High-corrosion-resistance low-rare-earth magnesium alloy and preparation method thereof

Abstract

The application discloses a high-corrosion-resistance low-rare-earth magnesium alloy and a preparation method thereof, and belongs to the field of magnesium alloys. The application aims at solving the problem that a large number of strong cathode second phases are introduced into the magnesium alloy after alloying elements are added, the areas with large potential difference on the surface of the magnesium alloy are preferentially corroded, and a smooth and dense corrosion product film with excellent protection cannot be formed on the surface of the alloy due to serious local corrosion. The high-corrosion-resistance low-rare-earth magnesium alloy is composed of Mg, Sm and Mn; the method comprises the following steps: I, weighing and melting; II, refining; III, casting forming; IV, homogenizing treatment; and V, hot extrusion. The application is used for the high-corrosion-resistance low-rare-earth magnesium alloy and the preparation thereof.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloys. Background Technology

[0002] Magnesium alloys possess excellent properties such as low density, high specific strength, and good biocompatibility. Currently, high-performance magnesium alloy engineering materials are widely used in both military and civilian applications. In recent years, magnesium alloys have developed rapidly as lightweight structural materials, with a large number of commercial magnesium alloys (such as AZ31, AZ61, AM80, and WE54) already in use. However, in practical applications, the main problem exposed by most magnesium alloys is that their corrosion resistance is far lower than that of other metallic structural materials. Improving the corrosion resistance of magnesium alloys is a challenging issue that urgently needs to be addressed to promote their engineering applications.

[0003] For many years, magnesium alloys have suffered from poor corrosion resistance. This poor corrosion resistance is closely related to the chemical properties of magnesium. First, magnesium has a very low standard electrode potential (2.37V compared to the standard hydrogen electrode (SHE)) and is extremely chemically reactive compared to other common metallic structural materials. Therefore, although most of the second phases in magnesium alloys have a good strengthening effect, their potentials are higher than those of the magnesium matrix, and the potential difference between them is large. During the corrosion process of magnesium alloys, the Mg matrix usually acts as the anolyte phase, while the second phase (or impurities) acts as a strong cathodic phase for microgalvanic corrosion, leading to severe localized corrosion. Second, the MgO produced during the corrosion process of magnesium alloys is soluble in water and cannot provide long-term protection. Third, a "negative differential effect" exists during the corrosion process of magnesium alloys, which accelerates the cathodic hydrogen evolution reaction, causing severe peeling and failure of the Mg(OH)2 protective film.

[0004] The addition of rare earth elements can promote the formation of a denser corrosion product film on the surface of magnesium alloys, thereby effectively improving the corrosion resistance of magnesium alloys. The PBR value is usually used to indicate the integrity and density of the oxide film. If PBR < 1, the oxide coating is insufficient to protect the metal; if PBR ≥ 2, the internal stress is too high, and the oxide film is prone to cracking and peeling; if PBR is 1 to 2, a completely dense protective film can be formed. The PBR value of the surface oxide film formed after magnesium oxidation is 0.81 (< 1), while the addition of rare earth elements will produce rare earth oxides in the surface film, improving the density and protection of the film layer (making its PBR between 1 and 2). However, the addition of rare earth elements will introduce a large number of second phases. Different second phases have different potential differences with the magnesium matrix. Due to the presence of micro-galvanic corrosion, the areas with large potential differences on the magnesium alloy surface will be preferentially corroded, resulting in severe local corrosion, corrosion pits, and difficulty in forming a smooth and dense corrosion product film on the alloy surface. Summary of the Invention

[0005] The problem this invention aims to solve is that the addition of alloying elements to magnesium alloys typically introduces a large amount of strongly cathodic second phase, leading to preferential corrosion in areas with large potential differences on the magnesium alloy surface, resulting in severe localized corrosion and making it difficult to form a smooth, dense, and highly protective corrosion product film on the alloy surface. This invention addresses this problem by improving the corrosion resistance of magnesium alloys, providing a high-corrosion-resistant, low-rare-earth magnesium alloy and its preparation method.

[0006] A high corrosion-resistant, low rare-earth magnesium alloy, which is composed of 4%–6% Sm, 0.8%–1.0% Mn and the balance Mg by mass percentage.

[0007] A method for preparing a high corrosion-resistant, low-rare-earth magnesium alloy comprises the following steps:

[0008] I. Weighing and Melting:

[0009] Weigh out pure Mg ingots, Mg-24Sm master alloy and Mg-10Mn master alloy with a mass percentage of 4% to 6% Sm, 0.8% to 1.0% Mn and balance Mg to obtain raw materials. Melt the raw materials to obtain the molten alloy.

[0010] II. Refining:

[0011] Under conditions of 680℃~750℃, the molten alloy is stirred evenly, and then the temperature inside the furnace is raised to 750℃~780℃ and argon gas is introduced. Under the conditions of argon atmosphere and temperature of 750℃~780℃, the alloy liquid is refined for 5min~10min to obtain the alloy liquid.

[0012] III. Casting and Molding:

[0013] The alloy liquid is cooled to 690℃~710℃ and cast into a molded magnesium alloy. The surface layer of the molded magnesium alloy is removed by turning, and finally cut to obtain a magnesium alloy casting rod.

[0014] IV. Homogenization treatment:

[0015] The magnesium alloy casting rod was heated to 520℃~530℃ at a heating rate of 8℃ / min~10℃ / min, and homogenized at 520℃~530℃ for 6h~8h, and finally air-cooled to obtain the homogenized magnesium alloy casting rod.

[0016] V. Hot Extrusion:

[0017] The extrusion die and the homogenized magnesium alloy casting are preheated and then hot-extruded to obtain a high corrosion-resistant, low rare earth magnesium alloy.

