Aluminum alloy for storage tank and manufacturing method thereof

Abstract

The invention discloses an aluminum alloy for a storage tank, which comprises Al and inevitable impurity elements, and further comprises the following chemical elements in percentage by mass: 0.02 to 0.09 percent of Si, 4.0 to 4.6 percent of Mg, 0.10 to 0.30 percent of Fe, 0.2 to 0.8 percent of Mn, 0.002 to 0.012 percent of Cu and 0.06 to 0.12 percent of Cr. The invention also discloses a manufacturing method of the aluminum alloy for the storage tank, which comprises the following steps: smelting and casting to obtain a cast ingot: the flow of cooling water during casting is 190-2200L / s; milling the surface; heating the cast ingot; rough rolling, wherein the total reduction rate of rough rolling is controlled to be 95% or above; finish rolling; coiling: controlling the coiling temperature to be 350-380 DEG C;

Description

Technical Field

[0001] This invention relates to an aluminum alloy and its manufacturing method, and more particularly to an aluminum alloy for cans and its manufacturing method. Background Technology

[0002] Liquefied natural gas (LNG) tanks often use aluminum alloys for their outer shells, which require flaw detection, hydrostatic testing, and rust prevention processes, thus demanding high product quality.

[0003] Because aluminum alloys are widely used and require high strength, it is necessary to improve the strength of aluminum alloys while keeping production costs low. In existing technologies:

[0004] For example, Chinese patent document CN108977706A, published on December 11, 2018, entitled "An Aluminum Alloy Plate for Liquefied Gas Storage Tanks and Its Preparation Method", discloses a new product for liquefied gas storage tanks. By increasing the Mg content of the alloy, the material strength is improved. In the preparation method, a separate homogenization process is used. Through better control of the homogenization process, the segregation of ingot components is effectively eliminated, the chemical composition is made uniform, and the strength and toughness of the aluminum alloy plate are effectively improved.

[0005] For example, Chinese patent document CN103981411A, published on August 13, 2014, entitled "A Low-Temperature Resistant Aluminum Alloy Profile and Its Preparation Method", discloses a method for producing a low-temperature resistant profile. This aluminum alloy profile has excellent low-temperature resistance, maintaining high strength, plasticity, and toughness even at a low temperature of 20K. It is not prone to cold brittle transition and can be used to manufacture liquid hydrogen and liquid oxygen storage tanks for space shuttles and rocket propulsion systems, as well as structural support components for low-temperature superconducting magnets. Summary of the Invention

[0006] One of the objectives of this invention is to provide an aluminum alloy for storage tanks, which, through material design and process improvements, can ensure the strength and weldability of the aluminum alloy while maintaining its basic properties.

[0007] To achieve the above objectives, the present invention provides an aluminum alloy for storage tanks, which contains Al and unavoidable impurity elements, and further contains the following chemical elements in the following mass percentages:

[0008] Si: 0.02-0.09%, Mg: 4.0-4.6%, Fe: 0.10-0.30%, Mn: 0.2-0.8%, Cu: 0.002-0.012%, Cr: 0.06-0.12%.

[0009] Furthermore, in the aluminum alloy for storage tanks described in this invention, the mass percentage content of each chemical element is as follows:

[0010] Si: 0.02-0.09%, Mg: 4.0-4.6%, Fe: 0.10-0.30%, Mn: 0.2-0.8%, Cu: 0.002-0.012%, Cr: 0.06-0.12%; balance is Al and unavoidable impurity elements.

[0011] The design principles of the chemical composition of the aluminum alloy for storage tanks described in this invention are as follows:

[0012] Si: In the aluminum alloy for storage tanks described in this invention, Si is the main component that improves the flow properties of the aluminum alloy and can greatly improve its casting performance. Adding a certain amount of Si can improve the tensile strength, hardness, and corrosion resistance of the aluminum alloy; however, when the mass percentage content of Si is too high, hard Si-containing particles will appear in the aluminum alloy, leading to increased alloy brittleness and deterioration of weldability. Therefore, in the aluminum alloy for storage tanks described in this invention, in order to improve the weldability of the aluminum alloy, the mass percentage content of Si is controlled between 0.02% and 0.09%.

[0013] Mg: In the aluminum alloy for storage tanks described in this invention, Mg can improve the strength, hardness, heat resistance, corrosion resistance, and machinability of the aluminum alloy. For aluminum alloys used in storage tanks, the strength improvement mainly utilizes the solid solution strengthening effect of Mg. However, hot rolling is required for sheet metal forming, and the resulting Mg₂Si will make the alloy brittle. Therefore, in the aluminum alloy for storage tanks described in this invention, the mass percentage content of Mg is controlled between 4.0% and 4.6%.

