CN116005054A - Low-cost high-strength high-heat-conductivity magnesium alloy and preparation method thereof - Google Patents
Low-cost high-strength high-heat-conductivity magnesium alloy and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a low-cost high-strength high-heat-conductivity magnesium alloy which comprises the following components in percentage by mass: 1.6-2.9% of Zn, 0.3-0.8% of Ca, 0.2-0.3% of Mn, 0-0.4% of Ce, and the balance of Mg and unavoidable impurities; the preparation method of the magnesium alloy comprises the following steps: 1. preheating; 2. smelting and casting; 3. homogenizing; 4. extruding and deforming; 5. accumulating rolling deformation; 6. and (5) low-temperature annealing treatment. The magnesium alloy adopts Zn and Ca as main alloying elements, improves the strength and plasticity of the magnesium alloy, reduces the influence of solid solution atoms on the heat conductivity of the magnesium alloy, ensures the heat conductivity of the magnesium alloy and reduces the cost of raw materials; the invention adopts extrusion and rolling combination deformation, refines the grain size of the magnesium alloy, improves the comprehensive mechanical property of the magnesium alloy, and combines short-time low-temperature annealing treatment to improve the elongation, the heat conductivity and the strength of the magnesium alloy.
Description
Technical Field
The invention belongs to the technical field of nonferrous metal materials, and particularly relates to a low-cost high-strength high-heat-conductivity magnesium alloy and a preparation method thereof.
Background
Along with the rapid development of 5G communication, the power of electronic components is rapidly increased, and meanwhile, the electronic components are continuously developed to be miniaturized and light-weighted, so that the heating value per unit volume is larger and larger, the requirements on the heat conduction performance and the mechanical performance of the light heat dissipation material are higher and higher, and meanwhile, the good plasticity and the machinability of the material are required to be ensured. Magnesium alloys have received much attention for their low density and good thermal conductivity. The density of pure magnesium is 1.74g/cm 3 The thermal conductivity at room temperature was 157W/(mK). However, the tensile strength of pure magnesium is only about 70-80 MPa, and the strength requirement of the general structural material is difficult to meet. On the basis of pure magnesium, one or more alloying elements are added, and the mechanical properties of the magnesium alloy can be greatly improved through fine crystal strengthening, solid solution strengthening and precipitation strengthening, but the magnesium lattice is inevitably distorted strongly by the above methods, so that the mean free path of electrons is increased, and the thermal conductivity of the alloy is reduced. For example, die-cast AZ91 alloys reported in the literature have a tensile strength of 230MPa, a yield strength of 150MPa, and a thermal conductivity of 54W/(mK) at room temperature; the tensile strength of the ZM31 alloy in an extrusion state is 321MPa at room temperature, the yield strength is 168MPa, and the thermal conductivity is 113MPa; aging treatment is carried out after extrusion deformation, the tensile strength of the ZM31 alloy is improved to 283MPa, the yield strength is improved to 211MPa, and the thermal conductivity is improved to 125W/(m.K); after T6 treatment, the room temperature tensile strength of the WE54 alloy can reach 250MPa, the yield strength is 172 MPa, and the thermal conductivity is only 51.3W/(m.K). From the above results, it is clear that the magnesium alloy series commonly used in the market at present cannot meet the performance requirements of high strength and high thermal conductivity at the same time in the conventional preparation method, and therefore there is an urgent need for component design and processingInnovating the technology to obtain the high-strength high-heat-conductivity magnesium alloy and the preparation technology thereof.
