CN114318096A - Corrosion-resistant magnesium alloy and preparation method thereof - Google Patents
Corrosion-resistant magnesium alloy and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a corrosion-resistant magnesium alloy which comprises the following chemical elements in percentage by mass: 0.3 percent of scandium, 0.1 to 0.5 percent of calcium, and the balance of magnesium and inevitable impurities, wherein the total content of the impurities is not more than 0.01 percent. The invention also discloses a preparation method of the corrosion-resistant magnesium alloy. The corrosion-resistant magnesium alloy provided by the invention is formed into an Mg-Sc alloy with excellent corrosion resistance by adding Sc element with higher hydrogen evolution overpotential; then, by adopting a microalloying technology, on the basis of Mg-Sc single-phase alloy, trace Ca elements are added, and the addition of the trace Ca elements can effectively refine the grain structure of the alloy and improve the components and the structure of a second phase; cathode dynamics are inhibited, and the electrochemical performance of the cathode is improved; the components and the structure of the magnesium alloy corrosion product film are improved, more stable metal oxide is generated, and more compact corrosion product film and the like are formed to improve the corrosion resistance of the magnesium alloy.
Description
Technical Field
The invention belongs to the technical field of aluminum alloy, and particularly relates to a corrosion-resistant magnesium alloy and a preparation method thereof.
Background
The magnesium alloy is known as a green engineering material in the 21 st century, and is widely applied to the fields of automobile manufacturing, 3C industry, national defense military industry, aerospace and the like due to the advantages of high specific strength and specific stiffness, excellent electromagnetic shielding performance, good cutting processing performance, damping and shock absorbing performance, good fatigue resistance and the like. However, the electrode potential of magnesium is relatively negative (-2.37V), and the corrosion product film is relatively loose, so that the magnesium alloy has a high corrosion rate in most environments; poor corrosion resistance is one of the major obstacles limiting the application and development of magnesium alloys.
Improving the corrosion resistance of the magnesium alloy has irreplaceable effect on promoting the application and development of the magnesium alloy. Alloying is one of the most effective ways to improve the corrosion resistance of the magnesium alloy. At present, in the related research of improving the corrosion resistance of magnesium alloy by alloying, the addition amount of alloying elements is generally higher. However, the addition of a large amount of alloying elements may adversely affect other properties of the alloy while improving the corrosion resistance of the magnesium alloy. Researches show that the addition of trace alloy elements can also effectively improve the microstructure of the magnesium alloy and the morphology and structure of a corrosion product film, thereby achieving the effect of improving the corrosion resistance of the magnesium alloy; in addition, microalloying is also beneficial to controlling the mechanical property and the production cost of the magnesium alloy. Therefore, the research on the influence of micro-alloying on the corrosion resistance of the magnesium alloy is of great significance.
Galvanic corrosion between the second phase and the magnesium matrix is very likely to be the starting point of corrosion and gradually forms severe localized corrosion, possibly accelerating corrosion of the magnesium alloy. Compared with multiphase magnesium alloy, the single-phase magnesium alloy can avoid galvanic corrosion caused by a second phase, and is beneficial to the improvement of the corrosion resistance of the alloy. However, the single-phase alloy generally has a large grain size because of its single composition. In addition, the corrosion product film of the alloy is relatively monotonous in composition, a very compact corrosion product film is not easy to form, and the protection effect on the alloy matrix is limited. Therefore, by adopting a micro-alloying technology, on the basis of a single-phase alloy, trace alloy elements are added, so that the grain structure of the alloy can be refined under the condition of introducing a very small amount of second phase, the compactness of a corrosion product film is increased, and the corrosion resistance of the alloy is further improved, but related researches are still deficient at present.
Sc element has larger solid solubility in Mg and is easy to form single-phase alloy with Mg. Moreover, Sc element has higher hydrogen evolution overpotential and lattice parameters very close to those of Mg, so that the Mg-Sc alloy possibly has excellent corrosion resistance. The Ca element is a common alloying element in the magnesium alloy, can effectively improve the high-temperature performance and the casting performance of the magnesium alloy, and is widely applied to the magnesium alloy. A large number of researches show that Ca element also has a remarkable improvement effect on the corrosion resistance of magnesium alloy, and the reasons are mainly as follows: on one hand, Ca element can be used as a grain nucleating agent in the smelting preparation process of the magnesium alloy, so that the grain structure of the alloy is effectively refined; on the other hand, the addition of Ca may also cause the alloy to form a second phase which is uniformly and continuously distributed, hindering the diffusion of corrosion in the alloy; in addition, the addition of Ca element can also increase the compactness of a corrosion product film, thereby improving the protection effect of the corrosion product film on an alloy matrix.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, the invention mainly aims to provide a corrosion-resistant magnesium alloy, and aims to disclose the rule and the mechanism of action of the influence of the addition of trace Ca element on the structure and the corrosion behavior of Mg-Sc single-phase alloy and provide the magnesium alloy with simple components, low cost and good corrosion resistance. The invention also provides a preparation method of the corrosion-resistant magnesium alloy.
The purpose of the invention is realized by the following technical scheme:
in a first aspect: a corrosion-resistant magnesium alloy comprises the following chemical elements in percentage by mass: 0.3% of scandium, 0.1-0.5% of calcium, and the balance of magnesium and inevitable impurities, wherein the total content of the impurities is less than or equal to 0.01%.
