380MPa-grade heat-resistant aluminum alloy sleeve and manufacturing method thereof

Abstract

The invention discloses a 380MPa-grade heat-resistant aluminum alloy casing pipe and a manufacturing method thereof, and belongs to the technical field of petroleum casing pipes. The aluminum alloy comprises, by weight, 3.8%-4.9% of Cu, 1.2%-1.8% of Mg, 0.3%-0.9% of Mn, smaller than or equal to 0.3% of Zn, smaller than or equal to 0.15% of Ti, smaller than or equal to 0.15% of Zr, smaller than or equal to 0.05% of Fe, smaller than or equal to 0.05% of Si and the balance Al and inevitable impurities. Through reasonable design of the components, compared with a traditional steel sleeve, the aluminum alloy sleeve has the excellent characteristics of high specific strength, high temperature resistance, corrosion resistance, small frictional resistance and the like, and has natural advantages in severe oil and gas wells such as deep wells, ultra-deep wells, directional wells, acid gas wells and deep sea oil and gas wells. The performance of the manufactured 380MPa-grade high-strength heat-resistant aluminum alloy sleeve is as follows: (a) the tensile property of a pipe body is as follows: Rt0.2 is equal to 380-400MPa, Rm is greater than or equal to 500MPa, and delta is greater than or equal to 12.0; and (b) the heat resistance of the pipe body is realized, and the yield strength of the pipe body is greater than or equal to 266 MPa after the pipe body is thermally exposed for 500 hours at 160 DEG C. And (c) the microstructure of the pipe body is mainly composed of a dispersed and refined S phase.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil casing, and relates to a 380 MPa grade heat-resistant aluminum alloy casing and a manufacturing method thereof. Background Art

[0002] Oil casing is a steel pipe used to support the wellbore of oil and gas wells. It is the main tool for supporting the wellbore and preventing formation water and other non-reservoir environmental media from invading, so as to ensure the progress of the drilling process and the normal operation of the entire oil well after completion. For each well, several layers of casing are required according to different drilling depths and geological conditions. After the casing is lowered into the well, cementing is required. Different from tubing and drill pipes, it cannot be reused and belongs to disposable consumable materials. Therefore, the consumption of casing accounts for more than 70% of all oil well pipes, and it is the pipe with the largest consumption among oil well pipes. Oil special pipes are mainly used for the drilling of oil and gas wells and the transportation of oil and gas. It includes oil drill pipes, oil casings, and production tubing. Oil drill pipes are mainly used to connect drill collars and drill bits and transmit drilling power. Oil casings are mainly used to support the wellbore during the drilling process and after completion to ensure the progress of the drilling process and the normal operation of the entire oil well after completion. Production tubing mainly transports oil and gas at the bottom of the oil well to the ground. Oil casing is the lifeline for maintaining the operation of oil wells. Due to different geological conditions, the stress state underground is complex, and tensile, compressive, bending, and torsional stresses act on the pipe body comprehensively, which puts high requirements on the quality of the casing itself. Once the casing itself is damaged due to some reason, it may lead to a reduction in production of the entire well or even abandonment. According to the strength of the steel itself, the casing can be divided into different steel grades, namely J55, K55, N80, L80, C90, T95, P110, Q125, V150, etc. Different steel grades are adopted according to different well conditions and depths. In a corrosive environment, the casing itself is also required to have corrosion resistance. In places with complex geological conditions, the casing is also required to have collapse resistance.

[0003] The currently used steel casings have low strength, and failure accidents such as stress corrosion cracking, fatigue cracking, leakage, and overload that occur under complex working conditions in oil and gas production pose a great threat to the safe production of oil and gas wells. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problems of low strength of the existing steel casings and failure accidents such as stress corrosion cracking, fatigue cracking, leakage, and overload that are likely to occur under complex working conditions in oil and gas production, and to provide a 380 MPa grade heat-resistant aluminum alloy casing and a manufacturing method thereof.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] The present invention provides a heat-resistant aluminum alloy casing of 380 MPa grade, which, by weight percentage, comprises: Cu: 3.8 - 4.9%, Mg: 1.2 - 1.8%, Mn: 0.3 - 0.9%, Zn: ≤0.3%, Ti: ≤0.15%, Zr: ≤0.15%, Fe: ≤0.05%, Si: ≤0.05%, and the balance is Al and inevitable impurities.

