earth dispersed phases, and spheroidizes coarse iron-rich phases. Low-temperature hot extrusion retains high-density dislocations and fine precipitates, avoiding rare earth phase coarsening, ultimately improving the corrosion resistance and mechanical properties of 3103 aluminum alloy.

[0016] 2. This invention employs a low-speed buffer casting process followed by steady-state uniform molding and a low-speed steady-flow finishing process. This balances molding efficiency with microstructure uniformity. The process involves slow-speed rapid cooling molding through the inner wall of the crystallizer, followed by high-speed molding after the billet separates, and a low-speed steady-flow finishing process. This achieves smooth, layer-by-layer solidification from the outside in, significantly shortening the segregation range of rare earth elements and Mn and Fe elements. It effectively suppresses the formation of continuous lamellar iron-rich phases at grain boundaries and coarse rare earth agglomerates. Finally, the low-speed steady-flow finishing process eliminates shrinkage cavities, porosity, and end-face hot cracks in the ingot. The final product is a Φ80-200 mm cylindrical aluminum alloy ingot with dense grains, uniform composition, and no rare earth agglomeration defects. The defective sections at the beginning and end of the ingot are then removed for later use.

[0017] 3. Under the low-temperature hot extrusion molding conditions of this invention, the temperature inside and outside of the cast ingot can be made uniform, casting segregation can be appropriately eliminated, and the coarsening of the rare earth second phase can be suppressed while ensuring extrusion plasticity, avoiding the risk of overheating. Insufficient holding time will cause uneven billet temperature and residual segregation, while excessive holding time will cause the second phase particles to mature and grow, deteriorating the strengthening effect. Preheating the extrusion cylinder to 400-410℃, slightly lower than the cast ingot temperature, can avoid rapid cooling of the billet surface and stabilize the temperature field in the deformation zone. Excessive cylinder temperature is prone to aluminum adhesion and overheating in the product, and accelerated die wear. Excessive cylinder temperature will increase the extrusion load, and the product is prone to surface tearing and peeling defects.

[0018] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0019] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0020] Figure 1 This is a scanning electron microscope (SEM) image of the aluminum alloy prepared in Example 1 of the present invention; Figure 2 Polarization curves of 3103 aluminum alloys prepared with different amounts of rare earth Sm after electrochemical testing; Figure 3 The image shown is an electron microscope image of the aluminum alloy prepared in Example 1 of this invention. Figure 4 The image shown is an electron microscope image of the aluminum alloy prepared in Example 3 of this invention. Figure 5 This is an electron microscope image of the aluminum alloy prepared in Comparative Example 3 of the present invention. Detailed Implementation

[0021] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0022] A specific embodiment of the present invention discloses a method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy, comprising the following steps: S1: According to the chemical composition of the raw materials: select high-purity aluminum ingots, Al-10Mn master alloy, Al-20Si master alloy, Al-10Zr master alloy, Al-5Ti master alloy, Al-10Cr master alloy, and Al-10Sm master alloy. S2: High-purity aluminum ingots, Al-10Mn master alloy, Al-20Si master alloy, Al-10Zr master alloy, Al-5Ti master alloy and Al-10Cr master alloy are heated and melted, and after cooling, Al-10Sm master alloy is added, stirred and modified to obtain a melt. S3: The melt is subjected to argon rotary blowing refining, slag removal and impurity removal in sequence to obtain a high-purity melt; S4: The high-purity melt is transported to a semi-continuous casting crystallizer and cast using stepped variable speed casting to obtain aluminum alloy casting rods; S5: The aluminum alloy casting rod is subjected to high-temperature homogenization treatment, air-cooled to room temperature, and then hot-extruded at low temperature to obtain 3103 aluminum alloy with improved corrosion resistance and mechanical properties.

[0023] The method of this invention involves adding Sm to the raw materials for melt modification treatment. The rare earth Sm forms a dispersed AlMnFeSm intermetallic compound, refining α-Al grains, breaking up continuous, flaky, Fe / Mn-rich harmful second phases, and blocking grain boundary corrosion channels. Strength, plasticity, and corrosion resistance are simultaneously improved through grain refinement strengthening and second phase strengthening. A semi-continuous casting process with staged variable-speed casting significantly improves the density and uniformity of the billet, resulting in stable billet quality suitable for large-scale continuous industrial production and a high finished product qualification rate. High-temperature homogenization treatment effectively eliminates casting dendrite segregation, promotes uniform precipitation of the rare earth dispersed phase, and spheroidizes coarse, iron-rich phases. Low-temperature hot extrusion retains high-density dislocations and fine precipitates, preventing rare earth phase coarsening, ultimately improving the corrosion resistance and mechanical properties of 3103 aluminum alloy.