Preferably, the chemical element composition comprises the following components in percentage by mass: 0.3% of scandium, 0.1% of calcium and the balance of magnesium and inevitable impurities, wherein the total content of the impurities is less than or equal to 0.01%.
Preferably, the chemical element composition comprises the following components in percentage by mass: 0.3% of scandium, 0.2% of calcium and the balance of magnesium and inevitable impurities, wherein the total content of the impurities is less than or equal to 0.01%.
Preferably, the chemical element composition comprises the following components in percentage by mass: 0.3 percent of scandium, 0.4 percent of calcium, and the balance of magnesium and inevitable impurities, wherein the total content of the impurities is less than or equal to 0.01 percent.
In a second aspect, a method for preparing the corrosion-resistant magnesium alloy comprises the following steps:
A) preparing and smelting an industrial pure magnesium ingot, a magnesium-scandium intermediate alloy and a magnesium-calcium intermediate alloy according to the mass fractions to obtain a ternary alloy melt;
B) casting, molding and machining the ternary alloy melt obtained in the step A) to obtain a cylindrical cast ingot;
C) and C), carrying out extrusion forming, heat treatment, rolling processing and annealing treatment on the cast ingot in the step B) to obtain the corrosion-resistant plate containing the Mg-Sc-Ca magnesium alloy.
Preferably, the step a) is specifically:
putting a pure magnesium ingot into a crucible, heating the pure magnesium ingot along with a resistance furnace to the temperature of 290-2And SF6Mixing protective gas, continuously heating to 710-730 ℃ until the pure magnesium ingot is completely melted, then sequentially adding magnesium-scandium intermediate alloy and magnesium-calcium intermediate alloy, stirring uniformly after the intermediate alloy is completely melted, and scraping scum on the surface of the melt to obtain the ternary alloy melt.
Preferably, step B) is specifically: standing the ternary alloy melt prepared in the step A) for 10-20min, pouring the ternary alloy melt into a metal mold, air cooling, turning and cutting to obtain an alloy ingot with the diameter of 85mm and the height of 100mm, carrying out solution treatment on the alloy ingot at the temperature of 400 ℃ for 24h, and then milling the alloy ingot after the solution treatment to obtain a cylindrical ingot with the diameter of 80mm and the height of 60 mm.
Preferably, the step C) is specifically: extruding and molding the cylindrical cast ingot prepared in the step B) in an extruder to obtain an extruded sheet with the width of 60mm and the thickness of 5 mm; and then carrying out heat treatment on the extruded plate at the temperature of 400 ℃ for 20min, and then carrying out multi-pass rolling processing and annealing treatment to obtain the corrosion-resistant magnesium alloy plate with the width of 60mm and the thickness of 2 mm.
Preferably, wherein the extrusion forming conditions are: the extrusion temperature is 260 ℃ and 300 ℃, the extrusion ratio is 18.9, and the extrusion speed is 0.5-1.5 m/min.
Preferably, the rolling processing and annealing treatment specifically comprises: rolling the extruded plate by four passes, wherein the rolling reduction of each pass is 18-22%, and simultaneously performing intermediate annealing treatment on the plate between the rolling processing of each pass, wherein the intermediate annealing treatment is to maintain the plate at the annealing temperature of 370-430 ℃ for 5-15 min; after the rolling process is finished, maintaining the plate at the annealing temperature of 370 ℃ and 430 ℃ for 45-75 min.
Compared with the prior art, the invention has at least the following advantages:
1) according to the corrosion-resistant magnesium alloy provided by the invention, Sc element has higher solid solubility in Mg, and is easy to form single-phase alloy with Mg; meanwhile, Sc element has higher hydrogen evolution overpotential and lattice parameters very close to those of Mg, so that the Mg-Sc alloy has excellent corrosion resistance. By adopting a microalloying technology, trace Ca elements are added on the basis of Mg-Sc single-phase alloy, and the addition of the trace Ca elements can effectively refine the grain structure of the alloy and improve the components and the structure of a second phase; cathode dynamics are inhibited, and the electrochemical performance of the cathode is improved; the components and the structure of the magnesium alloy corrosion product film are improved, more stable metal oxide is generated, a more compact corrosion product film is formed, and the corrosion resistance of the magnesium alloy is improved; in addition, the microalloying technology is adopted, which is beneficial to reducing the production cost of the magnesium alloy.
2) The preparation method of the corrosion-resistant magnesium alloy provided by the invention has the advantages of simple raw materials, easy obtainment, no pollution to the environment, simple overall process, greenness and environmental protection, can meet the requirements of industrial development and mass production, and can further expand the application range of the magnesium alloy.
Drawings
In order to more clearly illustrate the embodiments of the present invention, reference will now be made briefly to the embodiments or to the accompanying drawings that are needed in the description of the prior art.
