A high corrosion-resistant magnesium alloy sheet with filiform corrosion characteristics and a preparation method thereof

Abstract

The present invention belongs to the technical field of metal materials, and particularly relates to a high-corrosion-resistant magnesium alloy sheet having filiform corrosion characteristics and a preparation method thereof. Based on the total amount of the magnesium alloy sheet, in terms of mass percentage, the magnesium alloy sheet contains the following elements: Al: 6-9%, Sc: 0.05-0.15%, Y: 0.05-0.15%, Mn: 0.05-0.15%, and the balance is Mg and inevitable impurity elements; the alloy preparation method includes: alloy ingot melting, ingot solution treatment, extrusion into sheets, and then multi-pass rolling treatment and aging heat treatment regulation. Among them, the magnesium alloy sheet has a phase structure of dispersed Mg 17 Al 12 phase, and its corrosion behavior is typical filiform corrosion characteristics, which has the advantages of shallow corrosion depth and small destructiveness compared with traditional pitting corrosion. The magnesium alloy sheet in the present invention has excellent mechanical properties and corrosion resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials, and particularly relates to a high-corrosion-resistant magnesium alloy sheet having filiform corrosion characteristics and a preparation method thereof. Background Art

[0002] As the lightest metal structural material, the density of magnesium alloy is only 2 / 3 of that of aluminum and 1 / 4 of that of steel. It has the advantages of high specific strength, easy processing and forming, good thermal and electrical conductivity, excellent shock absorption performance, electromagnetic shielding performance, good biocompatibility and biodegradability, etc., and has been widely used in the fields of aerospace, automobile manufacturing, consumer electronics and biomedicine. Although magnesium alloy has many excellent physical and mechanical properties, its corrosion resistance is poor. Especially in humid and saline environments, its corrosion resistance is inferior to that of aluminum alloy and steel materials, which greatly limits the practical application of magnesium alloy. This is because on the one hand, magnesium has active chemical properties and has the lowest standard electrode potential (-2.37 V / SHE) among structural metals, which causes it to be extremely prone to galvanic corrosion with the cathode phase or other metals. Secondly, the PBR (Pilling-Bedworth ratio) of the MgO oxide film on the magnesium surface is 0.81, which is less than 1, that is, the volume of the oxide formed on the magnesium surface is less than the volume of the consumed metal, and the oxide film cannot cover the magnesium surface densely and completely. Therefore, in an environment containing chlorides, chloride ions are extremely likely to damage the oxide film on the magnesium surface and induce severe local pitting corrosion, resulting in severe corrosion of the magnesium alloy. For example, the commercial AZ91 alloy is extremely prone to local pitting corrosion. Pitting corrosion will also cause a rapid decline in the mechanical properties of the magnesium alloy, resulting in premature aging of the alloy. Therefore, the occurrence of local pitting corrosion should be avoided as much as possible.

[0003] At present, the method for improving the corrosion resistance of magnesium alloy usually adopts the surface treatment method. For example, in CN105970170B, an Hf / Si3N4 multi-layer structure coating with good electrical conductivity and corrosion resistance is prepared by alternately depositing an Hf coating and an Si3N4 coating. This coating can effectively block the continuous growth of columnar defects and change the growth orientation of the coating, while significantly reducing the corrosion rate of the magnesium alloy matrix and improving the corrosion resistance of the magnesium alloy. However, the stability and durability of the surface coating are still a challenge. Under the action of external forces, the coating is extremely prone to peeling and damage, resulting in a decline in corrosion resistance. In addition, it may also cause local corrosion at the damaged part of the coating.

[0004] Therefore, developing magnesium alloys with high intrinsic corrosion resistance is the most direct and effective way to improve the corrosion resistance of magnesium alloys and is the key to realizing the large-scale application of magnesium alloys. Summary of the Invention

[0005] The object of the present invention is to provide a high corrosion-resistant magnesium alloy sheet with filiform corrosion characteristics and a preparation method thereof. This method combines alloy composition design and microstructure control, and by suppressing the local pitting corrosion of the alloy, the alloy exhibits filiform corrosion characteristics that develop along the surface of the matrix. This filiform corrosion can effectively slow down the corrosion propagation rate and does not undergo accelerated corrosion like local pitting corrosion. In addition, the filiform corrosion only spreads on the surface of the alloy and does not penetrate into the interior of the alloy, thereby maintaining the integrity of the material and avoiding premature failure of the alloy.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides a high corrosion-resistant magnesium alloy sheet with filiform corrosion characteristics. Based on the total amount of the magnesium alloy sheet, by mass percentage, the magnesium alloy sheet contains the following elements: Al: 6 - 9%, Sc: 0.05 - 0.15%, Y: 0.05 - 0.15%, Mn: 0.05 - 0.15%, and the balance is Mg and inevitable impurity elements; wherein, the magnesium alloy sheet has a phase structure of dispersed Mg 17 Al 12 phase.

[0008] The magnesium alloy sheet in the present invention has excellent corrosion resistance. Based on the low-cost Mg - Al alloy system, by adding a small amount of Sc and Y elements with high solid solubility, the magnesium alloy sheet has excellent corrosion resistance. This may be because by adding a small amount of Sc and Y elements with high solid solubility, on the one hand, alloying elements can be dissolved into the magnesium matrix as much as possible to improve the chemical stability of the matrix, thereby avoiding the formation of a large number of high-potential second phases and weakening the galvanic corrosion of the magnesium matrix; on the other hand, the PBR values of the oxides Sc2O3 and Y2O3 formed by Sc and Y elements are 1.19 and 1.28 respectively, which can effectively fill the compactness of the MgO oxide film and improve the protection performance of the oxide film. In addition, the doping of Sc2O3 and Y2O3 in the oxide film can effectively improve the chemical and physical barrier capabilities of the oxide film against chloride ions and reduce the adsorption ability of chloride ions on the oxide film. In addition, the addition of rare earth elements Sc and Y can purify the melt, reduce the influence of impurity elements on the corrosion resistance performance. At the same time, the addition of Mn element can increase the allowable limit of impurity Fe in the magnesium-aluminum alloy and reduce the content of impurity Fe.

[0009] In the present invention, to avoid the influence of impurity elements on the performance of the magnesium alloy sheet, further, based on the total amount of the magnesium alloy sheet, the mass content of the inevitable impurity elements is less than 0.02%.

[0010] The inevitable impurities in the present invention refer to other impurity elements except Mg, Al, Sc, Y, and Mn. In some embodiments, the inevitable impurity elements include at least one of Fe, Ni, and Cu. This embodiment is only an exemplary illustration of the types of impurities, and the present invention is not limited thereto.

[0011] In one embodiment of the present invention, a high corrosion-resistant magnesium alloy sheet with filiform corrosion characteristics is provided. Based on the total amount of the magnesium alloy sheet, in terms of mass percentage, the magnesium alloy sheet contains the following elements: Al: 8%, Sc: 0.1%, Y: 0.1%, Mn: 0.1%. The inevitable impurity elements include Fe, Cu, and Ni impurity elements, and the total content of the inevitable impurity elements is less than 0.02%, and the balance is Mg.

