Aluminum alloy storage tank forge piece for FLNG and preparation method of aluminum alloy storage tank forge piece

Abstract

The invention provides an aluminum alloy storage tank forge piece for FLNG and a preparation method of the aluminum alloy storage tank forge piece for the FLNG, and the aluminum alloy storage tank forge piece for the FLNG comprises the following chemical components in percentage by mass: less than or equal to 0.20 wt% of Si, less than or equal to 0.20 wt% of Fe, less than or equal to 0.10 wt% of Cu, 0.4-1.0 wt% of Mn, 4.5-4.9 wt% of Mg, 0.05-0.25 wt% of Cr, less than or equal to 0.25 wt% of Zn, less than or equal to 0.15 wt% of Ti and the balance of Al and inevitable impurities. By adjusting the content of chemical elements in the forge piece and optimizing the preparation method, the physical property and stability of the forge piece are improved, meanwhile, forming of the large aluminum alloy cylindrical forge piece is achieved, the material utilization rate is effectively increased, and the production cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of mechanical manufacturing and relates to an aluminum alloy storage tank forging, and in particular to an aluminum alloy storage tank forging for FLNG and a preparation method thereof. Background Art

[0002] With the growth of global demand for liquefied natural gas, the number of FLNG (floating liquefied natural gas) projects continues to increase, and the demand for high-quality, high-performance large-scale aluminum alloy storage tank forgings has also increased. Especially in the pursuit of energy conservation and emission reduction and optimization of spatial layout in modern offshore oil and gas development, aluminum alloy storage tanks are favored because of their light weight and high efficiency. Enterprises that can successfully develop and manufacture large aluminum alloy storage tank forgings for FLNG will gain a competitive advantage in the international market, especially in the field of high-end offshore equipment manufacturing, which will help Chinese companies enhance their position in the global industrial chain and strive for more international cooperation opportunities. With the introduction of attention and support for the development of clean energy and marine resources at home and abroad, the research and development of FLNG technology and related supporting equipment has been encouraged and supported, and the market prospects are broad.

[0003] CN 101520127A discloses a liquefied natural gas storage tank for a floating marine structure, which specifically discloses the internal structure of the liquefied natural gas storage tank, but does not disclose a method for preparing the tank forgings. CN 117548606A discloses a method for manufacturing forgings for ultra-high pressure nitrogen storage tanks, comprising the following steps: blanking: using 35CrNi3MoVR forging rounds for blanking; heating: including two firings; in the first firing, the forging rounds are heated from room temperature to 1220-1240°C and kept warm for 4-5 hours; in the second firing, the forging rounds are returned to the furnace for heat preservation, cooled to 1040-1060°C and kept warm for 3 hours; upsetting and drawing: the forging rounds are subjected to at least two upsetting and two drawing, and the processing is completed. Total forging ratio ≥ 8.4; hydrogen annealing after forging; light flaw detection; heat treatment: including normalizing: sending the forging into the furnace, heating to 900-920℃ normalizing, keeping warm for 8-10h, then taking out of the furnace and air cooling to room temperature; quenching: sending the forging into the furnace, heating to 850-870℃ quenching, keeping warm for 8-10h, then taking out of the furnace and water cooling to room temperature; tempering: sending the forging into the furnace, heating to 605-625℃ tempering, keeping warm for 10-12h, then taking out of the furnace and air cooling to room temperature. Although the patent provides a method for manufacturing forgings, the forgings obtained by the papyrus method cannot be applied to FLNG projects.

[0004] Therefore, it is necessary to provide a forging and a preparation method suitable for FLNG projects. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide an aluminum alloy storage tank forging for FLNG and a preparation method thereof. The preparation method provided by the present invention can improve the quality and stability of the forgings, realize the forming of large aluminum alloy cylindrical forgings, effectively improve material utilization, and reduce production costs.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides an aluminum alloy storage tank forging for FLNG, wherein the chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si≤0.20wt%, Fe≤0.20wt%, Cu≤0.10wt%, Mn 0.4~1.0wt%, Mg 4.5~4.9wt%, Cr 0.05~0.25wt%, Zn≤0.25wt%, Ti≤0.15wt%, and the balance is Al and unavoidable impurities.