In recent years, magnesium alloys with high strength and high heat conductivity and a preparation method thereof are disclosed and reported at home and abroad, and alloy components disclosed in Chinese patent publication No. CN111218597B contain 3.7% -4.2% of Zn, 0.4% -0.5% of Mn, 0.2% -0.4% of Ca and 0.15% -0.25% of La; under the hot extrusion state, the yield strength at room temperature is 180-250 MPa, the tensile strength is 250-320 MPa, the elongation is 30-36%, and the thermal conductivity is 130W/(m.K) -140W/(m.K). However, the alloy strength is still lower under the condition of ensuring good heat conduction performance and elongation, and the requirements of high strength and high heat conduction cannot be met. The alloy composition disclosed in the Chinese patent with publication number of CN111218595B contains 0.4-0.6% of Zr, 4-6% of Zn and 0.4-0.8% of Ca; the tensile strength of the alloy is more than 325MPa, the yield strength is more than 280MPa, the elongation is more than 15%, and the thermal conductivity is more than 120W/(m.K). However, the alloy needs to be subjected to aging treatment for 30 hours, and the preparation period is long; meanwhile, the alloy has higher Zn content, poorer heat cracking resistance and poor formability under the high-speed deformation condition.
Therefore, in order to better meet the requirements of fields such as electronics, automobiles and the like on high-strength high-heat-conductivity light alloy, the problem that the high strength and the high heat-conductivity of the magnesium alloy are difficult to be compatible is urgently solved, and a novel magnesium alloy heat-dissipating material with relatively low cost and shorter preparation period is developed.
Disclosure of Invention
The invention aims to solve the technical problem of providing a magnesium alloy with low cost, high strength and high heat conductivity aiming at the defects of the prior art. The alloy adopts Zn and Ca as main alloying elements, improves the strength and plasticity of the magnesium alloy through Zn reinforcement, and the simultaneous addition of Zn and Ca is favorable for forming stable Ca 2 Mg 6 Zn 3 The method reduces the influence of solid solution atoms on the heat conductivity of the magnesium alloy, ensures the heat conductivity of the magnesium alloy, and has low alloy raw material cost, wherein the magnesium alloy consists of Zn, ca and Mn elements and a small amount of rare earth Ce.
In order to solve the technical problems, the invention adopts the following technical scheme: the magnesium alloy with low cost, high strength and high heat conductivity is characterized by comprising the following components in percentage by mass: 1.6-2.9% of Zn, 0.3-0.8% of Ca, 0.2-0.3% of Mn, 0-0.4% of Ce, and the balance of Mg and unavoidable impurities.
Aiming at the problems that the high-alloy magnesium alloy has high strength but low heat conductivity and low elongation, and the low-alloy magnesium alloy has high heat conductivity and low elongation but insufficient strength, the magnesium alloy of the invention effectively improves the strength and plasticity of the magnesium alloy by adding Zn, and forms a nano-grade precipitated phase in the heat treatment process of the magnesium alloy to generate a strengthening effect; since Zn has an atomic radius of 0.139 μm smaller than that of Mg and Ca has an atomic radius of 0.197 μm larger than that of Mg, the negative value of the mixing enthalpy between Zn and Ca atoms is relatively large, and simultaneous addition of Zn and Ca is favorable for forming stable Ca 2 Mg 6 Zn 3 The phase effectively reduces the influence of solid solution atoms Zn and Ca on the degree of Mg lattice distortion when the solid solution atoms Zn and Ca are independently added, thereby reducing the influence of the solid solution atoms on the heat conductivity of the magnesium alloy.
According to the magnesium alloy, the Mn and the impurity element Fe which is contained in the magnesium raw material and introduced in the smelting process are added to form the Fe-Mn precipitation phase, so that the corrosion behavior and the elongation of the magnesium alloy are improved by reducing the Fe content, and meanwhile, the Mn refines grains in the magnesium, so that the mechanical property of the magnesium alloy is improved.
According to the magnesium alloy, the Ce is added to refine the grain size, so that the basal plane texture strength is weakened, non-basal plane slip is stimulated, and the elongation of the alloy is improved; meanwhile, the addition of Ce promotes the precipitation of the Mg-Zn-Ca ternary phase, and reduces the influence of solid solution elements on the heat conducting property of the magnesium alloy.
The Ca, mn and Ce elements in the magnesium alloy have very low solid solubility in Mg under the condition of room temperature, and are almost insoluble in a Mg matrix, so that the influence on the scattering of electrons or phonons is small, and the influence of the alloy elements on the heat conduction performance is small; in addition, the simultaneous addition of Zn and Ca in the present invention precipitates Ca from the matrix 2 Mg 6 Zn 3 The phase, thereby reducing the content of Zn and Ca atoms dissolved in the matrix and improving the heat of the magnesium alloyConductivity.