[0007] The present invention also provides a manufacturing method for preparing the above-mentioned heat-resistant aluminum alloy casing of 380 MPa grade, which successively comprises the following steps:

[0008] Smelting, casting, multi-stage homogenization treatment, extrusion treatment, two-stage solution treatment, pre-deformation and aging treatment.

[0009] A further improvement of the present invention lies in:

[0010] The smelting is as follows:

[0011] Smelt Cu: 3.8 - 4.9%, Mg: 1.2 - 1.8%, Mn: 0.3 - 0.9%, Zn: ≤0.3%, Ti: ≤0.15%, Zr: ≤0.15%, Fe: ≤0.05%, Si: ≤0.05%, with the balance being Al, to obtain an alloy liquid.

[0012] The casting is as follows:

[0013] Cast the alloy liquid into a tube blank.

[0014] The multi-stage homogenization treatment is as follows:

[0015] Heat the tube blank to 410 - 425 °C and hold for 8 - 12 h; then heat to 445 - 460 °C and hold for 10 - 15 h; finally heat to 480 - 495 °C and hold for 20 - 24 h; then naturally cool to room temperature to obtain a homogenized tube blank.

[0016] The heating rate is 10 - 20 °C / min.

[0017] The extrusion treatment is as follows:

[0018] Heat the tube blank after multi-stage homogenization treatment to 420 - 435 °C, hold for 20 min and then perform extrusion, with an extrusion ratio greater than 18 and an extrusion speed of 48 mm / min, to obtain an extruded tube blank.

[0019] The two-stage solution treatment is as follows:

[0020] Heat the extruded tube blank to 470 - 480 °C, hold for 1 - 2 h, then heat to 490 - 500 °C and hold for 1 - 1.5 h, with a heating rate greater than 20 °C / min; then cool by spraying water, with a cooling rate of 30 - 50 °C / s, to obtain the tube blank after double-stage solution treatment.

[0021] The pre-deformation is as follows:

[0022] Perform pre-tensile deformation on the tube blank after double-stage solution treatment, with a deformation amount of 2 - 3%, to obtain the tube blank after pre-tensile deformation.

[0023] The aging treatment is as follows:

[0024] Perform natural aging or artificial aging treatment on the tube blank after pre-tensile deformation. The artificial aging is to hold at 185 - 195 °C for 6 - 60 h to obtain a 380 MPa grade heat-resistant aluminum alloy casing.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention discloses a 380 MPa grade heat-resistant aluminum alloy casing. Compared with the steel components of conventional casings, the present invention has a higher Cu content (3.8 - 4.9%), a certain Mg content (1.2 - 1.8%), a lower Mn (0.3 - 0.9%), an appropriate Zn (Zn: ≤0.3%), trace amounts of Ti (≤0.15%) and Zr (≤0.15%) based on aluminum as the matrix in the alloy formula. The composition design is simple and the cost is low, making full use of the precipitation strengthening effect of Cu and Mg elements and the solid solution strengthening effect of Mn and Zn elements; the above components are combined with the thermomechanical treatment process, which not only improves the comprehensive performance of the product, but also enables a flexible extrusion production process to improve productivity. The product produced by combining a high Cu content with thermomechanical treatment and double-stage aging process has high strength and improved heat resistance, making the aluminum alloy casing pipe have good high-temperature resistance performance. Compared with traditional steel casings, the aluminum alloy casing has excellent properties such as high specific strength, high temperature resistance, corrosion resistance, and low frictional resistance, and has natural advantages in harsh oil and gas wells such as deep wells, ultra-deep wells, directional wells, sour gas wells, and deep-sea oil and gas wells. The performance of the 380 MPa grade high-strength heat-resistant aluminum alloy casing manufactured by the present invention is as follows:

[0027] a) Tensile properties of the pipe body, yield strength R t0.2 = 380 - 400 MPa, tensile strength R m ≥500 MPa, elongation δ≥12.0.