[0018] The beneficial effects of this invention are:

[0019] 1. This invention prepares highly corrosion-resistant magnesium alloys by combining rare earth element (Sm) and another alloying element, Mn. The reasons for the preferred use of these two elements and their content are as follows:

[0020] ①Sm: The present invention selects 4% to 6% Sm by mass because within this range, Sm only forms Mg with the matrix. 41 The Sm5 phase does not produce other second phases. In magnesium alloys, most second phases have a high potential difference with the matrix, such as the common strengthening phase Mg. 17 Al 12 (80mV~200mV), MgZn2 (500mV~600mV), Al8Mn5 (350mV~450mV), etc. are all strong cathodic phases, which will cause severe micro-galvanic corrosion tendency, while Mg 41 The potential difference between the Sm5 phase and the magnesium matrix is ​​very low (30mV~40mV), classifying it as a weakly cathodic phase, which significantly reduces the tendency for localized micro-galvanic corrosion. Furthermore, the addition of Sm introduces Sm2O3 into the corrosion product film, resulting in a PBR value of 1~2 for the magnesium alloy corrosion film, thus improving film stability. Therefore, the addition of Sm enables the magnesium alloy to form a uniform and highly stable dense corrosion product film while simultaneously undergoing uniform corrosion.

[0021] ②Mn: In the alloy, Mn does not form a second phase with the magnesium matrix or Sm elements, therefore it does not affect the weak cathode Mg. 41 The formation of Sm5, and when the mass fraction of Mn element added is 0.8% to 1.0%, can not only greatly improve the passivation effect of the alloy during the corrosion process, but also adsorb impurity elements introduced during the smelting process of magnesium alloy, reducing the possibility of impurity elements damaging the corrosion product film during the corrosion process.

[0022] Furthermore, if other alloying elements are added, such as to form a quaternary alloy, the formation of other strong cathode phases will also affect the weak cathode second phase Mg in the alloy. 41 The formation of Sm5. Therefore, the selection of the combination of Sm and Mn and their appropriate content are crucial for simultaneously solving two key problems in magnesium alloy corrosion (i.e., the large potential difference of the strengthening phase and the poor protective properties of the product film).

[0023] 2. The total mass percentage of alloying elements in this invention does not exceed 7%, the types of alloying elements are few, and the second phase in the alloy is Mg. 41 The Sm5 phase and α-Mn phase make the control of the second phase simpler and more convenient for subsequent industrial production.

[0024] 3. Compared with other corrosion-resistant magnesium alloys, the content of alloying elements added in this invention is lower, resulting in lower cost and higher economic value. Furthermore, the extrusion process of this invention is simpler and easier to implement in industrial production. Attached Figure Description

[0025] Figure 1 The microstructure of the high corrosion-resistant, low rare earth magnesium alloy prepared in Example 3;

[0026] Figure 2 The X-ray diffraction pattern of the high corrosion resistance low rare earth magnesium alloy prepared in Example 3;

[0027] Figure 3 The surface film morphology of the high corrosion-resistant low rare earth magnesium alloy prepared in Example 3 after immersion in a 3.5% NaCl solution for 168 hours;

[0028] Figure 4 The morphology of the surface film removed after the high corrosion resistance low rare earth magnesium alloy prepared in Example 3 was immersed in a 3.5% NaCl solution for 168 hours. Detailed Implementation

[0029] Specific implementation method one: This implementation method is a high corrosion resistant low rare earth magnesium alloy, which is composed of 4% to 6% Sm, 0.8% to 1.0% Mn and the balance Mg by mass percentage.

[0030] In this specific embodiment, by adding a small amount of Sm element to the magnesium alloy, a stable and dense corrosion product film (Sm2O3, MgO, Mg(OH)2) will be formed during the corrosion process, thereby improving the corrosion resistance of the magnesium alloy.

[0031] In this specific embodiment, the deformation process is hot extrusion. High temperature, low speed, and a large extrusion ratio are selected to allow for complete dynamic recrystallization of the alloy while reducing dynamic precipitation. Furthermore, extrusion deformation allows the second phase in the alloy to be more finely and dispersedly distributed within the magnesium matrix, avoiding the presence of large second phases that could lead to severe localized corrosion.

[0032] The beneficial effects of this embodiment are:

[0033] 1. This embodiment prepares a high corrosion-resistant magnesium alloy by combining the addition of rare earth element (Sm) and another alloying element, Mn. The reasons for the preferred choice of these two elements and their content are as follows:

[0034] ①Sm: In this embodiment, a mass fraction of 4% to 6% Sm is chosen because within this range, Sm only forms Mg with the matrix. 41 The Sm5 phase does not produce other second phases. In magnesium alloys, most second phases have a high potential difference with the matrix, such as the common strengthening phase Mg. 17 Al 12(80mV~200mV), MgZn2 (500mV~600mV), Al8Mn5 (350mV~450mV), etc. are all strong cathodic phases, which will cause severe micro-galvanic corrosion tendency, while Mg 41 The potential difference between the Sm5 phase and the magnesium matrix is ​​very low (30mV~40mV), classifying it as a weakly cathodic phase, which significantly reduces the tendency for localized micro-galvanic corrosion. Furthermore, the addition of Sm introduces Sm2O3 into the corrosion product film, resulting in a PBR value of 1~2 for the magnesium alloy corrosion film, thus improving film stability. Therefore, the addition of Sm enables the magnesium alloy to form a uniform and highly stable dense corrosion product film while simultaneously undergoing uniform corrosion.