[0008] Exemplarily, the Si content in the aluminum alloy storage tank forging for FLNG is ≤0.20wt%, for example, it can be 0.20wt%, 0.18wt%, 0.16wt%, 0.14wt%, 0.12wt% or 0.10wt%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0009] The Fe content in the aluminum alloy storage tank forging for FLNG is ≤ 0.20wt%, for example, it can be 0.20wt%, 0.18wt%, 0.16wt%, 0.14wt%, 0.12wt% or 0.10wt%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0010] The Cu content in the FLNG aluminum alloy storage tank forging is ≤0.10wt%, for example, it can be 0.10wt%, 0.08wt%, 0.06wt% or 0.04wt%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0011] The Mn content in the FLNG aluminum alloy storage tank forging is 0.4-1.0wt%, for example, it can be 0.4wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt% or 1.0wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0012] The Mg content in the aluminum alloy storage tank forging for FLNG is 4.5-4.9wt%, for example, it can be 4.5wt%, 4.6wt%, 4.7wt%, 4.8wt% or 4.9wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0013] The Cr content in the aluminum alloy storage tank forging for FLNG is 0.05-0.25wt%, for example, it can be 0.05wt%, 0.09wt%, 0.13wt%, 0.17wt%, 0.21wt% or 0.25wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0014] The Zn content in the aluminum alloy storage tank forging for FLNG is ≤ 0.25wt%, for example, it can be 0.25wt%, 0.24wt%, 0.23wt%, 0.22wt%, 0.21wt% or 0.20wt%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0015] The Ti content in the FLNG aluminum alloy storage tank forging is ≤0.15wt%, for example, it can be 0.15wt%, 0.14wt%, 0.13wt%, 0.12wt%, 0.11wt% or 0.10wt%, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0016] The present invention further improves the physical properties of the FLNG aluminum alloy storage tank forging by adjusting the content of chemical components in the FLNG aluminum alloy storage tank forging;

[0017] More specifically, the element Mg affects the mechanical properties of the aluminum alloy tank forgings for FLNG, especially the tensile strength and yield strength. In addition, the presence of Mg can further enhance the seawater corrosion resistance, making the aluminum alloy forgings very suitable for applications in marine environments, such as hull structures and offshore platforms. An appropriate amount of Mg can also improve the processing properties of the material, including cold formability and weldability;

[0018] The element Si will affect the physical properties of the aluminum alloy tank forging for FLNG. Too high Si content may increase brittleness or reduce the corrosion resistance of the material. A small amount of Si content can also react with Mg to form Mg2Si phase, which helps to enhance the strength of the alloy, but too much Si content will affect the ductility of the material. Therefore, the Si content should not be too high.

[0019] The element Fe is regarded as an impurity element in the aluminum alloy tank forging for FLNG. The presence of Fe is usually due to insufficient purity of the raw materials or contamination during the smelting process. A high content of Fe will form a hard FeAl3 phase in the alloy, which will become a crack initiation point, reduce the plasticity and toughness of the material, and may affect the welding quality. Therefore, the Fe content should not be too high.

[0020] As a preferred technical solution of the present invention, the tensile strength of the aluminum alloy storage tank forging for FLNG is 300-380 MPa, for example, it can be 300 MPa, 310 MPa, 320 MPa, 330 MPa, 340 MPa, 350 MPa, 360 MPa, 370 MPa or 380 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] Preferably, the yield strength of the aluminum alloy storage tank forging for FLNG is 120-200 MPa, for example, it can be 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, 170 MPa or 180 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] Preferably, the elongation of the aluminum alloy storage tank forging for FLNG is 20-30%, for example, it can be 20%, 22%, 24%, 26%, 28% or 30%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0023] In a second aspect, the present invention provides a method for preparing an aluminum alloy storage tank forging for FLNG as provided in the first aspect, the preparation method comprising the following steps:

[0024] (1) preparing materials according to the chemical composition content, and then performing smelting treatment, casting and homogenization treatment in sequence to obtain an aluminum alloy cylindrical ingot;

[0025] (2) subjecting the aluminum alloy cylindrical ingot obtained in step (2) to sequential forming treatment, annealing treatment and air cooling treatment to obtain the aluminum alloy storage tank forging for FLNG;

[0026] The surface temperature of the aluminum alloy columnar ingot during the forming process is controlled to be ≥280°C, for example, it can be 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C or 350°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0027] In the present invention, the aluminum alloy storage tank forging for FLNG is a large cylindrical aluminum alloy forging. Due to its large weight and long length, the process conditions of the forming process need to be strictly controlled to achieve the purpose of increasing material utilization and thus reducing costs.

