An Al-Zn-Cu-Mg aluminum alloy bar and its preparation method

Abstract

The present invention discloses an Al-Zn-Cu-Mg aluminum alloy bar and a preparation method thereof, belonging to the technical field of metal materials. By regulating the content of each component of the aluminum alloy and the Zn / Mg ratio, the solubility of the main strengthening phases η(MgZn2) and T(AlZnMgCu) is increased, the hardenability of the aluminum alloy is improved, and the mechanical properties of the Al-Zn-Cu-Mg aluminum alloy bar are enhanced. Moreover, the Al-Zn-Cu-Mg aluminum alloy bar has small segregation, and there are fewer remaining coarse second phases such as η(MgZn2), T(AlZnMgCu), S(Al2CuMg), and CrAl7. The second-phase compounds precipitate out from the solid solution and are dispersedly distributed in the uniform and fine alloy structure.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and particularly relates to an Al-Zn-Cu-Mg aluminum alloy bar and a preparation method thereof. Background Art

[0002] The Al-Zn-Mg-Cu alloy is developed by adding Cu on the basis of the Al-Zn-Mg alloy. Its strength is higher than that of the 2xxx series aluminum alloy, and it is called an ultra-high strength aluminum alloy. It has a high yield ratio, a high specific strength, and particularly good low-temperature strength. It is suitable for load-bearing structural parts used at normal temperature and below 120°C. The alloy is easy to process, has good corrosion resistance and high toughness, and is widely used in the fields of aerospace and weapons, and has become one of the most important structural materials in the field.

[0003] With the rapid development of aerospace and weapons, integral structural parts can significantly reduce the weight of components and reduce the assembly cost. Therefore, the parts of aluminum alloy materials are developing towards large-scale, the components are developing towards large integralization, and the shapes of the parts are becoming more complex. However, the Al-Zn-Mg-Cu alloy has strong quenching sensitivity, and there are significant differences in mechanical properties between the surface layer and the core of the product after quenching and aging.

[0004] Due to the high degree of alloying of the Al-Zn-Mg-Cu alloy, its crystallization temperature range is wide, the plasticity in the solid-liquid zone is low, and it has a great tendency to form hot cracks and porosity. As the aluminum alloy billet develops towards the super-large and super-thick direction, the ingot specification increases and the casting performance deteriorates. At the same time, after the size of the aluminum alloy billet becomes thicker, the performance of the middle layer of the large-section semi-finished product depends on the hardenability (for example, the hardenability of the 7075 alloy is only 25 mm). The larger the size, the more obvious the reduction of the middle part performance, especially the yield strength, resulting in it being difficult for high-strength bars with a specification of Φ100 - 250 mm to meet the user's requirements.

[0005] The chemical composition and the solubility of the main alloying elements (or second phases) have a great influence on the hardenability. However, with the optimization and adjustment of the composition, the control difficulty increases, and the casting performance also deteriorates. Therefore, the requirements for the chemical composition design, casting and heat treatment processes of the Al-Zn-Mg-Cu alloy are very high. The current production process is prone to casting cracking, unqualified performance, etc., which seriously restricts the rapid development of the application of this aluminum alloy thick-section material. It is difficult to meet the product requirements for the existing technology of Al-Zn-Mg-Cu aluminum alloy. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide an Al-Zn-Cu-Mg aluminum alloy bar and a preparation method thereof. The Al-Zn-Cu-Mg aluminum alloy bar has good hardenability and mechanical properties.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides an Al-Zn-Cu-Mg aluminum alloy bar, which, by mass percentage, comprises:

[0009] Si ≤ 0.10%;

[0010] Fe ≤ 0.25%;

[0011] Cu: 0.8% - 1.5%;

[0012] Mn ≤ 0.10%;

[0013] Mg: 1.6% - 2.5%;

[0014] Cr: 0.10% - 0.25%;

[0015] Zn: 5.7% - 7.5%;

[0016] Ti ≤ 0.05%;

[0017] Na ≤ 0.0005%;

[0018] Be: 0.0005% - 0.002%;

[0019] The balance is Al;

[0020] wherein Zn / Mg is 2.6 - 4.67.

[0021] In the above Al-Zn-Cu-Mg aluminum alloy bar, Zn and Mg are the main strengthening elements, producing the main strengthening phases MgZn2 and AlZnMgCu. The increase in the contents of Zn and Mg can significantly improve the strength and hardness of the Al-Zn-Cu-Mg aluminum alloy bar, but will reduce its plasticity, stress corrosion resistance and fracture toughness.

[0022] By controlling the content of Cu in the above Al-Zn-Cu-Mg aluminum alloy bar to be 0.8 wt% - 1.5 wt%, the content of Mg to be 1.6 wt% - 2.5 wt%, the content of Zn to be 5.7 wt% - 7.5 wt%, and the contents of Zn and Mg satisfy Zn / Mg of 2.6 - 4.67, the hardenability of the Al-Zn-Cu-Mg aluminum alloy can be improved.

[0023] Because when the Cu content is constant, the quenching sensitivity first decreases and then increases with the increase of the Zn / Mg ratio. When the Zn / Mg ratio increases in the range of 2.6 - 4.67, the quenching sensitivity shows a decreasing trend, while the hardenability depth shows an increasing trend, indicating better hardenability. When the Zn / Mg ratio increases in the range of 2.6 - 4.67, with the increase of the Zn mass fraction in the alloy, more and more stable Zn-containing clusters and a large number of vacancies are produced. The Mg-containing clusters are easily decomposed, and the large number of vacancies can promote the diffusion of Mg atoms and transform into η' phases with smaller particle size, higher density and better strengthening effect during aging.

