Method for regulating and controlling magnesium alloy aging precipitated phase based on atomic cluster design

Abstract

The invention discloses a method for regulating and controlling an aging precipitated phase of a magnesium alloy based on atomic cluster design, and relates to the technical field of magnesium alloys. The invention comprises XX. According to the method, the proportion of key atoms of a solid solution atomic cluster is designed, the Sn / Zn atomic ratio is set to be 1, Mg2Sn and Mg2Zn aging precipitated phases which have the maximum number and are separated out in groups are obtained at the appropriate aging temperature, and due to the fact that the phase angles between Mg2Sn and Mg2Zn and a magnesium base body are different, the Mg2Sn and Mg2Zn can be pinned in groups to be dislocated in different directions in the deformation process, so that the strength of the magnesium alloy is improved, and the strength of the magnesium alloy is improved. The reason is that solute atomic clusters with the Sn / Zn atomic ratio being about 1 can serve as preferential nucleation positions, precipitation phase formation is promoted in subsequent artificial aging, the material strength is improved, Mg2Sn and Mg2Zn are different from magnesium base phase angles, Mg2Sn-Mg2Zn precipitation plays a remarkable pinning and hindering role on dislocation movement, the critical shear stress of the magnesium alloy is improved, and the mechanical property of the magnesium alloy is improved. Therefore, the yield strength of the material is improved.

Description

Technical Field

[0001] The invention relates to the technical field of magnesium alloys, and in particular to a method for designing and regulating aging precipitation phases of magnesium alloys based on atomic clusters. Background Art

[0002] As the lightest metal structural material, magnesium alloy has the advantages of high specific strength / specific stiffness, dimensional stability, easy processing and forming, good thermal and electrical conductivity, damping and vibration reduction, electromagnetic shielding and easy recycling. Therefore, it is known as the "21st century green engineering material" and is widely used in the fields of automobiles, aerospace, high-speed rail, rail transportation, electronic products, etc. Among the existing metal structural materials for commercial engineering applications, magnesium alloy has the smallest density, about 1.75-1.95g / cm3, about 2 / 3 of aluminum and 1 / 4 of steel. Magnesium alloy can replace or partially replace aluminum alloy and steel structural components mainly used in automobiles, rail transportation, military industry, aerospace, etc., and can effectively achieve lightweighting.

[0003] The global magnesium-based new materials industry has great development potential. In recent years, with the rapid development of new energy vehicles, aerospace and other industries, the demand for magnesium metal has continued to increase, and will continue to maintain a steady growth trend in the next few years. Magnesium metal is most widely used in the automotive industry, mainly used for body structural parts, engine components, wheels, etc. With the advancement of the "dual carbon" goals, electric vehicles and hybrid vehicles have developed rapidly. Magnesium metal has become a key material due to its excellent weight reduction performance and is expected to maintain a double-digit growth rate in the next five years. The demand for lightweight materials in the new energy vehicle field continues to rise, especially in battery packs, motors, vehicle structures, etc. The application prospects of magnesium metal are even broader.

[0004] However, industrial pure magnesium has low strength and poor room temperature plasticity. For example, the yield strength and tensile strength of pure magnesium sand casting test bars are only 21.9MPa and 90MPa, which cannot be used directly as a structural material. The mechanical properties of magnesium alloys can be greatly improved through the comprehensive use of various methods such as alloying, heat treatment, and plastic deformation. The strength of magnesium alloys is usually improved by solid solution strengthening, second phase strengthening, fine grain strengthening, aging precipitation strengthening, etc.

[0005] Magnesium alloys cannot undergo phase transformation during heat treatment, and their close-packed hexagonal crystal structure results in fewer slip systems, which in turn results in poor plasticity. This makes phase transformation strengthening and work hardening less important in magnesium alloys than in steel and aluminum alloys. Although grain refinement has a good effect on magnesium alloys, a universal grain refiner with suitable cost has not yet been found.

[0006] Age precipitation strengthening refers to the process in which, after the alloy elements are dissolved, the alloy elements dissolved at high temperature are precipitated in some form (such as intermetallic compounds) at room temperature or under heated conditions to form dispersed hard particles, which resist dislocation cutting and increase strength.

