Patent Application
20210062315
The present invention belongs to the technical field of preparation of metal materials, and particularly relates to a preparation method of a lithium-containing magnesium/aluminum matrix composite.
Magnesium-lithium alloys have the advantages of being low in density, high in specific strength, and good in vibration damping properties, electromagnetic shielding properties and machinability, and are ideal materials with lightweight structure. In recent years, great attention has been paid to research and application of magnesium-lithium alloys. However, magnesium-lithium alloys also have the problems of being difficult in plastic deformation, poor in creep resistance at high temperature and poor in corrosion resistance, wherein low strength, poor mechanical properties and easy yield deformation are one of the important reasons that limit the application field of magnesium-lithium alloys. Generally, magnesium-lithium alloys cannot be used even as secondary stressed members, but can only be used as housing parts, which severely restrict the application field.
The aluminum-lithium alloys have the advantages of being low in density, high in specific strength, high in specific rigidity, and the like, the melting and casting properties of the aluminum-lithium alloys are also better than those of traditional aluminum alloys, and the aluminum-lithium alloys are also an ideal material with lightweight structure. However, aluminum-lithium alloys have serious anisotropy of mechanical properties, and low plasticity and toughness and the like, so that the aluminum-lithium alloys are inferior to other aluminum alloys.
Therefore, in order to expand the application range of lightweight alloys, reinforcements with stable chemical properties are often added to improve the mechanical properties of the metallic composite materials.
Compared with traditional magnesium, aluminum alloys, the magnesium and aluminum matrix composite not only has excellent mechanical properties, but also has some special properties and other good comprehensive properties. At present, methods for preparing metallic composites mainly include a traditional mechanical stirring casting method, a squeeze casting method, an injection molding method, an in-situ reaction composite method, and the like.
The method of powder metallurgy comprises the steps of mixing the metal powder with the reinforcement powder by ball milling, and then performing sinter molding by hot pressing under the vacuum condition. By the powder metallurgy method, the matrix alloys do not need to be heated to a molten state, so that the matrix and the reinforcements can prevent the reaction at the interface. After mixing, the reinforcements are uniformly distributed in the matrix and play a good reinforcing role. However, due to the large differences in size, shape and properties between the reinforcements and the matrix alloys, compared with the interface bonding strength of the composite produced by the casting method, the interface bonding strength of the composite can be reduced after bonding is performed. In addition, the process method of powder metallurgy determines that the process method is more suitable for small functional materials, but not for larger structural materials. The process method is complicated and costly in technological process, and many problems also exist in the transportation process. Therefore, the method of powder metallurgy greatly limits the preparation and production of light alloy matrix composites as structural materials.
The traditional mechanical stirring casting method lies in that reinforcements such as particles, whiskers and fibers are added into a molten metal melt, and the reinforcements are uniformly distributed in a matrix by the mechanical stirring method. The traditional mechanical stirring casting method has the advantages of being low in cost and simple in technological process, can realize large-scale production and large-volume production, and is widely applied in industries of aerospace, automobile manufacturing and the like. How to uniformly distribute the reinforcements in the metal melt is a key problem in the preparation of light alloy composites. However, most of the reinforcements tend to agglomerate or precipitate when entering the molten metal melt due to its high surface energy or interfacial tension, so that the reinforcements are difficult to uniformly disperse in the melt. In addition, during the stirring process, gas or oxide impurities can be mixed along with stirring, and the particles of the reinforcements can increase the melt viscosity and enable the gas to be difficult to escape, so that people have high requirements for mechanical stirring, and the reason lies in density differences between the reinforcements and metal melt, which can inevitably lead to specific gravity segregation. If the reinforcements have poor wettability to liquid metal, the reinforcements cannot be well dispersed in the matrix.
The squeeze casting method is an accurate casting method that enables liquid metal or semi-solid metal to be subjected to mold filling and solidifying through the action of high pressure. Firstly, the reinforcements are preformed, and then are heated, molten metal or metal melt is poured in the heated reinforcements, then pressing in of a mold is performed, and through cooling, a composite casting is obtained. The squeeze casting method can reduce influence of gas impurities on the quality of products, and has low requirements for wettability. High integrity and uniform castings can be obtained, the percentage by volume of the added reinforcements is also increased by 30%-50%, and the properties of the composite can also be notably improved. However, the problem that pressure affects the casting quality also exists. When the pressure is high, the molten melt can be turbulent, resulting in oxidation and gas retention. When the pressure is small, part of the gas cannot be removed, resulting in the phenomenon that the casting is low integrity. In addition, the squeeze casting method neither can be used for producing large-volume castings, nor can be used for batch automated production.