[0024] Adding 0.8wt% - 1.5wt% Cu can improve the corrosion resistance of Al-Zn-Cu-Mg aluminum alloy and increase the tensile strength. At the same time, within a certain range of Mg and Zn contents, the addition of Cu can also maintain the strength of Al-Zn-Cu-Mg aluminum alloy and improve its plasticity because the addition of Cu will improve the quenching effect and increase the concentration of supersaturated solid solution. However, when the Cu content exceeds 1.5wt%, more Zn, Cu, and Mg elements will dissolve in the aluminum matrix in the Al-Zn-Cu-Mg aluminum alloy rod, increasing the solid solubility of alloying elements (Zn, Cu, Mg), resulting in severe lattice distortion and hindering the movement of free electrons. Instead, it causes a significant decrease in the cooling rate during the quenching process, and the solid solution will decompose, precipitating some coarse secondary phases (such as η(MgZn2), T(AlZnMgCu), S(Al2CuMg), CrAl7) in the intragranular dispersed particles and grain boundaries. This greatly reduces the number of Zn and Mg solute atoms retained in the solid solution, so the number of precipitation strengthening phases obtained after aging decreases, thus causing the mechanical properties of the Al-Zn-Cu-Mg alloy to decline and making it difficult to meet user requirements.

[0025] For Al-Zn-Cu-Mg alloy, both Si and Fe are harmful impurities. Si reacts with Mg in the alloy to form the Mg2Si phase, reducing the amounts of MgZn2, AlMgZnCu, and Al2CuMg phases in the alloy. These phases have a higher strengthening effect than the Mg2Si phase. Therefore, a high content of Si will reduce the strength of the alloy. When the Fe content is within 0.25%, it can slightly increase the tensile strength. However, when it exceeds 0.25%, Fe will form insoluble compounds with Mn, Cr, etc., reducing the contents of Mn and Cr in the supersaturated melt, resulting in a decrease in both quenching and aging effects. At the same time, excessive Si and Fe contents will also increase the tendency of casting cracks.

[0026] In the present invention, the mass percentage content of the Si is preferably 0 - 0.08%.

[0027] Adding a small amount of Mn and Cr elements can increase the recrystallization temperature, refine the grains, and improve the stress corrosion resistance. The functions of Mn and Cr are basically the same. In terms of improving stress corrosion resistance, adding Cr has a better effect than Mn. Adding Cr can increase the stress corrosion cracking life by dozens to hundreds of times compared with the same amount of Mn. When the Cr content is 0.2wt%, the aging effect reaches the maximum value. However, both Mn and Cr are difficult-to-dissolve additives. As the contents of Mn and Cr increase, the aluminum aging process and the decomposition process of supersaturated solid solution will be accelerated, thus significantly reducing the hardenability. Therefore, controlling the contents of Mn and Cr within a certain range is beneficial to the improvement of mechanical properties.

[0028] In the present invention, the mass percentage content of Mn is preferably 0 to 0.08%.

[0029] The mass percentage content of Cr is preferably 0.15% to 0.25%.

[0030] The mass percentage content of Ti is preferably 0.01% to 0.03%.

[0031] The mass percentage content of Be is preferably 0.0005% to 0.0015%.

[0032] Preferably, the Al-Zn-Cu-Mg aluminum alloy bar in the present invention, by mass percentage, comprises:

[0033] Si ≤ 0.08%;

[0034] Fe ≤ 0.25%;

[0035] Cu: 0.8% to 1.5%;

[0036] Mn ≤ 0.08%;

[0037] Mg: 1.6% to 2.5%;

[0038] Cr: 0.15% to 0.25%;

[0039] Zn: 5.7% to 7.5%;

[0040] Ti: 0.01% to 0.03%;

[0041] Na ≤ 0.0005%;

[0042] Be: 0.0005% to 0.0015%;

[0043] The balance is Al;

[0044] wherein Zn / Mg is 2.6 to 4.67.

[0045] In some specific embodiments of the present invention, preferably, the Al-Zn-Cu-Mg aluminum alloy bar, by mass percentage, comprises:

[0046] Si: 0.05%;

[0047] Fe: 0.20%;

[0048] Cu: 1.40%;

[0049] Mn: 0.04%;

[0050] Mg: 2.30%;

[0051] Cr: 0.20%;

[0052] Zn: 6.02%;

[0053] Ti: 0.02%;

[0054] Be: 12 ppm;

[0055] Na: 2 ppm;

[0056] The balance is Al;

[0057] wherein, Zn / Mg is 2.62.

[0058] Preferably, the Al-Zn-Cu-Mg aluminum alloy bar, by mass percentage, comprises:

[0059] Si: 0.06%;

[0060] Fe: 0.19%;

[0061] Cu: 1.43%;

[0062] Mn: 0.05%;

[0063] Mg: 2.20%;

[0064] Cr: 0.21%;

[0065] Zn: 6.04%;

[0066] Ti: 0.02%;

[0067] Be: 10 ppm;

[0068] Na: 2 ppm;

[0069] The balance is Al;

[0070] wherein, Zn / Mg is 2.75.