[0028] In addition, the preparation method provided by the present invention can effectively improve the physical properties of the aluminum alloy storage tank forging, and the preparation method is simple, which is conducive to industrial application.

[0029] As a preferred technical solution of the present invention, the temperature of the smelting treatment in step (1) is 700-750°C, for example, it can be 700°C, 710°C, 720°C, 730°C, 740°C or 750°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the casting temperature in step (1) is 680-720°C, for example, 680°C, 690°C, 700°C, 710°C or 720°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the casting in step (1) also includes a cooling treatment.

[0032] As a preferred technical solution of the present invention, the temperature of the homogenization treatment in step (1) is 450-500°C, for example, it can be 450°C, 460°C, 470°C, 480°C, 490°C or 500°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] Preferably, the heating rate of the homogenization treatment in step (1) is 30 to 50°C / h, for example, 30°C / h, 34°C / h, 38°C / h, 42°C / h, 46°C / h or 50°C / h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] Preferably, the holding time for the homogenization treatment in step (1) is 12 to 24 hours, for example, it can be 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] As a preferred technical solution of the present invention, the forming process in step (2) includes upsetting, punching, hole expansion, mandrel lengthening and shaping.

[0036] As a preferred technical solution of the present invention, the upsetting treatment includes three upsetting steps and three drawing steps performed sequentially.

[0037] Preferably, the deformation amount in each upsetting process is 30-40%, for example, it can be 30%, 32%, 34%, 36%, 38% or 40%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] Preferably, the pressing speed in the upsetting process is 18 to 22 mm / s, for example, 18 mm / s, 19 mm / s, 20 mm / s, 21 mm / s or 22 mm / s, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] Preferably, the interval time between two adjacent upsetting processes in the upsetting process is 3 to 5 seconds, for example, 3 seconds, 3.4 seconds, 3.8 seconds, 4.2 seconds, 4.6 seconds or 5 seconds, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] In the present invention, the surface temperature of the aluminum alloy columnar ingot is controlled to be ≥280°C during the forming process, and the deformation amount is 30-40% each time, the purpose of which is to promote dynamic recrystallization and refine grains;

[0041] In addition, the present invention controls the pressing speed in the upsetting process to 18-22 mm / s to achieve slow and uniform pressing to prevent the temperature rise phenomenon caused by excessive deformation rate during forging; and controls the interval time between two adjacent upsetting processes to 3-5 s to prevent the temperature rise caused by excessive strain rate, which will lead to grain growth, precipitation and segregation of alloy elements, and reduce the mechanical properties of the material such as strength and toughness.

[0042] As a preferred technical solution of the present invention, the deformation of the core shaft is 30-40%, for example, it can be 30%, 32%, 34%, 36%, 38% or 40%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0043] As a preferred technical solution of the present invention, the temperature of the annealing treatment in step (2) is 290-310°C, for example, it can be 290°C, 295°C, 300°C, 305°C or 310°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] Preferably, the holding time of the annealing treatment in step (2) is 1.3-1.5 min / mm×effective thickness+120 min, wherein the specific value of 1.3-1.5 min / mm can be, for example, 1.3 min / mm, 1.34 min / mm, 1.38 min / mm, 1.42 min / mm, 1.46 min / mm or 1.5 min / mm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] In the present invention, the effective thickness is the maximum inscribed circle diameter that can be drawn by the cross-sectional shape of the forging before annealing.

