CN112662905B - Method for improving oxidation resistance of magnesium - Google Patents
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Abstract
The invention relates to the technical field of anti-oxidation treatment of metal compounds, in particular to a method for improving the anti-oxidation performance of magnesium, the method for improving the oxidation resistance of the magnesium controls the content of calcium oxide in the magnesium calcium oxide alloy, and the magnesium product with high-temperature oxidation resistance is obtained by heat treatment under the protective atmosphere at least containing hydrogen, the process flow is simple, the cost is low, has strong operability, high efficiency and no pollution, can combine with oxygen at high temperature to generate water through hydrogen, further reduces the oxygen partial pressure, so that the oxidation reaction is generated in the heat treatment process of the sample, the oxide film can effectively and completely cover the surface, the method has the advantages of simplifying process conditions, improving the high-temperature oxidation resistance of the magnesium alloy to the maximum extent, improving the utilization rate of the magnesium metal, being beneficial to expanding the application range of the magnesium metal, improving the competitive advantage of the magnesium metal and having wide market prospect.
Description
Technical Field
The invention relates to the technical field of metal compound antioxidant treatment, in particular to a method for improving the antioxidant property of magnesium.
Background
Magnesium is one of the lightest structural metal materials, has the advantages of high specific rigidity and specific strength, good electromagnetic shielding property and damping shock absorption property, easy recovery and the like, and has wide application prospect. Compared with other metals, magnesium products such as pure magnesium or magnesium alloy and the like prepared by taking magnesium as a raw material have the advantages of light weight, high specific strength, good vibration damping property, good thermal fatigue property, difficult aging and the like, and also have good thermal conductivity, strong electromagnetic shielding capability, very good die casting process performance and particularly easy recovery. Because of its good performance and the vigorous development of new energy industry in China, magnesium has been widely used in the automobile industry, especially in the electric automobile industry, such as the BYD electric automobile and Tesla automobile, to achieve the effects of reducing self weight, saving energy, reducing pollution and improving environment by using magnesium alloy. In order to adapt to the development trend of high integration, light weight and miniaturization of modern electronic and communication devices, the magnesium alloy is an ideal material for shells of products such as future traffic, electronic information, communication, computers, audio-visual equipment, portable tools, motors, forestry, textiles, nuclear power devices and the like.
However, in actual production, magnesium is active in chemical property and is easily oxidized at high temperature, so that the performance of magnesium products is seriously influenced, the service life is shortened, and huge industrial waste is caused. In the face of this problem, it is common in current industrial production to increase the usage rate of metallic magnesium by adding one or more elements such as Y, Al, La, Ca, etc. to magnesium to form a complex, however, the use of this process is limited because the use of these alloying elements in large amounts will affect the properties of magnesium itself, such as the decrease of electrical conductivity, thermal conductivity, and mechanical properties. In addition, the magnesium alloy has active chemical properties and belongs to metals which are difficult to carry out chemical plating and electroplating, even if the chemical plating and the electroplating can be realized, the magnesium alloy also has the environmental protection problem and has weak oxidation resistance.
Therefore, the above technical solutions have the following disadvantages in practical use: the prior magnesium product has the problem that the product performance is influenced because the product is easily oxidized at high temperature.
Disclosure of Invention
The embodiment of the invention aims to provide a method for improving the oxidation resistance of magnesium, so as to solve the problems that the existing magnesium product proposed in the background art is easy to oxidize at high temperature and the product performance is reduced caused by the oxidation. The invention develops a method for improving the high-temperature oxidation resistance of magnesium and/or magnesium alloy, which has the advantages of simple process flow, low cost, strong operability, high efficiency and no pollution; by the method, the oxidation resistance of the magnesium product is obviously improved, and the method has important significance for further expanding the application field of the magnesium product.
In order to achieve the above object, the embodiments of the present invention provide the following technical solutions:
a method for improving oxidation resistance of magnesium comprises the following steps:
1) adding calcium oxide into (pure) magnesium to prepare a magnesium-calcium oxide alloy, so that the content of calcium oxide (CaO) in the magnesium-calcium oxide (Mg-CaO) alloy is 0.01-10 wt.% (mass percent);
2) carrying out heat treatment on the magnesium-calcium oxide alloy at the temperature of not less than 300 ℃ in a protective atmosphere, and cooling to obtain a magnesium product with high-temperature oxidation resistance; wherein the protective atmosphere contains at least hydrogen.