[0024] Specifically, the chemical composition of the 3103 aluminum alloy, by mass percentage, is as follows: Mn 0.60~0.90%, for example, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%; Si 0.10~0.18%, for example, 0.10%, 0.12%, 0.14%, 0.16%, 0.18%; Fe 0.10~0.20%, for example, 0.10%, 0.12%, 0.14%, 0.16%, 0.18%, 0.20%; Cu≤0.05%, for example, 0.05%, 0.04%, 0.03%, 0.02%; Mg≤0.05%; Cr 0.05~0.15%, for example, 0.05%, 0.07%, 0.09%, 0.11%, 0.13%, 0.15%; Zn ≤ 0.05%, for example, 0.05%, 0.04%, 0.03%; Ti 0.05~0.10%, for example, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%; Zr 0.05~0.12%, for example, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%; Sm 0.09–0.28%, for example, 0.09%, 0.11%, 0.13%, 0.15%, 0.17%, 0.19%, 0.21%, 0.23%, 0.25%, 0.27%, 0.28%, single impurity ≤0.02%, for example, 0.02%, 0.015%, 0.010%, total impurities ≤0.10%, for example, 0.10%, 0.09%, 0.08%, 0.07%, balance Al.

[0025] In the 3103 aluminum alloy of this invention, the Sm content needs to be controlled between 0.09% and 0.28%. When the Sm addition is less than 0.09%, the grain refinement, microstructure optimization and corrosion resistance improvement effects are insufficient. When the Sm addition is greater than 0.28%, micron-sized coarse rare earth agglomerates are easily generated, which induces microstructural defects and reduces the alloy's plasticity and pitting corrosion resistance.

[0026] Specifically, in S2, the heating and melting temperature is 740~760℃, for example, 740℃, 742℃, 744℃, 746℃, 748℃, 750℃, 752℃, 754℃, 756℃, 758℃, 760℃, and the cooling temperature is 710~730℃, for example, 710℃, 712℃, 714℃, 716℃, 718℃, 720℃, 722℃, 724℃, 726℃, 728℃, 730℃, and the deterioration time is 10~20min, for example, 10min, 12min, 14min, 16min, 18min, 20min.

[0027] Using the cooling temperature described above can ensure the deterioration effect of Sm. Too high a temperature will affect the deterioration of Sm. Too short a deterioration time will easily lead to insufficient deterioration, while too long a time will easily lead to over-deterioration.

[0028] Preferably, in step S2, the stirring is electromagnetic stirring, and the stirring time is 8-12 minutes, for example, 8 minutes, 9 minutes, 10 minutes, 11 minutes, or 12 minutes. Under the above stirring conditions, the primary Al6Mn intermetallic phase in the melt can be uniformly dispersed, effectively suppressing local segregation of Mn elements and achieving preliminary homogenization of the melt composition.

[0029] Adding Sm in the form of Al-10Sm master alloy can avoid rare earth oxidation and burn-off, and ensure uniform and stable composition.

[0030] Specifically, in S3, the argon flow rate in the argon rotary jet refining process is 7-10 L / min, for example, 7 L / min, 7.5 L / min, 8 L / min, 8.5 L / min, 9 L / min, 9.5 L / min, or 10 L / min; the rotor speed is 350-500 r / min, for example, 350 r / min, 370 r / min, 390 r / min, 410 r / min, 430 r / min, 450 r / min, 470 r / min, 490 r / min, or 500 r / min; and the refining time is 18-22 min, for example, 18 min, 19 min, 20 min, 21 min, or 22 min.

[0031] It should be noted that too low an argon flow rate will result in fewer bubbles and poor hydrogen and slag removal, while too high a flow rate will cause the liquid surface to churn and roll up the oxide film, leading to secondary hydrogen absorption. Too low a rotor speed will result in large bubbles, insufficient stirring, and poor degassing, while too high a speed will cause slag and air to be rolled up, resulting in greater rotor wear. Too short a refining time will result in insufficient removal of hydrogen and slag, while too long a refining time will result in secondary hydrogen absorption, a large temperature drop, and low efficiency.