[0035] ②Mn: In the alloy, Mn does not form a second phase with the magnesium matrix or Sm elements, therefore it does not affect the weak cathode Mg. 41 The formation of Sm5, and when the mass fraction of Mn element added is 0.8% to 1.0%, can not only greatly improve the passivation effect of the alloy during the corrosion process, but also adsorb impurity elements introduced during the smelting process of magnesium alloy, reducing the possibility of impurity elements damaging the corrosion product film during the corrosion process.

[0036] Furthermore, if other alloying elements are added, such as to form a quaternary alloy, the formation of other strong cathode phases will also affect the weak cathode second phase Mg in the alloy. 41 The formation of Sm5. Therefore, the selection of the combination of Sm and Mn and their appropriate content are crucial for simultaneously solving two key problems in magnesium alloy corrosion (i.e., the large potential difference of the strengthening phase and the poor protective properties of the product film).

[0037] 2. In this embodiment, the total mass percentage of alloying elements does not exceed 7%, the types of alloying elements are few, and the second phase in the alloy is Mg. 41 The Sm5 phase and α-Mn phase make the control of the second phase simpler and more convenient for subsequent industrial production.

[0038] 3. Compared with other corrosion-resistant magnesium alloys, the content of alloying elements added in this embodiment is lower, resulting in lower cost and higher economic value. Furthermore, the extrusion process of this embodiment is simpler and easier to implement in industrial production.

[0039] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the total mass percentage of impurities in the high corrosion-resistant low rare earth magnesium alloy is ≤0.02%, wherein the mass percentage of impurity Fe is ≤0.005%, the mass percentage of impurity Cu is ≤0.001%, the mass percentage of impurity Ni is ≤0.001%, the mass percentage of impurity Co is ≤0.001%, and the total mass percentage of other impurity elements is ≤0.01%. Everything else is the same as in Specific Implementation Method One.

[0040] Specific Implementation Method 3: This implementation method provides a method for preparing a high corrosion-resistant, low rare-earth magnesium alloy, which is carried out according to the following steps:

[0041] I. Weighing and Melting:

[0042] Weigh out pure Mg ingots, Mg-24Sm master alloy and Mg-10Mn master alloy with a mass percentage of 4% to 6% Sm, 0.8% to 1.0% Mn and balance Mg to obtain raw materials. Melt the raw materials to obtain the molten alloy.

[0043] II. Refining:

[0044] Under conditions of 680℃~750℃, the molten alloy is stirred evenly, and then the temperature inside the furnace is raised to 750℃~780℃ and argon gas is introduced. Under the conditions of argon atmosphere and temperature of 750℃~780℃, the alloy liquid is refined for 5min~10min to obtain the alloy liquid.

[0045] III. Casting and Molding:

[0046] The alloy liquid is cooled to 690℃~710℃ and cast into a molded magnesium alloy. The surface layer of the molded magnesium alloy is removed by turning, and finally cut to obtain a magnesium alloy casting rod.

[0047] IV. Homogenization treatment:

[0048] The magnesium alloy casting rod was heated to 520℃~530℃ at a heating rate of 8℃ / min~10℃ / min, and homogenized at 520℃~530℃ for 6h~8h, and finally air-cooled to obtain the homogenized magnesium alloy casting rod.

[0049] V. Hot Extrusion:

[0050] The extrusion die and the homogenized magnesium alloy casting are preheated and then hot-extruded to obtain a high corrosion-resistant, low rare earth magnesium alloy.

[0051] The purity of the pure Mg ingot mentioned in step one is 99.99%.

[0052] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method Three in that: the mass percentage of Sm in the Mg-24Sm master alloy described in step one is 24%; and the mass percentage of Mn in the Mg-10Mn master alloy described in step one is 10%. Everything else is the same as in Specific Implementation Method Three.

[0053] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods Three or Four in that: the raw material melting described in step one is specifically carried out under a protective atmosphere, by placing pure Mg ingots in a resistance furnace at a furnace temperature of 495℃~505℃, then raising the temperature to 740℃~760℃, and holding at 740℃~760℃ until the pure Mg ingots melt. Then, the temperature is lowered to 710℃~730℃, and Mg-24Sm master alloy and Mg-10Mn master alloy are added. The temperature is then held at 710℃~730℃ until all Mg-24Sm master alloy and Mg-10Mn master alloy have melted, yielding the molten alloy. Everything else is the same as in Specific Implementation Methods Three or Four.

[0054] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods Three to Five in that the protective atmosphere is a mixture of CO2 and SF6, and the volume percentage of SF6 in the protective atmosphere is 0.8% to 1.5%. Everything else is the same as in Specific Implementation Methods Three to Five.

[0055] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods Three to Six in that it cools to 710℃ to 730℃ at a cooling rate of 1℃ / min to 3℃ / min. Everything else is the same as in Specific Implementation Methods Three to Six.

[0056] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods Three to Seven in that: in step three, the alloy liquid is cooled to 690℃ to 710℃ at a cooling rate of 1℃ / min to 3℃ / min. Everything else is the same as in Specific Implementation Methods Three to Seven.

[0057] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods Three to Eight in that the preheating described in step five is specifically preheated at a temperature of 380℃ to 410℃ for 0.5h to 1.5h. Everything else is the same as in Specific Implementation Methods Three to Eight.

[0058] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods Three to Nine in that the hot extrusion described in step five is carried out under the conditions of an extrusion temperature of 380℃~410℃, an extrusion ratio of (25~30):1, and an extrusion speed of 0.1mm / s~0.3mm / s. Everything else is the same as in Specific Implementation Methods Three to Nine.

[0059] The beneficial effects of the present invention are verified using the following embodiments:

[0060] Example 1:

[0061] A high corrosion-resistant, low rare-earth magnesium alloy, which is composed of 4.3% Sm, 0.9% Mn and the balance Mg by mass percentage.