[0007] In the development process of high-performance magnesium alloy materials, the optimization of microstructure is the core and link, and the improvement of macroscopic performance is achieved through the design and processing of alloy composition and the regulation of heat treatment process. This is a key scientific issue in the basic research of magnesium alloys and a key technical difficulty in industrial applications.

[0008] The high strength of ZK series magnesium alloys mainly comes from aging precipitation strengthening, that is, dispersed nanoscale precipitate phase particles with characteristic crystal structure are precipitated in the supersaturated solid solution, which plays a significant pinning and hindering role on dislocation movement, increases the critical shear stress, and thus increases the yield strength of the material.

[0009] The existing technology lacks a method to easily control the strength of magnesium alloy materials by changing the interaction mode between dislocations and precipitates by controlling the number and shape of aging precipitates. Therefore, a new solution to the above problem is needed. Summary of the invention

[0010] The purpose of the present invention is to provide a method for designing and regulating the aging precipitation phase of magnesium alloy based on atomic clusters, by controlling the number and shape of the aging precipitation phase to change the interaction mode between dislocations and precipitation phases, thereby regulating the strength of the magnesium alloy material to solve the problems in the background technology.

[0011] To achieve the above object, the present invention provides the following technical solution: a method for designing and regulating the aging precipitation phase of magnesium alloy based on atomic clusters, comprising at least the following steps:

[0012] S1: Material selection: select raw materials according to the Sn / Zn atomic ratio that satisfies the condition that Sn / Zn is approximately equal to 1, and divide the raw materials into master batches and sub-batch materials.

[0013] S2: Smelting: Under gas protection, in a cast iron crucible, first melt the masterbatch at a certain temperature. After the masterbatch is completely melted and the temperature is stabilized, slag is removed. Then, preheated sub-materials are added to the crucible in sequence. The melt is left to stand at 720°C for 10 to 20 minutes, and the scum on the surface is removed.

[0014] S3: Casting, cooling the melt of S2 to 720°C, and pouring it into an iron mold preheated to a certain temperature under the protection of a mixed gas of CO2 and SF6 to prepare an ingot;

[0015] S4: machining, lathe processing the ingot obtained in S3 to a size suitable for the extrusion cylinder;

[0016] S5: homogenization treatment;

[0017] S6: hot extrusion. First, the ingot treated in S5 is kept at the extrusion temperature for 2 hours, and then forward hot extrusion is performed on a 500-ton horizontal extruder to obtain a magnesium alloy rod. Since magnesium alloys are prone to sticking during the extrusion process, a layer of boron nitride needs to be coated on the surface of the magnesium alloy for lubrication.

[0018] S7: aging treatment, the bars obtained in S6 were heat treated at 450 °C for 5 h, and then heat treated at 175 °C for 15 h to 20 h to obtain the final sample;

[0019] S8: TEM observation is performed on the sample to observe the precipitated phase.

[0020] Furthermore, the master batch at least includes industrial pure magnesium ingots, and the sub-batch at least includes industrial pure zinc and Mg-40% Sn.

[0021] Furthermore, the gas in S2 is CO2 containing SF6 with a volume fraction of 0.5% to 1.5%, the smelting temperature in S2 is 720°C to 740°C, the slag removal temperature is a stable 740°C, the preheating temperature of the sub-material is 200°C to 350°C, and the.

[0022] Furthermore, the preheating temperature of the iron mold in S3 is 250°C to 350°C.

[0023] Furthermore, the S5 at least includes the following steps:

[0024] The ingot obtained by S4 processing was kept at 400 °C for 3 h;

[0025] Eliminate the segregation structure of the alloy, and then raise the temperature to the homogenization temperature of the alloy at a heating rate of 100℃ / h;

[0026] All alloys were kept at the corresponding homogenization temperature for 24 h;

[0027] Then quench in cold water.

[0028] Furthermore, the extrusion temperature in S6 is 250° C. to 300° C., the extrusion ratio is 25:1, and the extrusion diameter is 16 mm.

[0029] Furthermore, the TEM observation was conducted under a Zeiss LIBRA200 FEI transmission electron microscope with an accelerating voltage of 200 kV, and the TEM observation required the preparation of a transmission sample.