Compared with the prior art, the invention has the beneficial effects that:
the method for improving the oxidation resistance of the magnesium provided by the embodiment of the invention controls the content of calcium oxide in the magnesium calcium oxide alloy, and the magnesium product with high-temperature oxidation resistance is obtained by heat treatment under the protective atmosphere at least containing hydrogen, the process flow is simple, the cost is low, the operability is strong, the efficiency is high, no pollution is caused, water can be generated by combining hydrogen with oxygen at high temperature in the heat treatment process, the oxygen partial pressure is further reduced, so that the sample is oxidized in the heat treatment process, the oxide film can effectively and completely cover the surface, the method has the advantages of simplifying process conditions, improving the high-temperature oxidation resistance of the magnesium alloy to the maximum extent, improving the utilization rate of metal magnesium, being beneficial to expanding the application range of the magnesium alloy, improving the competitive advantage of the magnesium alloy, solving the problem that the product performance is influenced because the existing magnesium product is easily oxidized at high temperature, and having wide market prospect.
Drawings
Fig. 1 is an XPS elemental depth profile characterization diagram of a Mg-3CaO sample according to an embodiment of the present invention.
FIG. 2 is a XPS elemental valence state characterization of a sample of Mg-3CaO provided in accordance with an embodiment of the present invention as a spectrum of Ca2 p.
FIG. 3 is an XPS elemental valence state characterization of an Mg1s spectrum for a Mg-3CaO sample provided in accordance with an embodiment of the present invention.
FIG. 4 is a thermogravimetric plot of different samples obtained by the present invention.
FIG. 5 is a SEM representation of a Mg-1CaO sample obtained by the present invention after heat treatment.
FIG. 6 is an SEM representation of a sample of Mg-3CaO obtained by the present invention after heat treatment.
FIG. 7 is an SEM representation of a sample of Mg-5CaO obtained by the present invention after heat treatment.
FIG. 8 is a SEM representation of the cross section of a Mg-3CaO sample obtained by the invention after heat treatment.
FIG. 9 is an elemental distribution diagram of a heat-treated Mg-3CaO sample obtained in the present invention.
Fig. 10 is an SEM characterization of pure magnesium after oxidation.
FIG. 11 is a TEM representation of a heat treated Mg-3 wt.% CaO microalloy resulting from the present invention.
Fig. 12 is a view of fig. 11.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention. The invention is only a brand new method and process for cubic boron nitride surface composite treatment, and part of the content adopts standard equipment or the prior art, so that the originality problem does not exist, namely the part which is not involved in the invention can be realized by the prior art, and the description is omitted.
The embodiment of the invention provides a method for improving oxidation resistance of magnesium, in particular to a method for improving high-temperature oxidation resistance of magnesium alloy through a heat treatment process, which comprises the following steps:
1) adding calcium oxide into (pure) magnesium to prepare a magnesium calcium oxide alloy, so that the content of calcium oxide in the magnesium calcium oxide alloy is 0.01-10 wt.% (mass percent);
2) carrying out heat treatment on the magnesium-calcium oxide alloy at the temperature of not lower than 300 ℃ in a protective atmosphere, and cooling to obtain a magnesium product with high-temperature oxidation resistance; wherein the protective atmosphere contains at least hydrogen.
As another preferred embodiment of the present invention, the temperature of the heat treatment is 300 ℃ to 500 ℃, and the time of the heat treatment is 6h to 12 h.
Preferably, the temperature of the heat treatment is 400 ℃, and the time of the heat treatment is 8 h.
As another preferred embodiment of the present invention, the magnesium-calcium oxide alloy can be an existing product, or can be a paper published by HA Seong-Ho et al: the contents of the document of Behavior of CaO and Calcium in pure Magnesium (red Metals, vol.25, spec.issue, Dec 2006, p.150) are specifically selected according to the requirements, and are not limited herein as long as the content of Calcium oxide in the Magnesium Calcium oxide alloy can be 0.1 wt.% to 10 wt.%.
As another preferred embodiment of the present invention, the protective atmosphere is a mixed gas containing hydrogen and an inert gas, and the inert gas may be helium, neon, argon, krypton, xenon, radon, etc., which is selected according to the requirement, and is not limited herein.
Preferably, the protective atmosphere is a mixed gas containing hydrogen and argon, namely an argon-hydrogen mixed gas, wherein the hydrogen can be combined with oxygen at a high temperature in the heat treatment process to generate water, the oxygen partial pressure is further reduced, so that an oxidation reaction occurs in the heat treatment process of the sample, an oxidation film can effectively and completely cover the surface, and if the oxygen content is too high, the inside of the matrix is oxidized under the condition that the oxidation film is not formed in time; in addition, the mixed gas containing argon and hydrogen can further reduce the volume content of oxygen in the atmosphere during the heat treatment, does not react with the metal, and can maintain a certain gas pressure.