[0012] In one embodiment of the present invention, a high corrosion-resistant magnesium alloy sheet with filiform corrosion characteristics is provided. Based on the total amount of the magnesium alloy sheet, in terms of mass percentage, the magnesium alloy sheet contains the following elements: Al: 8%, Sc: 0.15%, Y: 0.15%, Mn: 0.15%. The inevitable impurity elements include Fe, Cu, and Ni impurity elements, and the total content of the inevitable impurity elements is less than 0.02%, and the balance is Mg.

[0013] In one embodiment of the present invention, a high corrosion-resistant magnesium alloy sheet with filiform corrosion characteristics is provided. Based on the total amount of the magnesium alloy sheet, in terms of mass percentage, the magnesium alloy sheet contains the following elements: Al: 8%, Sc: 0.10%, Y: 0.10%, Mn: 0.10%. The inevitable impurity elements include Fe, Cu, and Ni impurity elements, and the total content of the inevitable impurity elements is less than 0.02%, and the balance is Mg.

[0014] The dispersed Mg 17 Al 12 phase means that the Mg 17 Al 12 phase has a fine structure and is dispersed in the phase structure, rather than being dispersed in a coarse network in the phase structure. The magnesium alloy sheet in the present invention has dispersed Mg 17 Al 12 phase can better improve the corrosion resistance of the magnesium alloy sheet. It may be because the existence of the fine and dispersed Mg 17 Al 12 phase can effectively weaken the microgalvanic effect of the Mg 17 Al 12 phase on the magnesium matrix. In addition, the Mg 17 Al 12 phase, as the cathode phase, has higher inertness to chloride ions. The fine, dense, and dispersed Mg 17 Al12 The phase can effectively block the deep expansion of local corrosion, thereby avoiding the occurrence of local pitting corrosion, and its corrosion form is a typical filiform corrosion morphology.

[0015] The magnesium alloy sheet in the present invention is an alloy material formed on the basis of the Mg-Al alloy system by adding a small amount of Sc, Y, and Mn elements. Specifically, the phase structure of the magnesium alloy sheet in the present invention is mainly an α-Mg phase structure, and among them, it may also contain Al2Y phase and Al8Mn4Y phase.

[0016] The density of the magnesium alloy sheet in the present invention is around 1.8 g / cm 3 nearby, the elastic modulus is around 46 GPa, and the crystal structure is a polyphase structure, in which the magnesium matrix is a close-packed hexagonal crystal structure.

[0017] In the second aspect, the present invention provides a preparation method of the high-corrosion-resistant magnesium alloy sheet with filiform corrosion characteristics described in the first aspect of the present invention. The preparation method includes:

[0018] (1) Weigh pure magnesium ingots, pure aluminum, Mg-Sc master alloy, Mg-Y master alloy, and Mg-Mn master alloy according to the element content of the magnesium alloy sheet, and then perform preheating treatment on them respectively;

[0019] (2) Under the protection gas of CO2 plus SF6, sequentially add the preheated pure magnesium, pure aluminum, Mg-Sc master alloy, Mg-Y master alloy, and Mg-Mn master alloy into the crucible for melting to obtain a magnesium alloy melt;

[0020] (3) Under the protection gas of CO2 plus SF6, in the presence of a refining agent, refine the magnesium alloy melt in step (2), and then perform static heat preservation treatment to obtain a purified magnesium alloy melt;

[0021] (4) Under the protection gas of CO2 plus SF6, perform slag skimming treatment on the purified magnesium alloy melt, and then pour the slag-skimmed magnesium alloy melt into a preheated metal mold to obtain a magnesium alloy ingot;

[0022] (5) Perform solution treatment on the magnesium alloy ingot, and then extrude it into a sheet;

[0023] (6) Perform at least two rolling treatments on the sheet to obtain a rolled sheet;

[0024] (7) Perform aging treatment on the rolled sheet to obtain the final high-corrosion-resistant magnesium alloy sheet.

[0025] The Mg-Sc master alloy that can be listed in the present invention is the Mg-30Sc master alloy, where Mg-30Sc means that the alloy contains 30 wt% of Sc, and the balance is Mg and unavoidable impurity elements.

[0026] The Mg-Y master alloys that can be cited in the present invention include Mg-30Y master alloy, where Mg-30Y means that the alloy contains 30 wt% of Y, and the balance is Mg and inevitable impurity elements.

[0027] The Mg-Mn master alloys that can be cited in the present invention include Mg-5Mn master alloy, where Mg-5Mn means that the alloy contains 5 wt% of Mn, and the balance is Mg and inevitable impurity elements.

[0028] In the present invention, the purpose of the preheating treatment is to remove the moisture that may be contained in the raw materials. Further, the conditions of the preheating treatment include: the preheating temperature is 200 - 300 °C, and the preheating time is 1 - 3 hours.

[0029] Further, in steps (2), (3), and (4), in the protective gas, the volume ratio of SF6 and CO2 is independently 1:(5 - 12), for example, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, and preferably 1:9.

[0030] Further, in step (2): Add pure magnesium ingots at 590 - 620 °C, and heat to 680 - 690 °C to melt the pure magnesium ingots; add Mg-Mn master alloy at 695 - 710 °C, and then heat to 715 - 740 °C to add pure aluminum ingots; then raise the temperature to 745 - 780 °C and add Mg-Sc master alloy and Mg-Y master alloy in sequence, and then keep warm until all raw materials are melted to obtain the magnesium alloy melt.

[0031] Further, in step (2): Add pure magnesium ingots at 600 °C, and heat to 690 °C to melt the pure magnesium ingots; add Mg-Mn master alloy at 700 °C, and then heat to 720 °C to add pure aluminum ingots; then raise the temperature to 750 °C and add Mg-Sc master alloy and Mg-Y master alloy in sequence, and then keep warm until all raw materials are melted to obtain the magnesium alloy melt.

[0032] The crucible in the present invention can be a conventional stainless steel crucible coated with a coating in the art.

[0033] Further, in step (3), the dosage of the refining agent is 0.05 - 0.3 wt% of the mass of the magnesium alloy melt, for example, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.12 wt%, 0.15 wt%, 0.18 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, and preferably 0.12 wt%.

[0034] Further, in step (3), the refining agent includes metal chlorides and fluorides.

[0035] Further, the mass ratio of the metal chloride to the fluoride is (10 - 20):1, such as 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, and preferably (15 - 16):1.

[0036] Further, the metal chloride includes a combination of KCl, CaCl2, BaCl2, and YCl3.

[0037] Further, the mass ratio of KCl, CaCl2, BaCl2, and YCl3 is (5 - 8):(3 - 4):(1.5 - 2.5):1.

[0038] Further, the fluoride is selected from CaF.

[0039] Further, the refining agent further includes 1-C3-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide, preferably 1-C6-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide.