FIG. 1 is a metallographic structure diagram of a corrosion-resistant magnesium alloy according to example 1 of the present invention;
FIG. 2 is a metallographic structure diagram of a corrosion-resistant magnesium alloy according to example 2 of the present invention;
FIG. 3 is a metallographic structure diagram of a corrosion-resistant magnesium alloy according to example 3 of the present invention;
FIG. 4 is a metallographic structure diagram of a corrosion-resistant magnesium alloy according to comparative example 2 of the present invention;
FIG. 5 is a scanning electron microscope image of the surface of the corrosion-resistant magnesium alloy provided in example 1 of the present invention;
FIG. 6 is a scanning electron microscope image of the surface of the corrosion-resistant magnesium alloy provided in example 2 of the present invention;
FIG. 7 is a scanning electron microscope image of the surface of the corrosion-resistant magnesium alloy provided in example 3 of the present invention;
FIG. 8 is a scanning electron microscope image of the surface of the corrosion-resistant magnesium alloy according to comparative example 2 of the present invention;
FIG. 9 is a graph of hydrogen evolution versus time for examples 1 to 3 and comparative example 2 of the present invention in which a corrosion resistant magnesium alloy is immersed in a NaCl solution for 60 hours;
FIG. 10 is a zeta potential polarization curve of the corrosion-resistant magnesium alloy provided by examples 1-3 and comparative example 2 of the present invention after being soaked in NaCl solution for 0.5 h;
FIG. 11 is a Nyquist plot of the impedance spectrum of the corrosion-resistant magnesium alloy provided in examples 1-3 of the present invention and comparative example 2 after soaking in NaCl solution for 0.5 h;
FIG. 12 is an impedance spectrum modulus-frequency curve of the corrosion-resistant magnesium alloy provided in examples 1-3 and comparative example 2 of the present invention after soaking in NaCl solution for 0.5 h;
FIG. 13 is a phase angle-frequency curve of an impedance spectrum of the corrosion-resistant magnesium alloy provided in examples 1 to 3 of the present invention and comparative example 2 after soaking in a NaCl solution for 0.5 h;
FIG. 14 is an impedance spectrum equivalent circuit diagram of the corrosion-resistant magnesium alloy provided in examples 1-3 and comparative example 2 of the present invention after soaking in NaCl solution for 0.5 h;
FIG. 15 shows the macroscopic corrosion morphology of the corrosion-resistant magnesium alloy provided in example 1 after being soaked in NaCl solution for 60 hours;
FIG. 16 is a macroscopic corrosion morphology of the surface of the corrosion-resistant magnesium alloy provided in embodiment 2 of the present invention after being soaked in a NaCl solution for 60 hours;
FIG. 17 is a macroscopic corrosion morphology of the surface of the corrosion-resistant magnesium alloy provided in embodiment 3 of the present invention after being soaked in a NaCl solution for 60 hours;
FIG. 18 is a macroscopic corrosion morphology of the surface of the corrosion-resistant magnesium alloy provided by comparative example 2 of the present invention after being soaked in NaCl solution for 60 hours;
FIG. 19 is a microscopic corrosion morphology of the surface of the corrosion-resistant magnesium alloy provided in example 1 of the present invention after being soaked in NaCl solution for 60 hours;
FIG. 20 is a microscopic corrosion morphology of the surface of the corrosion-resistant magnesium alloy provided in example 2 of the present invention after being soaked in a NaCl solution for 60 hours;
FIG. 21 is a microscopic corrosion morphology of the surface of the corrosion-resistant magnesium alloy provided in example 3 of the present invention after being soaked in NaCl solution for 60 hours;
FIG. 22 shows the micro-corrosion morphology of the corrosion-resistant magnesium alloy according to comparative example 2 after being soaked in NaCl solution for 60 h;
Detailed Description
The present invention will be further described with reference to the following drawings and examples, which are illustrative only and not intended to be limiting, and the scope of the present invention is not limited thereby.
When an amount, concentration, or other value or parameter is expressed as a range, preferred range, or upper and lower limit of the preferred value, it is to be understood that any range where any pair of upper limit or preferred value and any lower limit or preferred value of the range is combined is specifically disclosed, regardless of whether the range is specifically disclosed. Unless otherwise indicated, numerical range values set forth herein are intended to include the endpoints of the range, and all integers and fractions within the range.
All percentages, parts, ratios, etc. herein are by weight unless otherwise indicated.
The materials, methods, and examples herein are illustrative and, unless otherwise specified, are not to be construed as limiting.
The pure magnesium ingot, the magnesium-scandium master alloy and the magnesium-calcium master alloy used in the following examples of the present invention are commercially available.
The metallographic microscope used in the following examples of the invention was OLYMPUS PMG 3;
the scanning electron microscope adopted in the following embodiment of the invention is JSM-7800F;
the purity of the magnesium ingot in the following embodiment of the invention is more than or equal to 99.999 percent; the magnesium-scandium master alloy and the magnesium-calcium master alloy are collectively called magnesium master alloy, scandium and calcium in the magnesium master alloy respectively account for 10-25% of the total mass of the magnesium master alloy, and specifically, the magnesium-scandium master alloy is Mg-10Sc, and the magnesium-calcium master alloy is Mg-25 Ca.
The hydrogen evolution-time curve test in the following examples of the invention was carried out by soaking the magnesium alloy pieces, from which surface oils and oxide layers were removed, in Mg (OH) using a beaker with a solution volume of 250ml, an inverted funnel and an inverted basic burette2Collecting hydrogen generated by magnesium alloy corrosion in saturated 3.5 wt% NaCl solution by drainage methodThe corresponding relation between the amount of the magnesium alloy and the amount of the hydrogen further reflects the corrosion speed of the magnesium alloy in each time period according to PH＝2.088VHThe corrosion rate was calculated as/t.