The injection molding method lies in that inert gas is used to atomize the molten metal for injection, the molten metal is mixed with a reinforcement conveyed by the inert gas at the other end, and the mixture is deposited and cooled on a platform to obtain a metallic composite product. And the injection molding method uses a metal rapid solidification technology to inhibit grain growth and segregation formation, which enables grain refinement and distribution of the reinforcements to be uniform. Atomized metal and mixed deposition are two major influencing factors of the injection molding method. The process of atomizing metal is accompanied with gas transmission, which enables the products often to have large porosity and shrinkage porosity. If the solidification is too fast after deposition, the composite effect of the reinforcements and the matrix is not good or even does not occur. If solidification is slow, the reinforcements can be unevenly distributed or even segregated. Moreover, as a novel metallic composite preparation method, the injection molding method has high cost, so that the injection molding method is not suitable for automated batch production.
The in-situ reaction composite method is a novel method for preparing the metal matrix composite. According to the method, the reinforcements do not need to be directly added, but chemical reactions or other special reactions are used to generate reinforcements in the melt. Nucleation and growth are both completed in the matrix, so that the phenomenon of incompatibility or poor combination with the matrix does not exist, influence of wetting conditions is avoided and the composite can be uniform and pure. The method has the advantages of being low in cost, simple in technological process, and quality of the obtained products is high. However, the in-situ reaction composite method has the limitation that only a small quantity of the reinforcements can be added, so that requirements of batch production are also not achieved.
For the selection of the reinforcements, attention needs to be paid to whether there is good wettability between the reinforcements and the matrix, whether the interface bonding strength is appropriate, and whether chemical reaction exists at the interface. At present, the reinforcements are roughly divided into three types: whiskers, fibers and particles, such as lanthanum oxide particles, cerium oxide particles, silicon carbide whiskers and carbon fibers, wherein whiskers and particle reinforced metallic composites have the advantages of being easy to process and stable in size. In general, the reinforcements are high in melting point and cannot melt when being added to the alloy melt, and besides, cannot react chemically with the matrix. If the reinforcements can uniformly exist in the matrix and segregation of interstitial impurities at grain boundaries can be reduced, the grain boundary strengthening can be improved. In addition, the reinforcements as second phase exert the action of pinning for dislocation and hinder the movement of the dislocation, so that the strength of the alloys could be improved, and the plasticity cannot be reduced too much. However, if the reinforcements are directly added into the matrix melt, the particles can agglomerate due to poor wettability and cannot be well dispersed in the matrix, so that the dispersion strengthening effect cannot be achieved.
The present invention aims to provide a preparation method of a lithium-containing magnesium/aluminum matrix composite. A precursor of reinforcements was prepared by adding reinforcements into the molten flux, and then the solidified precursor composed of reinforcements wrapped with flux could be added easily to the lithium-containing aluminum/magnesium alloy melt, which is due to the relative low interfacial tension and high wettability between the reinforcements and the flux, and between the flux and the metallic matrix melt, so that the problem of the difficulty of adding reinforcements to the alloys is solved. And the process is simplified, and besides, the quality of the lithium-containing aluminum/magnesium matrix composite is improved. This method can be used to fabricate large-volume composites and large-size components.