[0062] The total mass percentage of impurities in high corrosion-resistant low rare earth magnesium alloys is ≤0.02%, of which the mass percentage of Fe impurity is 0.005%, the mass percentage of Cu impurity is ≤0.001%, the mass percentage of Ni impurity is ≤0.001%, the mass percentage of Co impurity is ≤0.001%, and the total mass percentage of other impurity elements is ≤0.01%.

[0063] The above-mentioned method for preparing a high corrosion-resistant, low rare-earth magnesium alloy comprises the following steps:

[0064] I. Weighing and Melting:

[0065] Weigh out pure Mg ingots, Mg-24Sm master alloy and Mg-10Mn master alloy with a mass percentage of 4.3% Sm, 0.9% Mn and balance Mg to obtain raw materials. Melt the raw materials to obtain the molten alloy.

[0066] II. Refining:

[0067] The molten alloy was stirred uniformly at a temperature of 730℃. Then, the temperature inside the furnace was raised to 750℃ and argon gas was introduced. Under the conditions of argon atmosphere and temperature of 750℃, the alloy liquid was refined for 10 minutes to obtain the alloy liquid.

[0068] III. Casting and Molding:

[0069] The alloy liquid was cooled to 690°C at a cooling rate of 3°C / min and cast into a shaped magnesium alloy. The surface layer of the shaped magnesium alloy was removed by turning and finally cut to obtain a magnesium alloy casting rod.

[0070] IV. Homogenization treatment:

[0071] The magnesium alloy casting rod was heated to 525℃ at a heating rate of 8℃ / min, and homogenized at 525℃ for 7 hours. Finally, it was air-cooled to obtain the homogenized magnesium alloy casting rod.

[0072] V. Hot Extrusion:

[0073] Under conditions of 400℃, the extrusion die and the homogenized magnesium alloy casting were preheated for 0.5h, and then hot extruded at an extrusion temperature of 400℃, an extrusion ratio of 25:1 and an extrusion speed of 0.1mm / s to obtain a high corrosion-resistant low rare earth magnesium alloy.

[0074] The mass percentage of Sm in the Mg-24Sm master alloy described in step one is 24%; the mass percentage of Mn in the Mg-10Mn master alloy described in step one is 10%.

[0075] The raw material melting described in step one specifically involves placing pure Mg ingots in a resistance furnace at a furnace temperature of 500°C under a protective atmosphere, then raising the temperature to 750°C and holding it at 750°C until the pure Mg ingots melt. Then, the temperature is lowered to 730°C at a cooling rate of 3°C / min, and Mg-24Sm master alloy and Mg-10Mn master alloy are added. The temperature is then held at 730°C until all Mg-24Sm and Mg-10Mn master alloys have melted, resulting in the molten alloy. The protective atmosphere is a mixture of CO2 and SF6, with a volume ratio of CO2 to SF6 of 99:1.

[0076] Under quasi-static tensile conditions at room temperature, the tensile rate is 1×10⁻⁶. -3 s -1 The high corrosion-resistant low rare earth magnesium alloy prepared in Example 1 has a tensile strength of 201 MPa, a yield strength of 138 MPa, and an elongation of 15%.

[0077] Example 2:

[0078] A high corrosion-resistant, low rare-earth magnesium alloy, which is composed of 4.8% Sm, 0.8% Mn and the balance Mg by mass percentage.

[0079] The total mass percentage of impurities in high corrosion-resistant low rare earth magnesium alloys is ≤0.02%, of which the mass percentage of Fe impurity is 0.004%, the mass percentage of Cu impurity is ≤0.001%, the mass percentage of Ni impurity is ≤0.001%, the mass percentage of Co impurity is ≤0.001%, and the total mass percentage of other impurity elements is ≤0.01%.

[0080] The above-mentioned method for preparing a high corrosion-resistant, low rare-earth magnesium alloy comprises the following steps:

[0081] I. Weighing and Melting:

[0082] Weigh out pure Mg ingots, Mg-24Sm master alloy and Mg-10Mn master alloy with a mass percentage of 4.8% Sm, 0.8% Mn and balance Mg to obtain raw materials. Melt the raw materials to obtain the molten alloy.

[0083] II. Refining:

[0084] The molten alloy was stirred uniformly at a temperature of 730℃. Then, the temperature inside the furnace was raised to 760℃ and argon gas was introduced. Under the conditions of argon atmosphere and temperature of 760℃, the alloy liquid was refined for 6 minutes to obtain the alloy liquid.

[0085] III. Casting and Molding:

[0086] The alloy liquid was cooled to 700°C at a cooling rate of 3°C / min and cast into a shaped magnesium alloy. The surface layer of the shaped magnesium alloy was removed by turning and finally cut to obtain a magnesium alloy casting rod.

[0087] IV. Homogenization treatment:

[0088] The magnesium alloy casting rod was heated to 525℃ at a heating rate of 10℃ / min, and homogenized at 525℃ for 7 hours. Finally, it was air-cooled to obtain the homogenized magnesium alloy casting rod.

[0089] V. Hot Extrusion:

[0090] Under the condition of 380℃, the extrusion die and the homogenized magnesium alloy casting were preheated for 0.75h, and then hot extruded under the conditions of extrusion temperature of 380℃, extrusion ratio of 25:1 and extrusion speed of 0.1mm / s to obtain a high corrosion resistant low rare earth magnesium alloy.

[0091] The mass percentage of Sm in the Mg-24Sm master alloy described in step one is 24%; the mass percentage of Mn in the Mg-10Mn master alloy described in step one is 10%.