[0040] Examples of 1-C6-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide that can be listed in the present invention include 1-hexyl-3-methylimidazolium hexafluorophosphate modified graphene oxide, 1-hexyl-3-methylimidazolium hexafluorophosphate modified graphene oxide, 1-heptyl-3-methylimidazolium hexafluorophosphate modified graphene oxide, 1-octyl-3-methylimidazolium hexafluorophosphate modified graphene oxide, 1-dodecyl-3-methylimidazolium hexafluorophosphate modified graphene oxide, etc.

[0041] Further, the mass ratio of the 1-C3-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide (preferably 1-C6-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide) to the fluoride is (1 - 1.5):1, such as 1:1, 1.2:1, 1.25:1, 1.3:1, 1.4:1, 1.5:1.

[0042] In the present invention, the use of metal chlorides and fluorides can purify the melt and remove impurities to a certain extent. When the refining agent contains a certain amount of 1-C3-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide, it can better improve the comprehensive properties of magnesium alloy sheets. It is speculated that this may be because YCl3 can form rare earth composite inclusions with other impurity components, and the specific gravity of the rare earth composite inclusions is close to that of the melt, making it difficult to deposit from the melt. 1-C3-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide has certain adsorption properties. On the one hand, through adsorption, it can make the rare earth composite inclusions deposit from the melt. On the other hand, the surface tension between it and the alloy liquid makes the refining agent form composite inclusions and the alloy liquid easy to separate, thereby reducing the impurity content. At the same time, it can also increase the number of crystal nuclei in the metal liquid, refine the grains, and thus better increase the strength and corrosion resistance of the alloy. At the same time, in combination with other components, it can greatly reduce the content of non-metallic oxides and hydrogen, increase the elongation rate and corrosion resistance. Further research found that when using 1-C6-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide, it can better improve the comprehensive properties of the alloy, probably because the modified carbon chain length is within a suitable range, which helps to enhance the interaction between the modified graphene and other refining components. When the carbon chain length is too short, the interaction is poor. When the carbon chain length is too long, the adsorption property of the modified graphene is poor.

[0043] Further, the preparation method of the 1-C3-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide includes: dispersing graphene oxide in water to form a suspension, then adding 1-C3-C12 alkyl-3-methylimidazolium hexafluorophosphate, reacting at 20-30 °C for 2-5 hours, then centrifuging and separating, discarding the supernatant, and drying the solid to obtain 1-C3-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide.

[0044] Further, when preparing the 1-C3-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide, the graphene oxide is monolayer graphene oxide, with an average sheet diameter of 0.5-5 μm and an average thickness of 0.8-1.2 nm.

[0045] The graphene oxide in the present invention can be obtained commercially, preferably monolayer graphene oxide purchased from Nanjing Xianfeng Nano Materials Technology Co., Ltd., with an average sheet diameter of 2.5 μm and an average thickness of 1 nm.

[0046] Further, when preparing the 1-C3-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide, the mass ratio of graphene oxide to water is 1:(8-12).

[0047] Further, when preparing 1-C3-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide, the weight ratio of graphene oxide to 1-C3-C12 alkyl-3-methylimidazolium hexafluorophosphate is 1:(0.05 - 0.2), preferably 1:(0.1 - 0.12).

[0048] Further, when preparing 1-C3-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide, the drying conditions include: drying at 105 - 120 °C for 2 - 5 h.

[0049] Further, in step (3), at a temperature of 740 - 750 °C (preferably 750 °C), a refining agent is added while manually stirring. After the addition of the refining agent is completed, stirring is continued for 5 - 20 minutes for the refining. The aforementioned manual stirring is a conventional stirring means in the art, and its purpose is to allow the refining agent to fully react with the impurities in the melt.

[0050] Further, in step (3), the conditions for static heat preservation include: first standing at 740 - 750 °C for 30 - 40 minutes, and then cooling to 705 - 720 °C (preferably 710 °C) and standing for 20 - 30 minutes.

[0051] Further, in step (4), the slag skimming treatment is a conventional operation means in the art. The conditions for the slag skimming treatment include: lowering the temperature to 690 - 700 °C (preferably 690 °C) and skimming the slag on the surface of the melt.

[0052] Further, in step (4), the casting temperature is 690 - 700 °C, and the preheating temperature of the metal mold is 190 - 210 °C (preferably 200 °C).

[0053] Further, in step (5), the conditions for solution treatment include: a temperature of 400 - 420 °C and a time of 18 - 32 hours (preferably 24 hours).

[0054] Further, in step (5), the conditions for extrusion include: an extrusion temperature of 350 - 390 °C, an extrusion speed of 0.5 - 1 m / min, and an extrusion ratio of 15:1 - 20:1.

[0055] Further, in step (6), the plate is subjected to three rolling treatments to obtain a rolled plate.

[0056] Further, in step (6), the conditions for each rolling treatment include: a rolling temperature of 250 - 300 °C, a single-pass reduction of 4 - 6% (preferably 5%), a total reduction of 12 - 18% (preferably 15%), and the initial thickness of the extrusion plate is 8 - 12 mm.

[0057] The present invention can effectively refine grains and break coarse network-shaped Mg 17 Al 12 phases through extrusion and multi-pass rolling deformation treatment, thereby significantly improving the mechanical properties of the alloy and reducing the microgalvanic corrosion effect of the coarse network-shaped phases. In addition, the multi-pass rolling treatment can provide a precipitation driving force for subsequent aging treatment by introducing a large number of dislocation and twin crystal defects, promoting the rapid formation of fine and dispersed Mg 17 Al 12 phases. Due to the addition of Sc and Y elements and the presence of a large number of fine and dispersed Mg 17 Al 12 phases in the matrix, the alloy exhibits filiform corrosion characteristics, effectively avoiding the occurrence of local pitting corrosion, thereby significantly improving the corrosion resistance of the alloy. The presence of a large number of fine and dispersed Mg 17 Al 12 phases in the magnesium matrix can effectively weaken the microgalvanic effect of Mg 17 Al 12 phases on the magnesium matrix. In addition, Mg 17 Al 12 phases, as cathode phases, have higher inertness to chloride ions. The fine, dense and dispersed Mg 17 Al 12 phases can effectively block the deep extension of local corrosion, thereby avoiding the occurrence of local pitting corrosion. Therefore, the serious local pitting corrosion caused by the coarse network-shaped Mg 17 Al 12 phases in traditional commercial AZ91 magnesium alloy is avoided.

[0058] Furthermore, in step (7), the conditions of the aging treatment include: an aging temperature of 175 - 200 °C and an aging time of 12 - 48 hours.

[0059] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0060] The present invention is based on a low-cost Mg-Al-based alloy, adding a small amount of rare earth Sc and Y elements, having the advantage of low cost. At the same time, compared with other surface coatings, the magnesium alloy of the present invention can be realized through alloying and conventional melting, extrusion, rolling and heat treatment processes, without complex surface treatment, and is suitable for large-scale production. At the same time, the alloy of the present invention has excellent mechanical properties on the basis of excellent corrosion resistance. The magnesium alloy of this application can not only be used in 3C electronic products, such as laptop computer casings, but also can be used under harsh conditions such as high humidity and salt spray, especially in complex moving environments such as ocean engineering and transportation. Description of the Drawings

[0061] Figure 1 SEM micrograph of the microstructure of the magnesium alloy prepared in Example 1.