The method of the present invention is performed through the following steps:
(1) Preparing magnesium ingots or aluminum ingots as raw materials, preparing lithium metal, and preparing flux and reinforcements, wherein the flux contains components in percentage by mass of 65%-85% of lithium chloride, 15%-35% of lithium fluoride and less than or equal to 20% of lithium bromide, the reinforcements are elemental metal powder, rare earth oxide, carbide, boride or metal oxide, the elemental metal powder is W, Mo or Ni, the rare earth oxide is La2O3, CeO2 or Y2O3, the carbide is TiC or SiC, the boride is ZrB2, and the metal oxide is MgO or SiO2, the reinforcements are 0.1%-30% of total volume of the raw materials, the reinforcements are 1%-50% of total volume of the flux, and the lithium metal is 0.1%-10% of total mass of the raw materials;
(2) Putting the flux into a clay crucible or a graphite crucible, performing heating to 673-773K to make a flux melt, adding the reinforcements to the flux melt, and performing stirring to enable the reinforcements to uniformly disperse to make a liquid-solid mixture;
(3) Pouring the liquid-solid mixture into the clay crucible or the graphite crucible at normal temperature, and performing cooling to normal temperature to obtain a precursor;
(4) Preheating crucible to 473-523K, then placing the raw materials in the crucible, and enabling the raw materials to melted at 923-1023 K to form a raw material melt, wherein if the raw materials are the magnesium ingots, the crucible is an iron crucible, and if the raw materials are aluminum ingots, the crucible is a graphite crucible;
(5) Controlling a temperature of the raw material melt at 973-993K, putting the lithium metal wrapped with tin foil in the raw material melt, performing uniform stirring and mixing, adding a precursor, continuing to perform uniform stirring and mixing, raising temperature to 993-1013K, and performing standing to separate impurity components from composite components to form scumming and composite melt; and
(6) Scumming operation should be carried out on a surface of the composite melt, then reducing a temperature of the composite melt to 983±5K, and performing casting to prepare the lithium-containing magnesium/aluminum matrix composite.
The purity of the aluminum ingots is greater than or equal to 99.8%, purity of the magnesium ingots is greater than or equal to 99.85%, and purity of the lithium metal is greater than or equal to 99.8%.
The reinforcements are in the form of fibers, particles or whiskers, wherein a particle size of the particles is 300 nm to 20 μm; the whiskers have a diameter of 0.1-1 m and a length of 10-100 μm; and the fibers have a diameter of 5-20 μm and a continuous length of 10-70 mm.
In the step (5), the precursor is firstly crushed to a particle size of less than or equal to 5 cm and then put into the raw material melt.
In the step (2), a stirring speed is 100-200 r/min, and a time is 5-10 min.
In the step (5), a stirring speed is 100-300 r/min, and a time is 2-15 min.
In the step (2), when the reinforcements are added to the flux melt, all the reinforcements are added in 3-5 times, wherein addition quantity each time is 50% or below of a total mass of the reinforcements.
In the step (5), a standing time is 10-20 min.
In the step (5), before still standing, argon gas is used to degas the materials in the crucible, the argon gas pressure is 0.2-0.5 MPa, and a degassing time is 2-5 min.
In the step (1), magnesium ingots/aluminum ingots and other metal components are prepared as raw materials; when the step (4) is performed, the magnesium ingots/aluminum ingots and the other metal components are placed together in an iron crucible, melted, stirred and mixed uniformly to form a raw material melt; when the magnesium ingots and the other metal components are used as raw materials, the other metal components are one or more of aluminum metal, zinc ingots, manganese chloride, magnesium-rare earth alloys, magnesium-zirconium alloys and magnesium-silicon alloys, and the aluminum, zinc, manganese, rare earth, zirconium and silicon in other metal components account for less than or equal to 10% of total mass of the raw materials; and when aluminum ingots and other metal components are used as raw materials, the other metal components are one or more of magnesium metal, zinc ingots, aluminum-manganese alloys, aluminum-rare earth alloys, aluminum-copper alloys, aluminum-titanium alloys and aluminum-silicon alloys, and the magnesium, zinc, manganese, rare earth, copper, titanium and silicon in the other metal components account for less than or equal to 10% of total mass of the raw materials.
In the lithium-containing magnesium/aluminum matrix composite, the reinforcement component accounts for 0.1%-22% of total volume.
The preparation method of the present invention is characterized in that the reinforcements are put in the molten flux, and are uniformly dispersed in molten flux through mechanical stirring, and the wettability of the reinforcements is improved by utilizing the good wetting property of the reinforcements and the molten flux; the flux can effectively refine the melt, remove impurities and cover the melt to prevent magnesium from overburning; in addition, fluxes such as fluorine salt, chlorine salt and bromine salt can improve the wettability of the reinforcements, so that the reinforcements are easy to disperse uniformly in the matrix; because the density of the selected molten flux differs greatly from that of the melt, the reinforcements are separated from the molten flux after being added to the melt; the reinforcements after surface modification have good wettability with the melt and can be uniformly dispersed in the melt; and as a special alloy, lithium salt needs to be used as the flux. The method provided by the present invention is simple in process and low in cost, the strength of the light alloy composite can be greatly improved, and the method can be used for preparing large-volume light alloy composite structural parts, can be used for automated production, and has important significance for development of the aerospace industry.
