High-strength corrosion-resistant Al-Zn-Mg-Cu-Sc-Zr alloy plate and preparation method thereof

Abstract

The invention discloses a high-strength corrosion-resistant Al-Zn-Mg-Cu-Sc-Zr alloy plate and a preparation method thereof, and belongs to the technical field of aluminum alloy materials. The alloy comprises the following components in percentage by mass: 7.0%-8.0% of Zn, 1.5%-2.0% of Mg, 1.4%-1.8% of Cu, 0.05%-0.15% of Sc, 0.05%-0.15% of Zr, less than or equal to 0.05% of Si, less than or equal to 0.1% of Fe, less than or equal to 0.01% of Mn, less than or equal to 0.01% of Cr, less than or equal to 0.01% of Ti and the balance of Al. The preparation method comprises the steps of smelting and pouring, homogenizing annealing, hot rolling, cold rolling and solid solution aging treatment. By synergistically adding Sc and Zr, a nanoscale Al3 (Sc, Zr) dispersed phase is formed, recrystallization is inhibited, grains are refined, meanwhile, grain boundary precipitated phase distribution is optimized, and the mechanical property and corrosion resistance of the alloy are improved. The tensile strength of the obtained alloy plate reaches 590 MPa or above, the yield strength reaches 540 MPa or above, the intergranular corrosion depth is smaller than or equal to 23 micrometers, the exfoliation corrosion depth is smaller than or equal to 117 micrometers, the corrosion current density is smaller than or equal to 0.53 microamperes / cm < 2 >, and the comprehensive performance is obviously superior to that of a traditional Al-Zn-Mg-Cu alloy.

Description

Technical Field

[0001] The present invention belongs to the technical field of non-ferrous metal materials, and specifically relates to a high-strength and corrosion-resistant Al-Zn-Mg-Cu-Sc-Zr alloy plate and a preparation method thereof. The present invention particularly aims to optimize the alloy composition by compositely adding trace Sc and Zr elements, and regulate the microstructure by combining rolling and heat treatment processes to achieve a synergistic improvement in high strength and excellent corrosion resistance. Background Art

[0002] Al-Zn-Mg-Cu alloys are widely used in aerospace and industrial fields due to their high strength, toughness, and corrosion resistance. Improving their overall performance is of great significance for expanding their application range. However, traditional Al-Zn-Mg-Cu alloys still have certain limitations in terms of strength and corrosion resistance. Generally speaking, while high Zn / Mg content improves strength, it also intensifies the continuous distribution of precipitated phases at grain boundaries, deteriorating corrosion resistance. As a result, the alloy is prone to pitting corrosion, intergranular corrosion (IGC), and exfoliation corrosion (EXCO) in marine or humid environments, which severely limits its service life and makes it difficult to meet the increasingly stringent application requirements.

[0003] In the prior art, the performance of alloys can be improved by adding the rare earth element Sc or the transition element Zr, but the effect of adding Sc or Zr alone is limited. For example, adding Sc alone tends to form a coarse Al3Sc primary phase with Al, consuming matrix Sc atoms, reducing the precipitation density of secondary phases, and weakening the effect of inhibiting recrystallization. Adding Zr alone generates an Al3Zr phase. Al3Zr particles can effectively pin dislocations and grain boundaries, inhibiting recrystallization, but have little effect on improving corrosion resistance. In addition, excessive addition of Sc or Zr increases costs and may even lead to performance degradation. Therefore, how to further improve the comprehensive performance of alloys through the synergistic effect of Sc and Zr has become a hot topic of current research.