[0028] b) Heat resistance of the pipe body, the yield strength after thermal exposure at 160 °C for 500 hours ≥266 MPa.

[0029] c) The microstructure of the tube body is mainly composed of dispersed and refined S phase.

[0030] The present invention also discloses a manufacturing method of a 380MPa grade heat-resistant aluminum alloy casing. By controlling the appropriate weight percentages of various elements, the precipitation strengthening of Cu and Mg elements, the solid solution strengthening and grain refinement of Mn element at the solution treatment temperature, the solid solution strengthening and aging strengthening of Zn element, and the grain refinement of the composite addition of Ti and Zr are utilized, and the composite effects of solid solution strengthening, precipitation strengthening, grain refinement, etc. are fully exerted, thereby improving the strength, hardness and hot strength of the tube body for aluminum alloy drill pipes. In the present invention, due to the simple alloy composition design and the absence of the need to add precious metal elements such as Ag to improve the hot strength, the cost is low.

[0031] Furthermore, the present invention adopts heat treatment processes such as multi-stage homogenization treatment, multi-stage solution treatment, aging, etc. that are matched with the alloy design composition. Through higher homogenization and solution temperature treatments, segregation and inhomogeneity inside the matrix are greatly eliminated, and the remelting of the unmelted eutectic phase inside the aluminum alloy matrix is significantly promoted. Through higher artificial aging temperature treatment, the stability of the dispersed precipitated strengthening phase is promoted, thereby improving the hot strength performance while maintaining high strength at room temperature.

[0032] Furthermore, in the present invention, Cu and Mg are used as the main alloying elements. Cu is solid-solved in the alloy matrix, causing lattice distortion and producing solid solution strengthening effect, which can improve the room temperature strength of the aluminum alloy. After aging treatment, body-centered tetragonal θ and θ′ phases precipitate, improving the heat resistance of the alloy. Cu can improve the hot working performance, inhibit the extrusion effect, and reduce the anisotropy caused by Mn in the alloy. Adding Mg element to the Al-Cu alloy can significantly increase the nucleation rate of the precipitated phase during the aging process of the alloy, refine the alloy grains, not only improve the microstructure of the Al-Cu alloy after aging, but also improve the strength and plasticity of the alloy after artificial aging. A binary θ(Al 2 Cu) phase is formed between Al and Cu, and Cu and Mg will form a high-concentration ternary solid solution S(Al 2 CuMg) phase with Al in the tube body. The solubility of these two phases in the aluminum alloy tube body decreases rapidly with the decrease of temperature, and they precipitate dispersedly to strengthen the aluminum alloy matrix. The strengthening effect increases with the increase of the contents of Cu and Mg elements, which is beneficial to maintaining high physical and mechanical properties of the aluminum alloy casing under long-term service conditions at 160°C. However, excessive contents of Cu and Mg elements will significantly reduce the plasticity and toughness of the aluminum alloy tube body. Therefore, the weight percentage content of Cu in the aluminum alloy tube body is controlled to be 3.8-4.9%, and the weight percentage content of Mg is controlled to be 1.2-1.8%.

[0033] Furthermore, Mn is an economical strengthening element in high-strength heat-resistant aluminum alloy sleeves. During the casting process, Mn and Al will form a metastable phase Al 6 Mn dispersed phase, which has the effect of hindering the movement of grain boundaries and dislocations, increasing the recrystallization temperature, and can prevent dynamic recrystallization during hot extrusion of aluminum alloy and recrystallization during solution treatment, significantly refining the recrystallized grains. Adding Mn can weaken the negative impact of impurity element Fe on the alloy, and the presence of Mn element can also delay and weaken the artificial over-aging process of the alloy, improving the heat-resistant strength of the alloy. However, excessive Mn will reduce the solubility of solute elements such as Zn and Mg in the matrix, thereby reducing the strength and toughness. Therefore, the weight percentage of Mn in the aluminum alloy tube body is controlled to be 0.3-0.9%.