Therefore, zn, ca, mn, ce is adopted as an alloying element, and the influence of solid solution of the alloying element in the magnesium matrix on the degree of lattice distortion is reduced by adopting lower content of the alloying element, so that the magnesium alloy is ensured to have good heat conduction performance and plastic processing performance, and meanwhile, the raw material cost is reduced; in addition, stable atomic combination can be formed among the alloy elements, and the alloy elements are separated out in a precipitate form, so that the strength of the magnesium alloy is improved, and the magnesium alloy with low cost, high strength and high heat conductivity is obtained.
The magnesium alloy with low cost, high strength and high heat conductivity is characterized by comprising the following components in percentage by mass: zn 2.0%, ca0.4%, mn0.2%, and Mg as the rest.
In addition, the invention also discloses a method for preparing the magnesium alloy with low cost, high strength and high heat conductivity, which is characterized by comprising the following steps:
step one, preheating: according to the design components of the target magnesium alloy, mg, zn, mg-Ca intermediate alloy, mg-Mn intermediate alloy and Mg-Ce intermediate alloy are proportioned and preheated for 30min at 300-400 ℃;
step two, smelting and casting: under the protection of mixed gas, placing the Mg preheated in the step one into a resistance furnace, keeping the temperature at 700-720 ℃ until the Mg is completely melted, sequentially adding the Zn, the Mg-Ca intermediate alloy, the Mg-Ce intermediate alloy and the Mg-Mn intermediate alloy preheated in the step one at 730-760 ℃, adding a refining agent, uniformly stirring and removing surface scum, standing and keeping the temperature for 20-40 min, casting by a metal mold or semi-continuous casting at 700-720 ℃, and casting to prepare an alloy cast ingot;
step three, homogenizing: under the protection of inert gas, preserving heat for 8-26 hours at 350-390 ℃ for the alloy ingot obtained in the second step, then air-cooling to room temperature, and removing a surface oxide layer to obtain the homogenized alloy ingot;
step four, extrusion deformation: preheating the homogenized alloy cast ingot obtained in the step three at 330-380 ℃ for 2 hours, extruding at a speed of 0.1-5 m/min through an extrusion die, extruding and air-cooling to room temperature to obtain an extruded magnesium alloy plate;
step five, accumulating rolling deformation: preheating the extruded magnesium alloy plate obtained in the step four at 300-350 ℃ for 30min, rolling at a rolling speed of 10-30 m/min, and cooling to room temperature by water to obtain a magnesium alloy plate;
step six, low-temperature annealing treatment: and (3) preserving heat for 5-20 min at the temperature of 250 ℃ and cooling the magnesium alloy plate obtained in the step (V) to room temperature by water to obtain the low-cost high-strength high-heat-conductivity magnesium alloy.
According to the invention, each raw material of the magnesium alloy is preheated, so that the raw materials are sufficiently dried, the reaction of moisture in the raw materials with Mg liquid and even the influence of splashing on smelting are avoided, meanwhile, the temperature difference between other raw materials and the Mg liquid formed by heat preservation and smelting is reduced, the surface burning of the other raw materials when the other raw materials are added due to the large temperature difference is avoided, and then the raw material sequential addition sequence is formulated according to the melting point and burning loss rate of each raw material alloy: the raw material alloy with low burning loss rate and lower melting point is usually added when the temperature of the Mg melt is lower, the raw material alloy with high burning loss rate and higher melting point is added when the temperature of the Mg melt is higher or the casting time is shorter, so that the burning loss of the raw material alloy is effectively reduced, and then a refining agent is added for smelting and casting to obtain an alloy cast ingot; homogenizing the alloy ingot to reduce segregation of solute elements in the alloy ingot, and simultaneously, dissolving part of the second phase back into the matrix, so that the forming performance of the alloy in the subsequent deformation process is improved; and then extrusion deformation and rolling deformation are sequentially carried out to further refine the grain size, improve the mechanical property of the magnesium alloy, and the magnesium alloy is obtained by low-temperature annealing after rolling, so that the occurrence of tissue recovery in the magnesium alloy is promoted, the dislocation density in the tissue is reduced, and the elongation and the heat conductivity of the magnesium alloy are improved.
