Low-cost high-strength corrosion-resistant magnesium alloy and preparation method thereof

Abstract

The invention discloses a low-cost high-strength corrosion-resistant magnesium alloy and a preparation method thereof, and belongs to the technical field of metal materials. The magnesium alloy comprises the following chemical components in percentage by weight: 0.5-3% of zinc, 0.1-1% of calcium, 0-0.6% of manganese, 0.2-2.0% of RE and the balance of magnesium. RE is one or more of neodymium, gadolinium, cerium and samarium; the preparation method comprises the steps of atmosphere protection smelting, rapid cast rolling, homogenization treatment, multi-pass rolling, solid solution heat treatment and artificial aging. According to the magnesium alloy and the preparation method thereof, the high-density atomic scale microstructure which is uniformly dispersed and distributed and is in a coherent relationship with a magnesium matrix is separated out in the magnesium alloy by adjusting alloy components and a thermal machining process, the microstructure contains Zn, Ca and rare earth elements, and the age hardening capacity of the alloy can be remarkably improved through the formation of the high-density microstructure; and meanwhile, local pitting corrosion can be converted into uniform corrosion through the uniformly dispersed and distributed microstructures, so that the corrosion resistance is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a low-cost, high-strength, corrosion-resistant magnesium alloy and a preparation method thereof. Background Art

[0002] As the lightest engineering structural metal material, magnesium alloys have broad application prospects in fields such as automotive and aerospace due to their high specific strength and excellent electrical and thermal conductivity. Among them, magnesium-zinc-calcium alloys are inexpensive, have weak texture properties, and excellent stamping capabilities, making them extremely promising. However, magnesium-zinc-calcium alloys often form highly cathodically active submicron / micron-sized Ca2Mg6Zn3 phases. This phase creates a large potential difference with the Mg matrix, leading to severe microgalvanic corrosion of the surrounding anodic α-Mg, resulting in severe localized pitting. Furthermore, existing magnesium-zinc-calcium alloys often precipitate nano-Ca2Mg6Zn3 phases during aging heat treatment. While this precipitate improves strength, it significantly degrades the alloy's corrosion resistance. Therefore, how to achieve a synergistic improvement in the strength and corrosion resistance of magnesium-zinc-calcium alloys by manipulating alloy composition and microstructure remains a key challenge that urgently needs to be addressed. Summary of the Invention

[0003] In order to address the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a low-cost, high-strength, corrosion-resistant magnesium alloy and a preparation method thereof. By adding a small amount of rare earth elements to the Mg-Zn-Ca alloy, a microstructure containing zinc, calcium and rare earth elements can be formed during the aging process, so that the strength and corrosion resistance of the Mg-Zn-Ca alloy can be simultaneously improved after aging treatment.

[0004] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0005] A low-cost, high-strength, corrosion-resistant magnesium alloy comprises, by weight percentage, 0.5-3% zinc, 0.1-1% calcium, 0-0.6% manganese, and 0.2-2.0% RE; the remainder is magnesium and unavoidable impurities; RE is a rare earth element, and RE is one or more of neodymium, gadolinium, cerium, and samarium.

[0006] Preferably, the chemical composition of the magnesium alloy by weight percentage is: zinc: 0.6-2.5%, calcium: 0.3-0.8%, manganese: 0.1-0.5%, RE: 0.3-1.5%; the balance is magnesium and inevitable impurities.

[0007] Furthermore, among the rare earth elements added to the magnesium alloy, the addition amount of each rare earth element is 0.2-1 wt. % (preferably 0.3-0.8 wt. %).

[0008] Furthermore, the total amount of inevitable impurity elements in the chemical composition of the magnesium alloy is ≤0.05 wt.%.

[0009] Furthermore, the magnesium alloy has an atomic-scale microstructure with high density and uniform dispersion distribution and a coherent relationship with the magnesium matrix. The microstructure contains Zn, Ca and rare earth elements, has a length of less than 20nm and a thickness of 1 to 5 atomic layers.

[0010] Furthermore, the magnesium alloy has a yield strength of 170-250 MPa and a corrosion rate of ≤0.2 mm / year.

[0011] Furthermore, the method for preparing the low-cost, high-strength, corrosion-resistant magnesium alloy comprises the following steps:

[0012] (1) Under the protection of a mixed gas of SF6 and CO2, various elemental raw materials are added according to the designed magnesium alloy chemical composition, heated to 660-760°C for melting and stirred evenly, and then refined, degassed and slag removed to obtain a magnesium alloy melt;

[0013] (2) rapidly casting and rolling the magnesium alloy melt obtained in step (1) to obtain a cast-rolled billet;

[0014] (3) placing the cast-rolled billet obtained in step (2) into a resistance furnace filled with argon or nitrogen for step homogenization heat treatment, and air cooling to room temperature to obtain a homogenized billet; the step homogenization heat treatment is to sequentially heat the cast-rolled billet at 320-370°C for 0.5-3 hours, 430-470°C for 0.5-3 hours, and 515-545°C for 0.5-3 hours;

[0015] (4) performing multiple rolling on the homogeneous billet obtained in step (3), wherein the rolling passes are 2 to 15, to obtain a rolled billet;

[0016] (5) subjecting the rolled billet obtained in step (4) to a high-temperature short-time solution heat treatment under argon protection, and then immediately air-cooling or water-cooling to obtain a solution billet;

[0017] (6) subjecting the solid solution billet obtained in step (5) to artificial aging heat treatment, wherein the artificial aging treatment temperature is 160-220° C. and the treatment time is 20-480 min; after the aging treatment, a low-cost, high-strength, corrosion-resistant magnesium alloy is obtained.