[0030] Furthermore, the preparation process of the transmission sample includes at least the following steps:

[0031] Slicing: 0.5 mm thick slices were cut from the metallographic samples using wire cutting technology;

[0032] Mechanical grinding: Fix the sheet on 1500# sandpaper with an eraser and grind the bright side. Glue it to the glass with 502 glue and grind the other side to 50-70μm on sandpaper.

[0033] Electrolytic thinning: Use a punch to punch out a Φ3mm disc and perform double-spray electrolytic thinning;

[0034] The electrolyte used was 5.3 g lithium chloride (LiCl), 11.16 g magnesium perchlorate (Mg(ClO4)2), 500 ml methanol and 100 ml ethylene glycol butyl ether, and the double-spray process parameters were: voltage 50-60 V, current 25-30 mA, and temperature around -50 °C;

[0035] Ion thinning: After double spraying, the sample is thinned at a small angle on an ion thinning instrument to remove the oxide layer and contaminants on the sample surface;

[0036] Finally, the microstructure was observed under a transmission electron microscope.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention sets the Sn / Zn atomic ratio to 1 through the design of the key atomic ratio of the solid solution atomic clusters, and obtains the Mg2Sn and Mg2Zn aging precipitation phases with the maximum number and grouped precipitation at an appropriate aging temperature. Since Mg2Sn and Mg2Zn have different phase angles with the magnesium matrix, Mg2Sn and Mg2Zn can pin dislocations in different directions in groups during deformation, thereby improving the strength of the magnesium alloy. The reason is that the solute atomic clusters with the Sn / Zn atomic ratio of about 1 can be used as preferential nucleation positions, promote the formation of precipitation phases in the subsequent artificial aging, and improve the material strength. Since Mg2Sn and Mg2Zn have different phase angles with the magnesium matrix, the Mg2Sn-Mg2Zn precipitation pair will play a significant pinning and hindering role on the movement of dislocations, thereby improving the critical shear stress of the magnesium alloy, thereby improving the yield strength of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0040] Figure 1 TEM image of the alloy microstructure of the present invention. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0042] The extruded bars obtained in Example 1 and Example 2 were tested for mechanical properties. The results are shown in Table 1. The microstructure of the alloy is as follows: Figure 1 , Figure 1 (a) is the extrusion-aged Mg-5Sn-3Zn (wt%) alloy. Figure 1 (b) is a single Mg2Sn precipitate phase of the extruded aged Mg-5Sn (wt%) alloy. Figure 1 (c) is a solid solution aged Mg-2.2Sn-0.5Zn (wt%) alloy, from the literature TT Sasaki, et al. Materials Science and Engineering A, 530 (2011): 1-8.

[0043] Depend on Figure 1 It can be seen that when the Sn / Zn atomic ratio is about 1, a large number of Mg2Sn-Mg2Zn precipitation pairs are precipitated in the extrusion-aged alloy, and all the precipitation phases are Mg2Sn-Mg2Zn precipitation pairs; when the Sn / Zn atomic ratio is about 2.4, there are only a small amount of Mg2Sn-Mg2Zn precipitation pairs; when the Sn / Zn atomic ratio is about 0, the precipitation phase is a single Mg2Sn.

[0044] The raw materials in the present invention at least include industrial pure magnesium ingots, industrial pure zinc and Mg-40% Sn master alloy, and may also be other different raw materials in different inventions.

[0045] The TEM observation of the present invention was carried out under a Zeiss LIBRA200 FEI transmission electron microscope with an accelerating voltage of 200 kV.

[0046] Other types of observation devices and voltages may also be used in different inventions.

[0047] The preparation process of the transmission sample is as follows: 1) Slicing: Use wire cutting technology to cut 0.5mm thick slices from the metallographic sample; 2) Mechanical thinning: Fix the slice on 1500# sandpaper with an eraser and grind one side to make it bright, then stick it to the glass with 502 glue, grind the other side, and thin it to 50-70μm on sandpaper; 3) Electrolytic thinning: Use a punch to punch out Φ3mm discs and perform double-spray electrolytic thinning. The electrolyte used is: (5.3g lithium chloride (LiCl), 11.16g magnesium perchlorate (Mg(ClO4)2), 500ml methanol and 100ml ethylene glycol butyl ether), the double spray process parameters are: voltage is 50-60V, current is 25-30mA, temperature is about -50℃; 4) Ion thinning: the sample after double spraying is thinned at a small angle on an ion thinning instrument to remove the oxide layer and contaminants on the surface of the sample; 5) Finally, the microstructure is observed under a transmission electron microscope.