[0071] Preferably, the Al-Zn-Cu-Mg aluminum alloy bar, by mass percentage, comprises: Si: 0.04%;

[0072] Fe: 0.18%;

[0073] Cu: 1.48%;

[0074] Mn: 0.02%;

[0075] Mg: 2.26%;

[0076] Cr: 0.21%;

[0077] Zn: 5.90%;

[0078] Ti: 0.02%;

[0079] Be: 9 ppm;

[0080] Na: 2 ppm;

[0081] The balance is Al;

[0082] wherein, Zn / Mg is 2.61.

[0083] Preferably, the Al-Zn-Cu-Mg aluminum alloy bar, by mass percentage, comprises: Si: 0.05%;

[0084] Fe: 0.16%;

[0085] Cu: 1.50%;

[0086] Mn: 0.03%;

[0087] Mg: 2.28%;

[0088] Cr: 0.21%;

[0089] Zn: 6.03%;

[0090] Ti: 0.03%;

[0091] Be: 10 ppm;

[0092] Na: 2 ppm;

[0093] The balance is Al;

[0094] wherein, Zn / Mg is 2.64.

[0095] For the Al-Zn-Cu-Mg aluminum alloy bar of the present invention, its diameter is preferably 100 - 250 mm.

[0096] When the diameter is 100 - 150 mm, the tensile strength of the Al-Zn-Cu-Mg aluminum alloy bar is ≥550 MPa, the yield strength is ≥470 MPa, and the elongation is ≥7%.

[0097] The tensile strength of the Al-Zn-Cu-Mg aluminum alloy bar is preferably 550 - 580 MPa.

[0098] The yield strength of the Al-Zn-Cu-Mg aluminum alloy bar is preferably 470 - 500 MPa.

[0099] The elongation of the Al-Zn-Cu-Mg aluminum alloy bar is preferably 7% - 10%; more preferably 7% - 8%.

[0100] In some specific embodiments of the present invention, when the diameter is preferably 140 mm, the tensile strength of the Al-Zn-Cu-Mg aluminum alloy bar is preferably 576 MPa, the yield strength is preferably 490 MPa, and the elongation is preferably 7.5%.

[0101] When the diameter is 150 - 250 mm, the tensile strength of the Al-Zn-Cu-Mg aluminum alloy bar is preferably ≥470 MPa, the yield strength is preferably ≥400 MPa, and the elongation is preferably ≥7%.

[0102] In some specific embodiments of the present invention, the diameter is preferably 200 mm, 230 mm or 155 mm.

[0103] The tensile strength of the Al-Zn-Cu-Mg aluminum alloy bar is preferably 520 - 600 MPa, more preferably 531 MPa, 550 MPa or 591 MPa.

[0104] The yield strength of the Al-Zn-Cu-Mg aluminum alloy bar is preferably 400 MPa - 520 MPa, more preferably 430 MPa, 450 MPa or 510 MPa.

[0105] The elongation of the Al-Zn-Cu-Mg aluminum alloy bar is preferably 8% - 13%; more preferably 10% - 11%; further preferably 10% or 11%.

[0106] The present invention also provides a method for preparing an Al-Zn-Cu-Mg aluminum alloy bar, comprising the following steps:

[0107] Melting the alloy raw materials, purifying the melt, refining the grains, casting, homogenizing annealing, extruding, stretch straightening, solution quenching, and aging treatment to obtain the Al-Zn-Cu-Mg aluminum alloy bar.

[0108] Preferably, the melting temperature is 730°C to 770°C.

[0109] Preferably in the present invention, the melt purification includes in-furnace purification, on-line purification, and on-line filtration.

[0110] Preferably, the in-furnace purification is carried out by one or more of powder injection purification, argon purification, and argon-chlorine mixed gas purification.

[0111] Preferably, the powder injection purification uses a granular refining agent.

[0112] Preferably, the on-line purification is carried out using argon or an argon-chlorine mixed gas. After completion, the hydrogen content of the melt is controlled to be ≤0.15 mL / 100 g Al, and the Na content is controlled to be ≤0.0005 wt%.

[0113] Trace impurity Na can damage the casting and hot deformation properties of the alloy, resulting in "sodium brittleness". Controlling the Na content ≤0.0005% in the present invention can prevent alloy cracking caused by sodium brittleness.

[0114] Preferably, the on-line filtration is selected from plate filtration or deep bed filtration.

[0115] Preferably, the grain refiner for grain refinement is selected from Al-5Ti-1B wire.

[0116] Preferably, the dosage of the Al-5Ti-1B wire is 1.4 to 2.2 kg / t.

[0117] Since the large-sized ingots of Al-Zn-Cu-Mg have a large crack tendency, a bottom-laying operation is carried out before casting. Because pure aluminum has good plasticity and a large linear shrinkage coefficient, it can effectively deform to resist the tensile stress at the bottom, effectively preventing cracks at the bottom of the ingot.

[0118] The larger the size of the Al-Zn-Cu-Mg aluminum alloy ingot, the greater the temperature difference between the inner and outer layers of the ingot, and the corresponding increase in the thermal stress in the ingot, increasing the crack tendency of the ingot. In order to reduce the thermal stress during casting, a wiper can be added while laying the bottom.

[0119] Preferably in the present invention, the casting is carried out by a combined treatment of the bottom-laying process and the wiper process.