[0092] The raw material melting described in step one specifically involves placing pure Mg ingots in a resistance furnace at a furnace temperature of 500°C under a protective atmosphere, then raising the temperature to 750°C and holding it at 750°C until the pure Mg ingots melt. Then, the temperature is lowered to 720°C at a cooling rate of 3°C / min, and Mg-24Sm master alloy and Mg-10Mn master alloy are added. The temperature is then held at 720°C until all Mg-24Sm and Mg-10Mn master alloys have melted, resulting in the molten alloy. The protective atmosphere is a mixture of CO2 and SF6, with a volume ratio of CO2 to SF6 of 99:1.

[0093] Under quasi-static tensile conditions at room temperature, the tensile rate is 1×10⁻⁶. -3 s -1 The high corrosion-resistant low rare earth magnesium alloy prepared in Example 2 has a tensile strength of 204 MPa, a yield strength of 142 MPa, and an elongation of 16%.

[0094] Example 3:

[0095] A high corrosion-resistant, low rare-earth magnesium alloy, which is composed of 5.1% Sm, 0.8% Mn and the balance Mg by mass percentage.

[0096] The total mass percentage of impurities in high corrosion-resistant low rare earth magnesium alloys is ≤0.02%, of which the mass percentage of Fe impurity is 0.004%, the mass percentage of Cu impurity is ≤0.001%, the mass percentage of Ni impurity is ≤0.001%, the mass percentage of Co impurity is ≤0.001%, and the total mass percentage of other impurity elements is ≤0.01%.

[0097] The above-mentioned method for preparing a high corrosion-resistant, low rare-earth magnesium alloy comprises the following steps:

[0098] I. Weighing and Melting:

[0099] Weigh out pure Mg ingots, Mg-24Sm master alloy and Mg-10Mn master alloy with a mass percentage of 5.1% Sm, 0.8% Mn and balance Mg to obtain raw materials. Melt the raw materials to obtain the molten alloy.

[0100] II. Refining:

[0101] The molten alloy was stirred uniformly at a temperature of 730℃. Then, the temperature inside the furnace was raised to 760℃ and argon gas was introduced. Under the conditions of argon atmosphere and temperature of 760℃, the alloy liquid was refined for 6 minutes to obtain the alloy liquid.

[0102] III. Casting and Molding:

[0103] The alloy liquid was cooled to 700°C at a cooling rate of 3°C / min and cast into a shaped magnesium alloy. The surface layer of the shaped magnesium alloy was removed by turning and finally cut to obtain a magnesium alloy casting rod.

[0104] IV. Homogenization treatment:

[0105] The magnesium alloy casting rod was heated to 525℃ at a heating rate of 8℃ / min, and homogenized at 525℃ for 7 hours. Finally, it was air-cooled to obtain the homogenized magnesium alloy casting rod.

[0106] V. Hot Extrusion:

[0107] Under the condition of 410℃, the extrusion die and the homogenized magnesium alloy casting rod are preheated for 0.5h, and then hot extruded under the conditions of extrusion temperature of 410℃, extrusion ratio of 25:1 and extrusion speed of 0.3mm / s to obtain a high corrosion resistant low rare earth magnesium alloy.

[0108] The mass percentage of Sm in the Mg-24Sm master alloy described in step one is 24%; the mass percentage of Mn in the Mg-10Mn master alloy described in step one is 10%.

[0109] The raw material melting described in step one specifically involves placing pure Mg ingots in a resistance furnace at a furnace temperature of 500°C under a protective atmosphere, then raising the temperature to 750°C and holding it at 750°C until the pure Mg ingots melt. Then, the temperature is lowered to 720°C at a cooling rate of 3°C / min, and Mg-24Sm master alloy and Mg-10Mn master alloy are added. The temperature is then held at 720°C until all Mg-24Sm and Mg-10Mn master alloys have melted, resulting in the molten alloy. The protective atmosphere is a mixture of CO2 and SF6, with a volume ratio of CO2 to SF6 of 99:1.

[0110] Under quasi-static tensile conditions at room temperature, the tensile rate is 1×10⁻⁶. -3 s -1 The high corrosion-resistant low rare earth magnesium alloy prepared in Example 3 has a tensile strength of 210 MPa, a yield strength of 146 MPa, and an elongation of 18%.

[0111] Example 4:

[0112] A high corrosion-resistant, low rare-earth magnesium alloy, which is composed of 5.6% Sm, 0.9% Mn and the balance Mg by mass percentage.

[0113] The total mass percentage of impurities in high corrosion-resistant low rare earth magnesium alloys is ≤0.02%, of which the mass percentage of Fe impurity is 0.005%, the mass percentage of Cu impurity is ≤0.001%, the mass percentage of Ni impurity is ≤0.001%, the mass percentage of Co impurity is ≤0.001%, and the total mass percentage of other impurity elements is ≤0.01%.

[0114] The above-mentioned method for preparing a high corrosion-resistant, low rare-earth magnesium alloy comprises the following steps:

[0115] I. Weighing and Melting:

[0116] Weigh out pure Mg ingots, Mg-24Sm master alloy and Mg-10Mn master alloy with a mass percentage of 5.6% Sm, 0.9% Mn and balance Mg to obtain raw materials. Melt the raw materials to obtain the molten alloy.

[0117] II. Refining:

[0118] The molten alloy was stirred uniformly at a temperature of 730℃. Then the temperature inside the furnace was raised to 780℃ and argon gas was introduced. Under the conditions of argon atmosphere and temperature of 780℃, the alloy liquid was refined for 10 minutes to obtain the alloy liquid.

[0119] III. Casting and Molding:

[0120] The alloy liquid was cooled to 690°C at a cooling rate of 3°C / min and cast into a shaped magnesium alloy. The surface layer of the shaped magnesium alloy was removed by turning and finally cut to obtain a magnesium alloy casting rod.