[0048] Embodiment 1

[0049] Preparation of deformable magnesium alloy containing a large amount of Mg2Sn-Mg2Zn precipitation pairs.

[0050] The deformed magnesium alloy containing a large amount of Mg2Sn-Mg2Zn precipitation pairs includes the following components by mass percentage: 5% Sn, 3% Zn, unavoidable impurities ≤ 0.15%, and the balance is Mg. The preparation method is as follows:

[0051] 1) Material selection: Raw materials are selected according to the Sn / Zn atomic ratio satisfying the condition that Sn / Zn is approximately equal to 1. The raw materials selected in this embodiment are industrial pure magnesium ingot, industrial pure zinc, and Mg-40% Sn master alloy.

[0052] 2) Smelting: Under the protection of CO2 containing SF6 with a volume fraction of 0.5% to 1.5%, first smelt industrial pure magnesium at 720°C in a cast iron crucible. After the masterbatch is completely melted, the temperature is stabilized to 740°C for slagging. Then, preheated industrial pure zinc and Mg-40% Sn master alloy are added to the crucible in sequence. The preheating temperature is about 250°C. The melt is left to stand at 720°C for 15 minutes, and the slag on the surface is removed.

[0053] 3) Casting: The melt of step 2) is cooled to 720°C and poured into an iron mold preheated to 300°C under the protection of a mixed gas of CO2 and SF6 to prepare an ingot.

[0054] 4) Machining: The ingot obtained in step 3) of the car body processing is made into a size suitable for the extrusion cylinder.

[0055] 5) Homogenization treatment: Some cast alloys have segregation, so during the homogenization process, the alloy is first kept at 400℃ for 3 hours to eliminate the segregation of the alloy, and then raised to the homogenization temperature of the alloy (heating rate is 100℃ / h). All alloys are kept at the corresponding homogenization temperature for 24 hours and then quenched in cold water.

[0056] 6) Hot extrusion: First, the ingot from step 4) is kept at the extrusion temperature (260°C) for 2 hours, and then subjected to forward hot extrusion on a 500-ton horizontal extruder with an extrusion ratio of 25:1 to form a magnesium alloy rod with a diameter of 16 mm. Since magnesium alloys are prone to sticking during the extrusion process, a layer of boron nitride needs to be coated on the surface of the magnesium alloy for lubrication.

[0057] 7) Aging treatment: The bar obtained in step 5) is heat treated at 450°C (T4) for 5 h, and then at 175°C for 20 h to obtain a sample after T6 heat treatment.

[0058] Embodiment 2

[0059] The difference from Example 1 is that the alloy contains only alloying element Sn but no Zn. The preparation method is the same as that of Example 1, but the raw material lacks industrial pure zinc.

[0060] The magnesium alloys in Example 1 and Comparative Example 1 were processed into room temperature tensile test specimens according to GB / T 228.1:2010 standard, and tested on a SANSI UTM5000 universal testing machine. The test results are shown in Table 1.

[0061] Table 1. Performance of alloys in the examples

[0062]

[0063]

[0064] As shown in Table 1, the tensile strength and yield strength of the extruded aged magnesium alloy in Example 1 are respectively increased by 8.66% and 30.43% compared with the alloy in Comparative Example 1, while the elongation can still be maintained at about 10%.

[0065] By designing the Sn / Zn atomic ratio to be about 1, perfect solid solution atomic clusters are formed in the Mg-Sn-Zn alloy solid solution, and the Mg2Sn and Mg2Zn aging precipitation phases precipitate in groups to form Mg2Sn-Mg2Zn precipitation pairs, and the number of precipitation pairs is maximized. The solute atomic clusters with a Sn / Zn atomic ratio of about 1 can serve as preferential nucleation sites, promote the formation of precipitation phases in subsequent artificial aging, and improve the strength of the alloy. The Mg2Sn-Mg2Zn precipitation pairs will play a significant role in pinning and hindering dislocation movement, increasing the critical shear stress of the magnesium alloy, thereby increasing the yield strength of the material.