[0120] Preferably, the above bottom-laying process uses Al99.70 aluminum ingots for bottom-laying.

[0121] Preferably, the temperature of the bottom-laying aluminum ingot is 730°C to 760°C; more preferably 730°C to 760°C.

[0122] Preferably, the thickness of the bottom-laying aluminum ingot is 40 to 100 mm; more preferably 40 to 100 mm.

[0123] In the wiper process described above, the length at which the wiper starts to wipe is preferably ≥400 mm, and the height of the wiper is preferably 150 - 300 mm.

[0124] Increasing the casting speed can make the ingot grains fine and improve the density of the ingot, but if it is too high, it will increase the tendency of central cracks. With the increase of the cooling intensity, the size of the primary crystal compounds can be refined, the regional segregation can be reduced, and the density of the ingot can be improved. In order to obtain a fine and uniform ingot structure and comprehensive product performance, in the present invention, the casting speed is 18 - 30 mm / min.

[0125] During the casting process, the water flow rate is preferably 5 - 15 m 3 / h / root, the temperature of the molten aluminum at the end of the launder is preferably 690°C - 720°C, and the water temperature is preferably 18°C - 30°C.

[0126] After the above casting is completed, it also includes homogenization heat treatment.

[0127] After the melt is cast to obtain an ingot, in order to eliminate the ingot stress, reduce the ingot segregation and obtain a dispersion-distributed compound, and meet the requirements of a uniform fine-grained bar, the ingot needs to be subjected to high-temperature homogenization annealing treatment. This annealing can cause partial decomposition of the solid solution and, through sufficient diffusion, reduce the coarse residual second phase.

[0128] In the present invention, the heating rate of the homogenization heat treatment is preferably 50 - 100°C / h.

[0129] The heating time of the homogenization heat treatment is preferably 6 - 10 h.

[0130] The heating temperature of the homogenization heat treatment is preferably 480°C - 550°C.

[0131] The holding temperature of the homogenization heat treatment is preferably 455°C - 475°C.

[0132] The holding time of the homogenization heat treatment is preferably 12 - 30 h.

[0133] After heat treatment, the obtained ingot is further processed to obtain an Al-Zn-Cu-Mg aluminum alloy bar.

[0134] The diameter of the bar is 100 - 250 mm, and its mechanical properties can better meet the needs of users.

[0135] When the diameter is 100 - 150 mm, the tensile strength of the Al-Zn-Cu-Mg aluminum alloy bar is ≥550 MPa, the yield strength is ≥470 MPa, and the elongation is ≥7%.

[0136] When the diameter is 150 - 250 mm, the tensile strength of the Al-Zn-Cu-Mg aluminum alloy bar is ≥470 MPa, the yield strength is ≥400 MPa, and the elongation is ≥7%.

[0137] Compared with the prior art, the Al-Zn-Cu-Mg aluminum alloy bar provided by the present invention regulates the content of each component of the aluminum alloy and the Zn / Mg ratio, increases the solubility of the main strengthening phases η(MgZn2) and T(AlZnMgCu), improves the hardenability of the aluminum alloy, and enhances the mechanical properties of the Al-Zn-Cu-Mg aluminum alloy bar. Moreover, the Al-Zn-Cu-Mg aluminum alloy bar has small segregation, and there are fewer remaining coarse second phases such as η(MgZn2), T(AlZnMgCu), S(Al2CuMg), and CrAl7. The second-phase compounds precipitate from the solid solution and are dispersed in the uniform and fine structure. Detailed implementation mode

[0138] To further illustrate the present invention, the following describes in detail the Al-Zn-Cu-Mg bar aluminum alloy bar and its preparation method provided by the present invention in conjunction with embodiments.

[0139] Example 1

[0140] The ingot specification is Φ500 mm, and the bar specification is Φ140 mm.

[0141] Add the raw material Al99.70 grade aluminum ingots, waste materials, master alloys, and pure metal ingredients into the melting furnace in a certain proportion and in a corresponding order. At the highest furnace gas temperature of 1150 °C, melt the raw materials, and perform manual, mechanical, or electromagnetic stirring during the melting process; after melting is completed, a melt is obtained.

[0142] Take a sample of the melt, analyze the content of each component, adjust the component content to the target value to meet the above formula. The inside of the furnace is purified with a mixed gas of argon and chlorine; after the in-furnace purification is completed, online purification is carried out with argon or an argon-chlorine mixed gas. The liquid hydrogen content of the melt after online purification is 0.12 mL / 100 g Al; after online purification, the melt is filtered with a 30 + 50 ppi foam ceramic filter plate.

[0143] After filtration, the obtained melt is refined with Al-5Ti-1B wire, and the dosage is 1.5 kg / t.

[0144] After grain refinement is completed, start casting. Use Al99.70 aluminum ingots to lay the bottom, the laying temperature is 740 °C, the thickness is 50 mm, the casting speed is 25 mm / min, the aluminum liquid temperature at the end of the runner is 702 °C, the cooling water temperature is 27 °C, and the cooling water flow rate is 8 m 3 / h / root.

[0145] The cast aluminum alloy is subjected to homogenization heat treatment. The heating rate for homogenization annealing of the ingot is 60 °C / h, the heating time is 9 h, the heating temperature is 500 °C, the holding temperature is 460 - 470 °C, and the holding time is 16 h; then it is sawed into blanks (ingots) for delivery.

