Pressure-induced ultrafine dendrite Al-Mg-Si-RE alloy and preparation method thereof

Abstract

This invention discloses a pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy. The alloy's chemical composition, by mass percentage, comprises: Mg 0.4-1.2%, Si 0.3-1.3%, Cu 0-0.4%, RE 0.1-0.6%, and Al 96.5-99.2%, with the total mass percentage of each chemical component being 100%. RE includes at least one of Sc, Yb, and Er. The matrix of the alloy is α-Al dendrites, with the primary dendrite arm spacing of 15-20 μm and the secondary dendrite arm spacing of 5-10 μm. This invention also discloses a method for preparing the above-mentioned pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy. By adding suitable rare earth elements to the Al-Mg-Si alloy and combining this with high-temperature and high-pressure treatment, an ultrafine dendritic structure can be obtained, thus improving strength.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, and in particular to a pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy and its preparation method. Background Technology

[0002] Aluminum alloys are indispensable lightweight structural materials in modern industry, with Al-Mg-Si alloys being widely used in transportation and construction due to their excellent comprehensive properties. These alloys are primarily strengthened through the precipitation of nanoscale Mg2Si phases (β'' phase) via aging. However, the coarse dendritic structure formed under traditional casting processes severely restricts further performance improvement. The coarse dendrite arms lead to severe compositional segregation, forming coarse and brittle phases between dendrites. These not only become stress concentration points, weakening the material's strength and toughness, but also deteriorate its formability, making subsequent hot working prone to defects, ultimately affecting the reliability and lifespan of the components. Furthermore, conventional refining methods have limited effectiveness. Summary of the Invention

[0003] Based on the technical problems existing in the background technology, the present invention proposes a pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy and its preparation method. The present invention adds suitable rare earth elements to the Al-Mg-Si alloy and combines it with high temperature and high pressure treatment, which can increase the number of α-Al dendrites and refine the dendrites, so that the spacing between the primary dendrite arms and the spacing between the secondary dendrite arms can be reduced to the micrometer or even submicrometer level, thereby obtaining an ultrafine dendritic structure and significantly improving the strength of the alloy.

[0004] This invention proposes a pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy, wherein the chemical composition of the alloy, by mass percentage, comprises: Mg 0.4-1.2%, Si 0.3-1.3%, Cu 0-0.4%, RE 0.1-0.6%, and Al 96.5-99.2%, with the total mass percentage of each chemical component being 100%. RE includes at least one of Sc, Yb, and Er; the matrix of the alloy structure is α-Al dendrites, the primary dendrite arm spacing of the α-Al dendrites is 15-20 μm, and the secondary dendrite arm spacing of the α-Al dendrites is 5-10 μm.

[0005] The above-mentioned primary dendrite arm spacing is the average primary dendrite arm spacing; the secondary dendrite arm spacing is the average secondary dendrite arm spacing.

[0006] Preferably, the chemical composition of the alloy, by mass percentage, includes: Mg 1.0%, Si 0.6%, Cu 0.28%, RE 0.1-0.5%, with the balance being Al; more preferably, when RE is Sc, its mass percentage is 0.1-0.3%; when RE is Yb, its mass percentage is 0.2-0.4%; and when RE is Er, its mass percentage is 0.1-0.5%.

[0007] Preferably, the chemical composition of the alloy, by mass percentage, includes: Mg 1.2%, Si 1.0%, Cu 0.2%, RE 0.1-0.3%, with the balance being Al; more preferably, when RE is Sc, its mass percentage is 0.1-0.3%; when RE is Yb, its mass percentage is 0.2-0.4%; and when RE is Er, its mass percentage is 0.1-0.5%.

[0008] Preferably, in the alloy microstructure, RE forms an Al3RE nanophase, which acts as a nucleation site to promote the formation of α-Al dendrites.

[0009] Preferably, the pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy has a room temperature compressive strength ≥600MPa and a Vickers hardness ≥95.

[0010] The Vickers hardness mentioned above is the micro Vickers hardness under a test force of 0.2 kg.

[0011] The present invention also proposes a method for preparing the above-mentioned pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy, comprising the following steps: subjecting the billet to high temperature and high pressure treatment to obtain the pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy; The high-temperature and high-pressure treatment involves a pressure of 1-2 GPa, a temperature of 800-1000℃, and a time of 3-4 hours. The chemical composition of the billet is the same as that of the pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy mentioned above.

[0012] The pressure can be 1, 1.5 or 2 GPa, and the temperature can be 800, 900 or 1000℃.

[0013] Preferably, the blanks are assembled into components and then subjected to high temperature and high pressure treatment.