[0062] Figure 2 SEM image of the surface corrosion morphology of the magnesium alloy in Example 1 after being immersed in 3.5 wt% NaCl solution for 7 days;

[0063] Figure 3 SEM image of the surface corrosion morphology of the magnesium alloy in Comparative Example 1 after being immersed in 3.5 wt% NaCl solution for 7 days.

[0064] Figure 4 SEM image of the cross - section corrosion morphology of the magnesium alloy in Comparative Example 3 after being immersed in 3.5 wt% NaCl solution for 7 days. Detailed implementation manners

[0065] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0066] Example 1

[0067] This example provides a preparation method for a magnesium alloy sheet, and the preparation method includes:

[0068] (1) Weigh pure magnesium ingots, pure aluminum, Mg - 30Sc master alloy, Mg - 30Y master alloy, and Mg - 5Mn master alloy according to the element content of the magnesium alloy sheet, and then perform pre - heating treatment at 300°C for 2 hours to remove moisture;

[0069] (2) Under a CO2 + SF6 protective gas with a volume ratio of 1:9, add pure magnesium ingots at 600°C and heat to 690°C to melt the pure magnesium ingots; add the Mg - 5Mn master alloy at 700°C, and then add pure aluminum ingots when heated to 720°C; then raise the temperature to 750°C and add the Mg - 30Sc master alloy and Mg - 30Y master alloy in sequence, and then keep it warm until all raw materials are melted to obtain a magnesium alloy melt;

[0070] (3) Under a CO2 + SF6 protective gas with a volume ratio of 1:9, add a refining agent to the magnesium alloy melt at a temperature of 750°C, stir manually while adding the refining agent, continue to stir for 10 minutes after the addition of the refining agent is completed, then first stand still at 750°C for 35 minutes, and then cool down to 710°C and stand still for 25 minutes to obtain a purified magnesium alloy melt;

[0071] (4) Under a protective gas of CO2 and SF6 with a volume ratio of 1:9, the temperature is lowered to 690 °C to remove the slag on the surface of the purified magnesium alloy melt. Then, the melt is cast into a metal mold preheated to 200 °C at 690 °C to obtain a magnesium alloy ingot;

[0072] (5) The magnesium alloy ingot is solution-treated at 420 °C for 24 hours, and then extruded into a sheet (the extrusion conditions include: extrusion temperature 350 °C, extrusion speed 1 m / min, extrusion ratio 15:1);

[0073] (6) The sheet is subjected to three rolling treatments to obtain a rolled sheet; the conditions for each rolling treatment include: rolling temperature 270 °C, single-pass reduction 5%, total reduction 15%, and the initial thickness of the extrusion plate is 10 mm;

[0074] (7) The rolled sheet is subjected to aging treatment (aging temperature 175 °C, aging time 16 hours) to obtain the high-corrosion-resistant magnesium alloy sheet.

[0075] In step (1): by mass percentage, Al: 8%, Sc: 0.1%, Y: 0.1%, Mn: 0.1%, the total content of impurity elements of Fe, Cu, and Ni is less than 0.02%, and the balance is Mg. Weigh the corresponding pure magnesium ingot, pure aluminum, Mg-Sc master alloy, Mg-Y master alloy, and Mg-Mn master alloy;

[0076] In step (3): the dosage of the refining agent is 0.12 wt% of the mass of the magnesium alloy melt; the refining agent is a metal chloride and a fluoride; the mass ratio of the metal chloride to the fluoride is 15.67:1; the metal chloride is a combination of KCl, CaCl2, BaCl2, and YCl3, and their mass ratio is 7:3.43:2:1; the fluoride is selected from CaF.

[0077] After testing, the chemical composition of the magnesium alloy in this example is as follows: Al 8.15 wt%, Sc 0.10 wt%, Y 0.11 wt%, Mn 0.12 wt%, inevitable impurities include: Fe 0.0053 wt%, Ni 0.0004 wt%, Cu 0.0005 wt%, and the balance is Mg.

[0078] The SEM micrograph of the microstructure of the magnesium alloy prepared in this example is as Figure 1 shown, and through Figure 1 it can be seen that the magnesium alloy has fine and dispersed Mg 17 Al 12 phases distributed in the magnesium matrix, and the Mg 17 Al 12 phases are distributed in rod and needle shapes, with a size of about a few micrometers. The uniformly dispersed Mg17 Al 12 The phase can significantly improve the mechanical properties of the alloy through precipitation strengthening. At the same time, the fine and uniformly distributed Mg 17 Al 12 phase, compared with the traditional coarse reticular Mg 17 Al 12 phase, can greatly weaken the micro-galvanic corrosion effect of the second phase on the magnesium matrix, making the alloy change from severe local pitting corrosion to mild filiform corrosion behavior, and significantly improving the corrosion resistance of the alloy. Specifically, the smaller the size of the second phase, the smaller the micro-galvanic acceleration on the magnesium matrix, and the uniform distribution of the second phase can further promote the uniform distribution of the micro-galvanic current in the matrix, avoiding local current concentration and thus avoiding the occurrence of local pitting corrosion. In addition, we found that the fine and dispersed Mg 17 Al 12 phase can block the deep penetration of corrosion, making the alloy exhibit a surface corrosion morphology similar to worm-like.

[0079] The corrosion surface morphology of Example 1 after being soaked in the corrosion medium for 7 days is as Figure 2 described. It can be found that the corrosion products on the alloy surface are distributed on the surface like worms. It can be seen that the wire width is about dozens of micrometers, the corrosion is relatively mild, and no local pitting corrosion appears, indicating that the alloy has excellent corrosion resistance. In addition, it can be found that the added Sc and Y elements in the present invention make the corrosion products on the alloy surface more uniform and dense, effectively blocking the invasion of the corrosion medium.