As another preferred embodiment of the present invention, in the method for improving oxidation resistance of magnesium, a step of surface treatment is further included, and the surface treatment is to grind and electropolish the magnesium-calcium oxide alloy before performing heat treatment.
As another preferred embodiment of the invention, the grinding is a sand paper grinding treatment, and since most of actual products of the magnesium calcium oxide alloy are metal plates, and the metal plates are not suitable for mechanical polishing, the process mainly uses a pre-grinder for grinding, the rotating speed is 300r/min, and the grinding is carried out from 60-mesh type sand paper to 7000-mesh sand paper in sequence, so that the surface is smooth and free of other pollutants.
In another preferred embodiment of the present invention, the electrolytic polishing is to electrify the polished magnesium-calcium oxide alloy in a polishing agent, and then to clean the magnesium-calcium oxide alloy to obtain the magnesium-calcium oxide alloy after surface treatment.
As another preferred embodiment of the present invention, the polishing agent is a mixture of phosphoric acid: ethanol ═ 1: 1.5-2.5 (volume ratio), wherein the electrification uses two copper sheets with the same surface area as the sample to be polished (magnesium calcium oxide alloy after grinding) as cathodes, uses the sample to be polished as an anode, and controls proper voltage and current, the electrolytic polishing is generally carried out for 20-30 s under the current of 0.7-0.8A, the polishing time is controlled in a short time, and the surface of the sample can be excessively corroded by electrolysis if not.
Preferably, the polishing agent is prepared from the following components in percentage by weight: ethanol ═ 1: 2 (volume ratio).
The polished sample is immediately washed by distilled water and placed in acetone for ultrasonic treatment, so that the surface of the magnesium-calcium oxide alloy is bright and the surface cleanliness of the sample is ensured.
As another preferred embodiment of the present invention, in the method for improving oxidation resistance of magnesium, the heat treatment equipment comprises a tubular atmosphere furnace, the tubular atmosphere furnace is communicated with a gas cylinder storing protective gas, and a flow meter is arranged at the communication position, the protective gas is conveyed through the gas cylinder to provide protective atmosphere for the tubular atmosphere furnace, so as to ensure that a magnesium calcium oxide alloy sample placed in the tubular atmosphere furnace is subjected to heat treatment under the protective atmosphere, meanwhile, the tubular atmosphere furnace adopts a quartz tube structure, a thermocouple is connected with a heating device and a temperature control device through a thyristor, so that temperature control can be performed, so as to realize temperature adjustment of the heat treatment, and the output end of the quartz tube is connected through a gas washing device, so that gas generated by the heat treatment can be discharged outdoors after being washed with oil.
As another preferred embodiment of the present invention, in the method for improving oxidation resistance of magnesium, before the heat treatment, firstly, in order to avoid introducing other contaminants on the surface of the magnesium-calcium oxide alloy, the magnesium-calcium oxide alloy is placed in a clean quartz boat, then, the placed quartz boat is placed in a constant temperature area of a tube-type atmosphere furnace, and then a protective gas is introduced for gas washing (gas washing, i.e. vacuumizing the tube-type atmosphere furnace and then charging the protective gas, the above process is repeated for 3-4 times, in order to ensure that the oxygen content in the whole experimental apparatus is extremely low).
The method for improving the oxidation resistance of the magnesium provided by the embodiment of the invention can obtain the magnesium product with high temperature oxidation resistance by controlling the content of calcium oxide in the magnesium-calcium oxide alloy and carrying out heat treatment at the temperature of not less than 300 ℃ in the protective atmosphere at least containing hydrogen, has simple process flow, low cost, strong operability, high efficiency and no pollution, and can effectively and completely cover the surface of the magnesium product by optimizing the thermal process, wherein the protective atmosphere at least contains hydrogen which can be combined with oxygen at the high temperature in the heat treatment process to generate water, thereby further reducing the oxygen partial pressure, leading the oxidation reaction to occur in the heat treatment process of the sample, leading an oxidation film to effectively and completely cover the surface, and if the oxygen content is too much, leading the oxidation film to not be formed in time to oxidize the inside of a matrix, thereby simplifying the process conditions as much as possible and improving the high temperature oxidation resistance of the magnesium alloy to the utmost extent, the utilization rate of the metal magnesium is improved, the application range of the metal magnesium is expanded, and the competitive advantage of the metal magnesium is improved.
The embodiment of the invention also provides a magnesium product prepared by the method for improving the oxidation resistance of magnesium.
The embodiment of the invention also provides application of the method for improving the oxidation resistance of magnesium in preparation of an alloy material with (high-temperature) oxidation resistance.