[0014] Fe: In the aluminum alloy for storage tanks described in this invention, Fe forms lamellar or acicular structures such as FeAl3, Fe2Al, or α-Al-Si-Fe. Its hard and brittle Fe-rich cathode phase easily segregates at grain boundaries, disrupting the continuity of the microstructure and reducing the material's formability. During welding, this Fe impurity phase also reduces the alloy's fluidity, leading to an increased tendency for weld hot cracking. Therefore, in the aluminum alloy for storage tanks described in this invention, the mass percentage content of Fe is controlled between 0.10% and 0.30%.

[0015] Mn: In the aluminum alloy for storage tanks described in this invention, the limiting solid solubility of Mn in the aluminum matrix is ​​1.82% (658℃). Except for a small amount of Mn dissolved in the matrix, the remainder reacts with Al to form the Al6Mn second phase. At the same content, the strengthening effect of Mn on aluminum alloy is almost twice that of Mg, while ensuring better stability of the alloy. The main optimization effects of Mn on aluminum alloy are: (1) making the β phase precipitate uniformly and improving the stability of the alloy structure; (2) enhancing corrosion resistance and reducing stress corrosion cracking; (3) increasing the recrystallization temperature and preventing grain coarsening; (4) playing a certain solid solution strengthening effect; (5) combining with impurity atoms such as Fe and Si to form Al6(FeMn), Al6(FeMnSi), Al 12 The second phase of (FeMn)3Si counteracts the negative impacts of impurities such as Fe and Si on the alloy. However, when the mass percentage content of Mn is too high, it not only fails to improve the alloy's strength but also significantly reduces its plastic deformation capacity. Furthermore, it readily interacts with Na during hot rolling, leading to "sodium embrittlement." Therefore, in the aluminum alloy for storage tanks described in this invention, to ensure the formability of the sheet metal during processing, the mass percentage content of Mn is controlled between 0.2% and 0.8%.

[0016] Cu: In the aluminum alloy for storage tanks described in this invention, Cu can improve the machinability and grinding properties of the aluminum alloy, and also reduce pitting corrosion. Adding a small amount of Cu can effectively prevent softening of the alloy in the weld heat-affected zone. Furthermore, Cu has a certain solid solution strengthening effect; as the Mg content increases, the limiting solubility of Cu in the Al matrix gradually decreases. When Cu exists in the form of Al2CuMg or Cu2FeAl7 intermetallic compounds, it is beneficial to reduce the tendency for stress corrosion cracking. When the mass percentage content of Cu is too high, it may increase the alloy's susceptibility to stress corrosion and intergranular corrosion. Therefore, in the aluminum alloy for storage tanks described in this invention, to ensure weld quality, the mass percentage content of Cu is controlled between 0.002-0.012%.

[0017] Cr: In the aluminum alloy for storage tanks described in this invention, the Cr element forms (CrFe)Al7(CrMn)Al in the aluminum. 12 Cr is an intermetallic compound. Cr can also inhibit the nucleation and growth process of recrystallization, thus strengthening the alloy and improving its high-temperature performance. In terms of weldability, Cr can also combine with Fe, reducing the harmful effects of Fe impurities, improving the alloy's resistance to stress corrosion, and reducing its tendency to hot cracking. Therefore, in the aluminum alloy for storage tanks described in this invention, the mass percentage content of Cr is controlled between 0.06% and 0.12%.

[0018] Furthermore, in the aluminum alloy for storage tanks described in this invention, the total amount of unavoidable impurity elements is ≤0.15%, and the content of a single impurity is ≤0.05%.

[0019] Furthermore, the microstructure of the aluminum alloy for storage tanks described in this invention comprises a second phase Al6(FeMn), Al6(FeMnSi), and Al... 12 At least one of (FeMn)3Si and (CrFe)Al7.

[0020] In this invention, through compositional design, the added Mn and Cr elements can both suppress the network precipitation of Fe. Mn can combine with Fe to form blocky second phases Al6(FeMn), Al6(FeMnSi), and Al... 12 (FeMn)3Si; Cr combines with Fe to form a second phase (CrFe)Al7, which has the effect of hindering the growth of coarse grains after welding. During smelting, it can be fully combined by SNIF stirring, which can minimize the precipitation of elemental Fe or aluminum-iron phase.