[0032] Preferably, in step S3, a refining agent is added during the refining process. The refining agent accounts for 0.2-0.5% of the total mass of the melt, for example, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or 0.5%. The refining agent is a low-fluorine, sodium-free chloride composite flux, and by mass percentage, the composite flux consists of 47% KCl, 47% MgCl2, and 6% CaF2.

[0033] Specifically, in S3, after refining, the melt is allowed to stand for 30 to 40 minutes, for example, 30 minutes, 32 minutes, 34 minutes, 36 minutes, 38 minutes, or 40 minutes. Gravity stratification allows the oxide slag and inclusions to float to the surface, and the oxide slag floating on the surface of the melt is removed layer by layer.

[0034] Specifically, in S3, the impurity removal process involves first passing the slag-removed melt through a single-stage graphite rotor to complete a secondary hydrogen removal process, and then passing it through a 30 PPI ceramic filter plate.

[0035] It should be noted that the single-stage graphite rotor removes dissolved hydrogen from the melt; then the melt flows through a 30 PPI ceramic filter plate to precisely trap small inclusions in the melt; the ceramic filter plate is preheated by baking at 250-300℃ to prevent new inclusion defects induced by cold material cooling and ensure high cleanliness of the melt.

[0036] Specifically, in S4, the high-purity melt is precisely temperature-controlled at 710~720℃, for example, 710℃, 712℃, 714℃, 716℃, 718℃, and 720℃. The melt is transported to the semi-continuous casting crystallizer under fully enclosed and heat-preserving conditions to prevent secondary oxidation of rare earth elements and agglomeration of second-phase particles.

[0037] Specifically, in S4, the stepped variable speed casting includes first low-speed buffer casting, then steady-state high-speed forming, and finally low-speed steady flow finishing.

[0038] Preferably, the low-speed buffer casting speed is 20–40 mm / min, for example, 20 mm / min, 22 mm / min, 24 mm / min, 26 mm / min, 28 mm / min, 30 mm / min, 32 mm / min, 34 mm / min, 36 mm / min, 38 mm / min, or 40 mm / min; the steady-state high-speed forming speed is 50–100 mm / min, for example, 50 mm / min, 55 mm / min, 60 mm / min, 65 mm / min, 70 mm / min, 75 mm / min, 80 mm / min, 85 mm / min, 90 mm / min, 95 mm / min, or 100 mm / min; and the low-speed steady-flow finishing speed is 10–25 mm / min. mm / min, for example, 10 mm / min, 12 mm / min, 14 mm / min, 16 mm / min, 18 mm / min, 20 mm / min, 22 mm / min, 24 mm / min, 25 mm / min.

[0039] Specifically, in S4, the aluminum alloy casting rod is a cylindrical shape with a diameter of Φ80 to 200 mm (e.g., 80 mm, 90 mm, 100 mm, 110 mm, 120 mm, 130 mm, 140 mm, 150 mm, 160 mm, 170 mm, 180 mm, 190 mm, 200 mm).

[0040] This invention employs a process of initial low-speed buffer casting, followed by steady-state uniform-speed forming, and then a low-speed steady-flow finishing process. This balances forming efficiency with microstructure uniformity. The process involves slow, rapid cooling forming on the inner wall of the crystallizer, followed by high-speed forming after the billet detaches, and then a low-speed steady-flow finishing process. This achieves gradual, layer-by-layer solidification from the outside in, significantly shortening the segregation range of rare earth elements and Mn and Fe elements. It effectively suppresses the formation of continuous lamellar iron-rich phases at grain boundaries and coarse rare earth agglomerates. Finally, the low-speed steady-flow finishing process eliminates shrinkage cavities, porosity, and end-face hot cracks in the ingot. The final product is a Φ80–200 mm cylindrical aluminum alloy ingot with dense grains, uniform composition, and no rare earth agglomeration defects. The defective sections at the beginning and end of the ingot are then removed for later use.

[0041] It should be noted that before casting, the casting container needs to be preheated to eliminate cold inclusion defects. The primary cooling water of the crystallizer and the secondary spray cooling water of the billet should be turned on, and the cooling water pressure should be precisely controlled at 0.08 to 0.15 MPa, for example, 0.08 MPa, 0.09 MPa, 0.10 MPa, 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, and 0.15 MPa.