As another preferred embodiment of the present invention, the alloy material may be a metal alloy such as a magnesium alloy, an aluminum alloy, a copper alloy, and the like, which is selected according to the requirement, and is not limited herein, and the metal alloy may be treated by the method for improving oxidation resistance of magnesium to improve oxidation resistance (at high temperature).
The technical effects of the method for improving oxidation resistance of magnesium according to the present invention will be further described below by referring to specific examples. The Mg-xCaO (x:0.1-10 wt.%) microalloy formed after different amounts of CaO are added is taken as a research object, the microalloy is subjected to heat treatment under an argon-hydrogen mixed protective atmosphere, and the oxidation behavior of an alloy sample subjected to heat treatment is discussed by using methods such as an electron scanning electron microscope and thermogravimetric analysis. And by optimizing the thermal process, the process conditions are simplified as far as possible, the high-temperature oxidation resistance of the magnesium alloy is improved to the maximum extent, the utilization rate of metal Mg is improved, the application range of the metal Mg is expanded, and the competitive advantage of the metal Mg is improved.
Example 1
A method for improving oxidation resistance of magnesium comprises the following steps:
adding calcium oxide into pure magnesium to prepare a magnesium-calcium oxide alloy, so that the content of calcium oxide in the magnesium-calcium oxide alloy is 1 wt.% (microalloy), thereby obtaining a magnesium product.
Example 2
A magnesium product was obtained in the same manner as in example 1, except that the content of calcium oxide in the magnesium calcium oxide alloy was 3 wt.% as compared with example 1.
Example 3
A magnesium article was obtained in the same manner as in example 1, except that the content of calcium oxide in the magnesium calcium oxide alloy was 5 wt.% as compared with example 1.
Example 4
The same as example 1 except that the content of calcium oxide in the magnesium calcium oxide alloy was 10 wt.% as compared with example 1.
Example 5
The same as example 1 except that the content of calcium oxide in the magnesium calcium oxide alloy was 0.01 wt.% as compared with example 1.
Example 6
The same as example 1 except that the content of calcium oxide in the magnesium calcium oxide alloy was 0.1 wt.% as compared with example 1.
Example 7
The same as example 1 except that the content of calcium oxide in the magnesium calcium oxide alloy was 2 wt.% as compared with example 1.
Example 8
A method for improving the oxidation resistance of magnesium comprises the following steps:
adding calcium oxide into pure magnesium to prepare a magnesium calcium oxide alloy, so that the content of calcium oxide in the magnesium calcium oxide alloy is 1 wt.% (microalloy);
and carrying out heat treatment on the magnesium-calcium oxide alloy in a protective atmosphere, and cooling to obtain the magnesium product with high-temperature oxidation resistance. Wherein the protective atmosphere is argon-hydrogen mixed gas, the temperature of the heat treatment is 380 ℃, and the time of the heat treatment is 8 h.
Example 9
The same as example 8 except that the content of calcium oxide in the magnesium calcium oxide alloy was 3 wt.% as compared with example 8.
Example 10
The same as example 8 except that the content of calcium oxide in the magnesium calcium oxide alloy was 5 wt.% as compared with example 8.
Example 11
A method for improving the oxidation resistance of magnesium comprises the following steps:
1) a magnesium-calcium oxide alloy is made by adding calcium oxide to pure magnesium so that the calcium oxide content in the magnesium-calcium oxide alloy is 1 wt.% (microalloy).
2) In order to ensure the accuracy of experimental data, the prepared magnesium-calcium oxide alloy is used as a micro-alloy metal sheet for surface treatment, and the method mainly comprises the following two steps: sanding and electrolytic polishing: a. the sanding of the abrasive paper is that the metal sheet is not suitable for mechanical polishing, so the process mainly uses a pre-grinder to carry out sanding, the rotating speed is 300r/min, and the sanding is carried out from 60-mesh type abrasive paper to 7000-mesh abrasive paper in sequence, so that the surface is smoother and has no other pollutants; b. performing electrolytic polishing, namely performing surface polishing on the sample polished by the abrasive paper by using polishing solution to remove fine scratches on the surface; wherein, the polishing solution is a phosphoric acid-ethanol mixed solution with a reasonable ratio, and the ratio is phosphoric acid: ethanol ═ 1: 2, the electrolytic polishing process is simplified and effective by reasonably regulating and controlling the polishing time and the polishing current and not using a brightener; the specific polishing process is to use two copper sheets with the surface area similar to that of a sample to be polished (polished magnesium calcium oxide alloy) as a cathode and the sample to be polished as an anode, and to control proper voltage and current, wherein the electrolytic polishing is generally carried out for 20-30 s under the current of 0.7-0.8A, the polishing time is controlled in a short time, and if the surface of the sample is excessively corroded by electrolysis; and (3) immediately washing the polished sample with distilled water, and placing the polished sample in acetone for ultrasonic treatment, so that the surface of the magnesium calcium oxide alloy sample to be detected is bright and the surface cleanliness of the sample is ensured.