[0121] IV. Homogenization treatment:

[0122] The magnesium alloy casting rod was heated to 525℃ at a heating rate of 10℃ / min, and homogenized at 525℃ for 7 hours. Finally, it was air-cooled to obtain the homogenized magnesium alloy casting rod.

[0123] V. Hot Extrusion:

[0124] Under conditions of 400℃, the extrusion die and the homogenized magnesium alloy casting rod were preheated for 1 hour, and then hot extruded under conditions of 400℃, extrusion ratio of 25:1 and extrusion speed of 0.3mm / s to obtain a high corrosion resistant low rare earth magnesium alloy.

[0125] The mass percentage of Sm in the Mg-24Sm master alloy described in step one is 24%; the mass percentage of Mn in the Mg-10Mn master alloy described in step one is 10%.

[0126] The raw material melting described in step one specifically involves placing pure Mg ingots in a resistance furnace at a furnace temperature of 500°C under a protective atmosphere, then raising the temperature to 750°C and holding it at 750°C until the pure Mg ingots melt. Then, the temperature is lowered to 710°C at a cooling rate of 3°C / min, and Mg-24Sm master alloy and Mg-10Mn master alloy are added. The temperature is then held at 710°C until all Mg-24Sm and Mg-10Mn master alloys have melted, resulting in the molten alloy. The protective atmosphere is a mixture of CO2 and SF6, with a volume ratio of CO2 to SF6 of 99:1.

[0127] Under quasi-static tensile conditions at room temperature, the tensile rate is 1×10⁻⁶. -3 s -1 The high corrosion-resistant low rare earth magnesium alloy prepared in Example 4 has a tensile strength of 208 MPa, a yield strength of 144 MPa, and an elongation of 17%.

[0128] Example 5:

[0129] A high corrosion-resistant, low rare-earth magnesium alloy, which is composed of 5.9% Sm, 1.0% Mn and the balance Mg by mass percentage.

[0130] The total mass percentage of impurities in high corrosion-resistant low rare earth magnesium alloys is ≤0.02%, of which the mass percentage of Fe impurity is 0.004%, the mass percentage of Cu impurity is ≤0.001%, the mass percentage of Ni impurity is ≤0.001%, the mass percentage of Co impurity is ≤0.001%, and the total mass percentage of other impurity elements is ≤0.01%.

[0131] The above-mentioned method for preparing a high corrosion-resistant, low rare-earth magnesium alloy comprises the following steps:

[0132] I. Weighing and Melting:

[0133] Weigh out pure Mg ingots, Mg-24Sm master alloy and Mg-10Mn master alloy with a mass percentage of 5.9% Sm, 1.0% Mn and balance Mg to obtain raw materials. Melt the raw materials to obtain the molten alloy.

[0134] II. Refining:

[0135] The molten alloy was stirred uniformly at a temperature of 730℃. Then, the temperature inside the furnace was raised to 770℃ and argon gas was introduced. Under the conditions of argon atmosphere and temperature of 770℃, the alloy liquid was refined for 8 minutes to obtain the alloy liquid.

[0136] III. Casting and Molding:

[0137] The alloy liquid was cooled to 710°C at a cooling rate of 3°C / min and cast into a shaped magnesium alloy. The surface layer of the shaped magnesium alloy was removed by turning and finally cut to obtain a magnesium alloy casting rod.

[0138] IV. Homogenization treatment:

[0139] The magnesium alloy casting rod was heated to 525℃ at a heating rate of 10℃ / min, and homogenized at 525℃ for 7 hours. Finally, it was air-cooled to obtain the homogenized magnesium alloy casting rod.

[0140] V. Hot Extrusion:

[0141] Under a temperature of 380℃, the extrusion die and the homogenized magnesium alloy casting were preheated for 1 hour, and then hot extruded at an extrusion temperature of 380℃, an extrusion ratio of 25:1 and an extrusion speed of 0.1 mm / s to obtain a high corrosion-resistant low rare earth magnesium alloy.

[0142] The mass percentage of Sm in the Mg-24Sm master alloy described in step one is 24%; the mass percentage of Mn in the Mg-10Mn master alloy described in step one is 10%.

[0143] The raw material melting described in step one specifically involves placing pure Mg ingots in a resistance furnace at a furnace temperature of 500°C under a protective atmosphere, then raising the temperature to 750°C and holding it at 750°C until the pure Mg ingots melt. Then, the temperature is lowered to 730°C at a cooling rate of 3°C / min, and Mg-24Sm master alloy and Mg-10Mn master alloy are added. The temperature is then held at 730°C until all Mg-24Sm and Mg-10Mn master alloys have melted, resulting in the molten alloy. The protective atmosphere is a mixture of CO2 and SF6, with a volume ratio of CO2 to SF6 of 99:1.

[0144] Under quasi-static tensile conditions at room temperature, the tensile rate is 1×10⁻⁶. -3 s -1 The high corrosion-resistant low rare earth magnesium alloy prepared in Example 5 has a tensile strength of 205 MPa, a yield strength of 143 MPa, and an elongation of 17%.

[0145] Comparative Experiment 1:

[0146] A high corrosion-resistant, low rare-earth magnesium alloy, which consists of 5.0% Sm and the balance Mg by mass percentage.

[0147] The total mass percentage of impurities in high corrosion-resistant low rare earth magnesium alloys is ≤0.02%, of which the mass percentage of Fe impurity is 0.005%, the mass percentage of Cu impurity is ≤0.001%, the mass percentage of Ni impurity is ≤0.001%, the mass percentage of Co impurity is ≤0.001%, and the total mass percentage of other impurity elements is ≤0.01%.

[0148] The above-mentioned method for preparing a high corrosion-resistant, low rare-earth magnesium alloy comprises the following steps:

[0149] I. Weighing and Melting:

[0150] Weigh out pure Mg ingots and Mg-24Sm master alloy with a mass percentage of 5.0% Sm and the balance Mg to obtain raw materials. Melt the raw materials to obtain the molten alloy.