The method is characterized in that the mixed gas in the second step comprises SF with the volume fraction of 0.1% -1% 6 And CO with the volume fraction of 99% -99.9% 2 Or N 2 . The small amount of SF6 in the mixed gas plays a role in preventing the combustion of magnesium liquid and protecting the smooth proceeding of the magnesium alloy smelting process, and occupies CO with a great volume fraction 2 Or N 2 The gas acts as a current carrier.
The method is characterized in that the inert gas in the third step is N 2 Or Ar.
The method is characterized in that the extrusion ratio adopted in the extrusion in the step four is 16-32. By controlling the extrusion ratio, the strain energy is reduced, the grain refinement effect is ensured, meanwhile, the phenomenon that the grain grows up due to the recovery phenomenon is avoided because the friction force in the extrusion deformation process is increased to cause the increase of heat because the extrusion ratio is overlarge and the extrusion force required by deformation is large is avoided.
The method is characterized in that the accumulated rolling reduction of the rolling in the step five is 60% -90%, the single rolling reduction is 15% -30%, and the rolling is carried out for 3min at 300 ℃ -350 ℃ after each rolling pass. Because the heat dispersion of the magnesium alloy is good, the temperature of the plate falls rapidly in the rolling deformation process, and the plate cracks in the rolling process, the furnace is returned for heat preservation after each pass of rolling in the multi-pass rolling process, the temperature of the rolled plate is ensured to be within a preset rolling temperature range, and the smooth rolling is ensured.
Compared with the prior art, the invention has the following advantages:
1. the magnesium alloy adopts Zn and Ca as main alloying elements, strength and plasticity of the magnesium alloy are improved by adding Zn for strengthening, and simultaneous addition of Zn and Ca is favorable for forming stable Ca 2 Mg 6 Zn 3 The phase effectively reduces the influence of solid solution atoms Zn and Ca on the degree of Mg lattice distortion when being independently added, thereby reducing the influence of the solid solution atoms on the heat conductivity of the magnesium alloy, ensuring the heat conductivity of the magnesium alloy, and the magnesium alloy consists of Zn, ca and Mn elements and a small amount of rare earth Ce, and has lower cost of alloy raw materials.
2. The Mn and Ce added into the magnesium alloy refines the grain size, improves the mechanical property of the magnesium alloy, and promotes Ca 2 Mg 6 Zn 3 And the three-phase is separated out, so that the influence on the heat conducting property of the magnesium alloy is reduced.
3. According to the preparation method, the extrusion and rolling combination deformation is adopted, so that the grain size of the magnesium alloy is thinned, and the comprehensive mechanical property of the magnesium alloy is improved; the low-temperature annealing treatment is carried out after rolling, so that the recovery of a structure in the magnesium alloy is promoted, the dislocation density in the structure is reduced, the elongation and the heat conductivity of the magnesium alloy are improved, and meanwhile, the short-time annealing treatment ensures that grains excessively grow in the annealing process, so that the magnesium alloy still has higher strength.
4. The plastic deformation processes such as extrusion, rolling and the like related in the preparation method can be completed by adopting general equipment, special transformation of the equipment is not needed, the additional preparation cost for transformation is reduced, and meanwhile, the preparation method does not comprise long-time aging treatment, so that the preparation period is shortened, and the production efficiency of the magnesium alloy is improved.
5. According to the invention, through controlling the components of the magnesium alloy and the preparation process of the magnesium alloy, grains are effectively refined, a precipitated phase is obtained, the strength of the magnesium alloy is improved, the influence on the heat conductivity of the magnesium alloy is reduced, and the high-strength high-heat-conductivity magnesium alloy with yield strength of more than 250MPa, tensile strength of more than 270MPa, elongation of more than 10% and room-temperature heat conductivity of more than 120W/(m.K) is obtained.