[0014] Preferably, the assembly includes: a blank with an external insulating layer, a graphite tube, a graphite sheet, and a conductive sealing sheet. The blank with the external insulating layer is placed inside the graphite tube, the graphite sheet seals both ends of the graphite tube, and the conductive sealing sheet is placed outside the graphite sheet and seals both ends of the graphite tube.

[0015] The blanks, graphite tubes, graphite sheets, and conductive sealing sheets in the above-mentioned assembly are all dried at 240°C and kept dry at 100°C for later use.

[0016] Graphite sheets and conductive sealing sheets serve to provide heating during high-temperature and high-pressure heat treatment.

[0017] The above-mentioned assembly was placed in an octahedral pyrophyllite block and transferred to a high-pressure pressurization device for high-temperature and high-pressure treatment; the above-mentioned octahedral pyrophyllite block is a pressure transmission carrier commonly used in high-temperature and high-pressure treatment.

[0018] After high-temperature and high-pressure treatment, heating is stopped and pressure is released, and the mixture is cooled to room temperature in a high-pressure pressurization device.

[0019] Preferably, raw materials of various chemical components are taken, smelted and cast in a protective gas atmosphere to obtain billets.

[0020] Preferably, the protective gas is at least one of argon and sulfur hexafluoride.

[0021] Preferably, the melting temperature is 740-760℃.

[0022] Preferably, the casting temperature is 715-725℃.

[0023] Preferably, the raw materials for each chemical component are Al ingots, Mg ingots, Al-Si master alloys, Al-Cu master alloys, and Al-RE master alloys.

[0024] The purity of the above-mentioned pure Al ingots and pure Mg ingots is above 99.9%; the Si content of the above-mentioned Al-Si master alloy can be 20wt%; the Cu content of the above-mentioned Al-Cu master alloy can be 50wt%; the RE content of the above-mentioned Al-RE master alloy can be 2-10wt%, such as Al-2wt%Sc master alloy, Al-10wt%Yb, etc.

[0025] The above casting can directly produce a blank of the target size; or it can cast a part and then cut it into blanks of the target size; the blanks can be ground and then further processed.

[0026] Beneficial effects: This invention, based on Al-Mg-Si alloys, adds suitable rare earth elements and combines them with high-temperature and high-pressure treatment. On the one hand, the rare earth elements form nanophases during high-pressure solidification, and these nanophases can serve as highly effective heterogeneous nucleation substrates for α-Al dendrites during high-pressure solidification, greatly increasing the number of nuclei and refining the dendrites. On the other hand, high pressure alters the thermodynamic and kinetic conditions of the alloy melt, such as increasing melt undercooling and suppressing atomic diffusion, thereby significantly increasing the nucleation rate and limiting grain growth, achieving ultra-fine dendrite structures. The spacing between the primary and secondary dendrite arms of α-Al dendrites can be reduced to the micrometer or even submicrometer level, obtaining ultra-fine or even nanoscale dendrite structures.

[0027] The alloy strengthening mechanism of this invention includes grain refinement strengthening, solid solution strengthening, precipitation strengthening, and dispersion strengthening. Under the combined effect of these strengthening mechanisms, the strength of the alloy is greatly improved.

[0028] This invention selects appropriate alloying elements to improve the density of the as-cast structure, thereby reducing or eliminating traditional homogenization and hot deformation (such as forging and rolling) processes to break up coarse as-cast structures, shortening the production process, and reducing energy consumption and costs.

[0029] The high-temperature and high-pressure processing technology of the present invention can be well integrated with existing casting equipment, is easy to upgrade and implement on the basis of existing industrial equipment, has good process reproducibility, and is conducive to large-scale production. Attached Figure Description

[0030] Figure 1 The as-cast microstructure (OM) diagram of the alloy prepared for Comparative Example 1.

[0031] Figure 2 SEM images of the alloys prepared in Comparative Examples 2-3 are shown, where a represents Comparative Example 2 and b represents Comparative Example 3.

[0032] Figure 3 SEM images of pressure-induced ultrafine dendritic Al-Mg-Si-RE alloys prepared in Examples 1-2, where a represents Example 1 and b represents Example 2.

[0033] Figure 4 The image shows the SEM image of the alloy prepared in Comparative Example 4.

[0034] Figure 5 The room temperature compression curves are for the alloys obtained in Examples 1-2 and Comparative Examples 1-4. Detailed Implementation

[0035] The technical solution of the present invention will now be described in detail through specific embodiments.

[0036] The chemical composition formulations and high-temperature and high-pressure processing parameters of the billets obtained in Examples 1-5 and Comparative Examples 1-4 are shown in Table 1.