[0004] In the prior art, patent CN104152761A uses electromagnetic induction melting and hot extrusion to produce an alloy containing Sc and Zr. The Sc content is 0.1-0.4% and the Zr content is 0.1-0.4%. The tensile strength in the T6 state reaches 746-756 MPa, but the elongation is only 6-11%, and the corrosion performance is not optimized. Patent CN113373354B discloses an ultra-high-strength Al-Zn-Mg-Cu-Sc-Zr alloy sheet. By adding 0.18-0.22% Sc and 0.08-0.12% Zr, combined with hot rolling and multi-stage regression re-aging treatment, it achieves a tensile strength of 705-725 MPa. However, this patent does not address the effect of the synergistic effect of Sc and Zr on corrosion resistance, and the high Sc content makes it cost-effective. Therefore, how to achieve the synergistic effect of Sc and Zr at low addition levels while balancing strength and corrosion resistance remains a technical problem that needs to be solved urgently. Based on this, the present invention proposes a design method for Al-Zn-Mg-Cu-Sc-Zr alloy plates that significantly inhibits recrystallization, refines grains and improves corrosion resistance by precisely controlling the Sc and Zr addition ratio (0.1% Sc + 0.1% Zr) and combining it with a specific hot working process. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-strength and corrosion-resistant Al-Zn-Mg-Cu-Sc-Zr alloy plate synergistically strengthened by Sc and Zr and a preparation method thereof. By combining rolling and solution aging processes, a fine and dispersed Al3(Sc,Zr) core-shell precipitate phase is formed, which inhibits recrystallization and blocks corrosion channels, significantly improving the mechanical properties and corrosion resistance of the alloy, achieving a tensile strength of ≥590MPa and a corrosion current density of ≤0.53μA / cm 2 The comprehensive performance solves the problem that traditional alloys are difficult to balance between strength and corrosion resistance.

[0006] To achieve the above objectives, the present invention discloses a highly alloyed Al-Zn-Mg-Cu-Sc-Zr alloy, wherein the alloy components, by mass percentage, are: Zn: 7.0%-8.0%, Mg: 1.5%-2.0%, Cu: 1.4%-1.8%, Sc: 0.05%-0.15%, Zr: 0.05%-0.15%, Si≤0.05%, Fe≤0.1%, Mn≤0.01%, Cr≤0.01%, Ti≤0.01%, and the balance is Al.

[0007] The preparation method of the alloy plate disclosed above is achieved through the following technical solutions:

[0008] (1) Melting and Casting: Pure aluminum, pure zinc, pure magnesium and Al-2wt.%Sc, Al-5wt.%Zr, Al-50wt.%Cu master alloys with a purity of ≥99.9wt.% are used as raw materials and weighed according to the designed proportions. Pure aluminum and Al-2wt.%Sc, Al-5wt.%Zr, Al-50wt.%Cu master alloys are placed in a crucible, and after adding a refining covering agent, the temperature is raised to 770-790°C in a pit-type melting furnace for melting. The temperature is kept for 18-28 minutes until the raw materials are completely melted. Hexachloroethane (C2Cl6) degassing agent is wrapped with aluminum foil and placed in a bell jar and pressed into the bottom of the melt for degassing (dosage: 6-8g / 1000g furnace charge). After two consecutive degassings, the slag is skimmed, and the covering agent is added and the temperature is allowed to cool. After the furnace temperature drops to 725-735°C, pure zinc is placed into a crucible using tongs and heated for 2-3 minutes until completely melted. Subsequently, pure magnesium is pressed into the melt through a bell jar. Once fully melted, the bell jar is removed and allowed to stand for 4-6 minutes before degassing, slag removal, and the addition of a coating agent. The furnace door is closed again and allowed to stand for 4-6 minutes. The furnace temperature is adjusted to around 715-725°C. The surface coating is skimmed off with a slag scoop and then cast into a water-cooled copper mold to produce a 250mm×150mm×25mm flat ingot.

[0009] (2) The ingots obtained in step (1) were subjected to a double-stage homogenization treatment at 420±5°C for 1.5-2.5h and 465±5°C for 28-32h in the same furnace.