The present invention will be described in details below with reference to embodiments.
In the embodiment of the present invention, thermocouples are adopted to detect the temperature, thus ensuring the temperature measurement accuracy.
Magnesium ingots, magnesium metal, aluminum ingots, aluminum metal and lithium metal adopted in the embodiment of the present invention are commercially available products.
The purities of lithium chloride, lithium bromide and lithium fluoride adopted in the embodiment of the present invention are commercially available analytical reagents.
The reinforcements adopted in the embodiment of the present invention are commercially available products.
The electron microscope used in the embodiment of the present invention is Shimadzu SSX550 from Japan.
The X-ray diffraction observation equipment adopted in the embodiment of the present invention is PANalytical X'Pert Pro from the Netherlands.
The metallographic microscope used in the embodiment of the present invention is Leica 1600X.
The magnesium-rare earth alloys, magnesium-zirconium alloys and magnesium-silicon alloys of the present invention are collectively referred to as magnesium master alloys, and the rare earth, zirconium and silicon in the magnesium master alloys respectively account for 10%-40% of the total mass of the magnesium master alloys.
The aluminum-manganese alloys, aluminum-rare earth alloys, aluminum-copper alloys, aluminum-titanium alloys and aluminum-silicon alloys of the present invention are collectively referred to as aluminum master alloys, and manganese, rare earth, copper, titanium and silicon in the aluminum master alloys respectively account for 10%-40% of the total mass of the aluminum master alloys.
According to the lithium-containing magnesium/aluminum matrix composite in the embodiment of the present invention, X-ray fluorescence spectrum analysis to calculate the percentage by mass of the reinforcements, and then the percentage by mass is converted into percentage by volume.
The purity of the aluminum ingots and the aluminum metal is greater than or equal to 99.8%, the purity of magnesium ingots and magnesium metal is greater than or equal to 99.85%, and the purity of lithium metal is greater than or equal to 99.8%.
In the embodiment, the reinforcements are in the form of fibers, particles or whiskers, wherein the particle size of the particles is 300 nm to 20 μm; the whisker has a diameter of 0.1-1 μm and a length of 10-100 μm; and the fibers have a diameter of 5-20 μm and a continuous length of 10-70 mm.
In the embodiment, before standing, argon gas is used to degas the materials in the crucible, the used argon gas pressure is 0.2-0.5 MPa, and the degassing time is 2-5 min.
Magnesium ingots and other metal components are prepared as raw materials, wherein the other metal components are aluminum metal and zinc ingots, the mass ratio of the aluminum metal to the zinc ingots is 1.5, and the aluminum metal and the zinc ingots account for 5% of the total mass of the raw materials; lithium metal is prepared; a flux and reinforcements are prepared; the flux contains 75% of lithium chloride, 15% of lithium fluoride and 10% of lithium bromide in percentage by mass; the reinforcements are La2O3 particles of rare earth oxide; the reinforcements are 0.5% of the total volume of the raw materials, the reinforcements are 2% of the total volume of the flux, and the lithium metal is 5% of the total mass of the raw materials;
The flux is put into a clay crucible, heating is performed to 673K to make a flux melt, the reinforcements are added to the flux melt, and stirring is performed to enable the reinforcements to uniformly disperse to make a liquid-solid mixture, wherein the stirring speed is 100 r/min, and the time is 10 min; when the reinforcements are added to the flux melt, and all the reinforcements are added in 3 times, wherein addition amount each time is 50% or below of the total mass of the reinforcements;
The liquid-solid mixture is poured into the clay crucible at normal temperature, and cooling is performed to normal temperature to obtain a precursor;
The crucible is preheated to 473K, then the raw materials are placed in a crucible, and the raw materials are melted at 923K to form a raw material melt, wherein the crucible is an iron crucible;