3) The polished magnesium calcium oxide alloy metal sheet needs to be punched to become a sample with the diameter of 4mm required by the experiment. During punching, the sample is wrapped by the parchment paper (the sample is prevented from being scratched) and placed into a metal groove of a punching die, a 4mm hole penetrating through the metal groove is formed in the die, a punch is placed into the hole, instant impact force is applied to the punch, the sample with the thickness of 4mm can be punched, the punched sample is placed into acetone for ultrasonic cleaning after sulfuric acid paper scraps are stripped, and the sample obtained through punching is marked as a sample which is not annealed 1.
4) The sample that the punching press obtained carries out thermal treatment, the equipment of thermal treatment is for containing tubular atmosphere stove, tubular atmosphere stove and the gas cylinder intercommunication that stores protective gas (argon-hydrogen mist), and the intercommunication department is equipped with the flowmeter, carries protective gas through the gas cylinder, in order to for provide protective atmosphere (protect through the argon-hydrogen mist) in the tubular atmosphere stove, can guarantee that the magnesium calcium oxide alloy sample of placing can carry out thermal treatment under protective atmosphere in the tubular atmosphere stove, simultaneously, tubular atmosphere stove adopts the quartz tube structure, and the thermocouple passes through the silicon controlled rectifier to be connected with heating device and temperature regulating device, can control the temperature to realize thermal treatment's temperature regulation, and in addition, the output of quartz tube passes through the gas washer and connects, can discharge the gas that thermal treatment produced outdoor after washing with oil. To avoid introducing other contaminants to the sample surface, the stamped alloy sample pieces were placed in a clean quartz boat. And then, placing the arranged quartz boat in a constant temperature area of a tubular atmosphere furnace, and then introducing protective gas for gas washing (the gas washing is to vacuumize the tubular atmosphere furnace and then introduce the protective gas, and the process is repeated for 3-4 times, so as to ensure that the oxygen content in the whole experimental device is extremely low).
5) And after the gas washing is finished, heating the tubular atmosphere furnace to the preset temperature for heat treatment, keeping the temperature for the preset experiment required time, stopping heating, cooling the punched sheet alloy sample to room temperature along with the furnace in a protective atmosphere environment, and obtaining a magnesium product which is recorded as a Mg-1CaO sample. The temperature and time parameters were: the temperature is 400 ℃ and the time is 8 h.
Example 12
In the same manner as in example 11 except that the content of calcium oxide in the magnesium calcium oxide alloy was 3 wt.% as compared with example 11, the sample obtained by stamping was referred to as unannealed 2 sample, and the magnesium product obtained by heat treatment was referred to as Mg-3CaO sample.
Example 13
In the same manner as in example 11 except that the content of calcium oxide in the magnesium calcium oxide alloy was 5 wt.% as compared with example 11, the sample obtained by stamping was referred to as unannealed 3 sample, and the magnesium product obtained by heat treatment was referred to as Mg-5CaO sample.
Example 14
The procedure of example 11 was repeated, except that the temperature was 315 ℃ and the time was 6 hours, as compared with example 11.
Example 15
The procedure of example 11 was repeated, except that the temperature was 328 ℃ and the time was 6 hours, as compared with example 11.
Example 16
The procedure of example 11 was repeated, except that the temperature was 300 ℃ and the time was 6 hours, as compared with example 11.
Example 17
The procedure of example 11 was repeated, except that the temperature was 350 ℃ and the time was 7 hours, as compared with example 11.
Example 18
The procedure of example 11 was repeated, except that the temperature was 450 ℃ and the time was 10 hours, as compared with example 11.
Example 19
The procedure of example 11 was repeated, except that the temperature was 500 ℃ and the time was 12 hours, as compared with example 11.
Example 20
The procedure was repeated as in example 11 except that the temperature was 480 ℃ and the time was 12 hours, as compared with example 11.
Example 21
The process was the same as example 11 except that the protective atmosphere contained only hydrogen as compared with example 11.
Example 22
The same as example 11 except that the atmosphere for protection was a mixed gas of helium and hydrogen as compared with example 11.