[0018] Furthermore, in the feeding process of step (1), raw materials of magnesium, zinc, calcium and manganese are first added in sequence, heated and melted at 660-760°C, and then raw materials of rare earth elements are added, stirred evenly at 660-730°C, and refined, degassed and slag removed; wherein: magnesium and zinc components are added as pure magnesium and pure zinc as raw materials; calcium and manganese are added in the form of magnesium-calcium master alloy and magnesium-manganese master alloy respectively; rare earth elements neodymium, gadolinium, cerium and samarium are added in the form of magnesium-neodymium master alloy, magnesium-gadolinium master alloy, magnesium-cerium master alloy and magnesium-samarium master alloy respectively.

[0019] Furthermore, in step (2), the rapid casting speed is 4-15 m / min, and the thickness of the cast billet is 2.5-7 mm.

[0020] Furthermore, in step (4), the rolling temperature of the multiple passes is 150-400° C., and the reduction in each pass is 5-30%.

[0021] Furthermore, in step (5), the high temperature short time solution heat treatment temperature is 450-520°C and the time is 30-90 minutes.

[0022] The design mechanism and beneficial effects of the present invention are as follows:

[0023] 1. The magnesium alloy of the present invention selects elements such as zinc and rare earth elements (neodymium, gadolinium, cerium, and samarium) as components. Taking advantage of their high solid solubility in magnesium under high temperature conditions and their significant decrease in solid solubility as the temperature decreases, the alloy is subjected to high-temperature solid solution and low-temperature artificial aging treatments to precipitate a high-density strengthening phase in the magnesium alloy. The addition of calcium can refine the precipitated phase and promote the precipitation of atomic-scale microstructures, thereby improving the alloy's age-hardening ability. A trace amount of manganese is added to form a thermally stable manganese-containing phase, pinning grain boundaries and inhibiting grain growth during the high-temperature solid solution process, thereby imparting high strength to the alloy. The atomic radii of both rare earth elements and calcium are larger than those of magnesium. Therefore, the addition of rare earth elements can participate in the formation of the microstructure and promote its precipitation.

[0024] 2. The magnesium alloy of the present invention has a high-density microstructure, with a number density of >1.3×10 23 , significantly higher than the number density of precipitated phases in commercial AZ alloys prepared under the same conditions. Furthermore, the weight ratio of zinc to calcium in the magnesium alloy composition of the present invention needs to be controlled within the range of (4-2):1. If the Zn ratio is too high, it is difficult to form the microstructure during aging, and instead a highly cathodically active Mg-Zn phase is formed, resulting in poor corrosion resistance. If the Ca ratio is too high, the alloy's formability deteriorates, and edge cracking is more likely to occur during rolling.

[0025] 3. In the prior art, artificial aging treatment of Mg-Zn-Ca alloys typically precipitates nano-Ca2Mg6Zn3 phases. While Ca2Mg6Zn3 phases can improve strength, they are large in size and, as cathodic phases, present a large potential difference with the magnesium matrix. Therefore, the formation of Ca2Mg6Zn3 phases accelerates the dissolution of the surrounding magnesium matrix, leading to severe local pitting and deteriorating the alloy's corrosion resistance. The present invention, by adding a small amount of rare earth elements (neodymium, gadolinium, cerium, and samarium) to the Mg-Zn-Ca alloy, forms a microstructure containing zinc, calcium, and rare earth elements during the aging process. This microstructure is small (less than 20 nm in length) and has a high number density, effectively hindering dislocation motion and achieving an age-hardening capacity of ~60-100 MPa. The precipitation of this microstructure can also improve the alloy's corrosion resistance by 2-5 times or more compared to before aging. This is primarily due to the small size of the microstructure, which prevents strong micro-galvanic corrosion and the formation of severe corrosion pits. In addition, the microstructure is uniformly dispersed, which can inhibit local pitting corrosion and promote uniform corrosion on the one hand, and on the other hand, it is conducive to the uniform densification of the corrosion product film on the alloy surface, thereby effectively resisting the corrosive Cl - corrosion and improve the protection ability of the magnesium matrix.

[0026] 4. In the prior art, although the strength of Mg-Zn-Ca alloys is improved after aging treatment, the plasticity is significantly reduced. This is mainly because the large-scale, unevenly distributed Ca2Mg6Zn3 phase can act as a crack source during tensile deformation, causing premature fracture. The alloy and preparation method provided by the present invention can form a microstructure with small size (thickness of 1-5 atomic layers) and uniform dispersion during the aging process. This microstructure can effectively hinder dislocation movement. Therefore, the yield strength of the alloy is significantly improved after aging, while the plasticity only slightly decreases or remains unchanged. For example, the yield strength of Mg-Zn-Ca alloys without rare earth elements is increased by 20-45MPa after aging, but the elongation is reduced by 6-9%. However, the alloys with rare earth elements such as neodymium, gadolinium, and samarium have a yield strength increase of 60-100MPa after aging, but the elongation is only reduced by ≤1.5%.