[0037] Table 1 Chemical composition formula (by mass percentage) and high-temperature and high-pressure treatment process parameters

[0038] The preparation methods of Examples 1-5 and Comparative Examples 1-4 above include the following steps: After holding the crucible at 450℃ for 30 minutes, pure Al ingots (Al content 99.99wt%), Al-Si master alloy (Si content 20wt%), Al-Cu master alloy (Cu content 50wt%), and Al-RE master alloy were added under an Ar protective atmosphere. The crucible was heated to 750℃ until the raw materials were completely melted. During this process, a graphite stirring rod was used for mechanical stirring to promote the melting of the raw materials and ensure uniform composition. When the melt temperature was maintained at 740℃, pure Mg ingots (Mg content 99.99wt%) were pressed in under an Ar protective atmosphere until they were completely melted. When the melt temperature was maintained at 740℃ again and no bubbles were observed, slag removal was performed. When the melt temperature was cooled to 720℃, it was poured. During pouring, a certain flow of Ar gas was maintained for protection. After pouring, the Ar gas was turned off, and the mixture solidified to obtain the casting. The casting was wire-cut into blanks with dimensions of Φ5×6.8 mm, and the surface was polished for later use. The blank is coated with an insulating layer and then embedded in a graphite tube. Graphite sheets are used to seal both ends of the graphite tube, and then conductive sealing sheets are used to seal both ends of the graphite tube to obtain an assembly. The assembly is placed in an octahedral pyrophyllite block and then transferred to a high-pressure pressurization device. The pressure is increased at a constant rate to a predetermined pressure. While maintaining the predetermined pressure, the sample is heated to a predetermined temperature to melt it and held at that temperature for a predetermined time. Then, the heating is stopped and the pressure is released. The sample is cooled to room temperature in the high-pressure pressurization device to obtain an Al-Mg-Si-RE alloy.

[0039] Detection Alloys from Example 1 and Comparative Examples 1-3 were tested, and the results are as follows: Figure 1-3 As shown.

[0040] Figure 1 The as-cast microstructure (OM) diagram of the alloy prepared for Comparative Example 1.

[0041] Figure 2 SEM images of the alloys prepared in Comparative Examples 2-3 are shown, where a represents Comparative Example 2 and b represents Comparative Example 3.

[0042] Figure 3 SEM images of pressure-induced ultrafine dendritic Al-Mg-Si-RE alloys prepared in Examples 1-2, where a represents Example 1 and b represents Example 2.

[0043] Figure 4 The image shows the SEM image of the alloy prepared in Comparative Example 4.

[0044] Depend on Figure 1 It can be seen that the gray matrix is ​​an α-Al matrix, and the Mg2Si phase is black and exists in the dendrites in a skeletal or blocky form.

[0045] Depend on Figure 1-2 It can be seen that, compared with the matrix alloy (i.e., Comparative Example 1), the addition of rare earth elements refines the grains, but the refining effect is not significant. Rare earth elements mainly react with aluminum to form high-melting-point intermetallic compounds (such as Al3Sc and Al3Yb) that match the α-Al lattice. These intermetallic compounds can serve as effective nucleation cores for α-Al grains, promoting the formation of equiaxed crystals and thus refining the grains. However, in 6XXX series aluminum alloys containing Si, Mg, and Cu, rare earth elements readily combine with Si and Cu in the matrix to form complex multi-component compounds. This consumes effective rare earth elements, making it difficult to form sufficient amounts of key nucleation cores, resulting in limited grain refining effect.

[0046] Depend on Figure 1-4 It can be seen that compared with the matrix alloy (i.e., Comparative Example 1) and Comparative Examples 2-4, the alloys of Examples 1-2 all obtained significantly refined dendrites; compared with the matrix alloy (i.e., Comparative Example 1), the dendrites of Comparative Examples 2 and 3 were somewhat refined; however, compared with Examples 1-2, the dendrites of Comparative Examples 2 and 3 were relatively coarse, and the alloy of Comparative Example 4 was completely dissolved and no dendrites were formed. This is because: on the one hand, the addition of rare earth elements causes them to form nanophases during high-pressure solidification. These phases can all serve as strong and effective heterogeneous nucleus substrates for α-Al crystals during high-pressure solidification, greatly increasing the number of crystal nuclei during solidification and thus refining the dendrites; on the other hand, high pressure changes the thermodynamic and kinetic conditions of the alloy melt, such as increasing the melt undercooling and suppressing atomic diffusion, thereby significantly increasing the nucleation rate and limiting grain growth, achieving ultra-refined dendritic structures; the spacing between the primary and secondary dendrite arms of α-Al dendrites can be reduced to the micrometer or even submicrometer level, obtaining ultra-fine or even nano-sized dendritic structures.

[0047] The average primary dendrite arm spacing and average secondary dendrite arm spacing of the alloys obtained in Examples 1-2 and Comparative Examples 2-4 are shown in Table 2.