[0042] Specifically, in S5, the high-temperature homogenization treatment involves heating at a rate of 3~5℃ / min (e.g., 3℃ / min, 3.2℃ / min, 3.4℃ / min, 3.6℃ / min, 3.8℃ / min, 4℃ / min, 4.2℃ / min, 4.4℃ / min, 4.6℃ / min, 4.8℃ / min, 5℃ / min) to a temperature of 580~620℃, e.g., 580℃, 585℃, 590℃, 595℃, 600℃, 605℃, 610℃, 615℃, 620℃, and holding at that temperature for 8~10h, e.g., 8h, 8.2h, 8.4h, 8.6h, 8.8h, 9h, 9.2h, 9.4h, 9.6h, 9.8h, 10h.

[0043] It should be noted that under the above-mentioned homogenization temperature and time, the segregation of casting dendrites can be effectively eliminated, and the uniform precipitation of rare earth dispersed phases and the formation of spheroidized coarse iron-rich phases can be promoted.

[0044] Specifically, in S5, the low-temperature hot extrusion molding includes: reheating the cast rod to 400~440℃ (e.g., 400℃, 405℃, 410℃, 415℃, 420℃, 425℃, 430℃, 435℃, 440℃) and holding it at that temperature for 1~2 hours, e.g., 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, while simultaneously preheating the extrusion cylinder to 400~410℃, e.g., 400℃, 402℃, 404℃, 406℃, 408℃, 410℃, and then performing extrusion molding.

[0045] It should be noted that under the aforementioned low-temperature hot extrusion molding conditions, the temperature inside and outside of the cast ingot can be made uniform, casting segregation can be appropriately eliminated, and the coarsening of the rare earth second phase can be suppressed while ensuring extrusion plasticity, thus avoiding the risk of overheating. Insufficient holding time will cause uneven billet temperature and residual segregation, while excessive holding time will cause the second phase particles to mature and grow, deteriorating the strengthening effect. Preheating the extrusion cylinder to 400-410℃, slightly lower than the cast ingot temperature, can avoid rapid cooling of the billet surface and stabilize the temperature field in the deformation zone. Excessive cylinder temperature can easily lead to aluminum adhesion and overheating in the product, and accelerated die wear; excessively low cylinder temperature will increase the extrusion load, and the product is prone to surface tearing and peeling defects.

[0046] Preferably, the extrusion ratio is 10 to 40, for example, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, and the extrusion speed is 0.3 to 1.2 m / min, for example, 0.3 m / min, 0.4 m / min, 0.5 m / min, 0.6 m / min, 0.7 m / min, 0.8 m / min, 0.9 m / min, 1.0 m / min, 1.1 m / min, 1.2 m / min.

[0047] It should be noted that in this invention, controlling the extrusion ratio between 10 and 40 ensures sufficient deformation, breaks down the as-cast structure and network second phase, and achieves dispersed distribution of rare earth particles. If the extrusion ratio is too small, deformation is insufficient, resulting in poor weldability and lower performance. If the extrusion ratio is too large, deformation heat overload and excessive load can easily lead to cracking and delamination. An extrusion speed of 0.3–1.2 m / min is suitable for the low-temperature extrusion regime of this invention, balancing heat generation and production efficiency. Too low a speed will reduce efficiency and cause coarsening of the second phase; too high a speed will cause instantaneous overheating in the deformation zone, making the product prone to surface tearing and abnormal grain growth.

[0048] Another specific embodiment of the present invention discloses a 3103 aluminum alloy with improved corrosion resistance and mechanical properties prepared by the above method.

[0049] Specifically, in the microstructure of the 3103 aluminum alloy with improved corrosion resistance and mechanical properties, the average grain size is ≤60μm, preferably ≤55μm.

[0050] Another specific embodiment of the present invention discloses an application of the above-mentioned 3103 aluminum alloy, wherein the 3103 aluminum alloy is used for automotive air conditioning extruded pipes, refrigeration heat exchange extruded profiles, outdoor corrosion-resistant extruded aluminum bars, or marine freshwater transportation extruded pipes. The 3103 aluminum alloy has a tensile strength ≥209MPa, an elongation after fracture ≥32.4%, and an electrochemical self-corrosion potential of -1.10~-0.72V.