[0146] The test results of the ingot are as follows:

[0147] (1) Macrostructure results of the ingot: Grain size is grade 1.5, and porosity is grade 1; the testing method is GB / T 3246.2 "Test Methods for Microstructure of Wrought Aluminum and Aluminum Alloy Products - Part 2 Macrostructure Inspection Methods".

[0148] (2) Chemical composition (wt%): Si 0.05%, Fe 0.20%, Cu 1.40%, Mn 0.04%, Mg 2.30%, Cr 0.20%, Zn 6.02%, Ti 0.02%, Be 12 ppm, Na 2 ppm, Zn / Mg 2.62; the testing methods are GB / T 20975 "Analytical Methods for Aluminum Alloys" and GB / T 7999 "Optical Emission Spectrometric Analysis Method for Aluminum and Aluminum Alloys".

[0149] (3) Liquid hydrogen content: 0.12 mL / 100 g Al; the testing method is YS / T 600 "Closed-Circuit Circulation Method for Measuring Hydrogen in Liquid Aluminum and Aluminum Alloys".

[0150] The above ingot is subjected to homogenization annealing, extrusion, stretch straightening, solution quenching, and aging treatment to obtain Al-Zn-Cu-Mg aluminum alloy bars.

[0151] The test results of the bars are as follows:

[0152] Mechanical property results: Tensile strength is 576 MPa, yield strength is 490 MPa, and elongation is 7.5%; the testing method is GB / T 228.1 - 2010 "Metallic Materials - Tensile Testing - Part 1: Method of Test at Room Temperature".

[0153] Example 2

[0154] The ingot size is Φ660 mm, and the bar size is Φ200 mm.

[0155] Raw material aluminum ingots of Al99.70 grade, scrap, master alloys, and pure metals are proportioned and added to the melting furnace in a corresponding order. At a maximum furnace gas temperature of 1150 °C, the raw materials are melted, and manual, mechanical, or electromagnetic stirring is carried out during the melting process; after melting is completed, a melt is obtained.

[0156] Take a sample of the melt, analyze the content of each component, adjust the component content to the target value to meet the above formula. Use a mixed gas of argon and chlorine for in-furnace purification; after the in-furnace purification is completed, use argon or a mixed gas of argon and chlorine for online purification. The liquid hydrogen content of the melt after online purification is 0.10 mL / 100 g Al; after online purification, filter the melt with a foam ceramic filter plate of 30 + 50 ppi.

[0157] After filtration, use Al-5Ti-1B wire to refine the grains of the obtained melt, and the dosage is 1.8 kg / t.

[0158] After grain refinement is completed, start casting. Use Al99.70 aluminum ingots to lay the bottom, the laying temperature is 745 °C, the thickness is 60 mm, the casting speed is 19 mm / min, the molten aluminum temperature at the end of the runner is 705 °C, the cooling water temperature is 25 °C, and the cooling water flow rate is 10 m 3 / h / root.

[0159] Perform homogenization heat treatment on the cast aluminum alloy. The heating rate for the homogenization annealing of the ingot is 60 °C / h, the heating time is 9 h, the heating temperature is 500 °C, the holding temperature is 460 - 470 °C, and the holding time is 20 h; then saw it into blanks (ingots) for delivery.

[0160] The test results of the ingot are as follows:

[0161] (1) Macrostructure result of the ingot: The grain size is grade 1.5, and the porosity is grade 1; the testing method is GB / T3246.2 "Test Methods for Microstructure of Wrought Aluminum and Aluminum Alloy Products - Part 2 Macrostructure Test Methods";

[0162] (2) Chemical composition (wt%): Si 0.06%, Fe 0.19%, Cu 1.43%, Mn 0.05%, Mg 2.20%, Cr 0.21%, Zn 6.04%, Ti 0.02%, Be 10 ppm, Na 2 ppm, Zn / Mg 2.75; the testing methods are GB / T 20975 "Analysis Methods for Aluminum Alloys" and GB / T 7999 "Optical Emission Spectrometric Analysis Methods for Aluminum and Aluminum Alloys";

[0163] (3) Liquid hydrogen content: 0.10 mL / 100 g Al; the testing method is YS / T600 "Closed-Circuit Circulation Method for Measuring Liquid Hydrogen in Aluminum and Aluminum Alloys";

[0164] Subject the above ingot to homogenization annealing, extrusion, stretch straightening, solution quenching, and aging treatment to obtain Al-Zn-Cu-Mg aluminum alloy bars.

[0165] The test results of the bars are as follows:

[0166] Mechanical property results: Tensile strength is 531 MPa, yield strength is 430 MPa, and elongation is 10%; The testing method is GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature".

[0167] Example 3

[0168] The ingot specification is Φ660 mm, and the bar specification is Φ230 mm.

[0169] Add the raw material Al99.70 grade aluminum ingots, scraps, master alloys, and pure metal ingredients into the melting furnace in a certain proportion and in the corresponding order. At the highest furnace gas temperature of 1150 °C, melt the raw materials, and conduct manual, mechanical, or electromagnetic stirring during the melting process; After melting is completed, a melt is obtained.

[0170] Take a sample of the melt, analyze the content of each component, adjust the component content to the target value to meet the above formula. Use a mixed gas of argon and chlorine for in-furnace purification; After in-furnace purification is completed, use argon or a mixed gas of argon and chlorine for on-line purification. The liquid hydrogen content of the melt after on-line purification is 0.13 mL / 100 g Al; After on-line purification, filter the melt with a 30 + 50 ppi foam ceramic filter plate.