Example 23
Compared with example 11, except that the polishing agent is phosphoric acid: ethanol ═ 1: 1.5 (volume ratio), and the other steps were the same as in example 11 except that the mixed solution was electropolished at a current of 0.7A for 30 seconds.
Example 24
Compared with example 11, except that the polishing agent is phosphoric acid: ethanol ═ 1: 2.5 (volume ratio), and the polishing was carried out by electropolishing at a current of 0.8A for 20 seconds, which was the same as in example 11.
Example 25
Elemental depth analyses were performed by a photoelectron spectroscopy (XPS) on Mg-1CaO samples (i.e., Mg-1 wt.% CaO), Mg-3CaO samples (i.e., Mg-3 wt.% CaO), and Mg-5CaO samples (i.e., Mg-5 wt.% CaO) obtained in examples 11, 12, and 13, respectively, after heat treatment at 400 ℃ for 8 hours, wherein the atomic percentage content of Mg, Ca, O, and C elements in the alloy oxide film of the Mg-3CaO samples changes with the increase of etching time as shown in fig. 1, and fig. 1 is an XPS elemental depth characterization analysis chart of the Mg-3 wt.% CaO alloy obtained by the present invention.
As can be seen in fig. 1, the C element is present in a large amount only on the outermost surface of the oxide film of the sample. The Ca element in the alloy has a slightly higher content on the surface of the oxide film, namely, the outermost layer of the oxide film formed by the sample after heat treatment is composed of more calcium oxide and magnesium oxide, and the content of the Ca element is slightly increased along with the prolonging of the etching time. The atomic percentage content of Mg element gradually increases along with the increase of etching time, namely along with the increase of depth, the content of MgO gradually increases, the content of MgO in the inner layer of the oxide film is relatively higher, and the content of the outer layer is less. In summary, even if the content of MgO gradually increases with increasing depth, the ratio of Mg to Ca element content becomes larger and larger. Therefore, it can be judged that the outermost layer of the oxide film of the Mg-3 wt.% CaO alloy is composed of a large amount of CaO and a small amount of MgO, and the inner layer of the oxide film is composed of a large amount of Mg oxide and a small amount of Ca element. Meanwhile, an oxidation film formed on the surface of the Mg-Ca alloy is very uniform and compact, so that the oxidation resistance of the alloy can be obviously improved.
Example 26
XPS elemental valence characterization is performed on the Mg-3CaO sample (i.e., Mg-3 wt.% CaO) obtained in example 12, and the characterization result is shown in fig. 2 and fig. 3, where fig. 2 is a Ca2p spectrum and fig. 3 is a Mg1s spectrum; as can be seen from the figure, the peak corresponding to Ca2p is 350.7eV, and the peak corresponding to Mg1s is 1304.1eV, and it is found from the energy level comparison literature that the MgO-CaO composite oxide film is formed on the surface of the Mg-3CaO sample after the heat treatment corresponding to CaO and MgO, respectively.
Example 27
The thermogravimetric oxidation resistance tests of the heat-treated Mg-xCaO (Mg-1CaO sample, Mg-3CaO sample, Mg-5CaO sample) and the non-annealed Mg-xCaO (non-annealed 1 sample, non-annealed 2 sample, non-annealed 3 sample) and pure magnesium obtained in example 11, example 12 and example 13 were performed, respectively, specifically, the samples were placed in a small crucible, then placed in a differential thermal analyzer of METTLER 1100LF, subjected to TGA (thermogravimetric analysis) experiments at a high temperature of 400 ℃ and in a pure oxygen environment, and the weight changes before and after the oxidation treatment were tested, and the test results are shown in fig. 4, where the thermogravimetric analysis parameters are: the heating temperature is 400 ℃; adding time for 2 h; the atmosphere was high purity oxygen with a gas flow rate of 100 ml/min. After the pure magnesium is oxidized in pure oxygen for 120min, the mass of the pure magnesium is increased by 3.769%, and the oxidation weight gains of the Mg-1CaO sample, the Mg-3CaO sample and the Mg-5CaO sample after heat treatment are generally much smaller than those of the unannealed 1 sample, the unannealed 2 sample and the unannealed 3 sample which are not subjected to heat treatment, so that the magnesium-calcium alloy obtained by the method provided by the embodiment of the invention has better oxidation resistance.
The results of the weight gain in the thermogravimetric antioxidant test obtained according to the results of fig. 4 are shown in table 1.
TABLE 1 table of weight gain results of thermogravimetric antioxidant test
According to the data in table 1, heat treatment significantly reduced the oxidation weight gain compared to the unannealed samples, indicating that heat significantly improved the oxidation resistance of the alloy.