[0051] The technical solution of the present invention will be further explained below with reference to specific embodiments.

[0052] Example 1 This embodiment describes a 3103 aluminum alloy with improved corrosion resistance and mechanical properties. The chemical composition of the aluminum alloy, by mass percentage, is as follows: Mn 0.72%, Si 0.13%, Fe 0.15%, Cu 0.03%, Mg 0.04%, Zn 0.02%, Cr 0.08%, Ti 0.06%, Zr 0.08%, Sm 0.18%, with a single impurity ≤0.02%, total impurity content ≤0.10%, and the balance being Al.

[0053] The preparation method of 3103 aluminum alloy in this embodiment includes the following steps: S1: According to the chemical composition of the raw materials: select high-purity aluminum ingots, Al-10Mn master alloy, Al-20Si master alloy, Al-10Zr master alloy, Al-5Ti master alloy, Al-10Cr master alloy, and Al-10Sm master alloy. S2: High-purity aluminum ingots, Al-10Mn master alloy, Al-20Si master alloy, Al-10Zr master alloy, Al-5Ti master alloy and Al-10Cr master alloy are heated to 750℃ and melted. After all alloys are completely melted and the melt composition is uniform, the temperature is lowered to 720℃ and Al-10Sm master alloy is added. After adding the materials, the mixture is stirred thoroughly for 8 minutes and kept at a constant temperature for 10 minutes for modification treatment to obtain the melt. S3: The melt is refined by rotary blowing with high-purity argon gas at a flow rate of 8.5 L / min and a rotor speed of 425 r / min for 20 min. After standing for 30 min, the slag on the surface of the melt is removed. The aluminum liquid after slag removal is first passed through a single-stage graphite rotor for secondary hydrogen removal, and then passed through a 30 PPI ceramic filter plate to accurately trap small inclusions in the melt. The ceramic filter plate is preheated to 280℃ to obtain a high-purity melt. S4: The high-purity melt is transported to the semi-continuous casting crystallizer. The primary cooling water of the crystallizer and the secondary spray cooling water of the billet are turned on. The cooling water pressure is precisely controlled at 0.10 MPa. The temperature of the high-purity melt is precisely controlled at 710℃. The casting is first started at a low speed of 30 mm / min, then formed at a high speed of 80 mm / min, and finished at a low speed of 18 mm / min to obtain an aluminum alloy casting rod with a diameter of 120 mm. S5: The aluminum alloy casting rod is heated to 600°C at a heating rate of 4°C / min, held at that temperature for 8 hours for homogenization treatment, air-cooled to room temperature, and then the casting rod is reheated to 420°C and held for 1.5 hours. Simultaneously, the extrusion cylinder temperature is preheated to 400°C. The extrusion ratio is 25, the extrusion speed is 0.6m / min, and after extrusion molding is completed, a Φ24 mm aluminum alloy extruded round tube is obtained.

[0054] Example 2 The chemical composition and preparation method of the 3103 aluminum alloy with improved corrosion resistance and mechanical properties in this embodiment are similar to those in Example 1, except that Sm is 0.09%.

[0055] Example 3 The chemical composition and preparation method of the corrosion-resistant and mechanically improved 3103 aluminum alloy in this embodiment are similar to those in Example 1, except that Sm is 0.28%.

[0056] Example 4 The chemical composition and preparation method of the corrosion-resistant and mechanically improved 3103 aluminum alloy in this embodiment are similar to those in Example 1, except that Sm is 0.15%.

[0057] Example 5 The chemical composition and preparation method of the corrosion-resistant and mechanically improved 3103 aluminum alloy in this embodiment are similar to those in Example 1, except that Sm is 0.20%.

[0058] Example 6 The chemical composition and preparation method of the 3103 aluminum alloy with improved corrosion resistance and mechanical properties in this embodiment are similar to those in Example 1. The difference is that the chemical composition of the aluminum alloy is as follows: Mn 0.6%, Si 0.18%, Fe 0.1%, Cu 0.05%, Mg 0.05%, Zn 0.05%, Cr 0.15%, Ti 0.10%, Zr 0.05%, Sm 0.09%, single impurity ≤0.02%, total impurity content ≤0.10%, and the balance is Al.