[0034] Furthermore, Zn is a strengthening element that improves the strength in high-strength heat-resistant aluminum alloy sleeves. When Zn, Cu, and Mg are added to the aluminum alloy simultaneously, an obvious strengthening effect can be produced, thereby increasing the tensile strength and yield strength of the material. The composite addition of Zn with alloying elements such as Zr, Si, and Mn has the effect of refining the dendrites of the Al-Cu-Mg alloy ingot, enhancing the thermal strength performance of the material to a certain extent. However, excessive Zn will lead to a decrease in the plasticity and corrosion resistance of the aluminum alloy tube body. Under deformation conditions, the improvement of the strength of the aluminum alloy by Zn is very limited, and there is a tendency of stress corrosion cracking. Therefore, the weight percentage of Zn in the aluminum alloy tube body is optimized and controlled to be ≤0.3%.

[0035] Furthermore, Ti and Zr are elements that refine grains and inhibit recrystallization in high-strength heat-resistant aluminum alloy sleeves. Zr is a transition element, which can significantly refine the as-cast grains of the alloy, obtain a non-dendritic structure, and improve the casting performance; after homogenization treatment, it combines with aluminum to form fine and dispersed high-melting-point Al 3 Zr particles, which have a strong pinning effect on dislocations and grain boundaries in the alloy, and can effectively prevent recrystallization and grain growth during hot working. The dispersed particles Al 3 Zr also has a coherent interface with the matrix, greatly reducing the possibility of precipitation of the equilibrium phase on the interface of the dispersed particles Al 3 Zr during quenching, thereby improving the quenching sensitivity of the alloy. The above effects can be achieved with trace amounts of Ti and appropriate amounts of Zr. Therefore, the weight percentage of Ti in the aluminum alloy tube body is controlled to be ≤0.15%, and the weight percentage of Zr is controlled to be ≤0.15%.

[0036] Furthermore, Fe and Si (silicon) are harmful impurities in high-strength heat-resistant aluminum alloy sleeves. They can form various insoluble primary phases and refractory non-equilibrium phases with Al and other alloying elements. Vacancies, holes, and cracks are likely to form at their phase interfaces, thereby reducing the plasticity, toughness, and fatigue resistance of the aluminum alloy. Therefore, the contents of Fe and Si should be strictly controlled. The weight percentage of Fe in the aluminum alloy tube body is controlled to be ≤0.15%, and the weight percentage of Si is controlled to be ≤0.15%. Detailed implementation manners

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention.

[0038] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0039] The present invention will be further described in detail below with reference to specific embodiments:

[0040] Embodiment 1

[0041] The composition of the 380MPa grade heat-resistant aluminum alloy sleeve by weight percentage is as follows:

[0042] Cu: 3.8%, Mg: 1.2%, Mn: 0.3%, Zn: 0.1%, Ti: 0.05%, Zr: 0.05%, Fe: 0.02%, Si: 0.02%, and the balance is Al and impurities. Its manufacturing method is carried out according to the following steps:

[0043] Step 1: Smelting

[0044] Cu: 3.8%, Mg: 1.2%, Mn: 0.3%, Zn: 0.3%, Ti: 0.05%, Zr: 0.05%, Fe: 0.02%, Si: 0.02%, and the balance is Al. Smelting is carried out to obtain alloy liquid.

[0045] Step 2: Casting

[0046] The alloy liquid is cast into a tube blank.

[0047] Step 3: Multi-stage homogenization treatment

[0048] Heat the tube blank to 410°C and hold for 8 h; then heat to 445°C and hold for 10 h; finally heat to 480°C and hold for 20 h; then naturally cool to room temperature to obtain a homogenized tube blank.

[0049] Step Four: Extrusion

[0050] Heat the tube blank after multi-stage homogenization to 420°C, hold for 20 min and then perform extrusion. The extrusion ratio is greater than 18 and the extrusion speed is 48 mm / min to obtain an extruded tube blank.

[0051] Step Five: Two-stage Solution Treatment

[0052] Heat the extruded tube blank to 470°C, hold for 1 h and then heat to 490°C and hold for 1 h. The heating rate is greater than 20°C / min; then cool by spraying water with a cooling rate of 30°C / s to obtain a tube blank after two-stage solution treatment.

[0053] Step Six: Pre-deformation

[0054] Perform pre-tensile deformation on the tube blank after two-stage solution treatment with a deformation amount of 2% to obtain a tube blank after pre-tensile deformation.