[0151] II. Refining:

[0152] The molten alloy was stirred uniformly at a temperature of 730℃. Then, the temperature inside the furnace was raised to 760℃ and argon gas was introduced. Under the conditions of argon atmosphere and temperature of 760℃, the alloy liquid was refined for 8 minutes to obtain the alloy liquid.

[0153] III. Casting and Molding:

[0154] The alloy liquid was cooled to 710°C at a cooling rate of 3°C / min and cast into a shaped magnesium alloy. The surface layer of the shaped magnesium alloy was removed by turning and finally cut to obtain a magnesium alloy casting rod.

[0155] IV. Homogenization treatment:

[0156] The magnesium alloy casting rod was heated to 525℃ at a heating rate of 10℃ / min, and homogenized at 525℃ for 7 hours. Finally, it was air-cooled to obtain the homogenized magnesium alloy casting rod.

[0157] V. Hot Extrusion:

[0158] Under a temperature of 380℃, the extrusion die and the homogenized magnesium alloy casting were preheated for 1 hour, and then hot extruded at an extrusion temperature of 380℃, an extrusion ratio of 25:1 and an extrusion speed of 0.1 mm / s to obtain a high corrosion-resistant low rare earth magnesium alloy.

[0159] The mass percentage of Sm in the Mg-24Sm master alloy described in step one is 24%; the mass percentage of Mn in the Mg-10Mn master alloy described in step one is 10%.

[0160] The raw material melting described in step one specifically involves placing pure Mg ingots in a resistance furnace at a furnace temperature of 500°C under a protective atmosphere, then raising the temperature to 750°C and holding it at 750°C until the pure Mg ingots melt. Then, the temperature is lowered to 720°C at a cooling rate of 3°C / min, and Mg-24Sm master alloy is added. The temperature is then held at 720°C until the Mg-24Sm master alloy is completely melted, yielding the molten alloy. The protective atmosphere is a mixture of CO2 and SF6, with a volume ratio of CO2 to SF6 of 99:1.

[0161] Under quasi-static tensile conditions at room temperature, the tensile rate is 1×10⁻⁶. -3 s -1 Compared with Experiment 1, the high corrosion-resistant low rare earth magnesium alloy prepared had a tensile strength of 202 MPa, a yield strength of 128 MPa, and an elongation of 26%.

[0162] Comparative Experiment 2:

[0163] A high corrosion-resistant, low rare-earth magnesium alloy, which consists of 5.0% Sm and the balance Mg by mass percentage.

[0164] The total mass percentage of impurities in high corrosion-resistant low rare earth magnesium alloys is ≤0.02%, of which the mass percentage of Fe impurity is 0.005%, the mass percentage of Cu impurity is ≤0.001%, the mass percentage of Ni impurity is ≤0.001%, the mass percentage of Co impurity is ≤0.001%, and the total mass percentage of other impurity elements is ≤0.01%.

[0165] The above-mentioned method for preparing a high corrosion-resistant, low rare-earth magnesium alloy comprises the following steps:

[0166] I. Weighing and Melting:

[0167] Weigh out pure Mg ingots and Mg-24Sm master alloy with a mass percentage of 5.0% Sm and the balance Mg to obtain raw materials. Melt the raw materials to obtain the molten alloy.

[0168] II. Refining:

[0169] The molten alloy was stirred uniformly at a temperature of 730℃. Then, the temperature inside the furnace was raised to 760℃ and argon gas was introduced. Under the conditions of argon atmosphere and temperature of 760℃, the alloy liquid was refined for 10 minutes to obtain the alloy liquid.

[0170] III. Casting and Molding:

[0171] The alloy liquid was cooled to 700°C at a cooling rate of 3°C / min and cast into a shaped magnesium alloy. The surface layer of the shaped magnesium alloy was removed by turning and finally cut to obtain a magnesium alloy casting rod.

[0172] IV. Homogenization treatment:

[0173] The magnesium alloy casting rod was heated to 525℃ at a heating rate of 10℃ / min, and homogenized at 525℃ for 7 hours. Finally, it was air-cooled to obtain the homogenized magnesium alloy casting rod.

[0174] V. Hot Extrusion:

[0175] Under the condition of 410℃, the extrusion die and the homogenized magnesium alloy casting rod are preheated for 0.5h, and then hot extruded under the conditions of extrusion temperature of 410℃, extrusion ratio of 25:1 and extrusion speed of 0.3mm / s to obtain a high corrosion resistant low rare earth magnesium alloy.

[0176] The mass percentage of Sm in the Mg-24Sm master alloy described in step one is 24%; the mass percentage of Mn in the Mg-10Mn master alloy described in step one is 10%.

[0177] The raw material melting described in step one specifically involves placing pure Mg ingots in a resistance furnace at a furnace temperature of 500°C under a protective atmosphere, then raising the temperature to 750°C and holding it at 750°C until the pure Mg ingots melt. Then, the temperature is lowered to 730°C at a cooling rate of 3°C / min, and Mg-24Sm master alloy is added. The temperature is then held at 730°C until the Mg-24Sm master alloy is completely melted, yielding the molten alloy. The protective atmosphere is a mixture of CO2 and SF6, with a volume ratio of CO2 to SF6 of 99:1.

[0178] Under quasi-static tensile conditions at room temperature, the tensile rate is 1×10⁻⁶. -3 s -1 Compared with Experiment 2, the high corrosion-resistant low rare earth magnesium alloy prepared had a tensile strength of 205 MPa, a yield strength of 134 MPa, and an elongation of 22%.