[0080] Example 2

[0081] This example provides a preparation method of a magnesium alloy sheet, and the preparation method includes:

[0082] (1) Weigh pure magnesium ingots, pure aluminum, Mg-30Sc master alloy, Mg-30Y master alloy and Mg-5Mn master alloy according to the element content of the magnesium alloy sheet, and then perform preheating treatment at 300 °C for 2 hours to remove moisture;

[0083] (2) Under the protection gas of CO2 plus SF6 with a volume ratio of 1:9, add pure magnesium ingots at 600 °C and heat to 690 °C to melt the pure magnesium ingots; add Mg-5Mn master alloy at 700 °C, and then add pure aluminum ingots at 720 °C; then raise the temperature to 750 °C and add Mg-30Sc master alloy and Mg-30Y master alloy in sequence, and then keep warm until all raw materials are melted to obtain a magnesium alloy melt;

[0084] (3) Under a protective gas of CO₂ and SF₆ with a volume ratio of 1:9, at a temperature of 750 °C, a refining agent is added to the magnesium alloy melt. The refining agent is added while manually stirring. After the addition of the refining agent is completed, stirring continues for 10 minutes. Then, it is first left standing at 750 °C for 35 minutes, and then cooled to 710 °C and left standing for 25 minutes to obtain a purified magnesium alloy melt;

[0085] (4) Under a protective gas of CO₂ and SF₆ with a volume ratio of 1:9, the temperature is lowered to 690 °C, and the slag on the surface of the purified magnesium alloy melt is removed. Then, the melt is cast into a metal mold preheated to 200 °C at 690 °C to obtain a magnesium alloy ingot;

[0086] (5) The magnesium alloy ingot is solution-treated at 420 °C for 24 hours and then extruded into sheets;

[0087] (6) The sheets are subjected to three rolling treatments to obtain rolled sheets; The conditions for each rolling treatment include: the rolling temperature is 270 °C, the single-pass reduction is 5%, the total reduction is 15%, and the initial thickness of the extrusion plate is 10 mm;

[0088] (7) The rolled sheets are subjected to aging treatment (aging temperature 175 °C, aging time 16 hours) to obtain the product.

[0089] In step (1): By mass percentage, Al: 8%, Sc: 0.15%, Y: 0.15%, Mn: 0.15%, unavoidable impurity elements are less than 0.02%, and the balance is Mg. Weigh the corresponding pure magnesium ingot, pure aluminum, Mg-Sc master alloy, Mg-Y master alloy, and Mg-Mn master alloy; The conditions for the preheating treatment include: the preheating temperature is 360 °C and the preheating time is 2 hours;

[0090] In step (3): The dosage of the refining agent is 0.12 wt% of the mass of the magnesium alloy melt; The refining agent is a metal chloride and a fluoride; The mass ratio of the metal chloride to the fluoride is 15.67:1; The metal chloride is a combination of KCl, CaCl₂, BaCl, and YCl₃, and their mass ratio is 7:3.43:2:1; The fluoride is selected from CaF.

[0091] After testing, the chemical composition of the magnesium alloy in this example is as follows: Al 8.06 wt%, Sc 0.14 wt%, Y 0.15 wt%, Mn 0.14 wt%, unavoidable impurities include: Fe 0.0057 wt%, Ni 0.0006 wt%, Cu 0.0004 wt%, and the balance is Mg.

[0092] The SEM micrograph of the microstructure of the magnesium alloy prepared in this example and Figure 1Similarly, it can be obtained that the magnesium alloy has fine and dispersed Mg 17 Al 12 phase.

[0093] Example 3

[0094] This example provides a method for preparing a magnesium alloy sheet, and the preparation method includes:

[0095] (1) Weigh pure magnesium ingots, pure aluminum, Mg-30Sc master alloy, Mg-30Y master alloy, and Mg-5Mn master alloy according to the elemental content of the magnesium alloy sheet, and then perform preheating treatment at 300°C for 2 hours respectively to remove moisture;

[0096] (2) Under a CO2 + SF6 protective gas with a volume ratio of 1:9, add pure magnesium ingots at 600°C and heat to 690°C to melt the pure magnesium ingots; add the Mg-5Mn master alloy at 700°C, and then add pure aluminum ingots when heated to 720°C; then raise the temperature to 750°C and add the Mg-30Sc master alloy and Mg-30Y master alloy in sequence, and then keep the temperature until all raw materials are melted to obtain a magnesium alloy melt;

[0097] (3) Under a CO2 + SF6 protective gas with a volume ratio of 1:9, add a refining agent to the magnesium alloy melt at a temperature of 750°C, stir manually while adding the refining agent, continue to stir for 10 minutes after the addition of the refining agent is completed, then first let it stand at 750°C for 35 minutes, and then cool down to 710°C and let it stand for 25 minutes to obtain a purified magnesium alloy melt;

[0098] (4) Under a CO2 + SF6 protective gas with a volume ratio of 1:9, lower the temperature to 690°C and remove the slag on the surface of the purified magnesium alloy melt, and then pour the melt into a metal mold preheated at 200°C at 690°C to obtain a magnesium alloy ingot;

[0099] (5) Perform solution treatment on the magnesium alloy ingot at 420°C for 24 hours, and then extrude it into a sheet (the extrusion conditions include: extrusion temperature 350°C, extrusion speed 1 m / min, extrusion ratio 15:1);

[0100] (6) Perform three rolling treatments on the sheet to obtain a rolled sheet; the conditions for each rolling treatment include: rolling temperature 270°C, single-pass reduction 4%, total reduction 12%, and the initial thickness of the extruded sheet is 10 mm;

[0101] (7) Perform aging treatment on the rolled sheet (aging temperature 200°C, aging time 24 hours) to obtain the desired product.

[0102] In step (1): by mass percentage, Al: 8%, Sc: 0.10%, Y: 0.10%, Mn: 0.10%, unavoidable impurity elements are less than 0.02%, and the balance is Mg. Weigh the corresponding pure magnesium ingots, pure aluminum, Mg-Sc master alloy, Mg-Y master alloy, and Mg-Mn master alloy. The conditions for preheating treatment include: preheating temperature is 360 °C, and preheating time is 2 hours.

[0103] In step (3): the dosage of the refining agent is 0.12 wt% of the mass of the magnesium alloy melt; the refining agent is a metal chloride and a fluoride; the mass ratio of the metal chloride to the fluoride is 15.67:1; the metal chloride is a combination of KCl, CaCl2, BaCl, and YCl3, and their mass ratio is 7:3.43:2:1; the fluoride is selected from CaF.

[0104] After testing, the chemical composition of the magnesium alloy in this example is as follows: Al 7.96 wt%, Sc 0.11 wt%, Y 0.10 wt%, Mn 0.13 wt%, unavoidable impurities include: Fe 0.0062 wt%, Ni 0.0010 wt%, Cu 0.0006 wt%, and the balance is Mg.

[0105] The SEM micrograph of the microstructure of the magnesium alloy prepared in this example is similar to Figure 1 and it can be obtained that the magnesium alloy has fine and dispersed Mg 17 Al 12 phase.

[0106] Example 4

[0107] The difference between this example and Example 1 is:

[0108] The refining agent is a metal chloride, a fluoride, and 1-octyl-3-methylimidazolium hexafluorophosphate modified graphene oxide; the mass ratio of the metal chloride, the fluoride, and 1-octyl-3-methylimidazolium hexafluorophosphate modified graphene oxide is 15.67:1:1.52; the metal chloride is a combination of KCl, CaCl2, BaCl, and YCl3, and their mass ratio is 7:3.43:2:1; the fluoride is selected from CaF;

[0109] The preparation method of 1-octyl-3-methylimidazolium hexafluorophosphate modified graphene oxide is as follows: Disperse graphene oxide in water to form a suspension, then add 1-octyl-3-methylimidazolium hexafluorophosphate, react at 25 °C for 4 hours, then centrifuge and separate, discard the supernatant, and dry the solid to obtain 1-octyl-3-methylimidazolium hexafluorophosphate modified graphene oxide; among them, the graphene oxide is monolayer graphene oxide purchased from Nanjing Xianfeng Nano Materials Technology Co., Ltd., with an average sheet diameter of 2.5 μm and an average thickness of 1 nm; the mass ratio of graphene oxide to water is 1:10; the weight ratio of graphene oxide to 1-octyl-3-methylimidazolium hexafluorophosphate is 1:0.12; the drying conditions include: drying at 110 °C for 3 h.