The technical scheme of the invention is further described in detail through the drawings and the embodiments.
Drawings
FIG. 1 is a flow chart of a preparation method of the magnesium alloy with low cost, high strength and high heat conductivity.
Fig. 2 is a microstructure of the low-cost, high-strength, high-thermal conductivity magnesium alloy prepared in example 3 of the present invention.
FIG. 3 is a microstructure of the magnesium alloy prepared in comparative example 1 of the present invention.
FIG. 4 is a microstructure of the magnesium alloy prepared in comparative example 2 of the present invention.
FIG. 5 is a graph showing tensile stress strain curves of the magnesium alloy of low cost, high strength and high thermal conductivity prepared in example 3 and the magnesium alloy prepared in comparative examples 1-2.
Detailed Description
Example 1
The low-cost high-strength high-heat-conductivity magnesium alloy comprises the following components in percentage by mass: zn 1.6%, ca0.3%, mn0.2%, ce 0.2%, and Mg and unavoidable impurities as the rest.
As shown in fig. 1, the preparation method of the low-cost high-strength high-heat-conductivity magnesium alloy in the embodiment comprises the following steps:
step one, preheating: according to the design components of the target magnesium alloy, mg ingots with the mass purity of 99.99%, zn ingots with the mass purity of 99.99%, mg-30% Ca intermediate alloy, mg-5% Mn intermediate alloy and Mg-30% Ce intermediate alloy are proportioned and all are placed in a resistance furnace to be preheated for 30min at 300 ℃;
step two, smelting and casting: SF at a volume fraction of 0.1% 6 N with volume fraction of 99.9% 2 Under the protection of the composed mixed gas, placing the Mg ingot preheated in the step one into a resistance furnace, keeping the temperature at 700 ℃ until the Mg ingot is completely melted, heating the melt to 730 ℃, sequentially adding the Zn ingot preheated in the step one and the Mg-30% Ca intermediate alloy, keeping the temperature until the Mg ingot is completely melted, heating the melt to 750 ℃, sequentially adding the Mg-5% Mn intermediate alloy preheated in the step one and the Mg-30% Ce intermediate alloy, keeping the temperature until the Mg ingot is completely melted, then cooling to 730 ℃ and adding RJ-5 refining agent with the mass of 1% of the melt, uniformly stirring, removing surface scum, standing, keeping the temperature for 20min, performing semicontinuous casting at 700 ℃, and preparing the alloy ingot after casting;
step three, homogenizing: under the protection of Ar atmosphere, the alloy cast ingot obtained in the second step is kept at 390 ℃ for 8 hours, then air-cooled to room temperature, and the surface oxide layer is removed, so that the homogenized alloy cast ingot is obtained;
step four, extrusion deformation: preheating the homogenized alloy cast ingot obtained in the step three for 2 hours at 380 ℃, extruding through an extrusion die at the speed of 5m/min and the extrusion ratio of 32, and extruding and air cooling to room temperature to obtain an extruded magnesium alloy plate with the thickness of 5 mm;
step five, accumulating rolling deformation: preheating the extruded magnesium alloy plate obtained in the step four for 30min at the temperature of 350 ℃, rolling at the rolling speed of 30m/min, cooling to room temperature by water, wherein the accumulated rolling reduction of rolling is 90%, the single-pass rolling reduction is 20%, and after each pass rolling, preserving heat for 3min at the temperature of 350 ℃, and then carrying out next pass rolling to obtain the magnesium alloy plate with the thickness of 0.5 mm;
step six, low-temperature annealing treatment: and (3) preserving the heat of the magnesium alloy plate obtained in the step (V) at the temperature of 250 ℃ for 5min, and cooling the magnesium alloy plate to room temperature by water to obtain the low-cost high-strength high-heat-conductivity magnesium alloy.