[0027] 5. The method provided by the present invention can simultaneously improve the strength and corrosion resistance of Mg-Zn-Ca alloys after aging treatment. For example, Mg-Zn-Ca alloys with the precipitated Ca2Mg6Zn3 phase have a yield strength increase of ~20-45 MPa after aging, but a decrease in corrosion resistance of ~40-70%. In contrast, alloys incorporating elements such as neodymium, gadolinium, and cerium not only increase their yield strength by ~60-100 MPa after aging, but also improve their corrosion resistance by ~2-5 times.

[0028] 6. The present invention significantly improves alloy strength and corrosion resistance by adding a small amount of rare earth elements, resulting in a low-cost magnesium alloy. Furthermore, the present invention's magnesium alloy preparation method is simple and reliable, with a high-strength, corrosion-resistant alloy obtained through sub-rapid solidification casting and rolling, multi-pass rolling, and heat treatment, thus maintaining cost control. The corrosion resistance of the magnesium alloy after optimizing the composition of the present invention is 5-10 times or more that of commercial AZ31 and AZ61 magnesium alloys, and its age-hardening ability is 1.5-3 times or more that of commercial AZ31 and AZ61 magnesium alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a scanning transmission image of the atomic-scale microstructure inside the magnesium alloy prepared in Example 1.

[0030] Figure 2 The atomic-scale microstructure scanning transmission image and the corresponding element distribution map of the magnesium alloy prepared in Example 1; wherein: (a) is the microstructure scanning transmission image; (b) is the corresponding element distribution map. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the accompanying drawings and examples so that those skilled in the art can better understand the present invention and implement it. However, the examples are not intended to limit the present invention.

[0032] The present invention provides a low-cost, high-strength, corrosion-resistant magnesium alloy and a preparation method thereof. By adjusting the alloy composition and thermomechanical processing technology, a high-density, uniformly dispersed atomic-scale microstructure with a coherent relationship with the magnesium matrix is ​​precipitated inside the magnesium alloy. The microstructure contains Zn, Ca, and rare earth elements, has a length of less than 20nm, and a thickness of 1-5 atomic layers. The formation of a high-density microstructure can significantly improve the aging hardening ability of the alloy. At the same time, the uniformly dispersed microstructure can transform local pitting corrosion into uniform corrosion, and improve the density and protectiveness of the corrosion product film, thereby achieving a significant improvement in corrosion resistance. The magnesium alloy of the present invention can simultaneously have high strength (yield strength of ~170-250MPa) and high corrosion resistance (corrosion rate of ≤0.2mm / year).

[0033] In the following examples, during the charging process for preparing a low-cost, high-strength, corrosion-resistant magnesium alloy, the raw materials of various elements are added according to the designed chemical composition ratio of the magnesium alloy. First, pure magnesium, pure zinc, a magnesium-calcium master alloy, and a magnesium-manganese master alloy are added in sequence and melted at 660-760°C. Subsequently, a magnesium-rare earth master alloy is added, stirred uniformly at 660-730°C, refined, degassed, and slag removed to obtain an alloy melt. The magnesium-calcium master alloy has a Ca content of 21.65 wt.%, with Mg as the balance; the magnesium-manganese master alloy has a Mn content of 30 wt.%, with Mg as the balance; and the magnesium-rare earth master alloy has a rare earth element content of 30 wt.%, with Mg as the balance (e.g., the magnesium-neodymium master alloy has a neodymium content of 30 wt.%, with Mg as the balance, and the magnesium-cerium master alloy has a cerium content of 30 wt.%, with Mg as the balance).

[0034] The total amount of inevitable impurities in the magnesium alloys prepared in the following examples is ≤0.05 wt.%.

[0035] Example 1:

[0036] The magnesium alloy prepared in this embodiment has the following chemical composition (wt.%): Zn 0.6%, Ca 0.25%, Mn 0.2%, Nd 0.8%, and the balance is magnesium (Mg-0.6Zn-0.25Ca-0.2Mn-0.8Nd magnesium alloy). The preparation process is as follows:

[0037] (1) Under the protection of a mixed gas of SF6 and CO2, the magnesium alloy chemical composition is designed. First, pure magnesium, pure zinc, magnesium-calcium master alloy and magnesium-manganese master alloy are added in sequence and heated to melt at 710°C. Then, magnesium-gadolinium master alloy is added and stirred uniformly at 695°C. After refining and degassing, the slag is removed to obtain an alloy melt.