[0110] After testing, the chemical composition of the magnesium alloy in this example is as follows: Al 8.12 wt%, Sc 0.11 wt%, Y 0.12 wt%, Mn 0.10 wt%, and the inevitable impurities include: Fe 0.0018 wt%, Ni 0.0002 wt%, Cu 0.0003 wt%, and the balance is Mg.

[0111] The SEM micrograph of the microstructure of the magnesium alloy prepared in this example is similar to Figure 1 and it can be obtained that the magnesium alloy has fine and dispersed Mg 17 Al 12 phase.

[0112] Example 5

[0113] The difference between this example and Example 4 is:

[0114] Replace 1-octyl-3-methylimidazolium hexafluorophosphate modified graphene oxide with 1-hexyl-3-methylimidazolium hexafluorophosphate modified graphene oxide; the preparation method of 1-hexyl-3-methylimidazolium hexafluorophosphate modified graphene oxide is the same as that of Example 4, except that 1-octyl-3-methylimidazolium hexafluorophosphate is replaced by 1-hexyl-3-methylimidazolium hexafluorophosphate during preparation.

[0115] After testing, the chemical composition of the magnesium alloy in this example is as follows: Al 8.11 wt%, Sc 0.12 wt%, Y 0.10 wt%, Mn 0.10 wt%, and the inevitable impurities include: Fe 0.0022 wt%, Ni 0.0005 wt%, Cu 0.0006 wt%, and the balance is Mg.

[0116] The SEM micrograph of the microstructure of the magnesium alloy prepared in this example is similar to Figure 1 and it can be obtained that the magnesium alloy has fine and dispersed Mg 17 Al 12 phase.

[0117] Example 6

[0118] The difference between this example and Example 4 is as follows:

[0119] Replace 1-octyl-3-methylimidazolium hexafluorophosphate modified graphene oxide with graphene oxide (the graphene oxide is monolayer graphene oxide purchased from Nanjing Xianfeng Nano Materials Technology Co., Ltd., with an average sheet diameter of 2.5 μm and an average thickness of 1 nm).

[0120] After testing, the chemical composition of the magnesium alloy in this example is as follows: Al 8.21 wt%, Sc 0.11 wt%, Y 0.15 wt%, Mn 0.13 wt%, and inevitable impurities include: Fe 0.0048 wt%, Ni 0.0003 wt%, Cu 0.0006 wt%, and the balance is Mg.

[0121] The SEM micrograph of the microstructure of the magnesium alloy prepared in this example is similar to that of Figure 1 and it can be obtained that the magnesium alloy has fine and dispersed Mg 17 Al 12 phase.

[0122] Example 7

[0123] The difference between this example and Example 4 is as follows:

[0124] Replace 1-octyl-3-methylimidazolium hexafluorophosphate modified graphene oxide with 1-hexadecyl-3-methylimidazolium hexafluorophosphate modified graphene oxide; the preparation method of 1-hexadecyl-3-methylimidazolium hexafluorophosphate modified graphene oxide is the same as that of Example 4, except that 1-octyl-3-methylimidazolium hexafluorophosphate is replaced with 1-hexadecyl-3-methylimidazolium hexafluorophosphate during the preparation.

[0125] After testing, the chemical composition of the magnesium alloy in this example is as follows: Al 8.17 wt%, Sc 0.11 wt%, Y 0.10 wt%, Mn 0.13 wt%, and inevitable impurities include: Fe 0.0046 wt%, Ni 0.0003 wt%, Cu 0.0004 wt%, and the balance is Mg.

[0126] The SEM micrograph of the microstructure of the magnesium alloy prepared in this example is similar to that of Figure 1 and it can be obtained that the magnesium alloy has fine and dispersed Mg 17 Al 12 phase.

[0127] Example 8

[0128] The difference between this example and Example 4 is as follows:

[0129] Replace 1-octyl-3-methylimidazolium hexafluorophosphate modified graphene oxide with 1-ethyl-3-methylimidazolium hexafluorophosphate modified graphene oxide; the preparation method of 1-ethyl-3-methylimidazolium hexafluorophosphate modified graphene oxide is the same as that in Example 4, except that 1-octyl-3-methylimidazolium hexafluorophosphate is replaced with 1-ethyl-3-methylimidazolium hexafluorophosphate during preparation.

[0130] After testing, the chemical composition of the magnesium alloy in this example is as follows: Al 8.12 wt%, Sc 0.12 wt%, Y 0.14 wt%, Mn 0.09 wt%, and inevitable impurities include: Fe 0.0046 wt%, Ni 0.0006 wt%, Cu 0.0008 wt%, and the balance is Mg.

[0131] The SEM micrograph of the microstructure of the magnesium alloy prepared in this example is the same as Figure 1 similar, and it can be obtained that the magnesium alloy has fine and dispersed Mg 17 Al 12 phase.

[0132] Comparative Example 1

[0133] The difference between this comparative example and Example 1 is as follows:

[0134] Step (1) is: Weigh pure magnesium ingots and pure aluminum according to the elemental content of the magnesium alloy sheet, and then perform preheating treatment at 300 °C for 2 hours to remove moisture;

[0135] Step (2) is: Under a CO2 + SF6 protective gas with a volume ratio of 1:9, add pure magnesium ingots at 600 °C, heat to 690 °C to melt the pure magnesium ingots, then heat to 720 °C to add pure aluminum ingots, and then keep warm until all raw materials are melted to obtain a magnesium alloy melt;

[0136] In step (1): By mass percentage, Al: 8%, the total content of impurity elements such as Fe, Cu, and Ni is less than 0.02%, and the balance is Mg. Weigh the corresponding pure magnesium ingots and pure aluminum; the conditions for the preheating treatment include: the preheating temperature is 300 °C and the preheating time is 2 hours.

[0137] After testing, the chemical composition of the magnesium alloy in this comparative example is as follows: Al 8.2 wt%, and inevitable impurities include: Fe 0.0078 wt%, Ni 0.0012 wt%, Cu 0.0011 wt%, and the balance is Mg.

[0138] The corrosion surface morphology of this comparative example after soaking in the corrosion medium (3.5 wt% NaCl solution) for 7 days is asFigure 3 As shown. It can be seen that serious local corrosion occurred in this comparative example, a large amount of corrosion products accumulated on the surface, and deep local pitting pits appeared on the surface, which would lead to rapid aging of the mechanical and corrosion properties of the alloy. It can be found that the comparative example did not show filiform corrosion characteristics.

