Rare earth aluminum alloy and preparation method thereof

Abstract

The invention provides a rare earth aluminum alloy and a preparation method thereof, and relates to the technical field of metal materials, and the preparation method comprises the following steps: step 1) carrying out smelting treatment on alloy raw materials, and obtaining an alloy melt after melting; wherein the alloy raw materials comprise rare earth elements; (2) the alloy melt is stirred at the set temperature, and semi-solid alloy slurry is obtained; and (3) the semi-solid alloy slurry is subjected to aftertreatment, and the rare earth aluminum alloy is obtained. Through stirring treatment, on one hand, thick and large columnar crystals in alloy melt can be crushed to form fine crystal grains; and on the other hand, heterogeneous nucleation can be promoted, the structure is further refined, components of the alloy are evenly distributed, and therefore the mechanical property of the alloy is promoted to be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials, and particularly relates to a rare earth aluminum alloy and a preparation method thereof. Background Art

[0002] Compared with Fe and Cu, Al has a higher specific strength and specific stiffness. For devices of the same size, the weight of aluminum parts is only one-third of that of iron and copper parts. In addition, aluminum alloys have good corrosion resistance and low processing costs, making aluminum alloys ideal materials for industries such as aerospace, automotive, shipbuilding, and electronic information. However, for as-cast Al-7% Si alloy, without modification treatment, the microstructure consists of coarse dendritic α-Al phase, and lamellar or needle-like eutectic silicon phase and needle-like Fe-rich intermetallic compounds distributed along its grain boundaries, which will have an adverse effect on the mechanical properties of Al-Si alloys.

[0003] Although the existing as-cast Al-7% Si aluminum alloy has a better microstructure morphology after heat treatment and tempering treatment, and also has a certain improvement in mechanical properties, the tensile strength is still difficult to reach above 280 MPa, which cannot meet the service condition requirements of high performance and long life. Research shows that rare earth elements have a good strengthening effect on aluminum alloys. Rare earth can not only purify the melt and refine the molten liquid, but also alloy with aluminum alloys, reducing the α-Al grain size and secondary dendrite arm spacing. This effect of refining grains and improving the morphology of eutectic silicon can improve the strength and toughness of materials.

[0004] However, in the prior art, in order to achieve the effect of microstructure modification, the addition amount of rare earth is usually 0.8 - 1.2%, resulting in the formation of inclusions due to the reaction of rare earth with oxygen and hydrogen. These inclusions are prone to thermal cracking during the casting process, and the interaction between various rare earth elements is relatively complex, which is prone to element segregation during solidification, forming coarse structures, thereby resulting in poor mechanical properties of the obtained rare earth aluminum alloy. Summary of the Invention

[0005] Therefore, the present invention provides a rare earth aluminum alloy and a preparation method thereof, which can solve the problem of poor mechanical properties caused by coarse microstructure of rare earth aluminum alloy in the prior art.

[0006] In order to solve the above problems, the present invention provides a preparation method of a rare earth aluminum alloy, comprising the following steps:

[0007] Step 1) Melting treatment is carried out on alloy raw materials to obtain an alloy melt; wherein, the alloy raw materials include rare earth elements;

[0008] Step 2) Stirring treatment is carried out on the alloy melt at a set temperature to obtain a semi-solid alloy slurry; the semi-solid alloy slurry contains primary α-Al;

[0009] Step 3) Post-treat the semi-solid alloy slurry to obtain the rare earth aluminum alloy.

[0010] Furthermore, by mass percentage, the alloy raw materials include: Si 6.0 - 8.0 wt%, Ti 0.1 - 0.3 wt%, Fe ≤ 0.15 wt%, Mg 0.3 - 0.5 wt%, Er 0.1 - 0.7 wt%, Sc 0.1 - 0.7 wt%, Er + Sc 0.4 - 0.8 wt%, and the balance is Al and inevitable impurity elements.

[0011] Furthermore, in the said Step 1), the steps of the melting treatment include:

[0012] Melting the Al raw material and the Al-Si alloy to obtain a first melt; when the first melt reaches a first temperature, adding the Al-Mg alloy, the Al-Sc alloy, and the Al-Er alloy, and melting to obtain a second melt; when the second melt reaches a second temperature, adding the Ti raw material and the Fe raw material, and melting to obtain an alloy melt;

[0013] Preferably, the Al raw material is industrial pure Al;

[0014] Preferably, the first temperature is 750 - 770 °C; the second temperature is 790 - 810 °C.

[0015] Furthermore, in the said Step 2), before the step of stirring treatment, it also includes: slag removal treatment of the alloy;

[0016] Preferably, the steps of the slag removal treatment include: introducing argon into the alloy melt while stirring;

[0017] More preferably, the pressure of the argon is 0.35 - 0.5 MPa.

[0018] Furthermore, in the said Step 2), the set temperature is 15 - 25 °C higher than the liquidus temperature of the rare earth aluminum alloy;

[0019] Preferably, the set temperature is 630 - 640 °C.

[0020] Furthermore, in the said Step 2), the time of the stirring treatment is 3 - 5 min; and / or

[0021] The stirring treatment is carried out in a manner of alternately stirring clockwise and counterclockwise; wherein, within each minute, the clockwise stirring is 60 - 80 times, and the counterclockwise stirring is 60 - 80 times.