In order to prove the technical effect that the temperature range designed for heat treatment in the embodiment of the invention is 300-500 ℃ and the time is 6-12 h, according to the preparation methods of the Mg-xCaO microalloys (Mg-1CaO sample, Mg-3CaO sample, Mg-5CaO sample) in the embodiment 11, the embodiment 12 and the embodiment 13, the heat treatment conditions are respectively changed as follows: 300 ℃ for 8 h; 8h at 450 ℃; 400 ℃ for 6 h; 400 ℃ for 10 h; at 400 ℃, for 12 h; 500 ℃ for 8 h. Six groups of heat-treated Mg-xCaO microalloys (Mg-1CaO sample, Mg-3CaO sample and Mg-5CaO sample) are tested according to the thermogravimetric oxidation resistance test method provided by the embodiment of the invention, and the thermogravimetric analysis parameters are as follows: the heating temperature is 400 ℃; adding for 2 h; the atmosphere was high purity oxygen with a gas flow rate of 100 ml/min. The weight gain results of the thermogravimetric antioxidant test are shown in tables 2 to 7.
TABLE 2 thermogravimetric antioxidation test weight gain results of samples after heat treatment at 300 ℃ for 8h
| Sample (I) | Pre-oxidation mass (mg) | Oxidized mass (mg) | Weight gain (mg) |
| Mg-1CaO | 14.6397 | 14.6501 | 0.0104 |
| Mg-3CaO | 13.9403 | 13.9964 | 0.0561 |
| Mg-5CaO | 14.8567 | 14.9214 | 0.0647 |
TABLE 3 thermogravimetric antioxidation test weight gain results of samples after 8h heat treatment at 450 deg.C
| Sample (I) | Pre-oxidation mass (mg) | Oxidized mass (mg) | Weight gain (mg) |
| Mg-1CaO | 15.1794 | 15.2493 | 0.0699 |
| Mg-3CaO | 14.3683 | 14.4404 | 0.0721 |
| Mg-5CaO | 15.4216 | 15.4956 | 0.074 |
TABLE 4 thermogravimetric antioxidation test weight gain results of samples after 6h heat treatment at 400 deg.C
| Sample (I) | Pre-oxidation mass (mg) | Oxidized mass (mg) | Weight gain (mg) |
| Mg-1CaO | 15.4098 | 15.4639 | 0.0541 |
| Mg-3CaO | 14.2508 | 14.3111 | 0.0603 |
| Mg-5CaO | 14.9894 | 15.0600 | 0.0706 |
TABLE 5 thermogravimetric antioxidation test weight gain results of samples after 10h heat treatment at 400 deg.C
| Sample (I) | Pre-oxidation mass (mg) | Oxidized mass (mg) | Weight gain (mg) |
| Mg-1CaO | 15.1558 | 15.2044 | 0.0486 |
| Mg-3CaO | 14.8585 | 14.9167 | 0.0582 |
| Mg-5CaO | 13.9752 | 14.0424 | 0.0672 |
TABLE 6 thermogravimetric antioxidation test weight gain results of samples after heat treatment at 400 ℃ for 12h
TABLE 7 thermogravimetric antioxidation test weight gain results of samples after 8h heat treatment at 500 deg.C
| Sample (I) | Pre-oxidation mass (mg) | Oxidized mass (mg) | Weight gain (mg) |
| Mg-1CaO | 15.3243 | 15.3864 | 0.0621 |
| Mg-3CaO | 14.0582 | 14.1184 | 0.0602 |
| Mg-5CaO | 14.649 | 14.7169 | 0.0679 |
In combination with the data in tables 2 to 7, it can be seen that the antioxidant effect is the best at a time of 400 ℃ and 8 hours. It should be noted that the temperature range designed for heat treatment is 300-500 deg.C, and the time is 6-12 h, which can improve the oxidation resistance.
Example 28
SEM characterizations were performed on the Mg-1CaO sample (i.e., Mg-1 wt.% CaO), the Mg-3CaO sample (i.e., Mg-3 wt.% CaO), and the Mg-5CaO sample (i.e., Mg-5 wt.% CaO) obtained in example 11, example 12, and example 13, respectively, after heat treatment at 400 ℃ for 8 hours, and the characterization results are shown in the attached FIGS. 5 to 8. Wherein, FIG. 5 is an SEM representation of Mg-1 wt.% CaO, FIG. 6 is an SEM representation of Mg-3 wt.% CaO, and FIG. 7 is an SEM representation of Mg-5 wt.% CaO. As can be seen from FIGS. 5 to 7, after the heat treatment, the MgO-CaO oxide composite film without cracks is formed on the surface of the magnesium-calcium oxide alloy, and the MgO-CaO oxide composite film is uniformly and completely covered on the alloy substrate. FIG. 8 is an SEM image of a cross-section of Mg-5 wt.% CaO, from which FIG. 8 it can be seen that the oxide film on the surface of the sample is dense and uniform with no significant defects.