The electrochemical tests in the following examples of the invention were carried out in a standard three-electrode system using the instrument Princeton electrochemical workstation (PARSTAT 4000), and the electrochemical tests include potentiodynamic polarization tests and electrochemical impedance spectroscopy tests. The scanning speed of the potentiodynamic polarization curve is 1mv s-1The scanning interval is-2.0 to-1.3V (vs. SCE); the frequency range of the Electrochemical Impedance Spectroscopy (EIS) test is 100 kHz-0.01 Hz, and the amplitude is 5 mV. Fitting polarization curve data to obtain self-corrosion potential and self-corrosion current density through Versa studio test software equipped in a Princeton electrochemical workstation; adopting ZSimpWin software to fit the electrochemical impedance spectrum data to obtain total electrochemical impedance and a fitting circuit diagram; and comparing the pure magnesium with the magnesium alloy obtained by implementation, calculating the corrosion inhibition efficiency.
In the following examples of the invention, the soaking experiment is carried out by a uniform corrosion full-soaking test method in a metal material laboratory according to a reference standard JB/T7901-.
All corrosion tests used herein were Mg (OH)2The purpose of saturating the NaCl solution is to ensure that the solution has the same pH value in the process of soaking experiment, thereby avoiding the influence of the change of the pH value of the solution on the corrosion rate of the alloy in the test process.
The invention researches the performance of the magnesium alloy with different components, and determines the limitation of the alloy content in the magnesium alloy.
Sc element is added into the magnesium alloy, and the Sc element has higher solid solubility in Mg, so that the Sc element and the Mg are easy to form single-phase alloy; meanwhile, Sc element has higher hydrogen evolution overpotential and lattice parameter very close to that of Mg, so that the Mg-Sc alloy has excellent corrosion resistance
The content of Sc element is 0.3 percent to ensure that the fine grain size is beneficial to improving the corrosion resistance of the magnesium alloy, and the size of the Sc element can be reduced by at least one time compared with the size of the pure magnesium grain and is single-phase alloy; when the introduction amount of Sc element is less than 0.3%, the magnesium alloy does not have a small enough grain size, atoms which enter the magnesium crystal in a solid solution manner are not enough, and no obvious crystal face offset exists; if the content of the metal element exceeds 0.3%, Mg-Sc phase can be precipitated, the potential difference between the Mg-Sc phase and a Mg matrix is large, and severe galvanic corrosion can be formed between the Mg-Sc precipitated phase and the magnesium matrix; the magnesium matrix is more negative in potential than the Mg-Sc phase particles, and therefore the magnesium matrix preferentially corrodes as an anode of galvanic corrosion; and when galvanic corrosion occurs, the equilibrium system of the alloy is destroyed, and the corrosion gradually diffuses and spreads, thereby accelerating the corrosion of the magnesium alloy.
The Ca element also has obvious improvement effect on the corrosion resistance of the magnesium alloy, and the reasons are as follows: on one hand, Ca element can be used as a grain nucleating agent in the smelting preparation process of the magnesium alloy, so that the grain structure of the alloy is effectively refined; on the other hand, the addition of Ca may also cause the alloy to form a second phase which is uniformly and continuously distributed, hindering the diffusion of corrosion in the alloy; in addition, the addition of Ca element can also increase the compactness of a corrosion product film, thereby improving the protection effect of the corrosion product film on an alloy matrix.
The content of calcium is selected to be 0.1-0.5% so as to obtain Mg with lower electrode potential than that of a magnesium matrix on the basis of ensuring that the mechanical property of the magnesium alloy is not influenced2Galvanic corrosion is formed between the Ca second phase and the magnesium matrix, and the Ca second phase serving as an anode of the galvanic corrosion is preferentially corroded, so that the corrosion of the magnesium matrix can be slowed down to a certain extent, and the corrosion resistance of the magnesium alloy is further improved; the calcium content is less than 0.1%, and Mg cannot be produced2A second phase of Ca; when the content is more than 0.5%, Mg2When the amount of the second phase of Ca is too large, the balance system on the surface of the alloy is damaged, the further damage of the corrosion medium chloride ions to the magnesium matrix is easily caused, and the corrosion resistance of the magnesium alloy is reduced.
The research on the performance of the magnesium alloy selected by each step and process parameter in the preparation method determines the limitations of the preparation steps and the process parameters in the magnesium alloy.
In the preparation method of the invention, in the step C), the extrusion molding conditions are as follows: the extrusion temperature is 260-300 ℃, the extrusion ratio is 18.9, and the extrusion speed is 0.5-1.0m/min, so as to ensure the uniform and smooth extrusion process, avoid belt breakage, control the heat of the extrusion deformation area, ensure the temperature of the metal surface and the internal temperature to be similar, and ensure the uniform structure; if the extrusion temperature is lower than 260 ℃, the extrusion ratio is lower than 18.9, and the extrusion speed is lower than 0.5m/min, a large number of defects such as difficult extrusion, unsmooth extrusion, uneven grain size and the like can occur; if the extrusion temperature is higher than 300 ℃, the extrusion ratio is higher than 18.9, and the extrusion speed is higher than 1.0m/min, the problems of excessive heat in the extrusion deformation area, short heat conduction time, increased temperature in the part, lowered temperature on the surface of the die, unsmooth extrusion, uneven distribution of the crystal grain structure and the like can occur.