[0046] As a preferred technical solution of the present invention, the second aspect of the present invention provides a method for preparing an aluminum alloy storage tank forging for FLNG as provided in the first aspect, comprising the following steps:

[0047] (1) preparing ingredients according to the chemical composition content, and then performing smelting treatment, casting and homogenization treatment in sequence to obtain an aluminum alloy cylindrical ingot;

[0048] The temperature of the smelting treatment is 700-750°C; the temperature of the casting is 680-720°C; the temperature of the homogenization treatment is 450-500°C, the holding time is 12-24h, and the heating rate is 30-50°C / h;

[0049] (2) subjecting the aluminum alloy cylindrical ingot obtained in step (2) to a forming process, an annealing process, and an air cooling process in sequence to obtain the aluminum alloy storage tank forging for FLNG;

[0050] Controlling the surface temperature of the aluminum alloy cylindrical ingot during the forming process to be ≥280°C;

[0051] The forming process includes sequentially performing upsetting, punching, hole expansion, mandrel lengthening and shaping;

[0052] The upsetting process includes three upsettings and three elongations performed sequentially; the deformation amount of each upsetting process is 30-40%; the pressing speed of the upsetting process is 18-22 mm / s; the interval time between two adjacent upsetting processes is 3-5 s; the deformation amount of the mandrel elongation is 30-40%;

[0053] The annealing treatment temperature is 290-310° C., and the heat preservation time is 1.3-1.5 min / mm×effective thickness+120 min.

[0054] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] (1) The present invention further improves the physical properties of the forgings by fine-tuning the chemical element composition in the forgings to meet the requirements of FLNG tanks;

[0057] (2) The present invention further improves the quality and stability of forgings by limiting the process and process parameters in the forming process during the forging preparation process, realizes the forming of large aluminum alloy cylindrical forgings, effectively improves material utilization, and reduces production costs. DETAILED DESCRIPTION

[0058] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0059] Example 1

[0060] The present embodiment provides an aluminum alloy storage tank forging for FLNG. The chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si 0.06wt%, Fe 0.16wt%, Cu 0.06wt%, Mn 0.7wt%, Mg 4.7wt%, Cr 0.15wt%, Zn 0.20wt%, Ti 0.10wt%, and the balance is Al and unavoidable impurities.

[0061] The method for preparing the aluminum alloy storage tank forging for FLNG comprises the following steps:

[0062] (1) preparing materials according to the chemical composition content, and then performing smelting treatment, casting and homogenization treatment in sequence to obtain an aluminum alloy cylindrical ingot;

[0063] The temperature of the smelting treatment is 725°C; the temperature of the casting is 700°C; the temperature of the homogenization treatment is 475°C, the holding time is 18h, and the heating rate is 40°C / h;

[0064] (2) subjecting the aluminum alloy cylindrical ingot obtained in step (2) to sequential forming treatment, annealing treatment and air cooling treatment to obtain the aluminum alloy storage tank forging for FLNG;

[0065] Controlling the surface temperature of the aluminum alloy columnar ingot during the forming process to be 320° C.;

[0066] The forming process includes sequentially performing upsetting, punching, hole expansion, mandrel lengthening and shaping;

[0067] The upsetting process includes three upsettings and three elongations performed sequentially; the deformation amount of each upsetting process is 35%; the pressing speed of the upsetting process is 20 mm / s; the interval time between two adjacent upsetting processes is 4 seconds; the deformation amount of the mandrel elongation is 35%;

[0068] The annealing treatment temperature is 300° C., and the heat preservation time is 1.4 min / mm×effective thickness+120 min.

[0069] Example 2

[0070] The present embodiment provides an aluminum alloy storage tank forging for FLNG. The chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si 0.20wt%, Fe 0.20wt%, Cu 0.10wt%, Mn 0.4wt%, Mg 4.5wt%, Cr 0.05wt%, Zn 0.25wt%, Ti 0.15wt%, and the balance is Al and unavoidable impurities.

[0071] The method for preparing the aluminum alloy storage tank forging for FLNG comprises the following steps:

[0072] (1) preparing ingredients according to the chemical composition content, and then performing smelting treatment, casting and homogenization treatment in sequence to obtain an aluminum alloy cylindrical ingot;

[0073] The temperature of the smelting treatment is 700°C; the temperature of the casting is 680°C; the temperature of the homogenization treatment is 450°C, the holding time is 24h, and the heating rate is 30°C / h;

[0074] (2) subjecting the aluminum alloy cylindrical ingot obtained in step (2) to a forming process, an annealing process, and an air cooling process in sequence to obtain the aluminum alloy storage tank forging for FLNG;

[0075] Controlling the surface temperature of the aluminum alloy cylindrical ingot during the forming process to be 280° C.;

[0076] The forming process includes sequentially performing upsetting, punching, hole expansion, mandrel lengthening and shaping;

[0077] The upsetting process includes three upsettings and three elongations performed sequentially; the deformation amount of each upsetting process is 30%; the pressing speed of the upsetting process is 18 mm / s; the interval time between two adjacent upsetting processes is 3s; the deformation amount of the mandrel elongation is 30%;

[0078] The annealing treatment temperature is 290° C., and the heat preservation time is 1.5 min / mm×effective thickness+120 min.