[0022] Further, in the step 2), the volume fraction of the solid phase in the semi-solid alloy slurry is 20-30%; and / or

[0023] the volume fraction of primary α-Al in the semi-solid alloy slurry is 20-30%; and / or

[0024] the grain size of the primary α-Al is 50-100 μm.

[0025] Further, in the step 3), the post-treatment steps include:

[0026] casting the semi-solid alloy slurry to obtain as-cast aluminum alloy; then heat-treating the as-cast aluminum alloy to obtain the rare earth aluminum alloy;

[0027] Preferably, the heat treatment includes solution treatment and aging treatment; wherein, the temperature of the solution treatment is 530-550 °C, and the time of the solution treatment is 4-8 hours; the temperature of the aging treatment is 140-200 °C, and the time of the aging treatment is 3-5 hours;

[0028] Preferably, before the step of casting treatment, it further includes: keeping the semi-solid alloy slurry warm and static for 1-3 min.

[0029] On the other hand, the present invention provides a rare earth aluminum alloy, and the microstructure of the rare earth aluminum alloy includes an α-Al matrix, an Al3(Sc,Er) phase, an AlFeSi phase, and an α-Al-Si eutectic;

[0030] wherein, the volume fraction of the α-Al-Si eutectic is less than 7%; the α-Al-Si eutectic is spherical or near-spherical, and its diameter is 4-5 μm;

[0031] the Al3(Sc,Er) phase and the AlFeSi phase are uniformly distributed in the α-Al matrix; the Al3(Sc,Er) phase and the AlFeSi phase are fibrous or short rod-shaped, and their length is 2-5 μm.

[0032] Further, the room temperature yield strength of the rare earth aluminum alloy > 200 MPa, the room temperature tensile strength > 300 MPa, and the elongation > 3%;

[0033] Preferably, the rare earth aluminum alloy is obtained by using the preparation method described in any one of the above.

[0034] A rare earth aluminum alloy and a preparation method thereof provided by the present invention have the following beneficial effects:

[0035] 1. On the one hand, the present invention provides a method for preparing a rare earth aluminum alloy, comprising the following steps: melting alloy raw materials to obtain an alloy melt; wherein the alloy raw materials include rare earth elements; stirring the alloy melt at a set temperature to obtain a semi-solid alloy slurry; and performing post-treatment on the semi-solid alloy slurry to obtain a rare earth aluminum alloy. It should be noted that based on the above method, on the one hand, stirring can break the coarse columnar crystals in the liquid phase (alloy melt) to form fine grains; on the other hand, it can promote the strengthening of heterogeneous nucleation by rare earth precipitation phases, further refine the structure, and make the composition distribution of the alloy uniform, thereby promoting the improvement of the mechanical properties of the alloy; and then through post-treatment, fine rare earth precipitation phases such as Al3(Sc,Er) and AlFeSi are dispersed in the matrix structure, further improving the mechanical properties of the alloy.

[0036] 2. Further, by introducing argon gas into the alloy melt for stirring, the present invention can remove hydrogen and inclusions in the alloy melt, thereby avoiding the formation of crack sources by inclusions during stretching, and further strengthening the mechanical properties of the alloy.

[0037] 3. On the other hand, the present invention provides a rare earth aluminum alloy obtained by the above preparation method. The microstructure of the rare earth aluminum alloy includes an α-Al matrix, Al3(Sc,Er) phase, AlFeSi phase, and α-Al-Si eutectic; wherein the volume fraction of the α-Al-Si eutectic is less than 7%; the α-Al-Si eutectic is spherical or near-spherical with a diameter of 4-5 μm; the Al3(Sc,Er) phase and AlFeSi phase are uniformly distributed in the α-Al matrix; the Al3(Sc,Er) phase and AlFeSi phase are fibrous or short rod-shaped with a length of 2-5 μm. Based on the above method, the structure of the alloy is effectively refined, and the mechanical properties of the alloy are improved. The room temperature yield strength of the rare earth aluminum alloy is >200 MPa, the room temperature tensile strength is >300 MPa, and the elongation is >3%. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. The drawings in the following description are only exemplary. For those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained based on the provided drawings.

[0039] Figure 1 It is a microscopic characterization diagram of the rare earth alloy in Example 1 of the present invention; wherein, Figure 1 a is a microscopic structure diagram; Figure 1 b is Figure 1 the EDS energy spectrum diagram of the precipitation phase in a;

[0040] Figure 2 It is the microstructural characterization diagram of the rare earth aluminum alloy in Comparative Example 1 of the present invention; among them, Figure 2 The microstructural diagram of a; Figure 2 b is Figure 2 The EDS energy spectrum diagram of the precipitated phase in a;

[0041] Figure 3 It is the microstructural characterization diagram of the rare earth aluminum alloy in Comparative Example 2 of the present invention; among them Figure 3 a is the microstructural diagram; Figure 3 b is Figure 3 The EDS energy spectrum diagram of the precipitated phase in a;

[0042] Figure 4 It is the microstructural diagram of the rare earth aluminum alloy in Comparative Example 3 of the present invention;

[0043] Figure 5 It is the microstructural diagram of the rare earth aluminum alloy in Comparative Example 4 of the present invention. Detailed implementation manners

[0044] In order to more clearly illustrate the implementation manners of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the implementation manners or the prior art. The drawings in the following description are only exemplary. For those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained by extending the provided drawings.