[0038] (2) rapidly casting and rolling the alloy melt obtained in step (1) at a casting and rolling speed of 7 m / min and a thickness of the cast-rolled billet of 2.8 mm to obtain a cast-rolled billet;

[0039] (3) subjecting the cast-rolled billet obtained in step (2) to a stepwise homogenization heat treatment, i.e., subjecting the cast-rolled billet to heat treatment at 340° C. for 1 hour, 445° C. for 1 hour, and 520° C. for 1 hour, followed by air cooling to room temperature to obtain a homogenized billet;

[0040] (4) performing multiple rolling of the homogeneous billet obtained in step (3), wherein the rolling passes are 8, the temperature is 175-315° C., and the reduction amount of each pass is 15-30%, to obtain a rolled billet;

[0041] (5) subjecting the rolled billet obtained in step (4) to a high-temperature short-time solid solution heat treatment in an argon-protected tubular furnace at a treatment temperature of 475° C. for 50 min, and immediately water cooling after the end of the insulation to obtain a solid solution billet;

[0042] (6) The solid solution billet obtained in step (5) is subjected to artificial aging heat treatment at an aging temperature of 160° C. for 240 min, and a low-cost, high-strength, and corrosion-resistant Mg-0.6Zn-0.25Ca-0.2Mn-0.8Nd magnesium alloy is obtained after aging treatment.

[0043] Figure 1 and Figure 2 The transmission image and element distribution diagram of the atomic-scale microstructure of the magnesium alloy prepared in this example show the formation of a high-density, uniformly dispersed atomic-scale microstructure within the magnesium alloy. This microstructure contains Zn, Ca, and Nd elements, with lengths less than 20 nm. After aging, the yield strength of the magnesium alloy in this example was 210 MPa, a 60 MPa increase compared to the pre-aging state. The corrosion rate was approximately 0.15 mm / year, and the corrosion resistance was doubled compared to the pre-aging state.

[0044] Comparative Example 1:

[0045] The difference from Example 2 is that the chemical composition of the magnesium alloy is (wt.%): Zn 0.6%, Ca 0.25%, Mn 0.2%, and the balance is magnesium (Mg-0.6Zn-0.25Ca-0.2Mn), that is, the magnesium alloy in this example does not contain rare earth elements.

[0046] According to tests, the yield strength of the magnesium alloy in this example after aging is only 170 MPa, which is only 25 MPa higher than before aging. The corrosion rate is about 0.8 mm / year, and the corrosion resistance is reduced by 40% compared with before aging.

[0047] Example 2:

[0048] The magnesium alloy prepared in this embodiment has the following chemical composition (wt.%): Zn 2.9%, Ca 1.0%, Mn 0.1%, Gd 0.5%, and the balance is magnesium (Mg-2.9Zn-1.0Ca-0.1Mn-0.5Gd magnesium alloy). The preparation process is as follows:

[0049] (1) Under the protection of a mixed gas of SF6 and CO2, the magnesium alloy chemical composition is added according to the designed composition. First, pure magnesium, pure zinc, magnesium-calcium master alloy and magnesium-manganese master alloy are added in sequence and heated to melt at 700°C. Then, magnesium-gadolinium master alloy is added and stirred evenly at 680°C. After refining and degassing, the slag is removed to obtain an alloy melt.

[0050] (2) rapidly casting and rolling the alloy melt obtained in step (1) at a casting and rolling speed of 12 m / min and a thickness of 3.0 mm of the cast-rolled billet to obtain a cast-rolled billet;

[0051] (3) subjecting the cast-rolled billet obtained in step (2) to a stepwise homogenization heat treatment, i.e., subjecting the cast-rolled billet to a heat treatment of 350° C. for 1 hour, 440° C. for 2 hours, and 515° C. for 0.5 hour in sequence, and then air-cooling to room temperature to obtain a homogenized billet;

[0052] (4) subjecting the homogeneous billet obtained in step (3) to multi-pass rolling, wherein the rolling passes are 5, the temperature is 150-250° C., and the reduction amount of each pass is 10-20%, to obtain a rolled billet;

[0053] (5) subjecting the rolled billet obtained in step (4) to a high-temperature short-time solid solution heat treatment in an argon-protected tubular furnace at a treatment temperature of 450° C. for 60 min, and immediately water cooling after the end of the insulation to obtain a solid solution billet;

[0054] (6) The solid solution billet obtained in step (5) is subjected to artificial aging heat treatment at an aging temperature of 200° C. for 100 min, and a low-cost, high-strength, corrosion-resistant Mg-2.9Zn-1.0Ca-0.1Mn-0.5Gd magnesium alloy is obtained after aging treatment.

[0055] The magnesium alloy prepared in this example has a high-density, uniformly dispersed atomic-scale microstructure containing Zn, Ca, and Gd. The magnesium alloy in this example has a yield strength of 230 MPa and an average corrosion rate of approximately 0.18 mm / year after immersion in sodium chloride solution for 14 days.

[0056] Comparative Example 2:

[0057] The yield strength of the commercial AZ61 magnesium alloy under the same shape and size conditions as those in Example 1 is about 200 MPa, and the corrosion rate is about 1.5 mm / year.