[0079] Example 3

[0080] The present embodiment provides an aluminum alloy storage tank forging for FLNG. The chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si 0.15wt%, Fe 0.12wt%, Cu 0.08wt%, Mn 1.0wt%, Mg 4.9wt%, Cr 0.25wt%, Zn 0.22wt%, Ti 0.12wt%, and the balance is Al and unavoidable impurities.

[0081] The method for preparing the aluminum alloy storage tank forging for FLNG comprises the following steps:

[0082] (1) preparing ingredients according to the chemical composition content, and then performing smelting treatment, casting and homogenization treatment in sequence to obtain an aluminum alloy cylindrical ingot;

[0083] The temperature of the smelting treatment is 750°C; the temperature of the casting is 720°C; the temperature of the homogenization treatment is 500°C, the holding time is 12h, and the heating rate is 50°C / h;

[0084] (2) subjecting the aluminum alloy cylindrical ingot obtained in step (2) to a forming process, an annealing process, and an air cooling process in sequence to obtain the aluminum alloy storage tank forging for FLNG;

[0085] Controlling the surface temperature of the aluminum alloy cylindrical ingot during the forming process to be 350° C.;

[0086] The forming process includes sequentially performing upsetting, punching, hole expansion, mandrel lengthening and shaping;

[0087] The upsetting process includes three upsettings and three elongations performed sequentially; the deformation amount of each upsetting process is 40%; the pressing speed of the upsetting process is 22 mm / s; the interval time between two adjacent upsetting processes is 5 s; the deformation amount of the mandrel elongation is 40%;

[0088] The annealing treatment temperature is 310° C., and the holding time is 1.3 min / mm×effective thickness+120 min.

[0089] Example 4

[0090] The present embodiment provides an aluminum alloy storage tank forging for FLNG. The chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si 0.18wt%, Fe 0.15wt%, Cu 0.06wt%, Mn 0.7wt%, Mg 4.8wt%, Cr 0.15wt%, Zn 0.20wt%, Ti 0.10wt%, and the balance is Al and unavoidable impurities.

[0091] The method for preparing the aluminum alloy storage tank forging for FLNG differs from that in Example 1 only in that:

[0092] In this embodiment, the pressing speed in the upsetting process in step (2) is adjusted to 15 mm / s.

[0093] Example 5

[0094] The present embodiment provides an aluminum alloy storage tank forging for FLNG. The chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si 0.18wt%, Fe 0.15wt%, Cu 0.06wt%, Mn 0.7wt%, Mg 4.8wt%, Cr 0.15wt%, Zn 0.20wt%, Ti 0.10wt%, and the balance is Al and unavoidable impurities.

[0095] The method for preparing the aluminum alloy storage tank forging for FLNG differs from that in Example 1 only in that:

[0096] In this embodiment, the pressing speed in the upsetting process in step (2) is adjusted to 25 mm / s.

[0097] Example 6

[0098] The present embodiment provides an aluminum alloy storage tank forging for FLNG. The chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si 0.18wt%, Fe 0.15wt%, Cu 0.06wt%, Mn 0.7wt%, Mg 4.8wt%, Cr 0.15wt%, Zn 0.20wt%, Ti 0.10wt%, and the balance is Al and unavoidable impurities.

[0099] The method for preparing the aluminum alloy storage tank forging for FLNG differs from that in Example 1 only in that:

[0100] In this embodiment, the interval between two adjacent upsetting operations in step (2) is adjusted to 1 s.

[0101] Example 7

[0102] The present embodiment provides an aluminum alloy storage tank forging for FLNG. The chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si 0.18wt%, Fe 0.15wt%, Cu 0.06wt%, Mn 0.7wt%, Mg 4.8wt%, Cr 0.15wt%, Zn 0.20wt%, Ti 0.10wt%, and the balance is Al and unavoidable impurities.