[0045] The present invention provides a preparation method for a rare earth aluminum alloy, comprising the following steps:

[0046] Step 1) Melting treatment is performed on the alloy raw materials to obtain an alloy melt after melting; among them, the alloy raw materials include rare earth elements;

[0047] This step is specifically as follows: Industrial pure Al (99.99%) and Al-Si alloy are preheated to remove surface moisture; among them, the preheating temperature is 120-150°C; then melting is performed to obtain a first melt; when the first melt reaches 750-770°C (the first temperature), Al-Mg alloy, Al-Sc alloy, and Al-Er alloy are added, and after melting, a second melt is obtained; when the second melt reaches 790-810°C (the second temperature), Ti raw material and Fe raw material are added, and after melting, an alloy melt is obtained, and it is kept warm at the second temperature for 25-35 min (preferably 30 min);

[0048] Among them, in terms of mass percentage, the alloy raw materials include: Si 6.0-8.0 wt%, Ti 0.1-0.3 wt%, Fe ≤ 0.15 wt%, Mg 0.3-0.5 wt%, Er 0.1-0.7 wt%, Sc 0.1-0.7 wt%, Er+Sc 0.4-0.8 wt%, and the balance is Al and inevitable impurity elements.

[0049] Step 2) Stir the alloy melt at a set temperature to obtain a semi-solid alloy slurry;

[0050] Specifically, this step is as follows: Argon is introduced into the alloy melt obtained in step 1) for stirring to remove slag from the alloy melt; among them, the pressure of argon is 0.35-0.5 MPa; then the slag-removed alloy melt is cooled to 630-640 °C (15-25 °C above the liquidus temperature of the rare earth aluminum alloy, preferably 20 °C above the liquidus temperature) and kept warm, while stirring is carried out to obtain a semi-solid alloy slurry; among them, the stirring treatment is carried out in an alternating manner of clockwise stirring and counterclockwise stirring; within each minute, the clockwise stirring is 60-80 times, and the counterclockwise stirring is 60-80 times; the time of the stirring treatment is 3-5 min.

[0051] Step 3) Perform post-treatment on the semi-solid alloy slurry to obtain a rare earth aluminum alloy.

[0052] Specifically, this step is as follows: The semi-solid alloy slurry obtained in step 2) is kept warm and static for 1-3 min. After the floating slag floats up, the oxidized slag is removed with a slag removal shovel, and then it is poured into a metal mold for casting treatment to obtain a cast aluminum alloy; then the cast aluminum alloy is successively subjected to solution treatment and aging treatment (heat treatment) to obtain a rare earth aluminum alloy;

[0053] Among them, the temperature of the solution treatment is 530-550 °C, and the time of the solution treatment is 4-8 hours; the temperature of the aging treatment is 140-200 °C, and the time of the aging treatment is 3-5 hours. During the static process, oxides, gas inclusions or molten slag with smaller densities will naturally float to the surface of the melt due to density differences, thereby reducing defects in the subsequent forming process and improving the purity of the alloy. After stirring, there may be local composition or temperature fluctuations in the semi-solid slurry. A short static treatment can make the liquid phase distribution more uniform, relieve the turbulence caused by stirring, and avoid the segregation of solid-phase particles. At the semi-solid temperature, the primary α-Al phase is adjusted through the Ostwald ripening mechanism. A short static time balances the contradiction between spheroidization and grain growth and is not sufficient to cause grain coarsening.

[0054] Based on the above method, at 15 - 25 °C above the liquidus temperature, coarse columnar crystals begin to appear in the liquid phase of the alloy melt. Through stirring treatment, the dendritic structure is broken and spheroidized to form fine, near-spherical primary α-Al, which can promote the heterogeneous nucleation effect of rare earth precipitation phases, further refine the microstructure, and make the composition distribution of the alloy uniform, thus promoting the improvement of the mechanical properties of the alloy. At the same time, a solid-phase structure with a volume fraction of 20 - 30% is formed in the liquid phase (i.e., the volume fraction of the solid phase in the semi-solid alloy slurry is 20 - 30%), that is, a granular slurry-like morphology appears in the aluminum alloy melt, and the stirring is stopped. Among them, the volume fraction of primary α-Al in the semi-solid alloy slurry is 20 - 30%; the grain size of primary α-Al is 50 - 100 μm; the spherical structure significantly improves the fluidity and anti-segregation performance of the melt. When casting, the near-spherical α-Al structure avoids the shrinkage porosity and hot cracking tendency between dendrites in traditional casting during the casting process, improving the compactness of the casting; the remaining liquid phase forms a uniformly distributed Al-Si eutectic during cooling, enhancing the matrix bonding force; during the heat treatment process, the near-spherical α-Al structure can obtain fine grains and a uniform microstructure, promoting the fine and dispersed precipitation of rare earth phases, making the material have both high strength and good elongation.

[0055] If the temperature is higher than 25 °C above the liquidus, the solid-phase volume fraction is 5 - 10%, and there are coarse columnar crystals in the alloy microstructure; if the temperature is lower than 15 °C above the liquidus, the solid-phase volume fraction is 30% - 50%, the grains in the microstructure are finer, but shrinkage cavities and porosity are likely to appear in the alloy, which is not conducive to casting; and the stirring treatment efficiency is low.