In the preparation method, in the step C), four passes of rolling processing are carried out, the rolling reduction of each pass is 18-22%, and meanwhile, intermediate annealing treatment is carried out on the plate between each pass of rolling processing, wherein the intermediate annealing treatment is carried out by maintaining the plate at the annealing temperature of 370 ℃ and 430 ℃ for 5-15 min; after the rolling processing is finished, maintaining the plate at the annealing temperature of 370-430 ℃ for 45-75min to ensure that the annealing can eliminate the internal stress of the sample and ensure that the next step of rolling does not generate edge crack, the sample is flat after rolling, and the crystal grains are further refined; if the pass, the pressing amount, the annealing temperature and the annealing time of the rolling processing are not within the range, the rolling process is influenced if the pass, the pressing amount, the annealing temperature and the annealing time are too low, the rolling thickness is inconsistent, edge cracks, even all cracks, the structure is not uniform, a large number of defects exist, segregation occurs, and the corrosion resistance of the magnesium alloy is reduced; if the magnesium alloy is too high, crystal grains grow and coarsen, the effect of deforming and refining the crystal grains cannot be realized, and the corrosion resistance of the magnesium alloy is reduced.
The proportions of the elements in the magnesium alloy, the individual process steps and the technical parameters of the preparation process in the present application are found experimentally and are optimal since they allow you to obtain the claimed combined technical result. The alloy performance is deteriorated and unstable without violating the element proportion, and the composite effect is not achieved.
Example 1
The corrosion resistance provided by the invention comprises the following chemical elements in percentage by mass: 0.3% of scandium, 0.1% of calcium and the balance of magnesium and inevitable impurities, wherein the total content of the impurities is less than or equal to 0.01%.
The invention also provides a preparation method of the corrosion-resistant magnesium alloy, which comprises the following steps:
1) the method comprises the following steps: cutting an industrial pure magnesium ingot, a magnesium-scandium intermediate alloy and a magnesium-calcium intermediate alloy, polishing oxide skins on the surfaces of the raw materials by using a grinding machine, calculating the weight of each raw material according to the mass fraction, and weighing the raw materials for later use;
2) uniformly coating technological equipment such as a crucible, a stirring rod, a slag ladle and the like of low-carbon steel with boron nitride for later use;
3) putting a pure magnesium ingot into a crucible, heating the pure magnesium ingot to 290 ℃ along with a resistance furnace, and introducing CO with the volume ratio of 99:12And SF6Mixing protective gas, continuously heating to 710 ℃ until the pure magnesium ingot is completely melted, then sequentially adding a magnesium-scandium intermediate alloy and a magnesium-calcium intermediate alloy, after the intermediate alloy is completely melted, uniformly stirring by using a stirring rod, and scraping scum on the surface of the melt by using a slag-scraping spoon to obtain a ternary alloy melt of Mg-0.3Sc-0.1 Ca;
4) standing the ternary alloy melt prepared in the step 3) for 10min, pouring the ternary alloy melt into a metal mold, air-cooling, turning and cutting to obtain an alloy ingot with the diameter of 85mm and the height of 100mm, carrying out solution treatment on the alloy ingot at the temperature of 400 ℃ for 24h, and then milling the alloy ingot after the solution treatment to obtain a cylindrical ingot with the diameter of 80mm and the height of 60 mm;
5) extruding and molding the cylindrical cast ingot prepared in the step 4) in an extruder with the extrusion temperature of 260 ℃, the extrusion ratio of 18.9 and the extrusion speed of 0.5m/min to obtain an extruded sheet with the width of 60mm and the thickness of 5 mm; then, after the extruded plate is subjected to heat treatment at the temperature of 400 ℃ for 20min, the plate is subjected to four-pass rolling processing, the rolling reduction of each pass is 18%, and meanwhile, the plate between the rolling processing of each pass is subjected to intermediate annealing treatment, wherein the intermediate annealing treatment is to maintain the annealing temperature of 370 ℃ for 15 min; after the rolling process is finished, maintaining the plate at the annealing temperature of 370 ℃ for 75min to obtain the corrosion-resistant magnesium alloy plate with the width of 60mm and the thickness of 2 mm.
In this example, the performance of the prepared corrosion-resistant magnesium alloy is tested, and the results are shown in table 1;
the metallographic structure of the corrosion-resistant magnesium alloy prepared in this example is shown in fig. 1, the surface electron microscope scanning image is shown in fig. 5, the hydrogen evolution amount-time curve obtained by soaking in NaCl solution for 60 hours is shown in fig. 9, the potentiodynamic polarization curve obtained by soaking in NaCl solution for 0.5 hour is shown in fig. 10, the impedance spectroscopy nyquist plot obtained by soaking in NaCl solution for 0.5 hour is shown in fig. 11, the impedance spectroscopy modulus-frequency curve graph 12 obtained by soaking in NaCl solution for 0.5 hour is shown in the impedance spectroscopy phase angle-frequency curve 13 obtained by soaking in NaCl solution for 0.5 hour, the impedance spectroscopy equivalent circuit diagram obtained by soaking in NaCl solution for 0.5 hour is shown in fig. 14, the surface macro corrosion morphology obtained by soaking in NaCl solution for 60 hours is shown in fig. 15, and the micro corrosion morphology obtained by soaking in NaCl solution for 60 hours is shown in fig. 19.