[0179] The high corrosion-resistant low rare earth magnesium alloys prepared in Examples 1 to 5 and Comparative Experiments 1 to 2 were subjected to immersion tests. Before the experiment, the alloys were processed into small square pieces of 30×15×3 (mm) by wire cutting (three parallel samples were taken for each alloy). The samples were polished with 320#, 1000#, and 3000# sandpaper in sequence (polished until the surface was smooth and clean). The size of the polished samples was then measured, and the surface area of ​​each experimental and comparative sample was calculated. The corrosive medium used in the immersion test was a 3.5% NaCl solution.

[0180] During the immersion experiment, the sample was suspended in the solution and immersed for 168 hours. The corrosive medium was replaced every 24 hours. The amount of hydrogen evolution of the alloy was recorded every 12 hours during the immersion experiment. After the immersion experiment was completed, the annual corrosion rate of the alloy was calculated using the following formula:

[0181] P H =2.279V H / T

[0182] Where: P H Annual corrosion rate (in mm / y); V H Hydrogen evolution rate (unit: mL / cm³) 2 T represents the soaking time (in days);

[0183] The experimental results are shown in the table below:

[0184] sample Corrosion rate (mm / y) Example 1 0.392 Example 2 0.427 Example 3 0.101 Example 4 0.247 Example 5 0.406 Comparative Experiment 1 1.026 Comparative Experiment 2 0.788

[0185] Figure 1 The figure shows the microstructure of the high corrosion-resistant low rare earth magnesium alloy prepared in Example 3. As can be seen from the figure, the alloy exhibits less dynamic precipitation after extrusion, and the second phase is fine and evenly distributed.

[0186] Figure 2 The X-ray diffraction pattern of the high corrosion-resistant, low rare-earth magnesium alloy prepared in Example 3 is shown in the figure. As can be seen from the figure, the phase composition of this alloy is Mg. 41 Sm5 phase and α-Mn phase.

[0187] Figure 3 The surface film morphology of the high corrosion-resistant low rare earth magnesium alloy prepared in Example 3 after immersion in a 3.5% NaCl solution for 168 hours is shown in the figure. As can be seen from the figure, the surface film is uniform and there are no large cracks.

[0188] Figure 4 The morphology of the high corrosion-resistant low rare earth magnesium alloy prepared in Example 3 after immersion in a 3.5% NaCl solution for 168 hours and removal of the surface film is shown in the figure. As can be seen from the figure, no large corrosion pits appeared on the alloy surface, indicating that the alloy underwent uniform corrosion without severe localized corrosion.

Claims

1. A high corrosion-resistant, low rare-earth magnesium alloy, characterized in that... It consists of 4%–5.9% Sm, 0.8%–1.0% Mn and the balance Mg by mass percentage; The aforementioned high corrosion-resistant, low rare-earth magnesium alloy is prepared according to the following steps: I. Weighing and Melting: Weigh out pure Mg ingots, Mg-24Sm master alloy, and Mg-10Mn master alloy with a mass percentage of 4%–5.9%, 0.8%–1.0% Mn, and the balance Mg to obtain raw materials. Under a protective atmosphere, place the pure Mg ingots in a resistance furnace at a furnace temperature of 495℃–505℃, then raise the temperature to 740℃–760℃ and hold it at 740℃–760℃ until the pure Mg ingots melt. Then, cool the temperature to 710℃–730℃ at a cooling rate of 1℃ / min–3℃ / min, add Mg-24Sm master alloy and Mg-10Mn master alloy, and hold at 710℃–730℃ until the Mg-24Sm master alloy and Mg-10Mn master alloy are completely melted to obtain the molten alloy. The protective atmosphere is a mixture of CO2 and SF6, and the volume percentage of SF6 in the protective atmosphere is 0.8% to 1.5%. II. Refining: Under conditions of 680℃~750℃, the molten alloy is stirred evenly, and then the temperature inside the furnace is raised to 750℃~780℃ and argon gas is introduced. Under the conditions of argon atmosphere and temperature of 750℃~780℃, the alloy liquid is refined for 5min~10min to obtain the alloy liquid. III. Casting and Molding: The alloy liquid was cooled to 690℃~710℃ at a cooling rate of 1℃ / min~3℃ / min and cast into a shaped magnesium alloy. The surface layer of the shaped magnesium alloy was removed by turning and finally cut to obtain a magnesium alloy casting rod. IV. Homogenization treatment: The magnesium alloy casting rod was heated to 520℃~530℃ at a heating rate of 8℃ / min~10℃ / min, and homogenized at 520℃~530℃ for 6h~8h, and finally air-cooled to obtain the homogenized magnesium alloy casting rod. V. Hot Extrusion: Under conditions of 380℃~410℃, the extrusion die and the homogenized magnesium alloy casting are preheated for 0.5h~1.5h, and then hot extruded at an extrusion temperature of 380℃~410℃, an extrusion ratio of (25~30):1, and an extrusion speed of 0.1mm / s~0.3mm / s to obtain a high corrosion-resistant low rare earth magnesium alloy.

2. The high corrosion-resistant, low rare-earth magnesium alloy according to claim 1, characterized in that... The total mass percentage of impurities in high corrosion-resistant low rare earth magnesium alloys is ≤0.02%, of which the mass percentage of impurity Fe is ≤0.005%, the mass percentage of impurity Cu is ≤0.001%, the mass percentage of impurity Ni is ≤0.001%, the mass percentage of impurity Co is ≤0.001%, and the total mass percentage of other impurity elements is ≤0.01%.

3. The high corrosion-resistant, low rare-earth magnesium alloy according to claim 1, characterized in that... The mass percentage of Sm in the Mg-24Sm master alloy described in step one is 24%; the mass percentage of Mn in the Mg-10Mn master alloy described in step one is 10%.

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