[0055] Step Seven: Aging Treatment

[0056] Perform natural aging or artificial aging treatment on the tube blank after pre-tensile deformation. The artificial aging is to hold at 185°C for 6 h to obtain a 380 MPa grade heat-resistant aluminum alloy casing.

[0057] Example 2

[0058] The composition of the 380 MPa grade heat-resistant aluminum alloy casing by weight percentage is:

[0059] Cu: 4.9%, Mg: 1.8%, Mn: 0.9%, Zn: 0.3%, Ti: 0.15%, Zr: 0.15%, Fe: 0.05%, Si: 0.05%, and the balance is Al and impurities. Its manufacturing method is carried out according to the following steps:

[0060] Step One: Smelting

[0061] Cu: 4.9%, Mg: 1.8%, Mn: 0.9%, Zn: 0.3%, Ti: 0.15%, Zr: 0.15%, Fe: 0.05%, Si: 0.05%, and the balance is Al, and perform smelting to obtain alloy liquid.

[0062] Step Two: Casting

[0063] Pour the alloy liquid into a tube blank.

[0064] Step 3: Multi-stage homogenization treatment

[0065] Heat the tube blank to 425°C and hold for 12 h; then heat to 460°C and hold for 15 h; finally heat to 495°C and hold for 24 h; then naturally cool to room temperature to obtain a homogenized tube blank.

[0066] Step 4: Extrusion treatment

[0067] Heat the tube blank after multi-stage homogenization treatment to 435°C, hold for 20 min and then perform extrusion with an extrusion ratio greater than 18 and an extrusion speed of 48 mm / min to obtain an extruded tube blank.

[0068] Step 5: Two-stage solution treatment

[0069] Heat the extruded tube blank to 480°C, hold for 1 - 2 h and then heat to 500°C and hold for 1.5 h with a heating rate greater than 20°C / min; then cool by spraying water with a cooling rate of 50°C / s to obtain a tube blank after two-stage solution treatment.

[0070] Step 6: Pre-deformation

[0071] Perform pre-tensile deformation on the tube blank after two-stage solution treatment with a deformation amount of 3% to obtain a tube blank after pre-tensile deformation.

[0072] Step 7: Aging treatment

[0073] Perform natural aging or artificial aging treatment on the tube blank after pre-tensile deformation. The artificial aging is to hold at 195°C for 60 h to obtain a 380 MPa grade heat-resistant aluminum alloy casing.

[0074] Example 3

[0075] The composition of the 380 MPa grade heat-resistant aluminum alloy casing by weight percentage is as follows:

[0076] Cu: 4.3%, Mg: 1.5%, Mn: 0.5%, Zn: 0.2%, Ti: 0.1%, Zr: 0.1%, Fe: 0.03%, Si: 0.03%, and the balance is Al and impurities. Its manufacturing method is carried out according to the following steps:

[0077] Step 1: Smelting

[0078] Cu: 4.3%, Mg: 1.5%, Mn: 0.5%, Zn: 0.2%, Ti: 0.1%, Zr: 0.1%, Fe: 0.03%, Si: 0.03%, and the balance is Al, perform smelting to obtain alloy liquid.

[0079] Step 2: Casting

[0080] Cast the alloy liquid into a tube blank.

[0081] Step 3: Multi-stage homogenization treatment

[0082] Heat the tube blank to 418 °C and hold for 10 h; then heat to 452 °C and hold for 13 h; finally heat to 488 °C and hold for 22 h; then naturally cool to room temperature to obtain a homogenized tube blank.

[0083] Step 4: Extrusion treatment

[0084] Heat the tube blank after multi-stage homogenization treatment to 428 °C, hold for 20 min and then perform extrusion. The extrusion ratio is greater than 18 and the extrusion speed is 48 mm / min to obtain an extruded tube blank.

[0085] Step 5: Two-stage solution treatment

[0086] Heat the extruded tube blank to 475 °C, hold for 1.5 h and then heat to 495 °C and hold for 1.25 h. The heating rate is 25 °C / min; then cool by spraying water. The cooling rate is 40 °C / s to obtain a tube blank after two-stage solution treatment.