[0056] During the stirring treatment, if unidirectional stirring (i.e., only clockwise or counterclockwise) is used, a stable laminar shear field will be formed in the melt, resulting in a single flow direction of the melt. This steady flow easily causes inclusions or primary phase particles to migrate along a fixed path, forming local enrichment or directional arrangement. The spiral solute channels formed by it will cause macroscopic segregation and reduce the mechanical properties. Alternating-direction stirring (clockwise / counterclockwise alternation) can increase the probability of dendrite arm fracture by different-direction shear forces through periodic reversal of the shear direction. Each direction switch promotes solute redistribution, which plays an effective role in suppressing segregation and grain growth.

[0057] When the stirring frequency is lower than 60 times per minute, the direction switching interval exceeds the relaxation time of the melt, resulting in incomplete reconstruction of the shear field, which is not conducive to suppressing the increase in the size of α-Al. When it exceeds 80 times per minute, excessive turbulence will be triggered, increasing the amount of miscellaneous gas adsorbed from the air in the melt, causing too many pores in the alloy, and increasing the risk of rupture of the surface oxide film of the alloy, causing more interface oxidation and resulting in waste of materials.

[0058] On the other hand, the present invention provides a rare earth aluminum alloy. The microstructure of the rare earth aluminum alloy includes an α-Al matrix, an Al3(Sc,Er) phase, an AlFeSi phase, and an α-Al-Si eutectic (Al-Si eutectic);

[0059] Among them, the volume fraction of the α-Al-Si eutectic is less than 7%; the α-Al-Si eutectic is spherical or near-spherical, and its diameter is 4-5 μm;

[0060] The Al3(Sc,Er) phase and the AlFeSi phase are uniformly distributed in the α-Al matrix; the Al3(Sc,Er) phase and the AlFeSi phase are fibrous or short rod-shaped, and their length is 2-5 μm.

[0061] Furthermore, the room temperature yield strength of the rare earth aluminum alloy > 200 MPa, the room temperature tensile strength > 300 MPa, and the elongation > 3%; preferably, the rare earth aluminum alloy is obtained by the preparation method of any one of the above.

[0062] The following further illustrates the present invention in conjunction with specific embodiments.

[0063] Example 1

[0064] This example provides a preparation method of a rare earth aluminum alloy, including the following steps:

[0065] Step 1) Preheat industrial pure Al (99.99%) and the Al-Si alloy and then carry out melting to obtain a first melt; when the first melt reaches 760 °C, add the Al-Mg alloy, the Al-Sc alloy, and the Al-Er alloy, and after melting, obtain a second melt; when the second melt reaches 790 °C, add the Ti raw material and the Fe raw material, and after melting, obtain an alloy melt, and keep it warm at 800 °C for 30 min; among them, in terms of mass percentage, the alloy raw materials include: Si 7.0 wt%, Ti 0.1 wt%, Fe ≤ 0.15 wt%, Mg 0.3 wt%, Er 0.2 wt%, Sc 0.4 wt%, Er + Sc 0.6 wt%, and the balance is Al and unavoidable impurity elements;

[0066] Step 2) Pass argon into the alloy melt obtained in Step 1 for stirring, and then cool the alloy melt after slag removal to 635 °C and keep it warm, while carrying out stirring treatment to obtain a semi-solid alloy slurry; among them, the stirring treatment is carried out in an alternating manner of clockwise stirring and counterclockwise stirring; among them, the pressure of argon is 0.4 MPa; within each minute, clockwise stirring is carried out 80 times and counterclockwise stirring is carried out 80 times; the time of the stirring treatment is 3 min;

[0067] Step 3) Keep the semi-solid alloy slurry obtained in Step 2 at a constant temperature for 1 min, remove the oxidation slag with a slag removal shovel, and then pour it into a metal mold for casting to obtain as-cast aluminum alloy; then perform solution treatment and aging treatment (heat treatment) on the as-cast aluminum alloy in sequence to obtain rare earth aluminum alloy; among them, the temperature of the solution treatment is 540 °C and the time of the solution treatment is 6 hours; the temperature of the aging treatment is 160 °C and the time of the aging treatment is 4 hours.

[0068] The microstructure of the rare earth aluminum alloy obtained in this example includes α-Al matrix, Al3(Sc,Er) phase, AlFeSi phase and α-Al-Si eutectic. Among them, Al3(Sc,Er) phase and AlFeSi phase are uniformly distributed in the α-Al matrix. As Figure 1 shown in Figs. 1a and 1b, the Al3(Sc,Er) phase (bright white in the figure, Sc- and Er-rich phase) is fibrous or short rod-shaped with a length of 2-5 μm; the α-Al-Si eutectic (grayish white in the figure, Al-Si) is spherical with a diameter of 4-5 μm. Among them, the spherical Al-Si eutectic phase can significantly reduce the stress concentration phenomenon at the interface, thereby reducing the risk of crack initiation, helping to coordinate the plastic deformation ability of different regions of the alloy, and at the same time

[0069] pinning the grain boundaries and strengthening the mechanical properties of the alloy, so its mechanical properties are better. As shown in Table 1, the tensile strength of the rare earth aluminum alloy obtained in this example at room temperature is 311 MPa, the yield strength at room temperature is 271.5 MPa, and the elongation is 3.75%.