[0058] Example 3:

[0059] The magnesium alloy prepared in this embodiment has the following chemical composition (wt.%): Zn 1.0%, Ca 0.5%, Mn 0.5%; Sm 0.6%, and the balance is magnesium (Mg-1Zn-0.5Ca-0.5Mn-0.6Sm magnesium alloy). The preparation process is as follows:

[0060] (1) Under the protection of mixed gas of SF6 and CO2, the designed chemical composition of magnesium alloy is charged, pure magnesium, pure zinc, magnesium-calcium intermediate alloy and magnesium-manganese intermediate alloy are added in sequence, and then heated and melted at 730°C; then magnesium-samarium intermediate alloy is added, stirred uniformly at 710°C, and refined and degassed, and after slag removal, alloy melt is obtained;

[0061] (2) The alloy melt obtained in step (1) is rapidly cast and rolled, the casting and rolling speed is 5 meters / min, the thickness of the as-cast and rolled blank is 3.5 mm, and the as-cast and rolled blank is obtained;

[0062] (3) The as-cast and rolled blank obtained in step (2) is subjected to stepwise uniformization heat treatment, i.e. the as-cast and rolled blank is subjected to heat treatment at 335°C for 1.5 hours, 435°C for 1 hour and 520°C for 1 hour in sequence, and then air-cooled to room temperature, and the homogenized blank is obtained;

[0063] (4) The homogenized blank obtained in step (3) is subjected to multi-pass rolling, the rolling pass is 9 passes, the temperature is 175-235°C, and the reduction per pass is 10-20%, and the rolled blank is obtained;

[0064] (5) The rolled blank obtained in step (4) is subjected to high-temperature short-time solid solution heat treatment in a tube furnace under argon protection, the treatment temperature is 485°C, the holding time is 40 min, and water cooling is performed immediately after holding, and the solid solution blank is obtained;

[0065] (6) The solid solution blank obtained in step (5) is subjected to artificial aging heat treatment, the aging temperature is 180°C, and the time is 180 min, and the low-cost high-strength corrosion-resistant Mg-1Zn-0.5Ca-0.5Mn-0.6Sm magnesium alloy is obtained after aging treatment.

[0066] The yield strength of the magnesium alloy obtained in step (6) of the example is 205 MPa, and the average corrosion rate after immersion in sodium chloride solution for 14 days is about 0.17 mm / year.

[0067] Example 4:

[0068] The chemical composition of the magnesium alloy prepared in this example is (wt. %): Zn 1.5%, Ca 0.75%, Mn 0.25%; Ce 0.9%, and the balance is magnesium (Mg-1.5Zn-0.75Ca-0.25Mn-0.9Ce magnesium alloy), and the preparation process is as follows:

[0069] (1) Under the protection of mixed gas of SF6 and CO2, the designed chemical composition of magnesium alloy is charged, pure magnesium, pure zinc, magnesium-calcium intermediate alloy and magnesium-manganese intermediate alloy are added in sequence, and then heated and melted at 740°C; subsequently, magnesium-cerium intermediate alloy is added, stirred uniformly at 715°C, and refined and degassed, and after cleaning slag, alloy melt is obtained.

[0070] (2) The alloy melt obtained in step (1) is rapidly cast and rolled at a casting and rolling speed of 13 meters / min, and a cast and rolled blank thickness of 4 millimeters, to obtain a cast and rolled blank;

[0071] (3) The cast and rolled blank obtained in step (2) is subjected to stepwise uniformization heat treatment, that is, the cast and rolled blank is sequentially subjected to heat treatment at 355°C for 2 hours, 450°C for 1 hour, and 530°C for 1.5 hours, and then air-cooled to room temperature to obtain a homogenized blank;

[0072] (4) The homogenized blank obtained in step (3) is subjected to multi-pass rolling, with 10 rolling passes, at a temperature of 200-275°C, and a reduction of 15-30% per pass, to obtain a rolled blank;

[0073] (5) The rolled blank obtained in step (4) is subjected to high-temperature short-time solid solution heat treatment in a tube furnace under argon protection, at a treatment temperature of 500°C and a holding time of 30 min, and then water-cooled after holding to obtain a solid-solution blank;

[0074] (6) The solid-solution blank obtained in step (5) is subjected to artificial aging heat treatment at an aging temperature of 200°C and a time of 180 min, to obtain a low-cost high-strength corrosion-resistant Mg-1.5Zn-0.75Ca-0.25Mn-0.9Ce magnesium alloy.

[0075] The yield strength of the magnesium alloy obtained in step (6) of the example is 210 MPa, and the average corrosion rate after immersion in a sodium chloride solution for 14 days is about 0.1 mm / year.

[0076] Comparative Example 3:

[0077] The yield strength of the commercial AZ31 magnesium alloy under the same conditions of the shape and size of Example 4 is 180 MPa, and the average corrosion rate is about 1.3 mm / year.

[0078] Example 5:

[0079] The chemical composition of the magnesium alloy prepared in this example is (wt. %): Zn 1.25%, Ca 0.4%, Mn 0.15%, Gd 0.3%, Ce 0.2%, and the balance being magnesium (Mg-1.25Zn-0.4Ca-0.15Mn-0.3Gd-0.2Ce magnesium alloy), and the preparation process is as follows:

[0080] (1) Under the protection of a mixed gas of SF6 and CO2, the magnesium alloy chemical composition is added according to the designed composition. First, pure magnesium, pure zinc, magnesium-calcium master alloy and magnesium-manganese master alloy are added in sequence and heated to melt at 725°C. Then, magnesium-gadolinium master alloy and magnesium-cerium master alloy are added and stirred uniformly at 700°C. After refining and degassing, the slag is removed to obtain an alloy melt.