[0087] Step 6: Pre-deformation

[0088] Perform pre-tensile deformation on the tube blank after two-stage solution treatment. The deformation amount is 2.5% to obtain a tube blank after pre-tensile deformation.

[0089] Step 7: Aging treatment

[0090] Perform natural aging or artificial aging treatment on the tube blank after pre-tensile deformation. The artificial aging is to hold at 190 °C for 50 h to obtain a 380 MPa grade heat-resistant aluminum alloy casing.

[0091] The present invention discloses a 380 MPa grade heat-resistant aluminum alloy casing. Compared with the steel components used in conventional casings, the present invention has a higher Cu content (3.8 - 4.9%), a certain Mg content (1.2 - 1.8%), a lower Mn (0.3 - 0.9%), an appropriate Zn (Zn: ≤0.3%), trace amounts of Ti (≤0.15%) and Zr (≤0.15%) based on aluminum as the matrix in the alloy formula. The composition design is simple and the cost is low, making full use of the precipitation strengthening effect of Cu and Mg elements and the solid solution strengthening effect of Mn and Zn elements. With the above components combined with the thermomechanical treatment process, not only the comprehensive performance of the product is improved, but also a flexible extrusion production process can be adopted to improve the production rate. The product produced with a higher Cu content combined with thermomechanical treatment and double-stage aging process has high strength and improved heat resistance, making the aluminum alloy casing pipe have good high-temperature resistance performance. Compared with traditional steel casings, the aluminum alloy casing has excellent characteristics such as high specific strength, high temperature resistance, corrosion resistance, and low frictional resistance, and has natural advantages in harsh oil and gas wells such as deep wells, ultra-deep wells, directional wells, sour gas wells, and deep-sea oil and gas wells. The performance of the 380 MPa grade high-strength heat-resistant aluminum alloy casing manufactured by the present invention is as follows:

[0092] a) Tensile properties of the pipe body, yield strength R t0.2 = 420 MPa, tensile strength R m = 530 MPa, elongation δ = 18.0.

[0093] b) Heat resistance of the pipe body, yield strength after thermal exposure at 160 °C for 500 hours = 280 MPa.

[0094] c) The microstructure of the pipe body is mainly composed of dispersed and refined S phases.

[0095] The working principle of the present invention is as follows:

[0096] (1) By controlling the appropriate weight percentages of each element, the present invention makes full use of the precipitation strengthening of Cu and Mg elements, the solid solution strengthening and grain refinement of Mn element at the solution treatment temperature, the solid solution strengthening and aging strengthening of Zn element, and the grain refinement of the composite addition of Ti and Zr, giving full play to the combined effects of solid solution strengthening, precipitation strengthening, and grain refinement, thereby improving the strength, hardness, and thermal strength of the pipe body for aluminum alloy drill pipes. In the present invention, due to the simple alloy composition design and the absence of the need to add precious metal elements such as Ag to improve thermal strength, the cost is low.

[0097] (2) In the process of this invention, heat treatment processes such as multi-stage homogenization treatment, multi-stage solution treatment, and aging, which are designed to match the alloy design, are adopted. Through higher homogenization and solution temperature treatment, segregation and non-uniformity inside the matrix are largely eliminated, the remelting of the unmelted eutectic phase inside the aluminum alloy matrix is significantly promoted, and through higher artificial aging temperature treatment, the stability of the dispersion-precipitated strengthening phase is promoted, thereby improving the hot strength performance while maintaining high strength at room temperature.