[0171] After filtration, use Al-5Ti-1B wire to refine the grains of the obtained melt, and the dosage is 1.8 kg / t.

[0172] After grain refinement is completed, start casting. Use Al99.70 aluminum ingots to lay the bottom, the laying temperature is 745 °C, the thickness is 70 mm, the casting speed is 18 mm / min, the molten aluminum temperature at the end of the runner is 702 °C, the cooling water temperature is 23 °C, and the cooling water flow rate is 11 m 3 / h / root.

[0173] Conduct homogenization heat treatment on the cast aluminum alloy. The heating rate of the ingot homogenization annealing is 50 °C / h, the heating time is 10 h, the heating temperature is 500 °C, the holding temperature is 460 - 470 °C, and the holding time is 20 h; Then saw it into blanks (ingots) for delivery.

[0174] The test results of the ingot are as follows:

[0175] (1) Macrostructure results of the ingot: Grain size is grade 2, and porosity is grade 1; The testing method is GB / T 3246.2 "Test methods for the structure of wrought aluminium and aluminium alloy products - Part 2: Macrostructure examination methods";

[0176] (2) Chemical composition (wt%): Si 0.04%, Fe 0.18%, Cu 1.48%, Mn 0.02%, Mg 2.26%, Cr 0.21%, Zn 5.90%, Ti 0.02%, Be 9 ppm, Na 2 ppm, Zn / Mg 2.61; The detection methods are GB / T 20975 "Analysis Methods for Aluminum Alloys" and GB / T 7999 "Optical Emission Spectrometric Analysis Methods for Aluminum and Aluminum Alloys";

[0177] (3) Liquid hydrogen content: 0.13 mL / 100 g Al; The detection method is YS / T 600 "Closed-loop Circulation Method for Measuring Hydrogen in Liquid Aluminum and Aluminum Alloys";

[0178] The above ingots are subjected to homogenization annealing, extrusion, stretch straightening, solution quenching, and aging treatment to obtain Al-Zn-Cu-Mg aluminum alloy bars.

[0179] The test results of the bars are as follows:

[0180] Mechanical property results: Tensile strength 550 MPa, yield strength 450 MPa, elongation 11%; The detection method is GB / T 228.1-2010 "Metallic Materials - Tensile Testing - Part 1: Method of Test at Room Temperature".

[0181] Example 4

[0182] Ingot specification: Φ482 mm, bar specification: Φ155 mm.

[0183] Raw material aluminum ingots of Al99.70 grade, scraps, master alloys, and pure metals are proportioned and added to the melting furnace in a corresponding order. At a maximum furnace gas temperature of 1150 °C, the raw materials are melted, and manual, mechanical, or electromagnetic stirring is carried out during the melting process; after melting is completed, a melt is obtained.

[0184] Samples are taken from the melt to analyze the contents of each component, and the component contents are adjusted to the target values to meet the above formula. A mixed gas of argon and chlorine is used for in-furnace purification; after in-furnace purification is completed, online purification is carried out using argon or an argon-chlorine mixed gas. The liquid hydrogen content of the melt after online purification is 0.12 mL / 100 g Al; after online purification, the melt is filtered using a foam ceramic filter plate with 30 + 50 ppi.

[0185] After filtration, the obtained melt is grain refined using Al-5Ti-1B wire, and the dosage is 1.6 kg / t.

[0186] After grain refinement is completed, casting begins. Use Al99.70 aluminum ingots to lay the bottom, the laying temperature is 745 °C, the thickness is 50 mm, the casting speed is 27 mm / min, the aluminum liquid temperature at the end of the runner is 702 °C, the cooling water temperature is 25 °C, and the cooling water flow rate is 7 m3 / h / root.

[0187] The cast aluminum alloy is subjected to homogenization heat treatment. The heating rate of the ingot homogenization annealing is 50 °C / h, the heating time is 10 h, the heating temperature is 500 °C, the holding temperature is 460 - 470 °C, and the holding time is 18 h; then it is sawed into blanks (ingots) for delivery.

[0188] The test results of the ingot are as follows:

[0189] (1) Macrostructure results of the ingot: Grain size is 1.5, and porosity is 1; The testing method is GB / T3246.2 "Test Methods for Microstructure of Wrought Aluminum and Aluminum Alloy Products - Part 2 Macrostructure Inspection Method";

[0190] (2) Chemical composition (wt%): Si 0.05%, Fe 0.16%, Cu 1.50%, Mn 0.03%, Mg 2.28%, Cr 0.21%, Zn 6.03%, Ti 0.03%, Be 10 ppm, Na 2 ppm, Zn / Mg 2.64; The testing methods are GB / T 20975 "Analytical Methods for Aluminum Alloys" and GB / T 7999 "Optical Emission Spectrometric Analysis Method for Aluminum and Aluminum Alloys";

[0191] (3) Liquid hydrogen content: 0.13 mL / 100 g Al; The testing method is YS / T600 "Closed-Circuit Circulation Method for Measuring Hydrogen in Liquid Aluminum and Aluminum Alloys";

[0192] The above ingot is subjected to homogenization annealing, extrusion, stretch straightening, solution quenching, and aging treatment to obtain Al-Zn-Cu-Mg aluminum alloy bars.