[0070] Table 1 Performance test results of rare earth aluminum alloys in the examples and comparative examples of the present invention

[0071]

[0072] Example 2

[0073] This example provides a preparation method of a rare earth aluminum alloy, including the following steps:

[0074] Step 1) Preheat industrial pure Al (99.99%) and Al-Si alloy and then melt them to obtain a first melt; when the first melt reaches 770 °C, add Al-Mg alloy, Al-Sc alloy and Al-Er alloy, and melt them to obtain a second melt; when the second melt reaches 810 °C, add Ti raw material and Fe raw material, melt them to obtain an alloy melt, and keep it at 810 °C for 25 min; among them, by mass percentage, the alloy raw materials include: Si 6.0 - wt%, Ti 0.3 wt%, Fe ≤ 0.15 wt%, Mg 0.5 wt%, Er 0.1 t%, Sc 0.3 wt%, Er + Sc 0.4 wt%, and the balance is Al and inevitable impurity elements;

[0075] Step 2) Argon gas is introduced into the alloy melt obtained in Step 1) for stirring, and then the alloy melt after slag removal is cooled to 640 °C and kept warm while stirring is carried out to obtain semi-solid alloy slurry; wherein, the stirring is carried out in an alternating manner of clockwise stirring and counterclockwise stirring; wherein, the pressure of argon gas is 0.35 MPa; the speed of clockwise stirring is 70 revolutions per minute; the speed of counterclockwise stirring is 70 revolutions per minute; the time of stirring is 4 min;

[0076] Step 3) The semi-solid alloy slurry obtained in Step 2) is kept warm and static for 2 min. After the floating slag floats up, the oxidized slag is removed with a slag removal shovel, and then it is poured into a metal mold for casting treatment to obtain as-cast aluminum alloy; then the as-cast aluminum alloy is subjected to solution treatment and aging treatment (heat treatment) in sequence to obtain rare earth aluminum alloy; wherein, the temperature of solution treatment is 550 °C and the time of solution treatment is 4 hours; the temperature of aging treatment is 200 °C and the time of aging treatment is 3 hours.

[0077] The microstructure of the rare earth aluminum alloy obtained in this example includes α-Al matrix, Al3(Sc,Er) phase, AlFeSi phase and α-Al-Si eutectic. Among them, the Al3(Sc,Er) phase and AlFeSi phase are uniformly distributed in the α-Al matrix. The Al3(Sc,Er) phase is fibrous or short rod-shaped with a length of 3-5 μm; the α-Al-Si eutectic is spherical with a diameter of 4-6 μm. The tensile strength of the rare earth aluminum alloy obtained in this example at room temperature is 322 MPa, the yield strength at room temperature is 272 MPa, and the elongation is 6%.

[0078] Example 3

[0079] This example provides a preparation method of rare earth aluminum alloy, including the following steps:

[0080] Step 1) Industrial pure Al (99.99%) and Al-Si alloy are preheated and then melted to obtain the first melt; when the first melt reaches 750 °C, Al-Mg alloy, Al-Sc alloy and Al-Er alloy are added, and after melting, the second melt is obtained; when the second melt reaches 790 °C, Ti raw material and Fe raw material are added, and after melting, an alloy melt is obtained and kept warm at 790 °C for 35 min; wherein, by mass percentage, the alloy raw materials include: Si 8.0 wt%, Ti 0.2 wt%, Fe ≤ 0.15 wt%, Mg 0.4 wt%, Er 0.4 wt%, Sc 0.4 wt%, Er+Sc 0.8 wt%, and the balance is Al and unavoidable impurity elements;

[0081] Step 2) Argon gas is introduced into the alloy melt obtained in Step 1) for stirring, and then the alloy melt after slag removal is cooled to 630 °C and kept warm while stirring is carried out to obtain semi-solid alloy slurry; among them, the stirring treatment is carried out in an alternating manner of clockwise stirring and counterclockwise stirring; among them, the pressure of argon gas is 0.5 MPa; within each minute, clockwise stirring is carried out 60 times and counterclockwise stirring is carried out 60 times; the time of the stirring treatment is 5 min;

[0082] Step 3) The semi-solid alloy slurry obtained in Step 2) is kept warm and static for 3 min. After the floating slag floats up, the oxidized slag is removed with a slag removal shovel, and then it is poured into a metal mold for casting treatment to obtain as-cast aluminum alloy; then the as-cast aluminum alloy is subjected to solution treatment and aging treatment (heat treatment) in sequence to obtain rare earth aluminum alloy; among them, the temperature of the solution treatment is 530 °C and the time of the solution treatment is 8 hours; the temperature of the aging treatment is 140 °C and the time of the aging treatment is 5 hours.

[0083] The microstructure of the rare earth aluminum alloy obtained in this example includes α-Al matrix, Al3(Sc,Er) phase, AlFeSi phase and α-Al-Si eutectic. Among them, the Al3(Sc,Er) phase and AlFeSi phase are uniformly distributed in the α-Al matrix. The Al3(Sc,Er) phase is fibrous or short rod-shaped with a length of 3-6 μm; the α-Al-Si eutectic is spherical with a diameter of 3-6 μm. The tensile strength of the rare earth aluminum alloy obtained in this example at room temperature is 299 MPa, the yield strength at room temperature is 260 MPa, and the elongation is 5%.