[0059] Example 7 The chemical composition and preparation method of the 3103 aluminum alloy with improved corrosion resistance and mechanical properties in this embodiment are similar to those in Example 1. The difference is that the chemical composition of the aluminum alloy is as follows: Mn 0.9%, Si 0.10%, Fe 0.2%, Cu 0.04%, Mg 0.03%, Zn 0.03%, Cr 0.05%, Ti 0.08%, Zr 0.12%, Sm 0.28%, single impurity ≤0.02%, total impurity content ≤0.10%, and the balance is Al.

[0060] Example 8 The chemical composition and preparation method of the 3103 aluminum alloy with improved corrosion resistance and mechanical properties in this embodiment are similar to those in Example 1, except that: In S2, high-purity aluminum ingots, Al-10Mn master alloy, Al-20Si master alloy, Al-10Zr master alloy, Al-5Ti master alloy and Al-10Cr master alloy are heated to 740℃ and melted. After all alloys are completely melted and the melt composition is uniform, the temperature is lowered to 710℃ and Al-10Sm master alloy is added. After adding the materials, the mixture is stirred thoroughly for 10 minutes and held at a constant temperature for 15 minutes for modification treatment to obtain the melt. In S3, the argon flow rate is 7 L / min, the rotor speed is 350 r / min, the refining time is 22 min, and then it is left to stand for 35 min; In S4, the high-purity melt is precisely temperature-controlled at 715℃. It is first started with a low-speed buffer at 20mm / min, then formed at a steady-state high speed of 50mm / min, and finished with a low-speed steady flow at 25mm / min. In step S5, the aluminum alloy casting rod is heated to 580°C at a heating rate of 3°C / min, held at that temperature for 9 hours for homogenization treatment, air-cooled to room temperature, and then reheated to 400°C and held for 1 hour. Simultaneously, the extrusion cylinder temperature is preheated to 405°C, the extrusion ratio is 10, and the extrusion speed is 0.3 m / min.

[0061] Example 9 The chemical composition and preparation method of the 3103 aluminum alloy with improved corrosion resistance and mechanical properties in this embodiment are similar to those in Example 1, except that: In S2, high-purity aluminum ingots, Al-10Mn master alloy, Al-20Si master alloy, Al-10Zr master alloy, Al-5Ti master alloy and Al-10Cr master alloy are heated to 760℃ and melted. After all alloys are completely melted and the melt composition is uniform, the temperature is lowered to 730℃ and Al-10Sm master alloy is added. After adding the materials, the mixture is stirred thoroughly for 12 minutes and held at a constant temperature for 20 minutes for modification treatment to obtain the melt. In S3, the argon flow rate is 10 L / min, the rotor speed is 500 r / min, the refining time is 18 min, and then it is left to stand for 40 min; In S4, the high-purity melt is precisely temperature-controlled at 720℃. It is first started with a low-speed buffer at 40mm / min, then formed at a steady-state high speed of 100mm / min, and finished with a low-speed steady flow at 10mm / min. In step S5, the aluminum alloy casting rod is heated to 620°C at a heating rate of 5°C / min, held at that temperature for 10 hours for homogenization treatment, air-cooled to room temperature, and then reheated to 440°C and held for 2 hours. Simultaneously, the extrusion cylinder temperature is preheated to 410°C, the extrusion ratio is 40, and the extrusion speed is 1.2 m / min.

[0062] Comparative Example 1 The chemical composition and preparation method of the 3103 aluminum alloy with improved corrosion resistance and mechanical properties in this embodiment are similar to those in Example 1, except that Sm is 0.08%.

[0063] Comparative Example 2 The chemical composition and preparation method of the 3103 aluminum alloy with improved corrosion resistance and mechanical properties in this embodiment are similar to those in Example 1, except that Sm is 0.29%.

[0064] Comparative Example 3 The chemical composition and preparation method of the 3103 aluminum alloy with improved corrosion resistance and mechanical properties in this embodiment are similar to those in Example 1, except that Sm is not added.

[0065] Comparative Example 4 The chemical composition and preparation method of the 3103 aluminum alloy with improved corrosion resistance and mechanical properties in this embodiment are similar to those in Example 1. The difference is that in S4, staged variable speed casting is not used, and casting is directly carried out at a speed of 80 mm / min.