[0010] (3) The flat ingot after annealing in step (2) is milled and kept in an annealing furnace at a temperature of 435-445°C for 2-4 hours, and hot rolled with a first pass reduction of ≤0.5mm and subsequent passes of 1.8-2.2mm, and a final rolling temperature of ≥380°C to obtain a plate with a thickness of 4.8-5.2mm.

[0011] (4) The hot-rolled plate obtained in step (3) is annealed at 440±5°C for 0.8-1.2h and then air-cooled, and cold-rolled to a thickness of 1.95-2.05mm at a reduction of 0.08-0.15mm / pass.

[0012] (4) The cold-rolled sheet in step (4) was subjected to solution treatment in a salt bath at 470±5°C for 0.8-1.2h, followed by cold water quenching, and then aged at 120±5°C for 23-25h to obtain a T6 alloy sheet.

[0013] Beneficial results of the present invention

[0014] By synergistically adding 0.1% Sc + 0.1% Zr microalloying elements, a high-density nanoscale Al3(Sc,Zr) dispersed phase (average size 24nm) is formed in the Al-7.5Zn-1.6Mg-1.5Cu alloy. This core-shell structured particle significantly improves the overall performance through a triple strengthening mechanism:

[0015] (1) Strongly inhibit recrystallization, so that the alloy maintains the fibrous structure and blocks the formation of corrosion channels.

[0016] (2) The synergistic strengthening effect makes the tensile strength and yield strength reach 590.02MPa and 544.86MPa, respectively, which are 17.7% and 22.4% higher than those of the alloy without addition;

[0017] (3) Optimizing the grain boundary characteristics, eliminating the continuous η phase distribution, and forming a wide precipitation-free zone (PFZ), the intergranular corrosion depth was reduced to 22.67 μm (a decrease of 46.83%), the exfoliation corrosion depth was reduced to 116.57 μm (a decrease of 60.80%), and the corrosion current density was reduced by 90.10% to 0.5289 μA / cm 2 , the corrosion rate slowed down by 90.10% to 0.00576mm / a.

[0018] What is particularly noteworthy is that this composite addition scheme increases the strength by 11.3% compared with the alloy with the single addition of 0.2% Sc, and increases the corrosion resistance by 44.4% compared with the alloy with the single addition of 0.2% Zr, with the same total amount of Sc, successfully resolving the technical contradiction that it is difficult to synergistically improve the strength and corrosion resistance of high-strength aluminum alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the microstructure of the alloy cold-rolled plate after solution aging treatment.

[0020] Figure 2 XRD analysis test of cast alloy

[0021] Figure 3 Line scanning analysis of precipitated phase particles in cold rolled sheet of 0.1% Sc + 0.1% Zr alloy after solution aging treatment

[0022] Figure 4 TEM microstructure photos and EDS analysis of alloy cold-rolled plates after solution aging treatment.

[0023] Figure 5 The stress-strain curve of alloy cold-rolled plate after solution aging treatment

[0024] Figure 6 This is the tensile fracture morphology of the alloy cold-rolled plate after solution aging treatment.

[0025] Figure 7 This is the metallographic morphology of intergranular corrosion of alloy cold-rolled plate after solution aging treatment.

[0026] Figure 8 This is the metallographic morphology of the exfoliation corrosion of the alloy cold-rolled plate after solution aging treatment.

[0027] Figure 9The potentiodynamic polarization curve of alloy cold-rolled plate after solution aging treatment in 3.5% NaCl solution

[0028] Figure 10 Electrochemical impedance spectroscopy (EIS) and equivalent circuit model of alloy cold-rolled plate in 3.5% NaCl solution after solution aging treatment. (a) Nyquist plot and fitting results; (b) Bode|Z|-frequency plot; (c) Bodeθ-frequency plot; (d) Equivalent circuit diagram DETAILED DESCRIPTION

[0029] The technical solution of the present invention is described in detail below through examples, and its process parameters and test results are all obtained from experimental verification.