[0084] Comparative Example 1

[0085] This comparative example provides a preparation method of rare earth aluminum alloy, including the following steps:

[0086] Step 1) Industrial pure Al (99.99%) and Al-Si alloy are preheated and then melted to obtain the first melt; when the first melt reaches 760 °C, Al-Mg alloy, Al-Sc alloy and Al-Er alloy are added, and after melting, the second melt is obtained; when the second melt reaches 790 °C, Ti raw material and Fe raw material are added, and after melting, an alloy melt is obtained and kept warm at 800 °C for 30 min; among them, by mass percentage, the alloy raw materials include: Si 7.0 wt%, Ti 0.1 wt%, Fe ≤ 0.15 wt%, Mg 0.3 wt%, Sc 0.4 wt%, and the balance is Al and inevitable impurity elements;

[0087] Step 2) Introduce argon gas into the alloy melt obtained in Step 1) and stir. Then cool the alloy melt after slag removal to 635 °C and hold the temperature while performing a stirring treatment to obtain a semi-solid alloy slurry. Among them, the stirring treatment is carried out in an alternating manner of clockwise stirring and counterclockwise stirring. Among them, the pressure of the argon gas is 0.4 MPa. Within each minute, the clockwise stirring is 80 times and the counterclockwise stirring is 80 times. The time of the stirring treatment is 3 min.

[0088] Step 3) Keep the semi-solid alloy slurry obtained in Step 2) warm and static for 1 min. After the floating slag floats up, remove the oxidized slag with a slag removal shovel, and then pour it into a metal mold for casting treatment to obtain an as-cast aluminum alloy. Then perform a solution treatment and an aging treatment (heat treatment) on the as-cast aluminum alloy in sequence to obtain a rare earth aluminum alloy. Among them, the temperature of the solution treatment is 540 °C and the time of the solution treatment is 6 hours. The temperature of the aging treatment is 160 °C and the time of the aging treatment is 4 hours.

[0089] The microstructure of the rare earth aluminum alloy obtained in this comparative example includes an α-Al matrix, an Al3Sc phase, and an α-Al-Si eutectic. Among them, the Al3Sc phase is distributed in the form of strip blocks near the α-Al-Si eutectic (Al-Si eutectic) phase, as Figure 2 shown in a and 2b. The length of the Al3Sc phase (the Sc-rich phase in the figure) is 5 - 10 μm and the width is 3 - 5 μm. The α-Al-Si eutectic (the Al-Si phase in the figure) is in the form of strip blocks and its length is 5 - 10 μm. Sc forms Al3Sc nanoparticles, which significantly refine the α-Al grains, but its effect is mainly concentrated in the primary aluminum phase. The modification of the eutectic silicon depends on other mechanisms. When Sc is added alone, Sc atoms may segregate at the grain boundaries or within the Al phase during solidification, rather than being uniformly distributed in the eutectic region. This makes the Al3Sc phase unable to effectively inhibit the coarsening of the eutectic silicon. Especially under slow cooling conditions, the strip-shaped Si phase is more likely to form. As shown in Table 1, the tensile strength of the rare earth aluminum alloy obtained in this comparative example at room temperature is 219.5 MPa, the yield strength at room temperature is 171.5 MPa, and the elongation is 8.5%.

[0090] Comparative Example 2

[0091] This comparative example provides a preparation method of a rare earth aluminum alloy, including the following steps:

[0092] Step 1) Preheat industrial pure Al (99.99%) and Al-Si alloy and then carry out melting to obtain the first melt. After the first melt reaches 760 °C, add Al-Mg alloy, Al-Sc alloy and Al-Er alloy, and after melting, obtain the second melt. After the second melt reaches 790 °C, add Ti raw material and Fe raw material, and after melting, obtain an alloy melt, and keep it at 800 °C for 30 min. Among them, by mass percentage, the alloy raw materials include: Si 7.0 wt%, Ti 0.1 wt%, Fe ≤ 0.15 wt%, Mg 0.3 wt%, Er 0.3 wt%, and the balance is Al and inevitable impurity elements;

[0093] Step 2) Pass argon into the alloy melt obtained in Step 1) for stirring, and then cool the alloy melt after slag removal to 635 °C and keep it warm while carrying out stirring treatment to obtain semi-solid alloy slurry. Among them, the stirring treatment is carried out in an alternating manner of clockwise stirring and counterclockwise stirring. Among them, the pressure of argon is 0.4 MPa. Within each minute, clockwise stirring is carried out 80 times and counterclockwise stirring is carried out 80 times. The time of the stirring treatment is 3 min;

[0094] Step 3) Keep the semi-solid alloy slurry obtained in Step 2) warm and static for 1 min. After the floating slag floats up, remove the oxidized slag with a slag removal shovel, and then pour it into a metal mold for casting treatment to obtain as-cast aluminum alloy. Then, carry out solution treatment and aging treatment (heat treatment) on the as-cast aluminum alloy in sequence to obtain rare earth aluminum alloy. Among them, the temperature of the solution treatment is 540 °C and the time of the solution treatment is 6 hours. The temperature of the aging treatment is 160 °C and the time of the aging treatment is 4 hours.