Example 2
The low-cost high-strength high-heat-conductivity magnesium alloy comprises the following components in percentage by mass: zn 2.9%, ca0.8%, mn 0.3%, ce 0.4%, and Mg and unavoidable impurities as the rest.
As shown in fig. 1, the preparation method of the low-cost high-strength high-heat-conductivity magnesium alloy in the embodiment comprises the following steps:
step one, preheating: according to the design components of the target magnesium alloy, mg ingots with the mass purity of 99.99%, zn ingots with the mass purity of 99.99%, mg-30% Ca intermediate alloy, mg-5% Mn intermediate alloy and Mg-30% Ce intermediate alloy are proportioned and all are placed in a resistance furnace to be preheated for 30min at 350 ℃;
step two, smelting and casting: SF at 1% volume fraction 6 CO with 99% volume fraction 2 Under the protection of the composed mixed gas, placing the Mg ingot preheated in the step one into a resistance furnace, keeping the temperature at 700 ℃ until the Mg ingot is completely melted, heating the melt to 740 ℃, sequentially adding the Zn ingot preheated in the step one and the Mg-30% Ca intermediate alloy, keeping the temperature until the Mg ingot is completely melted, heating the melt to 760 ℃, sequentially adding the Mg-5% Mn intermediate alloy preheated in the step one and the Mg-30% Ce intermediate alloy, keeping the temperature until the Mg ingot is completely melted, then cooling to 730 ℃ and adding RJ-5 refining agent with the mass of 1% of the melt, uniformly stirring, removing surface scum, standing, keeping the temperature for 40min, cooling to 720 ℃, pouring into a steel die, casting a metal die, and casting to prepare an alloy ingot;
step three, homogenizing: under the protection of Ar atmosphere, placing the alloy cast ingot obtained in the second step into a tube furnace, preserving heat for 26 hours at 350 ℃, then air-cooling to room temperature, and removing a surface oxide layer to obtain an alloy cast ingot after homogenization treatment;
step four, extrusion deformation: preheating the homogenized alloy cast ingot obtained in the step three for 2 hours at 330 ℃, extruding through an extrusion die at the speed of 0.1m/min and the extrusion ratio of 16, and extruding and air cooling to room temperature to obtain an extruded magnesium alloy plate with the thickness of 5 mm;
step five, accumulating rolling deformation: preheating the extruded magnesium alloy plate obtained in the step four for 30min at 300 ℃, rolling at a rolling speed of 10m/min, cooling to room temperature by water, wherein the accumulated rolling reduction of rolling is 60%, the single-pass rolling reduction is 15%, and after each pass of rolling, preserving heat for 3min at 300 ℃, and then carrying out next pass rolling to obtain a magnesium alloy plate with the thickness of 2 mm;
step six, low-temperature annealing treatment: and (3) preserving heat of the magnesium alloy plate obtained in the step (V) at 250 ℃ for 20min, and cooling the magnesium alloy plate to room temperature by water to obtain the low-cost high-strength high-heat-conductivity magnesium alloy.
Example 3
The low-cost high-strength high-heat-conductivity magnesium alloy comprises the following components in percentage by mass: zn 2.0%, ca0.4%, mn0.2%, and Mg as the rest.