[0103] The method for preparing the aluminum alloy storage tank forging for FLNG differs from that in Example 1 only in that:

[0104] In this embodiment, the deformation amount in each upsetting process in step (2) is adjusted to 25%.

[0105] Example 8

[0106] The present embodiment provides an aluminum alloy storage tank forging for FLNG. The chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si 0.18wt%, Fe 0.15wt%, Cu 0.06wt%, Mn 0.7wt%, Mg 4.8wt%, Cr 0.15wt%, Zn 0.20wt%, Ti 0.10wt%, and the balance is Al and unavoidable impurities.

[0107] The method for preparing the aluminum alloy storage tank forging for FLNG differs from that in Example 1 only in that:

[0108] In this embodiment, the deformation amount in each upsetting process in step (2) is adjusted to 45%.

[0109] Example 9

[0110] The present embodiment provides an aluminum alloy storage tank forging for FLNG. The chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si 0.18wt%, Fe 0.15wt%, Cu 0.06wt%, Mn 0.7wt%, Mg 4.8wt%, Cr 0.15wt%, Zn 0.20wt%, Ti 0.10wt%, and the balance is Al and unavoidable impurities.

[0111] The method for preparing the aluminum alloy storage tank forging for FLNG differs from that in Example 1 only in that:

[0112] In this embodiment, the temperature of the annealing treatment in step (2) is adjusted to 250°C.

[0113] Example 10

[0114] The present embodiment provides an aluminum alloy storage tank forging for FLNG. The chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si 0.08wt%, Fe 0.20wt%, Cu 0.06wt%, Mn 0.7wt%, Mg 4.27wt%, Cr 0.15wt%, Zn 0.20wt%, Ti 0.10wt%, and the balance is Al and unavoidable impurities.

[0115] The method for preparing the aluminum alloy storage tank forging for FLNG differs from that in Example 1 only in that:

[0116] In this embodiment, the temperature of the annealing treatment in step (2) is adjusted to 300°C.

[0117] Embodiment 11

[0118] The present embodiment provides an aluminum alloy storage tank forging for FLNG. The chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si 0.08wt%, Fe 0.20wt%, Cu 0.06wt%, Mn 0.7wt%, Mg 4.27wt%, Cr 0.15wt%, Zn 0.20wt%, Ti 0.10wt%, and the balance is Al and unavoidable impurities.

[0119] The method for preparing the aluminum alloy storage tank forging for FLNG differs from that in Example 1 only in that:

[0120] In this embodiment, the temperature of the annealing treatment in step (2) is adjusted to 350°C.

[0121] Example 12

[0122] The present embodiment provides an aluminum alloy storage tank forging for FLNG. The chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si 0.18wt%, Fe 0.15wt%, Cu 0.06wt%, Mn 0.7wt%, Mg 4.8wt%, Cr 0.15wt%, Zn 0.20wt%, Ti 0.10wt%, and the balance is Al and unavoidable impurities.

[0123] The method for preparing the aluminum alloy storage tank forging for FLNG differs from that in Example 1 only in that:

[0124] In this embodiment, the surface temperature of the aluminum alloy columnar ingot during the forming process is adjusted to 250°C.

[0125] Example 13

[0126] The present embodiment provides an aluminum alloy storage tank forging for FLNG. The chemical composition of the aluminum alloy storage tank forging for FLNG includes, by mass percentage, Si 0.06wt%, Fe 0.15wt%, Cu 0.06wt%, Mn 0.7wt%, Mg 4.8wt%, Cr 0.15wt%, Zn 0.20wt%, Ti 0.10wt%, and the balance is Al and unavoidable impurities.

[0127] The preparation method of the FLNG aluminum alloy storage tank forging is the same as that in Example 1.

[0128] Comparative Example 1

[0129] This comparative example provides an aluminum alloy storage tank forging for FLNG, and the aluminum alloy storage tank forging for FLNG is different from that of Example 1 only in that:

[0130] In this comparative example, the Si element content was adjusted to 0.40 wt %.

[0131] The preparation method of the FLNG aluminum alloy storage tank forging is the same as that in Example 1.