[0030] Example 1: Preparation of Al-Zn-Mg-Cu alloy sheet without Sc / Zr addition

[0031] (1) Weigh the raw materials by mass: pure aluminum (≥99.9%), pure zinc (≥99.9%), pure magnesium (≥99.9%), and Al-Cu master alloy (Cu content 5wt%). The target alloy composition is Al-7.5Zn-1.6Mg-1.5Cu. Place the pure aluminum and Al-Cu master alloy in a graphite crucible, cover with a refining agent, and then transfer to a pit crucible furnace.

[0032] (2) Heat the furnace to 780°C and hold for 25 minutes until completely melted. Turn off the temperature controller. Wrap the hexachloroethane degassing agent with aluminum foil and place it in a bell jar, pressing it into the bottom of the melt for degassing (dosage: 10g / 1500g charge). After two consecutive degassings, skim off the slag, add a covering agent, and let it cool.

[0033] (3) After the furnace temperature drops to 730°C, use preheated tongs to clamp pure zinc into the crucible and heat for about 2 minutes until it is completely melted. Then, press pure magnesium into the bottom of the melt through the bell jar. After it is fully melted, remove the bell jar and let it stand for 5 minutes before degassing, deslagging, and adding a covering agent.

[0034] (4) Close the furnace door again and let it stand, adjust the furnace temperature to about 720℃, use a slag scoop to skim off the surface covering, and then cast it into a water-cooled copper mold to produce a 250mm×150mm×25mm flat ingot.

[0035] (5) The flat ingots were homogenized at 420°C for 2 h and 465°C for 30 h, then headed and milled. They were then kept in an annealing furnace at 440°C for 3 h and hot rolled with a first pass reduction of 0.5 mm and subsequent passes of 2 mm to a final thickness of 5 mm. The resulting hot-rolled sheets were annealed at 440°C for 1 h, air-cooled, and cold rolled to a thickness of 2 mm at a reduction of 0.1 mm per pass.

[0036] (6) The specimens were cut along the rolling direction and subjected to solution treatment (water quenching) at 470°C for 1 h and aging at 120°C for 24 h (T6 state).

[0037] Example 2: Preparation of Al-Zn-Mg-Cu alloy sheet with 0.2% Zr added alone

[0038] (1) Raw materials: Al-Zr master alloy (Zr content 5 wt%) was added, and the amount of pure aluminum was adjusted so that the Zr content reached 0.2 wt%. The remaining ingredients were the same as in Example 1.

[0039] (2) The smelting process is the same as steps (1) to (4) of Example 1, and Al-Zr master alloy is added to the initial charge during refining.

[0040] (3) The rolling and heat treatment process is the same as steps (5)-(6) of Example 1.

[0041] Example 3: Preparation of Al-Zn-Mg-Cu alloy sheet with 0.2% Sc added alone

[0042] (1) Add Al-Sc master alloy (Sc content 2 wt%) to the raw materials and adjust the amount of pure aluminum ingot to make the Sc content reach 0.2 wt%.

[0043] (2) During smelting, Al-Sc master alloy was initially added along with the pure aluminum ingot, and the rest was the same as in Example 1.

[0044] (3) The rolling and heat treatment process is the same as steps (5)-(6) of Example 1.

[0045] Example 4: Preparation of Al-Zn-Mg-Cu alloy sheet with composite addition of 0.1% Sc + 0.1% Zr

[0046] (1) Al-Sc master alloy (Sc content 2 wt%) and Al-Zr master alloy (Zr content 5 wt%) were added simultaneously, and the Sc and Zr contents were controlled to be 0.1 wt%. The main components were the same as those in Example 1.

[0047] (2) The smelting process is the same as steps (1) to (4) of Example 1, and Al-Sc and Al-Zr intermediate alloys are added to the initial charge during refining.

[0048] (3) The rolling and heat treatment process is the same as steps (5)-(6) of Example 1.