[0048] Table 2. Detection results of alloy microstructure in Examples 1-2 and Comparative Examples 2-4

[0049] As shown in Table 2, the average secondary dendrite arm spacing of Example 1 was reduced by 70.2% compared to Comparative Example 2; the average secondary dendrite arm spacing of Example 2 was reduced by 50.4% compared to Comparative Example 3; and Comparative Example 4, without the addition of rare earth elements, only underwent high-temperature and high-pressure treatment, and did not form a dendritic structure, but was completely dissolved. This indicates that selecting an appropriate amount of rare earth elements and combining it with suitable high-temperature and high-pressure treatment can increase the volume fraction of α-Al dendrites, refine the particle size of α-Al dendrites, and refine the primary and secondary dendrite arm spacings to obtain ultrafine spacing.

[0050] The room temperature compressive strength of alloys from Examples 1-2 and Comparative Examples 1-4 was tested, and the results are as follows: Figure 5 As shown.

[0051] Figure 5 The room temperature compression curves are for the alloys obtained in Examples 1-2 and Comparative Examples 1-4.

[0052] Alloys from Examples 1-5 and Comparative Examples 1-4 were tested for their microVickers hardness under a test force of 0.2 kg. The results are shown in Table 3.

[0053] Table 3 Performance Test Results

[0054] From Table 3 and Figure 5 It can be seen that the pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy of the present invention has excellent room temperature compressive strength and hardness, which are much higher than those of comparative examples 1-3, and are also improved compared with comparative example 4.

[0055] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A pressure-induced ultrafine dendrite Al-Mg-Si-RE alloy, characterized in that, The chemical composition of the alloy comprises, in percentage by mass: Mg 0.4-1.2%, Si 0.3-1.3%, Cu 0-0.4%, RE 0.1-0.6%, Al 96.5-99.2%, and the sum of the percentages by mass of the chemical components is 100%. The RE comprises at least one of Sc, Yb and Er; the matrix of the alloy structure is α-Al dendrite, the primary dendrite arm spacing of the α-Al dendrite is 15-20 μm, and the secondary dendrite arm spacing of the α-Al dendrite is 5-10 μm.

2. The pressure-induced ultrafine dendrite Al-Mg-Si-RE alloy according to claim 1, wherein, In the alloy structure, the RE forms Al3RE nanophase, and the Al3RE nanophase promotes the formation of α-Al dendrite as a nucleation point.

3. The pressure-induced ultrafine dendrite Al-Mg-Si-RE alloy according to claim 1 or 2, characterized in that, The room temperature compression strength of the pressure-induced ultrafine dendrite Al-Mg-Si-RE alloy is ≥600 MPa, and the Vickers hardness is ≥95.

4. A method for producing the pressure-induced ultrafine dendrite Al-Mg-Si-RE alloy according to any one of claims 1 to 3, characterized by, The method comprises the following steps: high-temperature and high-pressure treatment of the blank to obtain the pressure-induced ultrafine dendrite Al-Mg-Si-RE alloy. The pressure of the high-temperature and high-pressure treatment is 1-2 GPa, the temperature is 800-1000 ℃, and the time is 3-4 h. The chemical composition of the blank is the same as that of the pressure-induced ultrafine dendrite Al-Mg-Si-RE alloy according to any one of claims 1-3.

5. The method for preparing the pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy according to claim 4, characterized in that, The blank is assembled into an assembly before the high-temperature and high-pressure treatment.

6. The method of claim 5, wherein the assembly is assembled by using a plurality of bolts. The method comprises the following steps: The blank with an outer cladding insulation layer, a graphite tube, a graphite sheet and a conductive sealing sheet, the blank with an outer cladding insulation layer is placed in the graphite tube, the graphite sheet seals the two ends of the graphite tube, and the conductive sealing sheet is placed outside the graphite sheet and seals the two ends of the graphite tube.

7. The method of producing a pressure-induced ultrafine dendrite Al-Mg-Si-RE alloy according to any one of claims 4 to 6, characterized in that, The raw materials of the chemical components are melted and cast in a protective gas atmosphere to obtain the blank.

8. The method for preparing the pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy according to claim 7, characterized in that, The protective gas is at least one of argon and sulfur hexafluoride.

9. The method for preparing the pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy according to claim 7 or 8, characterized in that, The melting temperature is 740-760 ℃; preferably, the casting temperature is 715-725 ℃.

10. The method for preparing the pressure-induced ultrafine dendritic Al-Mg-Si-RE alloy according to claim 7 or 8, characterized in that, The raw materials of the chemical components are Al ingot, Mg ingot, Al-Si intermediate alloy, Al-Cu intermediate alloy and Al-RE intermediate alloy.

Images