Example 2
The corrosion resistance provided by the invention comprises the following chemical elements in percentage by mass: 0.3% of scandium, 0.2% of calcium and the balance of magnesium and inevitable impurities, wherein the total content of the impurities is less than or equal to 0.01%.
The invention also provides a preparation method of the corrosion-resistant magnesium alloy, which comprises the following steps:
1) the method comprises the following steps: cutting an industrial pure magnesium ingot, a magnesium-scandium intermediate alloy and a magnesium-calcium intermediate alloy, polishing oxide skins on the surfaces of the raw materials by using a grinding machine, calculating the weight of each raw material according to the mass fraction, and weighing the raw materials for later use;
2) uniformly coating technological equipment such as a crucible, a stirring rod, a slag ladle and the like of low-carbon steel with boron nitride for later use;
3) putting a pure magnesium ingot into a crucible, heating the pure magnesium ingot to 300 ℃ along with a resistance furnace, and introducing CO with the volume ratio of 99:12And SF6Mixing protective gas, continuously heating to 720 ℃ until pure magnesium ingot is completely melted, then sequentially adding magnesium-scandium intermediate alloy and magnesium-calcium intermediate alloy, after the intermediate alloy is completely melted, uniformly stirring by using a stirring rod, and scraping dross on the surface of the melt by using a slag-scraping spoon to obtain Mg-0.3Sc-0A ternary alloy melt of 2 Ca;
4) standing the ternary alloy melt prepared in the step 3) for 15min, pouring the ternary alloy melt into a metal mold, air-cooling, turning and cutting to obtain an alloy ingot with the diameter of 85mm and the height of 100mm, carrying out solution treatment on the alloy ingot at the temperature of 400 ℃ for 24h, and then milling the alloy ingot after the solution treatment to obtain a cylindrical ingot with the diameter of 80mm and the height of 60 mm;
5) extruding and molding the cylindrical cast ingot prepared in the step 4) in an extruder with the extrusion temperature of 280 ℃, the extrusion ratio of 18.9 and the extrusion speed of 1.0m/min to obtain an extruded sheet with the width of 60mm and the thickness of 5 mm; then, after the extruded plate is subjected to heat treatment at the temperature of 400 ℃ for 20min, the plate is subjected to four-pass rolling processing, the rolling reduction of each pass is 20%, and meanwhile, the plate between each pass of rolling processing is subjected to intermediate annealing treatment, wherein the intermediate annealing treatment is to maintain the annealing temperature of 400 ℃ for 5-15 min; after the rolling processing is finished, maintaining the plate at the annealing temperature of 400 ℃ for 60min to obtain the corrosion-resistant magnesium alloy plate with the width of 60mm and the thickness of 2 mm.
In this example, the performance of the prepared corrosion-resistant magnesium alloy is tested, and the results are shown in table 1;
the metallographic structure of the corrosion-resistant magnesium alloy prepared in this example is shown in fig. 2, the scanning electron microscope surface image is shown in fig. 6, the hydrogen evolution amount-time curve obtained by soaking in NaCl solution for 60 hours is shown in fig. 9, the potentiodynamic polarization curve obtained by soaking in NaCl solution for 0.5 hour is shown in fig. 10, the nyquist diagram of the impedance spectrum obtained by soaking in NaCl solution for 0.5 hour is shown in fig. 11, the mode value-frequency curve graph 12 of the impedance spectrum obtained by soaking in NaCl solution for 0.5 hour is shown in fig. 12, the phase angle-frequency curve graph 13 of the impedance spectrum obtained by soaking in NaCl solution for 0.5 hour is shown in fig. 14, the macroscopic corrosion morphology of the surface obtained by soaking in NaCl solution for 60 hours is shown in fig. 16, and the microscopic corrosion morphology obtained by soaking in NaCl solution for 60 hours is shown in fig. 20.
Example 3
The corrosion resistance provided by the invention comprises the following chemical elements in percentage by mass: 0.3 percent of scandium, 0.4 percent of calcium, and the balance of magnesium and inevitable impurities, wherein the total content of the impurities is less than or equal to 0.01 percent.
The invention also provides a preparation method of the corrosion-resistant magnesium alloy, which comprises the following steps:
1) the method comprises the following steps: cutting an industrial pure magnesium ingot, a magnesium-scandium intermediate alloy and a magnesium-calcium intermediate alloy, polishing oxide skins on the surfaces of the raw materials by using a grinding machine, calculating the weight of each raw material according to the mass fraction, and weighing the raw materials for later use;
2) uniformly coating technological equipment such as a crucible, a stirring rod, a slag ladle and the like of low-carbon steel with boron nitride for later use;
3) putting a pure magnesium ingot into a crucible, heating the pure magnesium ingot to 310 ℃, and introducing CO with the volume ratio of 99:12And SF6Mixing protective gas, continuously heating to 730 ℃ until the pure magnesium ingot is completely melted, then sequentially adding a magnesium-scandium intermediate alloy and a magnesium-calcium intermediate alloy, after the intermediate alloy is completely melted, uniformly stirring by using a stirring rod, and scraping scum on the surface of the melt by using a slag-scraping spoon to obtain a ternary alloy melt of Mg-0.3Sc-0.4 Ca;
4) standing the ternary alloy melt prepared in the step 3) for 20min, pouring the ternary alloy melt into a metal mold, air-cooling, turning and cutting to obtain an alloy ingot with the diameter of 85mm and the height of 100mm, carrying out solution treatment on the alloy ingot at the temperature of 400 ℃ for 24h, and then milling the alloy ingot after the solution treatment to obtain a cylindrical ingot with the diameter of 80mm and the height of 60 mm;
5) extruding and molding the cylindrical cast ingot prepared in the step 4) in an extruder with the extrusion temperature of 300 ℃, the extrusion ratio of 18.9 and the extrusion speed of 0.5-1.5m/min to obtain an extruded sheet with the width of 60mm and the thickness of 5 mm; then, after the extruded plate is subjected to heat treatment at the temperature of 400 ℃ for 20min, the plate is subjected to four-pass rolling processing, the rolling reduction of each pass is 22%, and meanwhile, the plate between the rolling processing of each pass is subjected to intermediate annealing treatment, wherein the intermediate annealing treatment is to maintain the annealing temperature of 430 ℃ for 5 min; after the rolling process is finished, maintaining the plate at the annealing temperature of 430 ℃ for 45min to obtain the corrosion-resistant magnesium alloy plate with the width of 60mm and the thickness of 2 mm.