[0049] Comparative Example

[0050] The performance test results of the T6 alloy plates of Examples 1-4 are as follows:

[0051] As attached Figure 1As shown ((a): Example 1; (b): Example 2; (c): Example 3; (d): Example 4

[0052] ), all the grains of Example 1 showed obvious recrystallization and tended to be equiaxed grains, and the grains of the three alloys of Example 2, Example 3, and Example 4 all showed different degrees of fibrous elongation along the rolling direction. Among them, the fibrous grains of Example 3 were partially transformed into equiaxed crystals, and there was a local recrystallization phenomenon, while Examples 2 and 4 still maintained the fibrous structure in the rolling direction and no recrystallization occurred. This confirms that both Sc and Zr elements have the effect of inhibiting recrystallization, but the inhibitory effect of Example 3 with the addition of 0.2% Sc alone is weaker than that of Example 2 with the addition of 0.2% Zr alone and Example 4 with the composite addition of 0.1% Sc + 0.1% Zr. The reason is that when rare earth Sc or transition element Zr is added to the aluminum alloy, they will precipitate nano-scale Al3Sc or Al3Zr particles during the subsequent homogenization annealing process. The two are completely coherent with the matrix, can effectively pin dislocations and grain boundaries, and inhibit recrystallization. When the Sc element is added alone, Sc is prone to eutectic or divorced eutectic reaction with Al during the casting process to generate coarse Al3Sc primary phase, as shown in the attached figure. Figure 2 As shown in (Alloy 1: Example 1; Alloy 2: Example 2; Alloy 3: Example 3; Alloy 4: Example 4), a large amount of Sc atoms in the matrix is ​​consumed, resulting in a decrease in the amount of nano-scale Al3Sc secondary phase precipitated in the subsequent reaction, and a decrease in the ability to inhibit recrystallization.

[0053] In addition, by comparing Example 2 and Example 4, it is found that the width of the fibrous grains in Example 4 is significantly finer than that in Example 3, and the length of the grain fibers is also shorter, indicating that the grain size of Example 4 is finer than that in Example 3. This is because when Sc and Zr are added to the aluminum alloy at the same time, Zr atoms will wrap around the primary Al3Sc particles to form Al3(Sc,Zr) phase. This structure will reduce the elastic strain energy between the matrix and the secondary phase, hinder the growth of Al3(Sc,Zr) particles, and increase the number of non-uniform nucleation cores. In addition, as shown in the attached Figure 3 As shown, the enrichment level of Sc in the core region of the particles is significantly higher than that of Zr. This is because the diffusion rate of Zr during heat treatment is lower than that of Sc. When secondary Al3(Sc, Zr) particles nucleate, they preferentially use Al3Sc particles as their cores. Due to the lower diffusion rate of Zr, an Al3Zr shell is formed between Al3Sc and the (α)Al matrix. The core-shell structure of Al3(Sc, Zr) particles combines high thermal stability with a fine dispersion distribution (typically <50nm), which can strongly pin dislocations and hinder grain boundary migration, thereby effectively inhibiting the alloy's recrystallization process. Therefore, Example 4, which co-adds 0.1% Sc + 0.1% Zr, has the best ability to inhibit recrystallization.

[0054] As attached Figure 4 As shown ((a), (b): Example 1; (c), (d): Example 2; (e), (f): Example 3; (g), (h): Example 4), the grain boundary precipitation phase of Example 1 is mainly distributed in a continuous linear manner. EDS analysis of its grain boundary precipitation phase can be determined to be an η(MgZn2) phase that has dissolved part of the Cu element. The grain boundaries of the three alloys of Example 2, Example 3, and Example 4 show chain-like discontinuous distribution characteristics to varying degrees. No spherical dispersed phase particles appeared in the crystals of Example 1, while spherical dispersed phase particles were found in the crystals of the three alloys of Example 2, Example 3, and Example 4. EDS analysis shows that the dispersed phase particles in the crystals of Example 2 are Al3Zr, those of Example 3 are Al3Sc, and those of Example 4 are Al3(Sc, Zr) (see Figure 4 (d), (f), and (h) show that the average particle sizes of the three types of particles are approximately 35 nm, 98 nm, and 24 nm, respectively, and they all belong to the nanoscale secondary phase precipitated during the homogenization annealing process. Among the four alloy plates, Example 4 has the smallest dispersed phase particles and the largest number.