[0095] The microstructure of the rare earth aluminum alloy obtained in this comparative example includes an α-Al matrix, Al3Er phase and α-Al-Si eutectic. Among them, the Al3Er phase is distributed in the form of strip blocks near the α-Al-Si eutectic (Al-Si eutectic) phase, as Figure 3As shown in Figures 3a and 3b, the length of the Al3Er phase (the Sc-rich phase in the figure) is 20 μm, and the width is 3 - 5 μm; the α-Al-Si eutectic (the Al-Si phase in the figure) is strip-shaped, with a length of 5 - 10 μm. Er mainly forms Al3Er nanoparticles in the aluminum alloy, and these particles can serve as heterogeneous nucleation cores for α-Al, refining the primary α-Al grains. However, the modification effect of Er on the eutectic Si phase is weak, and it is difficult for Er to effectively inhibit the lamellar growth mode of the silicon phase. The atomic size of Er results in insufficient affinity with silicon and cannot significantly change the interfacial properties of the silicon phase. Therefore, when Er is added alone, the eutectic silicon still grows rapidly along the <111> crystal direction, retaining a strip-shaped or needle-like morphology. The Al3Er phase may be unevenly distributed, making it difficult to effectively pin the grain boundaries or hinder the coarsening of the eutectic phase. In addition, Er easily combines with impurity elements (such as Fe) at high temperatures to form coarse intermetallic compounds, which instead reduces the modification effect and results in larger sizes, thus leading to poor alloy performance. As shown in Table 1, the tensile strength of the rare earth aluminum alloy obtained in this comparative example at room temperature is 214 MPa, the yield strength at room temperature is 173.5 MPa, and the elongation is 4.25%.

[0096] Comparative Example 3

[0097] This comparative example provides a preparation method for a rare earth aluminum alloy, including the following steps:

[0098] Step 1) Preheat industrial pure Al (99.99%) and the Al-Si alloy and then carry out melting to obtain a first melt; when the first melt reaches 760 °C, add the Al-Mg alloy, Al-Sc alloy, and Al-Er alloy, and melt to obtain a second melt; when the second melt reaches 790 °C, add the Ti raw material and the Fe raw material, melt to obtain an alloy melt, and hold at 800 °C for 30 min; among them, by mass percentage, the alloy raw materials include: Si 7.0 wt%, Ti 0.1 wt%, Fe ≤ 0.15 wt%, Mg 0.3 wt%, Er 0.2 wt%, Sc 0.4 wt%, Er + Sc 0.6 wt%, and the balance is Al and inevitable impurity elements;

[0099] Step 2) Pass argon gas into the alloy melt obtained in Step 1 and stir.

[0100] Step 3) Let the alloy melt in Step 2 stand for 1 min. After the dross floats up, remove the oxidation dross with a slag removal shovel, and then pour it into a metal mold for casting treatment to obtain as-cast aluminum alloy; then perform solution treatment and aging treatment (heat treatment) on the as-cast aluminum alloy in sequence to obtain a rare earth aluminum alloy; among them, the solution treatment temperature is 540 °C, and the solution treatment time is 6 hours; the aging treatment temperature is 160 °C, and the aging treatment time is 4 hours.

[0101] The microstructure of the rare earth aluminum alloy obtained in this comparative example includes an α-Al matrix, Al3(Sc,Er) phase, and α-Al-Si eutectic. As Figure 4 shown, fewer Al3(Sc,Er) phases precipitate, and the α-Al-Si eutectic precipitates along the grain boundaries, with uneven distribution. Moreover, the eutectic phase is granular, with a size of 5 - 10 μm. Since stirring treatment was not carried out at 15 - 25 °C above the liquidus temperature of the alloy in this comparative example, alloy element segregation (α-Al-Si eutectic precipitating along the grain boundaries) occurred, resulting in poor alloy performance. As shown in Table 1, the tensile strength of the rare earth aluminum alloy obtained in this comparative example at room temperature is 245 MPa, the yield strength at room temperature is 185 MPa, and the elongation is 5.5%.

[0102] Comparative Example 4

[0103] This comparative example provides a preparation method for a rare earth aluminum alloy, including the following steps:

[0104] Step 1) Preheat industrial pure Al (99.99%) and Al-Si alloy and then carry out melting to obtain a first melt; when the first melt reaches 760 °C, add Al-Mg alloy, Al-Sc alloy, and Al-Er alloy, and after melting, obtain a second melt; when the second melt reaches 790 °C, add Ti raw material and Fe raw material, and after melting, obtain an alloy melt, and hold at 800 °C for 30 min; wherein, by mass percentage, the alloy raw materials include: Si 7.0 wt%, Ti 0.1 wt%, Fe ≤ 0.15 wt%, Mg 0.3 wt%, Er 0.2 wt%, Sc 0.4 wt%, Er + Sc 0.6 wt%, and the balance is Al and unavoidable impurity elements;

[0105] Step 2) Pass argon into the alloy melt obtained in Step 1) for stirring, then cool the alloy melt after slag removal to 700 °C and hold, while carrying out stirring treatment to obtain a semi-solid alloy slurry; wherein, the stirring treatment is carried out in an alternating manner of clockwise stirring and counterclockwise stirring; wherein, the pressure of argon is 0.4 MPa; within each minute, clockwise stirring is carried out 80 times and counterclockwise stirring is carried out 80 times; the time of the stirring treatment is 3 min;

[0106] Step 3) Hold the semi-solid alloy slurry obtained in Step 2) for static settlement for 1 min. After the floating slag floats up, use a slag removal shovel to remove the oxidized slag, and then pour it into a metal mold for casting treatment to obtain a cast aluminum alloy; then carry out solution treatment and aging treatment (heat treatment) on the cast aluminum alloy in sequence to obtain a rare earth aluminum alloy; wherein, the temperature of the solution treatment is 540 °C and the time of the solution treatment is 6 hours; the temperature of the aging treatment is 160 °C and the time of the aging treatment is 4 hours.