[0098] (3) In this invention, Cu and Mg are used as the main alloying elements. Cu is dissolved in the alloy matrix, causing lattice distortion and producing a solution strengthening effect, which can improve the room temperature strength of the aluminum alloy. After aging treatment, body-centered tetragonal θ and θ′ phases precipitate, improving the heat resistance of the alloy. Cu can improve the hot working performance, inhibit the extrusion effect, and reduce the anisotropy caused by Mn in the alloy. Adding Mg element to the Al-Cu alloy can significantly increase the nucleation rate of the precipitated phase during the aging process of the alloy, refine the alloy grains, not only improve the microstructure of the Al-Cu alloy after aging, but also improve the strength and plasticity of the alloy after artificial aging. A binary θ(Al 2 Cu) phase is formed between Al and Cu, and Cu and Mg will form a high-concentration ternary solid solution S(Al 2 CuMg) phase in the tube body with Al. The solubility of these two phases in the aluminum alloy tube body decreases rapidly with the decrease of temperature, and they are dispersed and precipitated to strengthen the aluminum alloy matrix. The strengthening effect increases with the increase of the content of Cu and Mg elements, which is beneficial to maintaining high physical and mechanical properties of the aluminum alloy casing under long-term service conditions at 160 °C. However, excessive content of Cu and Mg elements will significantly reduce the plasticity and toughness of the aluminum alloy tube body. Therefore, the weight percentage content of Cu in the aluminum alloy tube body is controlled to be 3.8 - 4.9%, and the weight percentage content of Mg is controlled to be 1.2 - 1.8%.

[0099] (4) Mn is an economical strengthening element in high-strength heat-resistant aluminum alloy casings. During the casting process, Mn and Al will form a metastable phase Al 6 Mn dispersion phase, which has the effect of hindering the movement of grain boundaries and dislocations, increasing the recrystallization temperature, and can prevent the dynamic recrystallization during the hot extrusion process of the aluminum alloy and the recrystallization process during the solution process, significantly refining the recrystallized grains. Adding Mn can weaken the negative impact of the impurity element Fe on the alloy, and the presence of Mn element can also delay and weaken the artificial over-aging process of the alloy, improving the heat-resistant strength of the alloy. However, excessive Mn will reduce the solubility of solute elements such as Zn and Mg in the matrix, thereby reducing the strength and toughness. Therefore, the weight percentage content of Mn in the aluminum alloy tube body is controlled to be 0.3 - 0.9%.

[0100] (5) Zn is a strengthening element that increases the strength in high-strength heat-resistant aluminum alloy sleeves. When Zn, Cu, and Mg are simultaneously added to the aluminum alloy, an obvious strengthening effect can be produced, thereby increasing the tensile strength and yield strength of the material. The combined addition of Zn with alloying elements such as Zr, Si, and Mn has the effect of refining the dendrites of the Al-Cu-Mg alloy ingot, enhancing the hot strength performance of the material to a certain extent. However, excessive Zn will lead to a decrease in the plasticity and corrosion resistance of the aluminum alloy tube body. Under deformation conditions, the improvement of the strength of the aluminum alloy by Zn is very limited, and there is also a tendency of stress corrosion cracking. Therefore, the weight percentage content of Zn in the aluminum alloy tube body is optimized and controlled to be ≤0.3%.

[0101] (6) Ti and Zr are elements that refine grains and inhibit recrystallization in high-strength heat-resistant aluminum alloy sleeves. Zr is a transition element, which can significantly refine the as-cast grains of the alloy, obtain a non-dendritic structure, and improve the casting performance; after homogenization treatment, it combines with aluminum to form fine and dispersed high-melting-point Al 3 Zr particles, which have a strong pinning effect on the dislocations and grain boundaries in the alloy, and can effectively prevent recrystallization and grain growth during hot processing. The dispersed particles Al 3 Zr also has an interface coherent with the matrix, greatly reducing the possibility of precipitation of the equilibrium phase on the interface of the dispersed particles Al 3 Zr during the quenching process, thereby improving the quenching sensitivity of the alloy. A trace amount of Ti and an appropriate amount of Zr can achieve the above effects. Therefore, the weight percentage content of Ti in the aluminum alloy tube body is controlled to be ≤0.15%, and the weight percentage content of Zr is controlled to be ≤0.15%.

[0102] (7) Fe and Si (silicon) are harmful impurities in high-strength heat-resistant aluminum alloy sleeves. They can form a variety of insoluble primary phases and refractory non-equilibrium phases with Al and other alloying elements. Vacancies, pores, and cracks are easily formed on their phase interfaces, thereby reducing the plasticity, toughness, and fatigue resistance of the aluminum alloy. Therefore, the contents of Fe and Si should be strictly controlled. The weight percentage content of Fe in the aluminum alloy tube body is controlled to be ≤0.15%, and the weight percentage content of Si is controlled to be ≤0.15%.