[0055] As attached Figure 5 As shown in Table 1 (Alloy 1: Example 1; Alloy 2: Example 2; Alloy 3: Example 3; Alloy 4: Example 4), Example 4 has the highest strength, with its tensile strength and yield strength reaching 590.02 MPa and 544.86 MPa respectively. Example 1 has the lowest strength, with tensile strength and yield strength being 501.21 MPa and 445.18 MPa respectively, indicating that after adding 0.1% Sc + 0.1% Zr to the alloy, the tensile strength is increased by 17.7% and the yield strength is increased by 22.4%. Although the elongation of Example 4 is slightly lower than that of the other three examples, it is still a high plasticity alloy. Taking all factors into consideration, Example 4 performs best in terms of mechanical properties.

[0056] Table 1 Mechanical properties test results of alloy plates

[0057]

[0058] As attached Figure 6 As shown ((a): Example 1; (b): Example 2; (c): Example 3; (d): Example 4

[0059] ), Example 4 with the co-addition of 0.1% Sc + 0.1% Zr has the largest number of dimples at the fracture, the smallest and shallowest size, and the second phase particles are more finely and dispersedly distributed. This is attributed to the strong dispersion strengthening and recrystallization inhibition effect of the nano-scale Al3 (Sc, Zr) particles precipitated in Example 4. The plasticity is relatively poor when the dimples are small and shallow, and the resistance to fracture increases with fine grains and more grain boundaries. This fracture morphology is consistent with the mechanical properties test results.

[0060] Attachment Figure 7 The metallographic morphology of the alloy plates after intergranular corrosion testing ((a): Example 1; (b): Example 2; (c): Example 3; (d): Example 4). The corrosion depths of Example 1, Example 2, and Example 3 are 42.64μm, 40.75μm, and 31.57μm, respectively, indicating that Example 1 and Example 2 have poor corrosion resistance, while Example 3 has improved corrosion resistance. The corrosion grades of the three alloys are all level 3. The corrosion depth of Example 4 is 22.67μm, and the corrosion grade is level 2. Its corrosion resistance is significantly better than that of Example 1, Example 2, and Example 3. Experiments show that compared with alloys with Sc or Zr added alone, the intergranular corrosion sensitivity of alloys with Sc and Zr added together is greatly reduced, the corrosion depth becomes shallower, and the intergranular corrosion resistance is significantly improved.

[0061] Attachment Figure 8 Figure 2 shows the cross-sectional metallographic morphologies of the alloy plates after exfoliation corrosion testing ((a): Example 1; (b): Example 2; (c): Example 3; (d): Example 4). The corrosion depths of the four alloys were 297.37 μm, 212.39 μm, 182.95 μm, and 116.57 μm, respectively. Example 4 still exhibits the best corrosion resistance.

[0062] As attached Figure 9 As shown in Table 2 (Alloy 1: Example 1; Alloy 2: Example 2; Alloy 3: Example 3; Alloy 4: Example 4), the corrosion current density value of Example 4 (0.5289 μA / cm 2 ) is the smallest, the corrosion rate (0.00576mm / a) is the slowest, and the polarization resistance value (6080.49Ω·cm 2 ) is the largest, and the corrosion current density is reduced by 90.10% and the corrosion rate is slowed down by 90.10% compared with Example 1 without adding Sc and Zr. It can be judged that it has excellent corrosion resistance.