[0139] Comparative Example 2

[0140] The difference between this comparative example and Example 1 is that in step (7): the aging temperature is 350 °C and the aging time is 1 hour.

[0141] Comparative Example 3

[0142] The difference between this comparative example and Example 1 is that the commercial AZ91D magnesium alloy is used in the comparative example, and the chemical composition of the magnesium alloy is: Al 8.93 wt%, Zn 0.64 wt%, Mn 0.27 wt%, Fe 0.0059 wt%, Ni 0.0015 wt%, Cu 0.0012 wt%.

[0143] The cross-sectional morphology of the corrosion of this comparative example after being immersed in the corrosion medium (3.5 wt% NaCl solution) for 7 days is as Figure 4 shown. It can be seen that due to the existence of coarse reticular secondary phases in the commercial magnesium alloy, serious local pitting corrosion behavior occurred in the alloy in the corrosion medium, which would seriously deteriorate the mechanical and corrosion resistance properties of the alloy.

[0144] Comparative Example 4

[0145] The difference between this comparative example and Example 1 is that the rolled sheet is obtained by performing a single rolling treatment on the sheet, and the conditions of the rolling treatment include: the rolling temperature is 270 °C, the single-pass reduction is 15%, and the initial thickness of the extrusion plate is 10 mm.

[0146] Comparative Example 5

[0147] The difference between this comparative example and Example 1 is:

[0148] Step (1) is: Weigh pure magnesium ingots, pure aluminum, Mg-30Y master alloy, and Mg-5Mn master alloy according to the element content of the magnesium alloy sheet, and then perform preheating treatment at 300 °C for 2 hours respectively to remove moisture;

[0149] Step (2) is: Under the protection gas of CO2 plus SF6 with a volume ratio of 1:9, add the Mg-5Mn master alloy at 700 °C, then heat to 720 °C and add the pure aluminum ingot; then raise the temperature to 750 °C and add the Mg-30Y master alloy, and then keep it warm until all raw materials are melted to obtain the magnesium alloy melt;

[0150] In step (1): by mass percentage, Al: 8%, Y: 0.1%, Mn: 0.1%, the total content of impurity elements of Fe, Cu, and Ni is less than 0.02%, and the balance is Mg. Weigh the corresponding pure magnesium ingots, pure aluminum, Mg-Y master alloy, and Mg-Mn master alloy; the conditions for preheating treatment include: the preheating temperature is 360 °C and the preheating time is 2 hours.

[0151] After testing, the chemical composition of the magnesium alloy in this comparative example is as follows: Al 8.18 wt%, Y 0.12 wt%, Mn 0.15 wt%, and the inevitable impurities include: Fe 0.0062 wt%, Ni 0.0004 wt%, Cu 0.0008 wt%, and the balance is Mg.

[0152] Comparative Example 6

[0153] The difference between this comparative example and Example 1 is:

[0154] Step (1) is: Weigh the pure magnesium ingot, pure aluminum, Mg-30Sc master alloy, and Mg-5Mn master alloy according to the element content of the magnesium alloy sheet, and then perform preheating treatment at 300 °C for 2 hours to remove moisture;

[0155] (2) Under a protective gas of CO2 and SF6 with a volume ratio of 1:9, add the pure magnesium ingot at 600 °C and heat it to 690 °C to melt the pure magnesium ingot; add the Mg-5Mn master alloy at 700 °C, and then add the pure aluminum ingot when heated to 720 °C; then raise the temperature to 750 °C and add the Mg-30Sc master alloy, and then keep it warm until all raw materials are melted to obtain a magnesium alloy melt;

[0156] In step (1): by mass percentage, Al: 8%, Sc: 0.1%, Y: 0.1%, Mn: 0.1%, the total content of impurity elements of Fe, Cu, and Ni is less than 0.02%, and the balance is Mg. Weigh the corresponding pure magnesium ingots, pure aluminum, Mg-Sc master alloy, and Mg-Mn master alloy; the conditions for preheating treatment include: the preheating temperature is 360 °C and the preheating time is 2 hours.

[0157] After testing, the chemical composition of the magnesium alloy in this example is as follows: Al 8.13 wt%, Sc 0.11 wt%, Mn 0.11 wt%, and the inevitable impurities include: Fe 0.0061 wt%, Ni 0.0003 wt%, Cu 0.0004 wt%, and the balance is Mg.

[0158] Among them, the corrosion surface morphology of the magnesium alloy in Example 1 after being immersed in 3.5 wt% NaCl solution for 7 days is as Figure 2As shown, it shows a slight filiform corrosion morphology; the surface corrosion morphology of the magnesium alloy in Comparative Example 1 after being immersed in 3.5 wt% NaCl solution for 7 days is as Figure 3 shown, which shows a severe local pitting morphology. The corrosion cross-section morphology of the magnesium alloy in Comparative Example 3 after being immersed in 3.5 wt% NaCl solution for 7 days is as Figure 4 shown, which has a severe local pitting morphology.

[0159] Performance Test

[0160] Mechanical property and corrosion property tests:

[0161] For the mechanical property test, the gauge length dimensions of the tensile sheet are 25 × 6 × 2 mm, with three parallel specimens, and the tensile test standard complies with the national standard GB / T228.1-2021.

[0162] The corrosion test solution is a neutral 3.5 wt% NaCl solution, the test temperature is room temperature 25°C, the sample size is 20×20×5mm, and the test time is 7 days. The immersion corrosion test complies with the national standard GB 10124-88, and the weight loss rate is calculated by calculating the weight difference between the sample before the corrosion test and the sample after being cleaned after the corrosion test. The weight loss rate (mg / cm 2 / day) is equal to the weight difference divided by the surface area of the specimen divided by the number of test days, and can be converted into the average depth corrosion rate (mm / year) through formula conversion.

[0163] The volume of hydrogen gas evolved from magnesium corrosion is equivalently recorded by the reduction amount of the solution in the burette through a simply constructed hydrogen evolution test device. The hydrogen evolution rate (mL / cm 2 / day) is obtained by dividing the volume of hydrogen gas evolved by the surface area of the specimen divided by the number of test days. The corrosion cleaning agent is 200 g / L CrO3 + 10 g / L AgNO3, which is a common method for cleaning magnesium alloy corrosion products and complies with the national standard GB / T 16545-2015.

[0164] The test results of the mechanical properties and the weight loss and hydrogen evolution rates of each group of magnesium alloys are shown in Table 1.

[0165] Table 1 Performance Test Results

[0166]

[0167] From the above performance test results, it can be seen that the magnesium alloys of Examples 1-8 have excellent corrosion resistance and mechanical properties. In particular, the comprehensive properties of the magnesium alloys of Examples 4-5 are the most prominent. This is mainly because the invention is based on a low-cost Mg-Al alloy system and by adding a small amount of Sc and Y elements with high solid solubility. On the one hand, it can make alloy elements dissolve into the magnesium matrix as much as possible to improve the chemical stability of the matrix. The multi-pass rolling treatment can provide the precipitation driving force for the subsequent aging treatment by introducing a large number of dislocation and twin crystal defects, and promote the rapid formation of fine and dispersed Mg 17 Al 12 phase. At the same time, during the refining process, the refining agent can better reduce the impurity content, and it can also increase the heterogeneous nucleation sites in the molten magnesium, refine the grains, and thus better increase the strength and corrosion resistance of the alloy.