In this example, the performance of the prepared corrosion-resistant magnesium alloy is tested, and the results are shown in table 1;
the metallographic structure of the corrosion-resistant magnesium alloy prepared in this example is shown in fig. 3, the surface electron microscope scanning image is shown in fig. 7, the hydrogen evolution amount-time curve obtained by soaking in NaCl solution for 60 hours is shown in fig. 9, the potentiodynamic polarization curve obtained by soaking in NaCl solution for 0.5 hour is shown in fig. 10, the impedance spectroscopy nyquist plot obtained by soaking in NaCl solution for 0.5 hour is shown in fig. 11, the impedance spectroscopy modulus-frequency curve graph 12 obtained by soaking in NaCl solution for 0.5 hour is shown in the impedance spectroscopy phase angle-frequency curve 13 obtained by soaking in NaCl solution for 0.5 hour, the impedance spectroscopy equivalent circuit diagram obtained by soaking in NaCl solution for 0.5 hour is shown in fig. 14, the surface macro corrosion morphology obtained by soaking in NaCl solution for 60 hours is shown in fig. 17, and the micro corrosion morphology obtained by soaking in NaCl solution for 60 hours is shown in fig. 21.
Comparative example 1
This comparative example relates to a corrosion-resistant magnesium alloy having substantially the same composition as example 2 except that scandium and calcium are not contained, and a magnesium alloy is prepared by the same method as example 1.
The comparative example tests the performance of the prepared corrosion-resistant magnesium alloy, and the results are shown in table 1;
comparative example 2
This comparative example relates to a corrosion-resistant magnesium alloy having substantially the same composition as example 1 except that calcium element is not contained, and prepared by the same method as example 1.
The comparative example tests the performance of the prepared corrosion-resistant magnesium alloy, and the results are shown in table 1;
wherein the metallographic structure of the corrosion-resistant magnesium alloy prepared by the comparative example is shown in fig. 4, the surface electron microscope scanning image is shown in fig. 8, the hydrogen evolution amount-time curve after soaking in the NaCl solution for 60 hours is shown in fig. 9, the potentiodynamic polarization curve after soaking in the NaCl solution for 0.5 hours is shown in fig. 10, the impedance spectroscopy nyquist plot after soaking in the NaCl solution for 0.5 hours is shown in fig. 11, the impedance spectroscopy modulus-frequency curve graph after soaking in the NaCl solution for 0.5 hours is shown in fig. 12, the impedance spectroscopy phase angle-frequency curve after soaking in the NaCl solution for 0.5 hours is shown in fig. 13, the impedance spectroscopy equivalent circuit diagram after soaking in the NaCl solution for 0.5 hours is shown in fig. 14, the surface macro corrosion morphology after soaking in the NaCl solution for 60 hours is shown in fig. 18, and the micro corrosion morphology after soaking in the NaCl solution for 60 hours is shown in fig. 22.
And (3) performance testing:
1. and (3) microstructure characterization:
1) the corrosion-resistant magnesium alloys of examples 1 to 3 and comparative example 2 were subjected to metallographic analysis using a metallographic microscope. As the content of Ca element increases, the crystal grains of the Mg-0.3Sc alloy become refined, and the crystal grain sizes of the Mg-0.3Sc alloy are about 22.3 μm, and the crystal grain sizes of the Mg-0.3Sc-0.1Ca, Mg-0.3Sc-0.2Ca and Mg-0.3Sc-0.4Ca alloys are about 20.6 μm, 19.4 μm and 18.3 μm, respectively.
Wherein MS, MS1Ca, MS2Ca and MS4Ca are abbreviations of Mg-0.3Sc alloy, Mg-0.3Sc-0.1Ca alloy, Mg-0.3Sc-0.2Ca alloy and Mg-0.3Sc-0.4Ca alloy, respectively.
3) The corrosion-resistant magnesium alloys of examples 1 to 3 and comparative example 2 were subjected to microstructure and intermetallic compound analysis using a scanning electron microscope (model JEOL-7800F); wherein FIGS. 2, 3, 4 and 1 are scanning electron micrographs of the corrosion-resistant magnesium alloys of examples 1-3 and comparative example 2, respectively, from which the number, morphology, size and distribution of phases and Mg of the corrosion-resistant magnesium alloy are more clearly seen2Distribution of Ca phase.