[0063] Table 2 Tafel fitting data of alloy polarization curves

[0064]

[0065] As attached Figure 10As shown in Table 3 (Alloy 1: Example 1; Alloy 2: Example 2; Alloy 3: Example 3; Alloy 4: Example 4), the charge transfer resistance R'p values ​​during electrochemical reactions on the surfaces of the four alloy electrodes are 44.73Ω·cm2, 47.57Ω·cm2, 68.82Ω·cm2, and 79.37Ω·cm2, respectively, which are consistent with the trend of the polarization resistance Rp values ​​obtained in Table 3. This result once again verifies the conclusion that Example 4 has the best corrosion resistance, followed by Example 3, and that Examples 2 and 1 have relatively poor corrosion resistance.

[0066] Table 3 Based on Figure 10 The equivalent circuit model shown in (d) is Figure 10 (a) Electrical parameters obtained after fitting the Nyquist curve

[0067]

[0068] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A high-strength, corrosion-resistant Al-Zn-Mg-Cu-Sc-Zr alloy plate, wherein the mass percentages of the components in the alloy are as follows: Zn: 7.0% to 8.0%, Mg: 1.5% to 2.0%, Cu: 1.4% to 1.8%, Sc: 0.05% to 0.15%, Zr: 0.05% to 0.15%, Si≤0.05%, Fe≤0.1%, Mn≤0.01%, Cr≤0.01%, Ti≤0.01%, and the balance is Al.

2. A high-strength, corrosion-resistant Al-Zn-Mg-Cu-Sc-Zr alloy plate and its preparation method. The preparation method of the alloy plate is achieved by the following technical solutions: (1) Melting and Casting: Pure aluminum, pure zinc, pure magnesium and Al-2wt.%Sc, Al-5wt.%Zr, Al-50wt.%Cu master alloys with a purity of ≥99.9wt.% are used as raw materials and weighed according to the designed proportions. Pure aluminum and Al-2wt.%Sc, Al-5wt.%Zr, Al-50wt.%Cu master alloys are placed in a crucible, and after adding a refining covering agent, the temperature is raised to 770-790°C in a pit-type melting furnace for melting. The temperature is kept for 18-28 minutes until the raw materials are completely melted. Hexachloroethane (C2Cl6) degassing agent is wrapped with aluminum foil and placed in a bell jar and pressed into the bottom of the melt for degassing (dosage: 6-8g / 1000g furnace charge). After two consecutive degassings, the slag is skimmed, and the covering agent is added and the temperature is allowed to cool. After the furnace temperature drops to 725-735°C, pure zinc is placed into a crucible using tongs and heated for 2-3 minutes until completely melted. Subsequently, pure magnesium is pressed into the melt through a bell jar. Once fully melted, the bell jar is removed and allowed to stand for 4-6 minutes before degassing, slag removal, and the addition of a coating agent. The furnace door is closed again and allowed to stand for 4-6 minutes. The furnace temperature is adjusted to around 715-725°C. The surface coating is skimmed off with a slag scoop and then cast into a water-cooled copper mold to produce a 250mm×150mm×25mm flat ingot. (2) The ingots obtained in step (1) were subjected to a double-stage homogenization treatment at 420±5°C for 1.5-2.5h and 465±5°C for 28-32h in the same furnace. (3) The flat ingot after annealing in step (2) is milled and kept in an annealing furnace at a temperature of 435-445°C for 2-4 hours, and hot rolled with a first pass reduction of ≤0.5mm and subsequent passes of 1.8-2.2mm, and a final rolling temperature of ≥380°C to obtain a plate with a thickness of 4.8-5.2mm. (4) The hot-rolled plate obtained in step (3) is annealed at 440±5°C for 0.8-1.2h and then air-cooled, and cold-rolled to a thickness of 1.95-2.05mm at a reduction of 0.08-0.15mm / pass. (4) The cold-rolled sheet obtained in step (4) was subjected to solution treatment in a salt bath at 470±5°C for 0.8-1.2 h, followed by cold water quenching, and then subjected to aging at 120±5°C for 23-25 ​​h to obtain a T6 alloy sheet.

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