[0066] Comparative Example 5 The chemical composition and preparation method of the corrosion-resistant and mechanically improved 3103 aluminum alloy in this embodiment are similar to those in Example 1, except that the high-temperature homogenization temperature in S5 is 650°C.

[0067] Comparative Example 6 The chemical composition and preparation method of the 3103 aluminum alloy with improved corrosion resistance and mechanical properties in this embodiment are similar to those in Example 1, except that the extrusion temperature in S5 is 450°C.

[0068] Experimental Example 1 (1) The tensile strength, elongation after fracture, electrochemical self-corrosion potential and average grain size of the aluminum alloys prepared in the examples and comparative examples were tested respectively, and the results are shown in Table 1.

[0069] Among them, the electrochemical self-corrosion potential test of aluminum alloys was carried out in accordance with GB / T 24196-2009 "Guidelines for the Measurement of Potential Stabilization and Potential Dynamic Polarization Curves of Electrochemical Test Methods for Corrosion of Metals and Alloys".

[0070] The experiment employed a three-electrode testing system, using the aluminum alloy sample as the working electrode, a platinum electrode as the auxiliary electrode, and a saturated calomel electrode as the reference electrode. A 3.5% NaCl aqueous solution was used as the corrosive medium. Corrosion potential data were collected after the sample was immersed until its open-circuit potential stabilized, and the test was conducted at room temperature. Three parallel samples were set up for each group, and outlier data were removed before averaging the results to ensure accuracy and reliability.

[0071] Table 1

[0072] As shown in Table 1, the 3103 aluminum alloy obtained by the method of the present invention has a tensile strength ≥209MPa, an elongation after fracture ≥32.4%, an electrochemical self-corrosion potential of -1.10~-0.72V, and an average grain size ≤55μm.

[0073] Adding an appropriate amount of Sm within the composition range of this invention can significantly optimize the mechanical and corrosion resistance properties of 3103 aluminum alloy and refine the grain structure. Comparative Example 3, without added Sm, has a tensile strength of only 175.4 MPa, an elongation after fracture of only 25.8%, an electrochemical self-corrosion potential as negative as -1.53 ​​V, and an average grain size of 68 μm. All properties are far inferior to the example with added Sm. When the Sm addition amount is within the preferred range of 0.15% to 0.20% of this invention, the tensile strength of 3103 aluminum alloy can stably reach above 230 MPa, the elongation after fracture is not less than 34%, the electrochemical self-corrosion potential is more positive, the corrosion resistance is better, and the average grain size can be controlled within 50 μm, resulting in the best overall performance. If the Sm addition amount is too low (less than 0.09%) or too high (greater than 0.28%), the grain refinement effect is weakened, and both mechanical and corrosion resistance properties will significantly decrease. The performance indicators of Comparative Examples 1 and 2 are inferior to those of the examples.

[0074] The special preparation process employed in this invention has a significant effect on performance improvement. Comparison shows that Comparative Example 4 (which did not use staged variable-speed casting), Comparative Example 5 (whose homogenization temperature deviated from the range of this invention), and Comparative Example 6 (whose extrusion temperature exceeded the preferred range) all exhibited lower tensile strength, elongation after fracture, and corrosion resistance than the embodiments of this invention, and had larger average grain sizes. This demonstrates that the composition design and preparation process of this invention can synergistically achieve grain refinement and second-phase control in 3103 aluminum alloy, ultimately simultaneously improving the alloy's mechanical properties and corrosion resistance, meeting the requirements of different application scenarios.

[0075] (2) The scanning electron microscope microstructure of the aluminum alloy prepared in Example 1 is shown below. Figure 1 As shown, the addition of 0.18% Sm resulted in the formation of fine AlSmFeMn rare earth phases, with the AlFeMn phases becoming significantly finer.

[0076] (3) The polarization curves of 3103 aluminum alloys prepared with different amounts of rare earth Sm after electrochemical testing are shown in the figure. Figure 2 As shown, the electrochemical self-corrosion potential increased significantly after adding 0.18% Sm, which improved the corrosion resistance of the 3103 alloy. Adding 0.09% and 0.28% Sm can also improve its corrosion resistance, but the improvement is relatively small.