[0103] (8) The properties of the 380 MPa grade high-strength heat-resistant aluminum alloy sleeve manufactured by the present invention are as follows:

[0104] a) The tensile properties of the tube body, the yield strength R t0.2 = 380 - 400 MPa, the tensile strength R m ≥500 MPa, and the elongation δ≥12.0.

[0105] b) The heat-resistant properties of the tube body, the yield strength after hot exposure at 160 °C for 500 hours ≥266 MPa.

[0106] c) The microstructure of the tube body is mainly composed of dispersed and refined S phases.

[0107] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A heat-resistant aluminum alloy casing of 380 MPa grade, characterized in that, by weight percentage, it includes: Cu: 3.8 - 4.9%, Mg: 1.2 - 1.8%, Mn: 0.3 - 0.9%, Zn: ≤0.3%, Ti: ≤0.15%, Zr: ≤0.15%, Fe: ≤0.05%, Si: ≤0.05%, and the balance is Al and unavoidable impurities.

2. A manufacturing method of the heat-resistant aluminum alloy casing of 380 MPa grade described in claim 1, characterized in that, successively includes the following steps: smelting, casting, multi-stage homogenization treatment, extrusion treatment, two-stage solution treatment, pre-deformation and aging treatment.

3. According to the manufacturing method of the heat-resistant aluminum alloy casing of 380 MPa grade described in claim 2, characterized in that, the smelting is: Smelt Cu: 3.8 - 4.9%, Mg: 1.2 - 1.8%, Mn: 0.3 - 0.9%, Zn: ≤0.3%, Ti: ≤0.15%, Zr: ≤0.15%, Fe: ≤0.05%, Si: ≤0.05%, and the balance is Al to obtain alloy liquid.

4. According to the manufacturing method of the heat-resistant aluminum alloy casing of 380 MPa grade described in claim 3, characterized in that, the casting is: Cast the alloy liquid into a tube blank.

5. According to the manufacturing method of the heat-resistant aluminum alloy casing of 380 MPa grade described in claim 4, characterized in that, the multi-stage homogenization treatment is: Heat the tube blank to 410 - 425 °C and hold for 8 - 12 h; then heat to 445 - 460 °C and hold for 10 - 15 h; finally heat to 480 - 495 °C and hold for 20 - 24 h; then naturally cool to room temperature to obtain a homogenized tube blank.

6. According to the manufacturing method of the heat-resistant aluminum alloy casing of 380 MPa grade described in claim 5, characterized in that, the heating rate is 10 - 20 °C / min.

7. According to the manufacturing method of the heat-resistant aluminum alloy casing of 380 MPa grade described in claim 6, characterized in that, the extrusion treatment is: Heat the tube blank after multi-stage homogenization treatment to 420 - 435 °C, hold for 20 min and then extrude, the extrusion ratio is greater than 18, and the extrusion speed is 48 mm / min to obtain an extruded tube blank.

8. According to the manufacturing method of the heat-resistant aluminum alloy casing of 380 MPa grade described in claim 7, characterized in that, the two-stage solution treatment is: Heat the extruded tube blank to 470 - 480 °C, hold for 1 - 2 h and then heat to 490 - 500 °C and hold for 1 - 1.5 h, the heating rate is greater than 20 °C / min; then cool by spraying water, and the cooling rate is 30 - 50 °C / s to obtain a tube blank after two-stage solution treatment.

9. According to the manufacturing method of the heat-resistant aluminum alloy casing of 380 MPa grade described in claim 8, characterized in that, the pre-deformation is: Perform pre-tensile deformation on the tube blank after two-stage solution treatment, and the deformation amount is 2 - 3% to obtain a tube blank after pre-tensile deformation.

10. The manufacturing method of the 380 MPa grade heat-resistant aluminum alloy casing according to claim 9, characterized in that, the aging treatment is as follows: naturally aging or artificially aging the tube blank after pre-stretching deformation, and the artificial aging is to keep the temperature at 185-195 °C for 6-60 h to obtain the 380 MPa grade heat-resistant aluminum alloy casing.