The temperature of the raw material melt is controlled to 973K; the lithium metal wrapped with tin foil is put in the raw material melt, uniform stirring and mixing are performed, the precursor is broken to the particle size less than or equal to 5 cm and then put in the raw material melt, uniform stirring and mixing are performed, then heating is performed to 993K, and standing is performed to separate impurity components from composite components to form scumming and composite melt, wherein the stirring speed is 100 r/min, the time is 15 min, and the standing time is 20 min;
Scumming on the surface of the composite melt is removed, then the temperature of the composite melt is reduced to 983±5K, and casting is performed to prepare the lithium-containing magnesium/aluminum matrix composite; the reinforcement component accounts for 0.39% of the total volume, lithium accounts for 4.47% of the total volume, and the rest is raw material components;
The percentage by volume of the reinforcements to the raw materials is adjusted, and parallel tests are performed according to the method, wherein the reinforcements respectively account for 1%, 3%, 5%, 7%, 9%, 15% and 20% of the total volume of the raw materials;
The product prepared according to the scheme that the reinforcements accounts for 0.5% of the total volume of the raw materials is taken as the composite #1, and the rest is the, composites #2, #3, #4, #5, #6, #7 and #8 in sequence. In the magnesium matrix composite containing lithium, the reinforcements are uniformly dispersed in the product, and the yield of the reinforcements is 70%-90%, wherein SEM images of the composites #1, #2 and #3 are shown in
Difference between the method and the embodiment 1 lies in that:
(1) Flux contains components in percentage by mass of 80% of lithium chloride, 17% of lithium fluoride and 3% of lithium bromide;
(2) The reinforcements are rare earth oxide and CeO2 particles;
(3) The reinforcements are 0.5% of the total volume of the raw materials, the reinforcements are 1% of the total volume of the flux, and the lithium metal is 4% of the total mass of the raw materials;
(4) The flux is put into a clay crucible, heating is performed to 773K to make a flux melt, the stirring speed is 200 r/min, the time is 5 min, the reinforcements are added to the flux melt, and all of the reinforcements are added in 4 times;
(5) The crucible is preheated to 523K, then the raw materials are placed in a crucible, and the raw materials are melted at 1023K to form a raw material melt;
(6) The temperature of the raw material melt is controlled to 983K, the temperature is raised to 1003K, standing is performed for 15 min, the stirring speed is 300 r/min, and the time is 2 min;
(7) For the lithium-containing magnesium matrix composite, reinforcement component accounts for 0.41% of the total volume, lithium accounts for 3.26% of the total volume, and the rest is raw material components.
The XRD image of the lithium-containing magnesium matrix composite is shown in
Difference between the method and the embodiment 1 lies in that:
(1) The magnesium ingots and other metal are prepared as raw materials, other metal components are manganous chloride and magnesium-rare earth alloys, manganous and rare earth in the other metal components are 3% of the total mass of the raw materials, the mass ratio of the rare earth to the manganous is 0.5, and the flux contains components in percentage by mass of 85% of lithium chloride and 15% of lithium fluoride;
(2) The reinforcements are elemental metal Mo;
(3) The reinforcements are 12% of the total volume of the raw materials, the reinforcements are 20% of the total volume of the flux, and the lithium metal is 1% of the total mass of the raw materials;
(4) The flux is put into a clay crucible, heating is performed to 723K to make a flux melt, the stirring speed is 150 r/min, the time is 8 min, the reinforcements are added to the flux melt, and all of the reinforcements are added in 5 times;
(5) The crucible is preheated to 493K, then the raw materials are placed in a crucible, and the raw materials are melted at 973K to form a raw material melt;
(6) The temperature of the raw material melt is controlled to 993K, the temperature is raised to 1013K, standing is performed for 10 min, the stirring speed is 200 r/min, and the time is 8 min; and
(7) For the lithium-containing magnesium matrix composite, reinforcement component accounts for 9.8% of the total volume, lithium accounts for 0.59% of the total volume, and the rest is raw material components.