[0021] Furthermore, the mechanical properties of the aluminum alloy for storage tanks described in this invention meet the following requirements: yield strength ≥ 160 MPa, tensile strength ≥ 290 MPa, and elongation ≥ 28%.

[0022] Furthermore, in the aluminum alloy for storage tanks described in this invention, the mechanical properties of the weld obtained after welding meet the following requirements: yield strength ≥ 155 MPa, tensile strength ≥ 295 MPa, and elongation ≥ 28%.

[0023] Another object of the present invention is to provide a method for manufacturing aluminum alloy for storage tanks, which can produce high-strength aluminum alloy plates and strips.

[0024] To achieve the above objectives, the present invention provides a method for manufacturing aluminum alloy for storage tanks, comprising the following steps:

[0025] Melting and casting to obtain ingots: the cooling water flow rate during casting is 190-220 L / s;

[0026] Milling;

[0027] Ingot heating;

[0028] Roughing: Control the total reduction rate of roughing to above 95%;

[0029] Precision rolling;

[0030] Winding: Control the winding temperature to 350-380℃.

[0031] In this invention, controlling the cooling water flow rate during casting to 190–220 L / s allows for rapid solidification of the microstructure. Under high cooling rates, dendrite growth is rapid but its width is controllable. Simultaneously, rapid cooling concentrates impurities and segregation extending to the ingot surface, and combined with milling, minimizes the content of impurities and segregation in the product. During hot rolling, the original grains undergo intense plastic deformation, transforming into flattened, elongated deformed structures. The final rolling process, employing a large reduction, breaks up coarse grains in the ingot and welds casting defects, playing a crucial role in improving the uniformity of hot-rolled products and significantly increasing the strength of hot-rolled aluminum alloy products for storage tanks. Furthermore, the deformation energy stored during rolling drives alloy recrystallization, and the appearance of recrystallized structures and large-angle grain boundaries balances the strength and toughness of the aluminum alloy. Therefore, using the process parameters described in this invention, high-strength finished products of aluminum alloys for storage tanks can be stably produced, and welding performance can be improved.

[0032] Furthermore, the high-temperature winding process of the present invention, i.e., controlling the winding temperature at 350-380°C, can utilize the material's own temperature and the slow heat dissipation effect after winding to generate a "self-annealing" effect. In addition to providing the material with a driving force for recrystallization, high-temperature winding also has the effect of reducing dislocation entanglement, thereby increasing the proportion of recrystallized structure and balancing the material's strength and plasticity.

[0033] Furthermore, in the smelting step of the manufacturing method described in this invention, the smelting temperature is controlled to be 680–750°C.

[0034] In this invention, if the melting temperature is too low, impurities will not be completely removed, and if the melting temperature is too high, the melt will be overburned and oxides will increase. Therefore, in this invention, the melting temperature is controlled at 680-750°C.

[0035] Furthermore, in the ingot heating step of the manufacturing method described in this invention, the ingot heating temperature is controlled at 475-485°C, and the temperature is maintained for 3-6 hours after reaching the set temperature.

[0036] Furthermore, in the roughing step of the manufacturing method described in this invention, 2 to 4 passes of vertical rolls are used before the head and tail are cut off in the roughing, with each pass having a rolling edge amount of 12 to 20 mm.

[0037] In this invention, 2 to 4 passes of vertical rolls are used before the roughing and cutting of the head and tail, and the edge rolling amount of each pass can be controlled to be 12 to 20 mm, which can further ensure that edge cracks do not occur during the rolling process.

[0038] Furthermore, in the roughing step of the manufacturing method described in this invention, the thickness of the intermediate billet obtained by roughing is 16 to 32 mm.

[0039] During the rolling process of this invention, the temperature of the sheet rises due to deformation. At high temperatures, the aluminum alloy sheet is relatively soft. To prevent the sheet from collapsing, the thickness of the intermediate billet can be controlled to be 16.2–32 mm.

[0040] Furthermore, in the winding step of the manufacturing method described in this invention, the winding tension is controlled to be 12-18 N / mm. 2 .

[0041] In this invention, the winding tension can be controlled at a low level to match the winding temperature and avoid scratches on the board surface caused by shrinkage during the hot cooling process.

[0042] The aluminum alloy for storage tanks and its manufacturing method described in this invention have the following characteristics and beneficial effects:

[0043] The aluminum alloy for storage tanks described in this invention, through material design and process improvements, can ensure the strength and weldability of the aluminum alloy while maintaining its basic properties.