[0081] (2) rapidly casting and rolling the alloy melt obtained in step (1) at a casting and rolling speed of 9 m / min and a thickness of 3.6 mm of the cast-rolled billet to obtain a cast-rolled billet;

[0082] (3) subjecting the cast-rolled billet obtained in step (2) to a stepwise homogenization heat treatment, i.e., subjecting the cast-rolled billet to a heat treatment of 355° C. for 2 hours, 455° C. for 1 hour, and 525° C. for 2 hours, followed by air cooling to room temperature to obtain a homogenized billet;

[0083] (4) subjecting the homogeneous billet obtained in step (3) to multi-pass rolling, wherein the rolling passes are 7, the temperature is 215-260° C., and the reduction amount of each pass is 13-25%, to obtain a rolled billet;

[0084] (5) subjecting the rolled billet obtained in step (4) to a high-temperature short-time solid solution heat treatment in an argon-protected tubular furnace at a treatment temperature of 490° C. for a holding time of 35 min, and immediately water cooling after the holding period to obtain a solid solution billet;

[0085] (6) The solid solution billet obtained in step (5) is subjected to artificial aging heat treatment at an aging temperature of 185° C. for 150 min, and a low-cost, high-strength, corrosion-resistant Mg-1.25Zn-0.4Ca-0.15Mn-0.3Gd-0.2Ce magnesium alloy is obtained after aging treatment.

[0086] After artificial aging treatment, the strength and corrosion resistance of the magnesium alloy in this embodiment are synergistically improved. The yield strength is 200 MPa, which is 70 MPa higher than that before aging. The corrosion rate is 0.13 mm / year, and the corrosion resistance is 2.1 times higher than that before aging.

[0087] Comparative Example 4:

[0088] The difference from Example 5 is that the magnesium alloy composition of this example is (wt.%): Zn 1.25%, Ca 0.4%, Mn 0.15%, and the balance is magnesium (Mg-1.25Zn-0.4Ca-0.15Mn magnesium alloy).

[0089] Under the same dimensions and processing conditions as Example 5, the yield strength of the Mg-1.25Zn-0.4Ca-0.15Mn magnesium alloy after aging is 190 MPa, which is 35 MPa higher than that before aging. The corrosion rate is 1.2 mm / year, and the corrosion resistance is reduced by 50% compared with that before aging.

[0090] Example 6:

[0091] The magnesium alloy prepared in this embodiment has the following chemical composition (wt.%): Zn 2.0%, Ca 0.6%, Mn 0.05%; Sm 0.3%, Nd 0.4%, and the balance is magnesium (Mg-2Zn-0.6Ca-0.05Mn-0.3Sm-0.4Nd magnesium alloy). The preparation process is as follows:

[0092] (1) Under the protection of a mixed gas of SF6 and CO2, the magnesium alloy chemical composition is added according to the designed composition. First, pure magnesium, pure zinc, magnesium-calcium master alloy and magnesium-manganese master alloy are added in sequence and heated to melt at 725°C. Then, magnesium-samarium master alloy and magnesium-neodymium master alloy are added and stirred evenly at 710°C. After refining and degassing, the slag is removed to obtain an alloy melt.

[0093] (2) rapidly casting and rolling the alloy melt obtained in step (1) at a casting and rolling speed of 10 m / min and a thickness of the cast-rolled billet of 4.3 mm to obtain a cast-rolled billet;

[0094] (3) subjecting the cast-rolled billet obtained in step (2) to a stepwise homogenization heat treatment, i.e., subjecting the cast-rolled billet to heat treatments at 360° C. for 1.5 hours, 455° C. for 1.5 hours, and 530° C. for 1 hour in sequence; and then air-cooling to room temperature to obtain a homogenized billet;

[0095] (4) performing multi-pass rolling on the homogeneous billet obtained in step (3), wherein the rolling passes are 11, the temperature is 215-260° C., and the reduction amount of each pass is 13-25%, to obtain a rolled billet;

[0096] (5) subjecting the rolled billet obtained in step (4) to a high-temperature short-time solid solution heat treatment in an argon-protected tubular furnace at a treatment temperature of 500° C. for a holding time of 30 min, and immediately water cooling after the holding is completed to obtain a solid solution billet;

[0097] (6) The solid solution billet obtained in step (5) is subjected to artificial aging heat treatment at an aging temperature of 200° C. for 140 min, and a low-cost, high-strength, corrosion-resistant Mg-2Zn-0.6Ca-0.05Mn-0.3Sm-0.4Nd magnesium alloy is obtained after aging treatment.

[0098] The average corrosion rate of the magnesium alloy prepared in this embodiment after being immersed in a sodium chloride solution for 14 days is about 0.14 mm / year, while the average corrosion rate of pure magnesium under the same external dimensions is about 1.0 mm / year.