[0193] The test results of the bars are as follows:

[0194] Mechanical property results: Tensile strength is 591 MPa, yield strength is 510 MPa, and elongation is 11%; The testing method is GB / T228.1 - 2010 "Metallic Materials - Tensile Testing - Part 1: Method of Test at Room Temperature".

[0195] The mechanical properties of the Al-Zn-Mg-Cu aluminum alloy bars prepared in the above Examples 1 - 4 all meet the usage requirements.

[0196] Comparative Example 1

[0197] Ingot specification: Φ482 mm, bar specification: Φ145 mm.

[0198] Charge the raw materials, i.e., Al99.70 grade aluminum ingots, scrap, master alloys, and pure metals, into the melting furnace in a certain proportion and in the corresponding order. At a maximum furnace gas temperature of 1150°C, melt the raw materials and conduct manual, mechanical, or electromagnetic stirring during the melting process; after melting is completed, obtain the melt.

[0199] Take samples of the melt, analyze the content of each component, adjust the component content to the target value to meet the above formula. Use a mixed gas of argon and chlorine for in-furnace purification; after in-furnace purification is completed, conduct online purification using argon or a mixed gas of argon and chlorine. The liquid hydrogen content of the melt after online purification is 0.15 mL / 100 g Al; after online purification, filter the melt using a foam ceramic filter plate with 30 + 50 ppi.

[0200] After filtration, refine the grains of the obtained melt using Al-5Ti-1B wire, with a dosage of 1.6 kg / t.

[0201] After grain refinement is completed, start casting. Use Al99.70 aluminum ingots to lay the bottom, with a laying temperature of 745°C, a thickness of 50 mm, a casting speed of 26 mm / min, the aluminum liquid temperature at the end of the runner being 700°C, the cooling water temperature being 25°C, and the cooling water flow rate being 7 m 3 / h / root.

[0202] Conduct homogenization heat treatment on the cast aluminum alloy. The heating rate for the ingot homogenization annealing is 50°C / h, the heating time is 10 h, the heating temperature is 500°C, the holding temperature is 460 - 470°C, and the holding time is 18 h; then saw it into blanks (ingots) for delivery.

[0203] The test results of the ingots are as follows:

[0204] (1) Macrostructure results of the ingot: Grain size is grade 1.5, and porosity is grade 1; the testing method is GB / T 3246.2 "Test Methods for Microstructure of Wrought Aluminum and Aluminum Alloy Products - Part 2 Macrostructure Inspection Method";

[0205] (2) Chemical composition (wt%): Si 0.05%, Fe 0.17%, Cu 1.82%, Mn 0.28%, Mg 2.50%, Cr 0.24%, Zn 5.91%, Ti 0.03%, Be 10 ppm, Na 2 ppm, Zn / Mg 2.36; the testing methods are GB / T 20975 "Analytical Methods for Aluminum Alloys" and GB / T 7999 "Optical Emission Spectrometric Analysis Method for Aluminum and Aluminum Alloys";

[0206] (3) Liquid hydrogen content: 0.13 mL / 100 g Al; the testing method is YS / T 600 "Closed-Circuit Circulation Method for Measuring Liquid Hydrogen in Aluminum and Aluminum Alloys";

[0207] The above ingots are subjected to homogenization annealing, extrusion, stretch straightening, solution quenching, and aging treatment to obtain Al-Zn-Cu-Mg aluminum alloy bars.

[0208] The test results of the bars are as follows:

[0209] Mechanical property results: tensile strength 539 MPa (with a small margin), yield strength 437 MPa, elongation 7.5%; the testing method is GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature". The results show that the Al-Zn-Cu-Mg aluminum alloy bars prepared in Comparative Example 1 do not meet the usage requirements.

[0210] Comparative Example 2

[0211] The ingot specification is Φ660 mm, and the bar specification is Φ205 mm.

[0212] The raw material Al99.70 grade aluminum ingots, scrap, master alloys, and pure metals are proportioned and added to the melting furnace in a corresponding order. At a maximum furnace gas temperature of 1150 °C, the raw materials are melted, and manual, mechanical, or electromagnetic stirring is carried out during the melting process; after melting is completed, a melt is obtained.

[0213] Samples are taken from the melt to analyze the content of each component, and the component content is adjusted to the target value to meet the above formula. A mixed gas of argon and chlorine is used for in-furnace purification in the furnace; after in-furnace purification is completed, argon or a mixed gas of argon and chlorine is used for on-line purification. The liquid hydrogen content of the melt after on-line purification is 0.15 mL / 100 g Al; after on-line purification, the melt is filtered with a 30 + 50 ppi foam ceramic filter plate.

[0214] After filtration, the obtained melt is subjected to grain refinement using Al-5Ti-1B wire, and the dosage is 1.6 kg / t.

[0215] After grain refinement is completed, casting starts. The bottom is paved with Al99.70 aluminum ingots, the paving temperature is 745 °C, the thickness is 50 mm, the casting speed is 26 mm / min, the aluminum liquid temperature at the end of the runner is 700 °C, the cooling water temperature is 25 °C, and the cooling water flow rate is 7 m 3 / h / root.

[0216] The cast aluminum alloy is subjected to homogenization heat treatment. The heating rate for ingot homogenization annealing is 50 °C / h, the heating time is 10 h, the heating temperature is 500 °C, the holding temperature is 460 - 470 °C, and the holding time is 18 h; then it is sawed into blanks (ingots) for delivery.