In this example, an elemental analysis of a Mg-3CaO sample (i.e., Mg-3 wt.% CaO) was performed, and the results are shown in fig. 9, where a is an SEM image of Mg-3 wt.% CaO, b is a distribution of Mg in a Mg-3 wt.% CaO alloy, c is a distribution of O in a Mg-3 wt.% CaO alloy, and d is a distribution of Ca in a Mg-3 wt.% CaO alloy. As can be seen, all elements are uniformly distributed, and the surface of the magnesium-calcium oxide alloy after heat treatment forms a crack-free MgO-CaO oxide composite film which is uniformly and completely covered on the alloy matrix.
Example 29
Pure magnesium (for comparison) and the Mg-3CaO sample (i.e., Mg-3 wt.% CaO) obtained in example 12 after heat treatment at 400 ℃ for 8 hours were subjected to field emission experiments, respectively, and the experimental results are shown in FIGS. 10 to 11. In fig. 10, a SEM image of the oxidized pure magnesium shows that a large number of cracks are generated on the surface of the oxidized pure magnesium after the oxidation, which indicates that the pure magnesium does not form an oxidation film having oxidation resistance during the oxidation process. FIG. 11 is a TEM and a spectrogram of Mg-3 wt.% CaO, in which a is a TEM image of Mg-3 wt.% CaO, b is a distribution diagram of Mg element in a Mg-3 wt.% CaO alloy, c is a distribution diagram of O element in a Mg-3 wt.% CaO alloy, and d is a distribution diagram of Ca element in a Mg-3 wt.% CaO alloy. As can be seen from the figure, the oxidation film formed by the Mg-CaO alloy through heat treatment is about 40-50nm thick, calcium is segregated to the surface of the alloy during the heat process, no obvious crack or defect is observed in the figure, and the film thickness is uniform, which shows that the oxidation film has better compactness and stronger interface bonding performance of a matrix.
In the above embodiment of the invention, the magnesium product with high-temperature oxidation resistance can be obtained by controlling the content of calcium oxide in the magnesium-calcium oxide alloy and carrying out heat treatment under the protective atmosphere at least containing hydrogen, the process flow is simple, the cost is low, the operability is strong, the efficiency is high, no pollution is caused, the process conditions are simplified as far as possible, the high-temperature oxidation resistance of the magnesium alloy is improved to the maximum extent by optimizing the thermal process, the utilization rate of metal magnesium is greatly improved, the application range of the metal magnesium is expanded, the service life of the magnesium product is prolonged, and the competitive advantage of the magnesium product is improved.
While the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the scope of the invention.
Claims (6)
1. The method for improving the oxidation resistance of magnesium is characterized by comprising the following steps:
1) Making magnesium into a magnesium calcium oxide alloy such that the calcium oxide content in the magnesium calcium oxide alloy is 0.01wt.% to 10 wt.%;
2) and carrying out heat treatment on the magnesium-calcium oxide alloy in a protective atmosphere, wherein the protective atmosphere is a mixed gas containing hydrogen and inert gas, the heat treatment temperature is 300-500 ℃, the heat treatment time is 6-12 h, and cooling to obtain the magnesium product.
2. The method for improving the oxidation resistance of magnesium according to claim 1, wherein the temperature of the heat treatment is 400 ℃ and the time of the heat treatment is 8 h.
3. The method for improving the oxidation resistance of magnesium as recited in claim 1, wherein the content of calcium oxide in the magnesium calcium oxide alloy is 1-5 wt.%.
4. The method for improving the oxidation resistance of magnesium as recited in claim 1, further comprising a surface treatment step of grinding and electropolishing the magnesium-calcium oxide alloy before the heat treatment.
5. The method for improving the oxidation resistance of magnesium according to claim 4, wherein the electrolytic polishing is to electrify the polished magnesium-calcium oxide alloy in a polishing agent and then clean the magnesium-calcium oxide alloy to obtain the magnesium-calcium oxide alloy after surface treatment.
6. The method for improving the oxidation resistance of magnesium as recited in claim 5, wherein the raw material of the polishing agent comprises phosphoric acid and ethanol, and the volume ratio of the phosphoric acid to the ethanol is 1: 1.5-2.5; the current is controlled to be 0.7A-0.8A when the power is on, and the power-on time is 20s-30 s.
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