[0099] Example 7:

[0100] The magnesium alloy prepared in this embodiment has the following chemical composition (wt.%): Zn 1.7%, Ca 0.7%, Mn 0.45%; Sm 0.7%, Gd 0.2%, and the balance is magnesium (Mg-1.7Zn-0.7Ca-0.45Mn-0.7Sm-0.2Gd magnesium alloy). The preparation process is as follows:

[0101] (1) Under the protection of a mixed gas of SF6 and CO2, the magnesium alloy is charged according to the designed chemical composition. First, pure magnesium, pure zinc, magnesium-calcium master alloy and magnesium-manganese master alloy are added in sequence and melted at 700°C. Then, magnesium-samarium master alloy and magnesium-gadolinium master alloy are added and stirred uniformly at 690°C. After refining and degassing, the slag is removed to obtain an alloy melt.

[0102] (2) rapidly casting and rolling the alloy melt obtained in step (1) at a casting and rolling speed of 11 m / min and a thickness of 3.8 mm of the cast-rolled billet to obtain a cast-rolled billet;

[0103] (3) subjecting the cast-rolled billet obtained in step (2) to a stepwise homogenization heat treatment, i.e., subjecting the cast-rolled billet to a heat treatment of 345° C. for 2 hours, 455° C. for 1 hour, and 525° C. for 2 hours, followed by air cooling to room temperature to obtain a homogenized billet;

[0104] (4) subjecting the homogeneous billet obtained in step (3) to multi-pass rolling, wherein the rolling passes are 7, the temperature is 175-245° C., and the reduction amount of each pass is 10-30%, to obtain a rolled billet;

[0105] (5) subjecting the rolled billet obtained in step (4) to a high-temperature short-time solid solution heat treatment in an argon-protected tubular furnace at a treatment temperature of 500° C. for a holding time of 45 min, and immediately water cooling after the holding is completed to obtain a solid solution billet;

[0106] (6) The solid solution billet obtained in step (5) is subjected to artificial aging heat treatment at an aging temperature of 190° C. for 180 min, and a low-cost, high-strength, corrosion-resistant Mg-1.7Zn-0.7Ca-0.45Mn-0.7Sm-0.2Gd magnesium alloy is obtained after aging treatment.

[0107] Example 8

[0108] The magnesium alloy prepared in this embodiment has the following chemical composition (wt.%): Zn 0.8%, Ca 0.3%, Mn 0.12%; Nd 0.4%, Ce 0.2%, and the balance is magnesium (Mg-0.8Zn-0.3Ca-0.12Mn-0.4Nd-0.2Ce magnesium alloy). The preparation process is as follows:

[0109] (1) Under the protection of a mixed gas of SF6 and CO2, the magnesium alloy chemical composition is added according to the designed composition. First, pure magnesium, pure zinc, magnesium-calcium master alloy and magnesium-manganese master alloy are added in sequence and melted at 730°C. Then, magnesium-neodymium master alloy and magnesium-cerium master alloy are added and stirred evenly at 715°C. After refining and degassing, the slag is removed to obtain an alloy melt.

[0110] (2) rapidly casting and rolling the alloy melt obtained in step (1) at a casting and rolling speed of 6 m / min and a thickness of the cast-rolled billet of 5.3 mm to obtain a cast-rolled billet;

[0111] (3) subjecting the cast-rolled billet obtained in step (2) to a stepwise homogenization heat treatment, i.e., subjecting the cast-rolled billet to a heat treatment of 355° C. for 3 hours, 445° C. for 1 hour, and 525° C. for 2 hours, followed by air cooling to room temperature to obtain a homogenized billet;

[0112] (4) performing multi-pass rolling on the homogeneous billet obtained in step (3), wherein the rolling passes are 12 times, the temperature is 250-300° C., and the reduction amount of each pass is 15-25%, to obtain a rolled billet;

[0113] (5) subjecting the rolled billet obtained in step (4) to a high-temperature short-time solid solution heat treatment in an argon-protected tubular furnace at a treatment temperature of 485° C. for a holding time of 60 min, and immediately water cooling after the holding is completed to obtain a solid solution billet;

[0114] (6) The solid solution billet obtained in step (5) is subjected to artificial aging heat treatment at an aging temperature of 215° C. for 60 min, and a low-cost, high-strength, corrosion-resistant Mg-0.8Zn-0.3Ca-0.12Mn-0.4Nd-0.2Ce magnesium alloy is obtained after aging treatment.

[0115] The average corrosion rate of the magnesium alloy obtained in step (6) of this embodiment after being immersed in a sodium chloride solution for 14 days is about 0.08 mm / year, and the corrosion resistance is improved by 2.3 times compared with that before aging.

[0116] Comparative Example 5:

[0117] The difference from Example 8 is that the magnesium alloy composition in this example is (wt.%): Zn 6%, Ca 0.3%, Mn 0.15%, Nd 0.4%, Ce 0.2%, and the balance is magnesium (Mg-6Zn-0.3Ca-0.12Mn-0.4Nd-0.2Ce magnesium alloy).

[0118] Under the same external dimensions and processing conditions as Example 8, the corrosion rate of the Mg-6Zn-0.3Ca-0.12Mn-0.4Nd-0.2Ce magnesium alloy after aging is about 5 mm / year, and the corrosion resistance is reduced by 60% compared with before aging. The main reason is that the mass ratio of Zn and Ca in the alloy exceeds 4:1, so it is difficult to form an atomic scale microstructure during the aging process. Instead, a high cathode active Mg-Zn phase is formed, which accelerates the dissolution of the surrounding magnesium matrix, resulting in poor corrosion resistance after aging.