[0217] The test results of the ingots are as follows:

[0218] (1) Macrostructure results of the ingot: Grain size is Grade 1.5, and porosity is Grade 1. The testing method is GB / T 3246.2 "Test Methods for Microstructure of Wrought Aluminum and Aluminum Alloy Products - Part 2 Macrostructure Test Methods".

[0219] (2) Chemical composition (wt%): Si 0.05%, Fe 0.14%, Cu 1.62%, Mn 0.19%, Mg 2.36%, Cr 0.19%, Zn 5.48%, Ti 0.03%, Be 9 ppm, Na 2 ppm, Zn / Mg 2.32. The testing methods are GB / T 20975 "Analytical Methods for Aluminum Alloys" and GB / T 7999 "Photoelectric Direct Reading Emission Spectrometric Analysis Method for Aluminum and Aluminum Alloys".

[0220] (3) Liquid hydrogen content: 0.13 mL / 100 g Al. The testing method is YS / T 600 "Closed-loop Circulation Method for Measuring Hydrogen in Liquid Aluminum and Aluminum Alloys".

[0221] The above ingot is subjected to homogenization annealing, extrusion, stretch straightening, solution quenching, and aging treatment to obtain Al-Zn-Cu-Mg aluminum alloy bars.

[0222] The test results of the bars are as follows:

[0223] (1) Mechanical property results: Tensile strength is 484 MPa (with a small surplus), yield strength is 350 MPa, and elongation is 7.5%. The testing method is GB / T 228.1-2010 "Metallic Materials - Tensile Testing - Part 1: Method of Test at Room Temperature". The results show that the Al-Zn-Cu-Mg aluminum alloy bars prepared in Comparative Example 2 do not meet the usage requirements.

[0224] In summary, when Zn / Mg < 2.6, the content of Cu is greater than 1.5 wt%, and the content of Mn is greater than 0.10 wt%, it has a great impact on the mechanical properties of the Al-Zn-Cu-Mg aluminum alloy, resulting in the Al-Zn-Cu-Mg aluminum alloy bars not meeting the usage requirements. Therefore, the present invention provides a method to regulate the content of each component and the ratio of the main strengthening elements Zn and Mg in the Al-Zn-Cu-Mg aluminum alloy, improve the mechanical properties of the Al-Zn-Cu-Mg aluminum alloy, and make the Al-Zn-Cu-Mg aluminum alloy bars with a diameter of 100 - 250 mm meet the user's needs.

[0225] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. An Al-Zn-Cu-Mg aluminum alloy bar, characterized in that, By mass percentage, it includes: Si: 0.05%; Fe: 0.20%; Cu: 1.40%; Mn: 0.04%; Mg: 2.30%; Cr：0.20％； Zn: 6.02%; Ti: 0.02%; Be: 12 ppm; Na: 2 ppm; The balance is Al; Among them, Zn / Mg is 2.62; Or, Si: 0.06%; Fe: 0.19%; Cu: 1.43%; Mn: 0.05%; Mg: 2.20%; Cr：0.21％； Zn: 6.04%; Ti: 0.02%; Be: 10 ppm; Na: 2 ppm; The balance is Al; Among them, Zn / Mg is 2.75; Or, Si: 0.04%; Fe: 0.18%; Cu: 1.48%; Mn: 0.02%; Mg: 2.26%; Cr：0.21％； Zn: 5.90%; Ti: 0.02%; Be: 9 ppm; Na: 2 ppm; The balance is Al; Among them, Zn / Mg is 2.61; Or, Si: 0.05%; Fe: 0.16%; Cu: 1.50%; Mn: 0.03%; Mg: 2.28%; Cr：0.21％； Zn: 6.03%; Ti: 0.03%; Be: 10 ppm; Na: 2 ppm; The balance is Al; Among them, Zn / Mg is 2.64; The specification of the Al-Zn-Cu-Mg aluminum alloy bar is Φ140 - 230 mm; The preparation method of the Al-Zn-Cu-Mg aluminum alloy bar includes the following steps: Melting the alloy raw materials, purifying the melt, refining the grains, casting, homogenizing annealing, extruding, stretch straightening, solution quenching, and aging treatment to obtain the Al-Zn-Cu-Mg aluminum alloy bar; The casting is carried out by the combined treatment of the bottom laying process and the wiper process.

2. The Al-Zn-Cu-Mg aluminum alloy bar according to claim 1, characterized in that, The temperature of the melting is 730 °C to 770 °C; The melt purification includes in-furnace purification, on-line purification, and on-line filtration.

3. The Al-Zn-Cu-Mg aluminum alloy bar according to claim 2, characterized in that, The in-furnace purification is carried out by one or more of powder injection purification, argon purification, and argon-chlorine mixed gas purification; The powder injection purification uses a particulate refining agent; The on-line purification is carried out with argon or argon-chlorine mixed gas, and after completion, the hydrogen content of the melt is controlled to be ≤0.15 mL / 100 g Al, and the Na content is controlled to be ≤0.0005%; The on-line filtration is selected from plate type or deep bed filtration.

4. The Al-Zn-Cu-Mg aluminum alloy bar according to claim 1, characterized in that, The grain refiner for the grain refinement is selected from Al-5Ti-1B wire; The dosage of the Al-5Ti-1B wire is 1.4 - 2.2 kg / t.