[0132] Comparative Example 2

[0133] This comparative example provides an aluminum alloy storage tank forging for FLNG, and the aluminum alloy storage tank forging for FLNG is different from Example 1 only in that:

[0134] In this comparative example, the Fe content was adjusted to 0.40 wt%.

[0135] The preparation method of the FLNG aluminum alloy storage tank forging is the same as that in Example 1.

[0136] Comparative Example 3

[0137] This comparative example provides an aluminum alloy storage tank forging for FLNG, and the aluminum alloy storage tank forging for FLNG is different from Example 1 only in that:

[0138] In this comparative example, the Mg element content was adjusted to 4.25 wt %.

[0139] The preparation method of the FLNG aluminum alloy storage tank forging is the same as that in Example 1.

[0140] Performance testing:

[0141] The physical properties of the aluminum alloy storage tank forgings for FLNG provided in the above-mentioned Examples 1, 10, 11 and 13 were tested, and the results are shown in Table 1.

[0142] Table 1

[0143] Tensile strength / MPa Yield strength / MPa Elongation / % Example 1 331 142 24.7 Example 10 293.75 135.75 20 Embodiment 11 315.75 144.5 17.5 Example 13 327.75 140.75 24.25

[0144] Analysis of the above embodiments, comparative examples and Table 1 shows the following points:

[0145] (1) Comprehensive analysis of Examples 1-3 and Example 13 shows that the aluminum alloy storage tank forgings for FLNG obtained by the preparation method provided by the present invention have excellent physical properties and can meet the service conditions of FLNG forgings;

[0146] (2) Comprehensive analysis of Example 1 and Examples 4-5 shows that the pressing speed in the upsetting process affects the surface temperature of the forging. When the pressing speed is too fast, the forging will experience a temperature rise, which will lead to grain growth and reduce the strength and toughness of the material. Alternatively, a temperature difference will be generated, resulting in large thermal stress inside the forging, thereby forming cracks and affecting the product size and quality. When the pressing speed is too slow, the deformation amount at each fire to the final forging temperature will be less than 30%, resulting in coarse grains and affecting the performance of subsequent products.

[0147] (3) Comprehensive analysis of Example 1 and Example 6 shows that when the interval between two adjacent upsettings is too short, the temperature rise due to the excessive strain rate will lead to grain growth, precipitation and segregation of alloy elements, and reduce the mechanical properties of the material such as strength and toughness;

[0148] (4) Comprehensive analysis of Example 1 and Examples 7-8 shows that when the deformation amount of each forging process is too high, it will cause cracking of the forging; when the deformation amount of each forging process is too low, it will cause insufficient grain refinement, resulting in a coarse grain or mixed grain state, affecting product performance, and failing to homogenize the internal stress of the forging, resulting in deformation during subsequent processing;

[0149] (5) Comprehensive analysis of Example 1 and Examples 9-11 shows that the temperature of the annealing treatment affects the effect of grain refinement; when the temperature of the annealing treatment is too low, the internal stress will not be completely eliminated, which will affect subsequent processing and use (deformation and cracks are likely to occur); when the temperature of the annealing treatment is too high, the grains will be coarse, the plasticity and toughness of the material will be reduced, and the high temperature will also affect the strength and hardness of the product;

[0150] (6) Comprehensive analysis of Example 1 and Example 12 shows that the surface temperature of the aluminum alloy cylindrical ingot during the forming process is controlled to be no less than 280° C., otherwise the forging will crack;

[0151] (7) Comprehensive analysis of Example 1 and Comparative Examples 1-3 shows that the content of chemical components in the FLNG aluminum alloy storage tank forging will affect the physical properties of the forging;

[0152] When the Si content in the forging is too high, the brittleness of the forging will increase or the corrosion resistance of the forging will decrease; in addition, excessive Si will also affect the ductility of the forging;

[0153] When the Fe element in the forging is too high, the high concentration of Fe will form a hard FeAl3 phase in the alloy, thereby reducing the plasticity and toughness of the forging;

[0154] When the Mg content in the forging is low, the tensile strength and yield strength of the forging will be reduced.

[0155] In summary, the present invention improves the physical properties and stability of the forgings by adjusting the content of chemical elements in the forgings and optimizing the preparation method, while achieving the forming of large aluminum alloy cylindrical forgings and effectively improving material utilization and reducing production costs.