Difference between the method and the embodiment 1 lies in that:
(1) Aluminum ingots and other metal components are prepared as raw materials, other metal components are magnesium metal, aluminum-copper alloys and aluminum-silicon alloys, magnesium, copper and silicon in the other metal components are 10% of total mass of the raw materials, the mass ratio of the magnesium to the copper to the silicon is 1 to 0.4 to 0.6, and the flux contains components in percentage by mass of 65% of lithium chloride and 35% of lithium fluoride;
(2) The reinforcements are borides ZrB2;
(3) The reinforcements are 23% of the total volume of the raw materials, the reinforcements are 40% of the total volume of the flux, and the lithium metal is 10% of the total mass of the raw materials;
(4) The flux is placed in the graphite crucible, and heating is performed to 683K to make the flux melt;
(5) The liquid-solid mixture is poured in the graphite crucible at normal temperature, and cooling is performed;
(6) The crucible is preheated to 483K, then the raw materials are placed in a crucible, and the raw materials are melted at 933K to form a raw material melt, wherein the crucible is a graphite crucible;
(7) The temperature of the raw material melt is controlled to 978K, the temperature is raised to 998K, standing is performed for 12 min, the stirring speed is 150 r/min, and the time is 12 min; and
(8) The lithium-containing aluminum matrix composite is made, wherein the reinforcement component accounts for 18.1% of the total volume, lithium accounts for 6.97% of the total volume, and the rest is raw material components.
Difference between the method and the embodiment 1 lies in that:
(1) Aluminum ingots and other metal components are prepared as raw materials, other metal components are aluminum-manganese alloys, aluminum-rare earth alloys and aluminum-titanium alloys, manganese, rare earth and titanium in the other metal components are 4% of total mass of the raw materials, the mass ratio of the manganese to the rare earth to the titanium is 1 to 0.2 to 0.4, and the flux contains components in percentage by mass of 67% of lithium chloride, 22% of lithium fluoride, and 11% of lithium bromide;
(2) The reinforcements are carbides SiC;
(3) The reinforcements are 30% of the total volume of the raw materials, the reinforcements are 50% of the total volume of the flux, and the lithium metal is 6% of the total mass of the raw materials;
(4) The flux is put into a graphite crucible, heating is performed to 703K to make a flux melt, the stirring speed is 200 r/min, the time is 5 min, the reinforcements are added to the flux melt, and all of the reinforcements are added in 4 times;
(5) The liquid-solid mixture is poured in the graphite crucible at normal temperature, and cooling is performed;
(6) The crucible is preheated to 503K, then the raw materials are placed in a crucible, and the raw materials are melted at 983K to form a raw material melt, wherein the crucible is a graphite crucible;
(7) The temperature of the raw material melt is controlled to 988K, the temperature is raised to 1008K, standing is performed for 14 min, the stirring speed is 250 r/min, and the time is 5 min; and
(8) The lithium-containing aluminum matrix composite is made, wherein the reinforcement component accounts for 22% of the total volume, lithium accounts for 4.33% of the total volume, and the rest is raw material components.
Difference between the method and the embodiment 1 lies in that:
(1) Aluminum ingots are prepared as raw materials, and flux contains components in percentage by mass of 76% of lithium chloride, 18% of lithium fluoride and 6% of lithium bromide;
(2) The reinforcements are metallic oxides MgO;
(3) The reinforcements are 8% of the total volume of the raw materials, the reinforcements are 16% of the total volume of the flux, and the lithium metal is 3% of the total mass of the raw materials;
(4) The flux is put into a graphite crucible, heating is performed to 753K to make a flux melt, the stirring speed is 150 r/min, the time is 6 min, the reinforcements are added to the flux melt, and all of the reinforcements are added in 5 times;
(5) The liquid-solid mixture is poured in the graphite crucible at normal temperature, and cooling is performed;
(6) The crucible is preheated to 513K, then the raw materials are placed in the crucible, and the raw materials are melted at 1003K to form a raw material melt, wherein the crucible is a graphite crucible;
(7) The temperature of the raw material melt is controlled to 993K, the temperature is raised to 1013K, standing is performed for 18 min, the stirring speed is 220 r/min, and the time is 6 min; and
(8) The lithium-containing aluminum matrix composite is made, wherein the reinforcement component accounts for 6.11% of the total volume, lithium accounts for 1.49% of the total volume, and the rest is raw material components.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201910807579.5 | Aug 2019 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2019/104189 | 9/3/2019 | WO | 00 |