[0168] In the comparative examples, since the necessary technical solutions were not adopted, their performance in the corresponding performance tests was significantly worse than that of the examples. In Comparative Example 1, there are no Sc, Y, and Mn elements. It can be seen that the mechanical properties and corrosion resistance decreased, proving that Sc, Y, and Mn elements have important influences on the mechanical properties and corrosion resistance of Mg alloys; in Comparative Example 2, the preparation aging process is different. It can be seen that its mechanical properties are significantly reduced and the corrosion resistance is reduced to a certain extent, proving that the aging process has an impact on the comprehensive properties of magnesium alloys, especially on the mechanical properties; in Comparative Example 3, it is the existing commercial AZ91D magnesium alloy. It can be seen that its mechanical properties are significantly reduced and the corrosion resistance is reduced to a certain extent, proving that the magnesium alloy in the present invention can avoid the serious local pitting corrosion caused by the coarse network Mg 17 Al 12 phase, and has excellent mechanical properties compared with the existing magnesium alloys; in Comparative Example 4, a single rolling treatment is carried out. It can be seen that the mechanical properties and corrosion resistance decreased, proving that multi-pass rolling treatment can significantly improve the mechanical properties of the alloy and reduce the microgalvanic corrosion effect of the coarse network phase; in Comparative Example 5, there is no Sc element. It can be seen that the mechanical properties and corrosion resistance decreased, proving that Sc element has important influences on the mechanical properties and corrosion resistance of Mg alloys; in Comparative Example 6, there is no Y element. It can be seen that the mechanical properties and corrosion resistance decreased, proving that Y element has important influences on the mechanical properties and corrosion resistance of Mg alloys.

[0169] The above is the preferred implementation mode of the present invention. It should be pointed out that for those of ordinary skill in the art in this technical field, without departing from the principle described in the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A high corrosion resistant magnesium alloy sheet with filiform corrosion characteristics, characterized in that: Based on the total amount of the magnesium alloy sheet, the magnesium alloy sheet contains the following elements in terms of mass percentage: Al: 6-9%, Sc: 0.05-0.15%, Y: 0.05-0.15%, Mn: 0.05-0.15%, and the balance is Mg and unavoidable impurity elements; wherein the magnesium alloy sheet has a dispersed Mg 17 Al 12 Phase structure of the phase; The preparation method of the high corrosion-resistant magnesium alloy sheet comprises: (1) Pure magnesium ingots, pure aluminum, Mg-Sc master alloy, Mg-Y master alloy and Mg-Mn master alloy are weighed according to the element content of the magnesium alloy plate, and then preheated respectively; (2) adding the preheated pure magnesium, pure aluminum, Mg-Sc master alloy, Mg-Y master alloy and Mg-Mn master alloy into a crucible in sequence for smelting under the protection of CO2 and SF6 to obtain a magnesium alloy melt; (3) refining the magnesium alloy melt in step (2) under the protection of CO2 and SF6 gas and in the presence of a refining agent, and then subjecting the molten magnesium alloy to a static insulation treatment to obtain a purified molten magnesium alloy; (4) Under the protection of CO2 and SF6, the purified magnesium alloy melt is subjected to slag removal treatment, and then the slag-removed magnesium alloy melt is cast into a preheated metal mold to obtain a magnesium alloy ingot; (5) Solution treating the magnesium alloy ingot and then extruding it into a plate; (6) performing at least two rolling processes on the plate to obtain a rolled plate; (7) performing aging treatment on the rolled plate to obtain a final high corrosion resistant magnesium alloy plate; the aging treatment conditions include: aging temperature of 175-200° C., and aging time of 12-48 hours; The refining agent is metal chloride, fluoride, and 1-C6-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide, with a mass ratio of (15-16):1:(1-1.5); The metal chlorides are KCl, CaCl2, BaCl2 and YCl3, with a mass ratio of (5-8):(3-4):(1.5-2.5):1; The fluoride is CaF; The preparation method of the 1-C6-C12 alkyl-3-methylimidazolium hexafluorophosphate modified graphene oxide is as follows: graphene oxide is dispersed in water to form a suspension, and then 1-C6-C12 alkyl-3-methylimidazolium hexafluorophosphate is added, reacted at 20-30° C. for 2-5 hours, and then centrifuged, the supernatant is discarded, and the solid is dried to obtain.

2. The magnesium alloy sheet according to claim 1, characterized in that: Based on the total amount of the magnesium alloy sheet, the mass content of the inevitable impurity elements is less than 0.02%; the inevitable impurity elements include at least one of Fe, Ni and Cu.

3. The magnesium alloy sheet according to claim 2, characterized in that: The preheating conditions include: a preheating temperature of 320-380° C. and a preheating time of 1-3 hours; in steps (2), (3) and (4), the volume ratio of SF6 and CO2 in the protective gas is independently 1:(5-12).

4. The magnesium alloy sheet material according to claim 3, characterized in that: In step (2): adding a pure magnesium ingot at 590-620°C and heating to 680-690°C to melt the pure magnesium ingot; adding a Mg-Mn master alloy at 695-710°C, then heating to 715-740°C and adding a pure aluminum ingot; then raising the temperature to 745-780°C and sequentially adding a Mg-Sc master alloy and a Mg-Y master alloy, and then keeping the temperature until all the raw materials are melted to obtain the magnesium alloy melt.

5. The magnesium alloy sheet material according to claim 4, characterized in that: In step (3): the amount of the refining agent used is 0.05-0.3wt% of the mass of the magnesium alloy melt.

6. The magnesium alloy sheet material according to claim 5, characterized in that: In step (3), the refining agent is added at a temperature of 740-750°C while stirring manually, and the refining is continued for 5-20 minutes after the refining agent is added. The conditions for standing and heat preservation include: first standing at 740-750°C for 30-40 minutes, and then cooling to 705-720°C and standing for 20-30 minutes.

7. The magnesium alloy sheet material according to claim 6, characterized in that: In step (4), the conditions for the slag removal treatment include: reducing the temperature to 690-700°C to remove the slag on the surface of the melt; in step (5), the conditions for the solution treatment include: a temperature of 400-420°C and a time of 18-32 hours; in step (5), the conditions for the extrusion include: an extrusion temperature of 350-390°C, an extrusion speed of 0.5-1 m / min, and an extrusion ratio of 15:1-20:

1.

8. The magnesium alloy sheet material according to claim 7, characterized in that: In step (6), the plate is subjected to three rolling processes to obtain a rolled plate; the conditions of each rolling process include: a rolling temperature of 250-300° C., a single-pass pressing amount of 4-6%, a total pressing amount of 12-18%, and an initial thickness of the extruded plate of 8-12 mm.

Images