[0156] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An aluminum alloy storage tank forging for FLNG, characterized in that: The chemical composition of the FLNG aluminum alloy storage tank forging includes, in percentage by mass: Si≤0.20wt%, Fe≤0.20wt%, Cu≤0.10wt%, Mn 0.4-1.0wt%, Mg4.5-4.9wt%, Cr 0.05-0.25wt%, Zn≤0.25wt%, Ti≤0.15wt%, and the balance is Al and unavoidable impurities.

2. The aluminum alloy storage tank forging for FLNG according to claim 1, characterized in that: The tensile strength of the aluminum alloy storage tank forging for FLNG is 300-380 MPa; Preferably, the yield strength of the aluminum alloy storage tank forging for FLNG is 120-200 MPa; Preferably, the elongation of the FLNG aluminum alloy storage tank forging is 20-30%.

3. A method for preparing an aluminum alloy storage tank forging for FLNG as claimed in claim 1 or 2, characterized in that: The preparation method comprises the following steps: (1) preparing materials according to the chemical composition content, and then performing smelting treatment, casting and homogenization treatment in sequence to obtain an aluminum alloy cylindrical ingot; (2) subjecting the aluminum alloy cylindrical ingot obtained in step (2) to sequential forming treatment, annealing treatment and air cooling treatment to obtain the aluminum alloy storage tank forging for FLNG; The surface temperature of the aluminum alloy columnar ingot during the forming process is controlled to be ≥280°C.

4. The preparation method according to claim 3, characterized in that: The temperature of the smelting treatment in step (1) is 700-750° C. Preferably, the casting temperature in step (1) is 680-720°C; Preferably, the casting in step (1) also includes a cooling treatment.

5. The preparation method according to claim 3 or 4, characterized in that: The temperature of the homogenization treatment in step (1) is 450-500° C. Preferably, the heating rate of the homogenization treatment in step (1) is 30 to 50° C. / h; Preferably, the holding time of the homogenization treatment in step (1) is 12 to 24 hours.

6. The preparation method according to any one of claims 3 to 5, characterized in that: The forming process in step (2) includes upsetting, punching, hole expansion, mandrel lengthening and shaping.

7. The preparation method according to claim 6, characterized in that: The upsetting and drawing process includes three upsetting and three drawing processes performed sequentially; Preferably, the deformation amount during each upsetting process is 30-40%; Preferably, the pressing speed in the upsetting process is 18 to 22 mm / s; Preferably, the interval between two adjacent upsetting processes in the upsetting process is 3 to 5 seconds.

8. The preparation method according to claim 6, characterized in that: The deformation amount of the mandrel when stretched is 30-40%.

9. The preparation method according to any one of claims 3 to 8, characterized in that: The temperature of the annealing treatment in step (2) is 290-310° C. Preferably, the holding time of the annealing treatment in step (2) is 1.3-1.5 min / mm×effective thickness+120 min.

10. The preparation method according to any one of claims 3 to 9, characterized in that: The preparation method comprises the following steps: (1) preparing materials according to the chemical composition content, and then performing smelting treatment, casting and homogenization treatment in sequence to obtain an aluminum alloy cylindrical ingot; The temperature of the smelting treatment is 700-750°C; the temperature of the casting is 680-720°C; the temperature of the homogenization treatment is 450-500°C, the holding time is 12-24h, and the heating rate is 30-50°C / h; (2) subjecting the aluminum alloy cylindrical ingot obtained in step (2) to sequential forming treatment, annealing treatment and air cooling treatment to obtain the aluminum alloy storage tank forging for FLNG; Controlling the surface temperature of the aluminum alloy cylindrical ingot during the forming process to be ≥280°C; The forming process includes sequentially performing upsetting, punching, hole expansion, mandrel lengthening and shaping; The upsetting process includes three upsettings and three elongations performed sequentially; the deformation amount of each upsetting process is 30-40%; the pressing speed of the upsetting process is 18-22 mm / s; the interval time between two adjacent upsetting processes is 3-5 s; the deformation amount of the mandrel elongation is 30-40%; The annealing treatment temperature is 290-310° C., and the heat preservation time is 1.3-1.5 min / mm×effective thickness+120 min.