[0107] The microstructure of the rare earth aluminum alloy obtained in this comparative example includes an α-Al matrix, an Al3(Sc,Er) phase, and an α-Al-Si eutectic. As Figure 5 shown, the size of the Al3(Sc,Er) phase is relatively large, 10 - 20 μm, and the α-Al-Si eutectic phase is granular, but there are already signs of coarsening, with a size of 10 μm. Since the stirring treatment in this comparative example was carried out at 85 °C above the liquidus temperature of the alloy, the eutectic phase in the alloy grew rapidly at high temperature, resulting in a relatively large size, and further leading to poor properties of the alloy. As shown in Table 1, the tensile strength of the rare earth aluminum alloy obtained in this comparative example at room temperature is 221 MPa, the yield strength at room temperature is 174 MPa, and the elongation is 6.5%.

[0108] It is easy for those skilled in the art to understand that, on the premise of no conflict, the advantageous technical features of the above various methods can be freely combined and superimposed.

[0109] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention. The above is only the preferred implementation manner of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and variations can still be made, and these improvements and variations should also be regarded as within the protection scope of the present invention.

Claims

1. A method for preparing a rare earth aluminum alloy, characterized in that: The following steps are involved: Step 1) smelting the alloy raw material to obtain an alloy melt; wherein the alloy raw material includes rare earth elements; Step 2) stirring the alloy melt at a set temperature to obtain a semi-solid alloy slurry; the semi-solid alloy slurry contains primary α-Al; Step 3) post-treating the semi-solid alloy slurry to obtain the rare earth aluminum alloy.

2. The method for preparing the rare earth aluminum alloy according to claim 1, characterized in that: Measured in percentage by mass, the alloy raw materials include: Si 6.0-8.0wt%, Ti 0.1-0.3wt%, Fe≤0.15wt%, Mg 0.3-0.5wt%, Er 0.1-0.7wt%, Sc 0.1-0.7wt%, Er+Sc 0.4-0.8wt%, and the remainder is Al and unavoidable impurity elements.

3. The method for preparing the rare earth aluminum alloy according to claim 1, characterized in that: In step 1), the smelting process comprises: An Al raw material and an Al-Si alloy are melted to obtain a first melt; when the first melt reaches a first temperature, an Al-Mg alloy, an Al-Sc alloy and an Al-Er alloy are added to obtain a second melt; when the second melt reaches a second temperature, a Ti raw material and a Fe raw material are added to obtain an alloy melt; Preferably, the Al raw material is industrial pure Al; before smelting the Al raw material and the Al-Si alloy, the process further comprises: preheating the Al raw material and the Al-Si alloy; wherein the preheating temperature is 120-150° C.; Preferably, the first temperature is 750-770°C; the second temperature is 790-810°C.

4. The method for preparing the rare earth aluminum alloy according to claim 1, characterized in that: In the step 2), before the stirring step, the process further includes: performing slag removal on the alloy; Preferably, the slag removal step comprises: introducing argon gas into the alloy melt while stirring; Further preferably, the pressure of the argon gas is 0.35-0.5 MPa.

5. The method for preparing the rare earth aluminum alloy according to claim 1, characterized in that: In the step 2), the set temperature is 15-25° C. higher than the liquidus temperature of the rare earth aluminum alloy; Preferably, the set temperature is 630-640°C.

6. The method for preparing the rare earth aluminum alloy according to claim 1, characterized in that: In step 2), the stirring time is 3-5 min; and / or The stirring treatment adopts a method of alternately stirring clockwise and counterclockwise; wherein, the clockwise stirring is performed 60-80 times and the counterclockwise stirring is performed 60-80 times per minute.

7. The method for preparing a rare earth aluminum alloy according to any one of claims 1 to 5, characterized in that: In the step 2), the volume fraction of the solid phase in the semi-solid alloy slurry is 20-30%; and / or The volume fraction of primary α-Al in the semi-solid alloy slurry is 20-30%; and / or The grain size of the primary α-Al is 50-100 μm.

8. The method for preparing the rare earth aluminum alloy according to claim 1, characterized in that: In step 3), the post-processing step includes: Casting the semi-solid alloy slurry to obtain a cast aluminum alloy; then heat treating the cast aluminum alloy to obtain the rare earth aluminum alloy; Preferably, the heat treatment includes solution treatment and aging treatment; wherein the temperature of the solution treatment is 530-550°C, and the time of the solution treatment is 4-8 hours; the temperature of the aging treatment is 140-200°C, and the time of the aging treatment is 3-5 hours; Preferably, before the step of casting, the method further comprises: keeping the semi-solid alloy slurry warm and standing for 1-3 minutes.

9. A rare earth aluminum alloy, characterized in that: The microstructure of the rare earth aluminum alloy includes an α-Al matrix, an Al3(Sc, Er) phase, an AlFeSi phase and an α-Al-Si eutectic; Wherein, the volume fraction of the α-Al-Si eutectic is less than 7%; the α-Al-Si eutectic is spherical or nearly spherical, and its diameter is 4-5 μm; The Al3(Sc, Er) phase and the AlFeSi phase are uniformly distributed in the α-Al matrix; the Al3(Sc, Er) phase and the AlFeSi phase are in the form of fibers or short rods, and the length thereof is 2-5 μm.

10. The rare earth aluminum alloy according to claim 8 or 9, characterized in that: The room temperature yield strength of the rare earth aluminum alloy is greater than 200 MPa, the room temperature tensile strength is greater than 300 MPa, and the elongation is greater than 3%; Preferably, the rare earth aluminum alloy is obtained by the preparation method described in any one of claims 1-8.

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