[0044] In some embodiments, the mechanical properties of the aluminum alloy for storage tanks described in this invention meet the following requirements: yield strength ≥ 160 MPa, tensile strength ≥ 290 MPa, and elongation ≥ 28%; the mechanical properties of the weld obtained after welding meet the following requirements: yield strength ≥ 155 MPa, tensile strength ≥ 295 MPa, and elongation ≥ 28%.

[0045] The finished aluminum alloy for storage tanks described in this invention can be widely used in cryogenic storage tanks, such as LNG liquid and liquid oxygen. High-strength, low-temperature resistant, and easy-to-weld aluminum plates have a wide range of applications and high economic value.

[0046] The aluminum alloy for storage tanks and its manufacturing method described in this invention are low in cost and energy consumption, require no additional equipment or material consumption, and can produce aluminum alloys for storage tanks with uniform structure and few defects. Attached Figure Description

[0047] Figure 1 A process flow diagram of the manufacturing method of the aluminum alloy for storage tanks described in this invention is shown. Detailed Implementation

[0048] The aluminum alloy for storage tanks and its manufacturing method described in this invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. However, this explanation and description do not constitute an undue limitation on the technical solution of this invention.

[0049] Examples 1-12

[0050] Figure 1 A process flow diagram of the hot rolling step of the present invention is shown.

[0051] For example Figure 1 As shown, the aluminum alloys for storage tanks in Embodiments 1-12 of the present invention are obtained by the following steps:

[0052] (1) Smelting: Argon blowing is used to protect the melt during the smelting process, and the SNIF rotor is run at low speed to reduce the mixing of surface oxide slag into the melt; the smelting temperature is controlled at 680℃~750℃.

[0053] (2) Casting: The cooling water flow rate during casting is 190-220 L / s; in some embodiments, the ingot thickness can be controlled to be 540-640 mm.

[0054] (3) Milling: After the aluminum alloy ingot is removed from the casting machine, milling operation is performed. The milling amount of the side surface (double side) is controlled to be ≥20mm, and the milling amount of the thickness surface (double side) is controlled between 20 and 30mm.

[0055] (4) Ingot heating: First, wipe the ingot: Use D40 to wipe the upper and lower surfaces of each ingot to ensure that there is no oil, aluminum shavings, or dust residue on the ingot surface; The process of ingot heating can be controlled as follows: differential heating to increase the heating rate, the furnace gas temperature can be 535℃, the ingot heating temperature is 475~485℃, the heating time is 3h, and the temperature is maintained for 3~6h after reaching the temperature.

[0056] (5) Rough rolling: To ensure that no edge cracks occur during the rolling process, 2 to 4 passes of vertical rolls are used before the head and tail of the rough rolling. The rolling amount per pass is 12 to 20 mm. The total reduction rate of the rough rolling is controlled at more than 95%. The thickness of the intermediate billet is controlled at 16 to 32 mm. Then it enters the rough rolling mill for reciprocating rolling. During this period, the head and tail of the 120 mm thick intermediate billet are cut off at the heavy shearing, and the head is cut off at the light shearing at the 30 mm thick billet.

[0057] In some implementations, before alloy rolling, the concentration of the rough rolling emulsion needs to be increased for a period of 24 hours, and the plate production is organized to ensure that the emulsion is in a stable emulsion state before rolling.

[0058] (6) Finishing rolling: Control the reduction of each rolling pass to 40-43%, and increase the reduction to 50% in the final rolling pass.

[0059] (7) Winding: The winding process is carried out in a Carrousel winding machine. The winding temperature can be controlled at 350-380℃, and the winding tension can be 12-18 N / mm. 2 .

[0060] Table 1 lists the mass percentage of each chemical element in the aluminum alloys used for storage tanks in Examples 1-12.

[0061] Table 1. (wt%, balance Al)

[0062]

[0063]

[0064] Tables 2-1 and 2-2 list the specific process parameters for manufacturing the aluminum alloys used in the storage tanks of Examples 1-12.

[0065] Table 2-1.

[0066]

[0067]

[0068] Table 2-2.

[0069]

[0070] Sampling was performed on the aluminum alloys used in the storage tanks of Examples 1-12, and their mechanical properties were tested and their microstructure observed. The test results are listed in Table 3. Among them:

[0071] Tensile test: Samples were prepared and tensile tests were performed in accordance with GB / T 228.1-2021 Metallic materials, tensile testing - Part 1: Test at room temperature.

[0072] Microstructure observation: The microstructure of the board was observed using transmission electron microscopy.