[0066] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for designing and regulating the aging precipitation phase of magnesium alloy based on atomic clusters, characterized in that: At least the following steps are included: S1: Material selection: select raw materials according to the Sn / Zn atomic ratio that satisfies the condition that Sn / Zn is approximately equal to 1, and divide the raw materials into master batches and sub-batch materials; S2: Smelting: Under gas protection, in a cast iron crucible, first melt the masterbatch at a certain temperature. After the masterbatch is completely melted and the temperature is stabilized, slag is removed. Then, preheated sub-materials are added to the crucible in sequence. The melt is left to stand at 720°C for 10 to 20 minutes, and the scum on the surface is removed. S3: Casting, cooling the melt of S2 to 720°C, and pouring it into an iron mold preheated to a certain temperature under the protection of a mixed gas of CO2 and SF6 to prepare an ingot; S4: machining, lathe processing the ingot obtained in S3 to a size suitable for the extrusion cylinder; S5: homogenization treatment; S6: hot extrusion. First, the ingot treated in S5 is kept at the extrusion temperature for 2 hours, and then forward hot extrusion is performed on a 500-ton horizontal extruder to obtain a magnesium alloy rod. Since magnesium alloys are prone to sticking during the extrusion process, a layer of boron nitride needs to be coated on the surface of the magnesium alloy for lubrication. S7: aging treatment, the bars obtained in S6 were heat treated at 450 °C for 5 h, and then heat treated at 175 °C for 15 h to 20 h to obtain the final sample; S8: TEM observation is performed on the sample to observe the precipitated phase.

2. The method for designing and controlling the aging precipitation phase of magnesium alloy based on atomic clusters according to claim 1, characterized in that: The master batch at least includes industrial pure magnesium ingots, and the sub-batch at least includes industrial pure zinc and Mg-40% Sn.

3. The method for designing and controlling the aging precipitation phase of magnesium alloy based on atomic clusters according to claim 1, characterized in that: The gas in the S2 is CO2 containing SF6 with a volume fraction of 0.5% to 1.5%, the smelting temperature in the S2 is 720°C to 740°C, the slag removal temperature is a stable 740°C, the preheating temperature of the sub-material is 200°C to 350°C, and the.

4. The method for designing and controlling the aging precipitation phase of magnesium alloy based on atomic clusters according to claim 1, characterized in that: The preheating temperature of the iron mold in S3 is 250°C to 350°C.

5. The method for designing and controlling the aging precipitation phase of magnesium alloy based on atomic clusters according to claim 1, characterized in that: The S5 at least comprises the following steps: The ingot obtained by S4 processing was kept at 400 °C for 3 h; Eliminate the segregation structure of the alloy, and then raise the temperature to the homogenization temperature of the alloy at a heating rate of 100℃ / h; All alloys were kept at the corresponding homogenization temperature for 24 h; Then quench in cold water.

6. The method for designing and controlling the aging precipitation phase of magnesium alloy based on atomic clusters according to claim 1, characterized in that: The extrusion temperature in S6 is 250° C. to 300° C., the extrusion ratio is 25:1, and the extrusion diameter is 16 mm.

7. The method for controlling the aging precipitation phase of magnesium alloy based on atomic cluster design according to claim 1, characterized in that: The TEM observation is conducted under a transmission electron microscope with an acceleration voltage of 200 kV. The TEM observation requires the preparation of a transmission sample.

8. The method for designing and controlling the aging precipitation phase of magnesium alloy based on atomic clusters according to claim 7, characterized in that: The preparation process of the transmission sample comprises at least the following steps: Slicing: 0.5 mm thick slices were cut from the metallographic samples using wire cutting technology; Mechanical grinding: Fix the sheet on 1500# sandpaper with an eraser and grind the bright side. Glue it to the glass with 502 glue and grind the other side to 50-70μm on sandpaper. Electrolytic thinning: Use a punch to punch out a Φ3mm disc and perform double-spray electrolytic thinning; Ion thinning: After double spraying, the sample is thinned at a small angle on an ion thinning instrument to remove the oxide layer and contaminants on the sample surface; Finally, the microstructure was observed under a transmission electron microscope.

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