[0077] In the figure, 3103 is the aluminum alloy prepared in Comparative Example 3, 3103+0.09Sm is the aluminum alloy prepared in Example 2, 3103+0.18Sm is the aluminum alloy prepared in Example 1, and 3103+0.28Sm is the aluminum alloy prepared in Example 3.

[0078] (4) Electron micrograph of the aluminum alloy prepared in Example 1 is shown below. Figure 3 As shown, the electron microscope image of the aluminum alloy prepared in Example 3 is as follows. Figure 4 As shown, the electron microscope image of the aluminum alloy prepared in Comparative Example 3 is as follows. Figure 5 As shown.

[0079] according to Figure 3 As can be seen, after adding 0.18% Sm, the second phase is evenly distributed and fine. Figure 4 It can be seen that increasing the rare earth Sm content will form large blocky AlSm phases, thereby affecting the corrosion resistance and mechanical properties of the alloy. Figure 5 It can be seen that a dense region of the second phase appears in the microstructure without added Sm. The second phase is unevenly distributed, and the mechanical properties and corrosion resistance of the alloy are significantly reduced.

[0080] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy, characterized in that, Includes the following steps: S1: According to the chemical composition of the raw materials: select high-purity aluminum ingots, Al-10Mn master alloy, Al-20Si master alloy, Al-10Zr master alloy, Al-5Ti master alloy, Al-10Cr master alloy, and Al-10Sm master alloy. S2: High-purity aluminum ingots, Al-10Mn master alloy, Al-20Si master alloy, Al-10Zr master alloy, Al-5Ti master alloy and Al-10Cr master alloy are heated and melted, and after cooling, Al-10Sm master alloy is added, stirred and modified to obtain a melt. S3: The melt is subjected to argon rotary blowing refining, slag removal and impurity removal in sequence to obtain a high-purity melt; S4: The high-purity melt is transported to a semi-continuous casting crystallizer and cast using stepped variable speed casting to obtain aluminum alloy casting rods; S5: The aluminum alloy casting rod is subjected to high-temperature homogenization treatment, air-cooled to room temperature, and then hot-extruded at low temperature to obtain 3103 aluminum alloy with improved corrosion resistance and mechanical properties.

2. The method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy according to claim 1, characterized in that, The 3103 aluminum alloy has the following chemical composition by mass percentage: Mn 0.60~0.90%, Si 0.10~0.18%, Fe 0.10~0.20%, Cu≤0.05%, Mg≤0.05%, Cr 0.05~0.15%, Zn≤0.05%, Ti 0.05~0.10%, Zr 0.05~0.12%, Sm 0.09~0.28%, single impurity ≤0.02%, total impurities ≤0.10%, balance Al.

3. The method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy according to claim 1, characterized in that, In S2, the heating and melting temperature is 740~760℃, the cooling temperature is 710~730℃, and the deterioration time is 10~20min.

4. The method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy according to claim 1, characterized in that, In S3, the argon flow rate in the argon rotary jet refining process is 7-10 L / min, the rotor speed is 350-500 r / min, and the refining time is 18-22 min.

5. A method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy according to any one of claims 1-4, characterized in that, In S4, the high-purity melt is precisely temperature-controlled at 710~720℃, and the melt is transported to the semi-continuous casting crystallizer under fully enclosed and heat-preserving conditions.

6. A method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy according to any one of claims 1-4, characterized in that, In S4, the stepped variable speed casting includes first low-speed buffer casting, then steady-state high-speed forming, and finally low-speed steady flow finishing.

7. The method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy according to claim 6, characterized in that, The low-speed buffer casting speed is 20–40 mm / min, the steady-state high-speed forming speed is 50–100 mm / min, and the low-speed steady-flow finishing speed is 10–25 mm / min.

8. A method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy according to any one of claims 1-4, characterized in that, In S5, the high-temperature homogenization process involves heating the temperature to 580-620°C at a heating rate of 3-5°C / min and holding it at that temperature for 8-10 hours.

9. The method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy according to claim 1, characterized in that, In S5, the low-temperature hot extrusion molding includes: reheating the cast rod to 400~440℃ and holding it at that temperature for 1~2 hours, while simultaneously preheating the extrusion cylinder to 400~410℃ for extrusion molding.

10. The method for improving the corrosion resistance and mechanical properties of 3103 aluminum alloy according to claim 9, characterized in that, The extrusion ratio is 10~40, and the extrusion speed is 0.3~1.2 m / min.

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