[0119] In summary, after artificial aging, the magnesium alloys obtained in Examples 1-8 exhibited a high-density, uniformly dispersed atomic-scale microstructure within the alloys, coherent with the magnesium matrix. This microstructure, containing Zn, Ca, and rare earth elements, was less than 20 nm in length and 1 to 5 atomic layers thick. This microstructure enables the magnesium alloys of the present invention to simultaneously possess high strength (yield strength of ~170-250 MPa) and high corrosion resistance (corrosion rate ≤0.2 mm / year), surpassing commercially pure magnesium or commercial AZ-based magnesium alloys.

[0120] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A low-cost, high-strength, corrosion-resistant magnesium alloy, characterized by: The chemical composition of the magnesium alloy is as follows by weight percentage: Zinc: 0.5-3%, calcium: 0.1-1%, manganese: 0-0.6%, RE: 0.2-2.0%; the balance is magnesium and inevitable impurities; wherein RE is a rare earth element, RE is one or more of neodymium, gadolinium, cerium and samarium.

2. The low-cost, high-strength, corrosion-resistant magnesium alloy according to claim 1, characterized in that: The chemical composition of the magnesium alloy is as follows by weight percentage: Zinc: 0.6-2.5%, Calcium: 0.3-0.8%, Manganese: 0.1-0.5%, RE: 0.3-1.5%; the balance is magnesium and inevitable impurities.

3. The low-cost, high-strength, corrosion-resistant magnesium alloy according to claim 1, characterized in that: The amount of each rare earth element added to the magnesium alloy is 0.2-1 wt. % (preferably 0.3-0.8 wt. %).

4. The low-cost, high-strength, corrosion-resistant magnesium alloy according to claim 1, characterized in that: The magnesium alloy has an atomic-scale microstructure with high density and uniform dispersion distribution and a coherent relationship with the magnesium matrix. The microstructure contains Zn, Ca and rare earth elements, has a length of less than 20nm and a thickness of 1 to 5 atomic layers.

5. The low-cost, high-strength, corrosion-resistant magnesium alloy according to claim 1, characterized in that: The magnesium alloy has a yield strength of 170-250 MPa and a corrosion rate of ≤0.2 mm / year.

6. The method for preparing a low-cost, high-strength, corrosion-resistant magnesium alloy according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: (1) Under the protection of a mixed gas of SF6 and CO2, various elemental raw materials are added according to the designed magnesium alloy chemical composition, heated to 660-760°C for melting and stirred evenly, and then refined, degassed and slag removed to obtain a magnesium alloy melt; (2) rapidly casting and rolling the magnesium alloy melt obtained in step (1) to obtain a cast-rolled billet; (3) placing the cast-rolled billet obtained in step (2) into a resistance furnace filled with argon or nitrogen for step homogenization heat treatment, and air cooling to room temperature to obtain a homogenized billet; the step homogenization heat treatment is to sequentially heat the cast-rolled billet at 320-370°C for 0.5-3 hours, 430-470°C for 0.5-3 hours, and 515-545°C for 0.5-3 hours; (4) performing multiple rolling on the homogeneous billet obtained in step (3), wherein the rolling passes are 2 to 15, to obtain a rolled billet; (5) subjecting the rolled billet obtained in step (4) to a high-temperature short-time solution heat treatment under argon protection, and then immediately air-cooling or water-cooling to obtain a solution billet; (6) subjecting the solid solution billet obtained in step (5) to artificial aging heat treatment, wherein the artificial aging treatment temperature is 160-220° C. and the treatment time is 20-480 min; after the aging treatment, a low-cost, high-strength, corrosion-resistant magnesium alloy is obtained.

7. The method for preparing a low-cost, high-strength, corrosion-resistant magnesium alloy according to claim 6, characterized in that: During the feeding process of step (1), raw materials of magnesium, zinc, calcium and manganese are first added in sequence, heated and melted at 660-760°C, and then raw materials of rare earth elements are added, stirred evenly at 660-730°C, and refined, degassed and slag removed; wherein: magnesium and zinc components are added as pure magnesium and pure zinc as raw materials; calcium and manganese are added in the form of magnesium-calcium master alloy and magnesium-manganese master alloy respectively; rare earth elements neodymium, gadolinium, cerium and samarium are added in the form of magnesium-neodymium master alloy, magnesium-gadolinium master alloy, magnesium-cerium master alloy and magnesium-samarium master alloy respectively.

8. The method for preparing a low-cost, high-strength, corrosion-resistant magnesium alloy according to claim 6, characterized in that: In step (2), the rapid casting speed is 4-15 m / min, and the thickness of the cast billet is 2.5-7 mm; in step (4), the multi-pass rolling temperature is 150-400°C, and the reduction in each pass is 5-30%.

9. The method for preparing a low-cost, high-strength, corrosion-resistant magnesium alloy according to claim 6, characterized in that: In step (5), the high temperature short time solution heat treatment temperature is 450-520°C and the time is 30-90min.

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