[0073] Table 3 lists the performance test results and microstructure observation results of the aluminum alloys used in storage tanks in Examples 1-12.

[0074] Table 3.

[0075]

[0076] As can be seen from Table 3 above, the microstructure of the aluminum alloys for storage tanks in Examples 1-12, prepared by the manufacturing method described in this invention, all possess the second phases Al6(FeMn), Al6(FeMnSi), and Al... 12 The aluminum alloys used in the storage tanks of Examples 1-12 also possess excellent mechanical properties, with yield strengths greater than 160 MPa, tensile strengths greater than 290 MPa, and elongation greater than 28%.

[0077] In addition, the weldability of the aluminum alloys used in the storage tanks of Examples 1-12 was tested using MIG welding with Ar shielding gas and ER5356 welding wire. After welding, the samples were annealed with furnace heating parameters of 3 hours to 420°C and then holding at that temperature for 10 hours. Samples of the welded aluminum alloys used in the storage tanks of Examples 1-12 were taken and their mechanical properties were tested. The results are listed in Table 4.

[0078] in:

[0079] Tensile test: Specimens were prepared and tensile tests were performed according to GB / T 2651-2023 Destructive testing of welds in metallic materials, transverse tensile test method.

[0080] Table 4 lists the test results of the welding performance of the aluminum alloys used in storage tanks in Examples 1-12.

[0081] Table 4.

[0082]

[0083] As can be seen from Table 4 above, the aluminum alloys for storage tanks in Examples 1-12, which are manufactured using the manufacturing method described in this invention, still have excellent mechanical properties after welding. Their yield strength is greater than 155 MPa, their tensile strength is greater than 295 MPa, and their elongation is greater than 28%.

[0084] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0085] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. An aluminum alloy for storage tanks, containing Al and unavoidable impurity elements, characterized in that, It also contains the following chemical elements in the following mass percentages: Si: 0.02-0.09%, Mg: 4.0-4.6%, Fe: 0.10-0.30%, Mn: 0.2-0.8%, Cu: 0.002-0.012%, Cr: 0.06-0.12%.

2. The aluminum alloy for storage tanks as described in claim 1, characterized in that, Its mass percentage content of each chemical element is as follows: Si: 0.02-0.09%, Mg: 4.0-4.6%, Fe: 0.10-0.30%, Mn: 0.2-0.8%, Cu: 0.002-0.012%, Cr: 0.06-0.12%; balance is Al and unavoidable impurity elements.

3. The aluminum alloy for storage tanks as described in claim 1 or 2, characterized in that, The total amount of unavoidable impurity elements is ≤0.15%.

4. The aluminum alloy for storage tanks as described in claim 1 or 2, characterized in that, Its microstructure contains second phases Al6(FeMn), Al6(FeMnSi), and Al 12 At least one of (FeMn)3Si and (CrFe)Al7.

5. The aluminum alloy for storage tanks as described in claim 1 or 2, characterized in that, Its mechanical properties meet the following requirements: yield strength ≥ 160 MPa, tensile strength ≥ 290 MPa, and elongation ≥ 28%.

6. The aluminum alloy for storage tanks as described in claim 1 or 2, characterized in that, The mechanical properties of the weld obtained after welding meet the following requirements: yield strength ≥ 155 MPa, tensile strength ≥ 295 MPa, and elongation ≥ 28%.

7. The method for manufacturing aluminum alloy for storage tanks as described in any one of claims 1-6, characterized in that, Including the following steps: Melting and casting to obtain ingots: the cooling water flow rate during casting is 190-220 L / s; Milling; Ingot heating; Roughing: Control the total reduction rate of roughing to above 95%; Precision rolling; Winding: Control the winding temperature to 350-380℃.

8. The manufacturing method as described in claim 7, characterized in that, During the smelting process, the smelting temperature is controlled at 680–750℃.

9. The manufacturing method as described in claim 7, characterized in that, In the ingot heating process, the ingot heating temperature is controlled at 475-485℃, and the temperature is maintained for 3-6 hours after reaching the set temperature.

10. The manufacturing method as described in claim 7, characterized in that, In the roughing process, 2 to 4 passes of vertical rolls are used before the head and tail of the roughing process, with each pass having a rolling edge allowance of 12 to 20 mm.

11. The manufacturing method as described in claim 7, characterized in that, In the roughing process, the thickness of the intermediate billet obtained by roughing is 16-32 mm.

12. The manufacturing method as described in claim 7, characterized in that, During the winding step, the winding tension is controlled at 12–18 N / mm. 2 .

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