2. And (3) corrosion resistance characterization:
examples 1-3 of the present invention and comparative example 2 were subjected to corrosion resistance tests according to the national standard of the test method for electrochemical performance of sacrificial anode of GB/T17848-.
Table 1: corrosion resistance of examples 1-3 and comparative example 2
As can be seen from Table 1 and FIGS. 9-22, the addition of Ca reduces the hydrogen evolution amount and the self-corrosion current density of the Mg-Sc alloy, improves the corrosion resistance of the magnesium alloy, and particularly greatly improves the corrosion resistance of the magnesium alloy compared with pure magnesium, and the corrosion inhibition efficiency is more than or equal to 117.6%. Meanwhile, it is found that the corrosion resistance of the alloy is improved and then reduced with the increase of the content of the Ca element because the addition of the Ca element refines the structure of the alloy and increases the protective effect of the corrosion product film. However, when the content of Ca element is continuously increased, the galvanic corrosion in the alloy is also increased, and the balance system of the alloy surface is damaged, thereby reducing the corrosion resistance of the alloy.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present invention, and they should be construed as being included in the following claims and description.
Claims (10)
1. The corrosion-resistant magnesium alloy is characterized by comprising the following chemical elements in percentage by mass: 0.3% of scandium, 0.1-0.5% of calcium, and the balance of magnesium and inevitable impurities, wherein the total content of the impurities is less than or equal to 0.01%.
2. The corrosion-resistant magnesium alloy according to claim 1, wherein the chemical element composition comprises, in mass fraction: 0.3% of scandium, 0.1% of calcium and the balance of magnesium and inevitable impurities, wherein the total content of the impurities is less than or equal to 0.01%.
3. The corrosion-resistant magnesium alloy according to claim 1, wherein the chemical element composition comprises, in mass fraction: 0.3% of scandium, 0.2% of calcium and the balance of magnesium and inevitable impurities, wherein the total content of the impurities is less than or equal to 0.01%.
4. The corrosion-resistant magnesium alloy according to claim 1, wherein the chemical element composition comprises, in mass fraction: 0.3 percent of scandium, 0.4 percent of calcium, and the balance of magnesium and inevitable impurities, wherein the total content of the impurities is less than or equal to 0.01 percent.
5. A method for preparing the corrosion-resistant magnesium alloy according to claim 1, comprising the steps of:
A) preparing and smelting an industrial pure magnesium ingot, a magnesium-scandium intermediate alloy and a magnesium-calcium intermediate alloy according to the mass fractions to obtain a ternary alloy melt;
B) casting, molding and machining the ternary alloy melt obtained in the step A) to obtain a cylindrical cast ingot;
C) and C), carrying out extrusion forming, heat treatment, rolling processing and annealing treatment on the cast ingot in the step B) to obtain the corrosion-resistant plate containing the Mg-Sc-Ca magnesium alloy.
6. The method for preparing the corrosion-resistant magnesium alloy according to claim 5, wherein the step A) is specifically as follows:
putting a pure magnesium ingot into a crucible, heating the pure magnesium ingot along with a resistance furnace to the temperature of 290-2And SF6Mixing protective gas, continuously heating to 710-730 ℃ until the pure magnesium ingot is completely melted, then sequentially adding magnesium-scandium intermediate alloy and magnesium-calcium intermediate alloy, stirring uniformly after the intermediate alloy is completely melted, and scraping scum on the surface of the melt to obtain the ternary alloy melt.
7. The method for preparing the corrosion-resistant magnesium alloy according to claim 5, wherein the step B) is specifically as follows: standing the ternary alloy melt prepared in the step A) for 10-20min, pouring the ternary alloy melt into a metal mold, air cooling, turning and cutting to obtain an alloy ingot with the diameter of 85mm and the height of 100mm, carrying out solution treatment on the alloy ingot at the temperature of 400 ℃ for 24h, and then milling the alloy ingot after the solution treatment to obtain a cylindrical ingot with the diameter of 80mm and the height of 60 mm.
8. The method for preparing the corrosion-resistant magnesium alloy according to claim 5, wherein the step C) is specifically as follows: extruding and molding the cylindrical cast ingot prepared in the step B) in an extruder to obtain an extruded sheet with the width of 60mm and the thickness of 5 mm; and then carrying out heat treatment on the extruded plate at the temperature of 400 ℃ for 20min, and then carrying out multi-pass rolling processing and annealing treatment to obtain the corrosion-resistant magnesium alloy plate with the width of 60mm and the thickness of 2 mm.
9. The method for preparing the corrosion-resistant magnesium alloy according to claim 8, wherein the extrusion molding conditions are as follows: the extrusion temperature is 260 ℃ and 300 ℃, the extrusion ratio is 18.9, and the extrusion speed is 0.5-1.5 m/min.
10. The method for preparing the corrosion-resistant magnesium alloy according to claim 8, wherein the rolling and annealing treatment is specifically: rolling the extruded plate by four passes, wherein the rolling reduction of each pass is 18-22%, and simultaneously performing intermediate annealing treatment on the plate between the rolling processing of each pass, wherein the intermediate annealing treatment is to maintain the plate at the annealing temperature of 370-430 ℃ for 5-15 min; after the rolling process is finished, maintaining the plate at the annealing temperature of 370 ℃ and 430 ℃ for 45-75 min.
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