As shown in fig. 1, the preparation method of the low-cost high-strength high-heat-conductivity magnesium alloy in the embodiment comprises the following steps:
step one, preheating: according to the design components of the target magnesium alloy, mg ingots with the mass purity of 99.99 percent, zn ingots with the mass purity of 99.99 percent, mg-30 percent Ca intermediate alloy and Mg-5 percent Mn intermediate alloy are proportioned and all are placed in a resistance furnace to be preheated for 30 minutes at 350 ℃;
step two, smelting and casting: SF at 1% volume fraction 6 99% by volume of N 2 Under the protection of the composed mixed gas, placing the preheated Mg ingot in the step one into a resistance furnace, keeping the temperature at 700 ℃ until the Mg ingot is completely melted, heating the melt to 740 ℃, sequentially adding the preheated Zn ingot in the step one and the Mg-30% Ca intermediate alloy, keeping the temperature until the Mg ingot is completely melted, heating the melt to 750 ℃, sequentially adding the preheated Mg-5% Mn intermediate alloy in the step one, keeping the temperature until the Mg ingot is completely melted, then cooling to 730 ℃, adding RJ-5 refining agent with the mass of 1% of the melt, uniformly stirring, removing surface scum, standing, keeping the temperature for 30min, cooling to 710 ℃, pouring into a steel die, and performingCasting by a metal mold, and preparing an alloy cast ingot with the diameter of 60mm after casting;
step three, homogenizing: at N 2 Under the protection of atmosphere, preserving the heat of the alloy ingot obtained in the second step for 20 hours at 380 ℃, then air-cooling to room temperature, and removing a surface oxide layer to obtain an alloy ingot after homogenization treatment;
step four, extrusion deformation: preheating the homogenized alloy cast ingot obtained in the step three for 2 hours at 350 ℃, extruding through an extrusion die at the speed of 0.2m/min and the extrusion ratio of 20, and extruding and air cooling to room temperature to obtain an extruded magnesium alloy plate with the thickness of 5 mm;
step five, accumulating rolling deformation: preheating the extruded magnesium alloy plate obtained in the step four for 30min at 320 ℃, rolling at a rolling speed of 20m/min, cooling to room temperature by water, wherein the accumulated rolling reduction of rolling is 80%, the single-pass rolling reduction is 20%, and after each-pass rolling, preserving heat for 3min at 320 ℃, and then carrying out next-pass rolling to obtain a magnesium alloy plate with the thickness of 1 mm;
step six, low-temperature annealing treatment: and (3) preserving the heat of the magnesium alloy plate obtained in the step (V) at the temperature of 250 ℃ for 10min, and cooling the magnesium alloy plate to room temperature by water to obtain the low-cost high-strength high-heat-conductivity magnesium alloy.
Fig. 2 is a microstructure diagram of the low-cost high-strength high-heat-conductivity magnesium alloy prepared in the embodiment, and as can be seen from fig. 2, the microstructure of the magnesium alloy shows a bimodal structure composed of coarse crystals and equiaxed fine crystals, and obvious recrystallization occurs in a part of the region, so that the magnesium alloy has good strength and elongation.
Comparative example 1
This comparative example differs from example 3 in that: the preparation method does not carry out the step five and the step six, and the extruded magnesium alloy plate obtained in the step four is used as a product magnesium alloy.
Fig. 3 is a microstructure of the magnesium alloy prepared in this comparative example, and as can be seen from fig. 3, the metallographic structure of the magnesium alloy is a plurality of recrystallized equiaxed grains.
Comparative example 2
This comparative example differs from example 3 in that: and step six is not carried out in the preparation method, and the magnesium alloy sheet material obtained in the step five is used as a product magnesium alloy.
Fig. 4 is a microstructure of the magnesium alloy prepared in this comparative example, and as can be seen from fig. 4, the metallographic structure of the magnesium alloy is mainly composed of deformed grains, and since the structure is not subjected to the low-temperature annealing treatment, recrystallized grains are rarely contained in the structure, and the average grain size is larger than that of the magnesium alloy of example 3.
Comparative example 3
This comparative example differs from example 3 in that: the magnesium alloy consists of the following components in percentage by mass: zn 5.6%, ca0.4%, mn0.2%, and Mg and unavoidable impurities as the rest
The alloy ingot in the fourth step of the preparation process of the comparative example has obvious hot cracks in the extrusion process, and a testable extruded magnesium alloy plate cannot be obtained.
The mechanical properties and the heat conducting properties of the low-cost, high-strength and high-heat conducting magnesium alloys prepared in examples 1 to 3 and the magnesium alloys prepared in comparative examples 1 to 3 are tested, and the results are shown in fig. 5 and table 1 below.
As can be seen from table 1 and fig. 5, compared with the magnesium alloy prepared by extrusion deformation in comparative example 1, which has the characteristics of high thermal conductivity but lower strength, and the magnesium alloy prepared by extrusion-combined rolling deformation in comparative example 2, which has the characteristics of high strength but lower thermal conductivity, the magnesium alloys prepared in examples 1 to 3 of the present invention both have the characteristics of high strength and high thermal conductivity; meanwhile, comparing the embodiment 3 with the comparative examples 1-2, and combining with the process of extrusion and rolling at first and combining with low-temperature annealing treatment, the invention can effectively adjust the size of refined grains, reduce dislocation density, and improve the heat conductivity of the magnesium alloy while improving the light degree of the magnesium alloy; comparing example 3 with comparative example 3, it is clear that the magnesium alloy of the present invention has a lower Zn content, ensuring good formability.
The above description is only of the preferred embodiments of the present invention, and is not intended to limit the present invention. Any simple modification, variation and equivalent variation of the above embodiments according to the technical substance of the invention still fall within the scope of the technical solution of the invention.
Claims (7)
1. The magnesium alloy with low cost, high strength and high heat conductivity is characterized by comprising the following components in percentage by mass: 1.6-2.9% of Zn, 0.3-0.8% of Ca, 0.2-0.3% of Mn, 0-0.4% of Ce, and the balance of Mg and unavoidable impurities.
2. The low-cost high-strength high-heat-conductivity magnesium alloy according to claim 1, which is characterized by comprising the following components in percentage by mass: zn 2.0%, ca0.4%, mn0.2%, and Mg as the rest.
3. A method of making the low cost, high strength, high thermal conductivity magnesium alloy of claim 1 or 2, comprising the steps of:
step one, preheating: according to the design components of the target magnesium alloy, mg, zn, mg-Ca intermediate alloy, mg-Mn intermediate alloy and Mg-Ce intermediate alloy are proportioned and preheated for 30min at 300-400 ℃;
step two, smelting and casting: under the protection of mixed gas, placing the Mg preheated in the step one into a resistance furnace, keeping the temperature at 700-720 ℃ until the Mg is completely melted, sequentially adding the Zn, the Mg-Ca intermediate alloy, the Mg-Ce intermediate alloy and the Mg-Mn intermediate alloy preheated in the step one at 730-760 ℃, adding a refining agent, uniformly stirring and removing surface scum, standing and keeping the temperature for 20-40 min, casting by a metal mold or semi-continuous casting at 700-720 ℃, and casting to prepare an alloy cast ingot;
step three, homogenizing: under the protection of inert gas, preserving heat for 8-26 hours at 350-390 ℃ for the alloy ingot obtained in the second step, then air-cooling to room temperature, and removing a surface oxide layer to obtain the homogenized alloy ingot;
step four, extrusion deformation: preheating the homogenized alloy cast ingot obtained in the step three at 330-380 ℃ for 2 hours, extruding at a speed of 0.1-5 m/min through an extrusion die, extruding and air-cooling to room temperature to obtain an extruded magnesium alloy plate;
step five, accumulating rolling deformation: preheating the extruded magnesium alloy plate obtained in the step four at 300-350 ℃ for 30min, rolling at a rolling speed of 10-30 m/min, and cooling to room temperature by water to obtain a magnesium alloy plate;
step six, low-temperature annealing treatment: and (3) preserving heat for 5-20 min at the temperature of 250 ℃ and cooling the magnesium alloy plate obtained in the step (V) to room temperature by water to obtain the low-cost high-strength high-heat-conductivity magnesium alloy.
4. The method according to claim 3, wherein the mixed gas in the second step includes SF having a volume fraction of 0.1% -1% 6 And CO with the volume fraction of 99% -99.9% 2 Or N 2 。
5. The method according to claim 3, wherein the inert gas in step three is N 2 Or Ar.
6. The method according to claim 3, wherein the extrusion ratio used in the extrusion in the fourth step is 16 to 32.
7. A method according to claim 3, wherein the rolling in the fifth step has a cumulative rolling reduction of 60% -90%, a single rolling reduction of 15% -30%, and each rolling pass is followed by a 3min incubation at 300 ℃ -350 ℃ for a subsequent rolling pass.
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