Al-Cu-Mg alloy with fatigue crack propagation resistance and high surface smoothness as well as preparation method and application of Al-Cu-Mg alloy

Abstract

The invention provides an Al-Cu-Mg alloy with fatigue crack propagation resistance and high surface smoothness as well as a preparation method and application of the Al-Cu-Mg alloy, and belongs to the technical field of non-ferrous metal manufacturing. The Al-Cu-Mg alloy resistant to fatigue crack propagation and high in surface smoothness, provided by the invention, comprises the following chemical components in percentage by mass: 5.0 to 8.0 percent of Cu, 1.2 to 3.0 percent of Mg, 0.5 to 1.0 percent of Mn, 0.08 to 0.2 percent of Zr, 0.2 to 2.0 percent of Sc + RE and the balance of Al. The fatigue expansion rate of the Al-Cu-Mg alloy provided by the invention is 6.34 * 10 <-5 >-6.12 * 10 <-4 > mm / cycle, the microhardness value of the Al-Cu-Mg alloy is 135-142 HV, and the Al-Cu-Mg alloy has excellent mechanical properties and fatigue resistance, and meanwhile, the surface roughness of the Al-Cu-Mg alloy is relatively small, and the surface quality is good.

Description

Technical Field

[0001] The present invention relates to the technical field of non-ferrous metal manufacturing, and particularly relates to an Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish, and a preparation method and application thereof. Background Art

[0002] Al-Cu-Mg series alloys are often used as materials for aircraft skins and bulkheads due to their high strength, good toughness, and excellent fatigue resistance. However, with the rapid development of the aviation field, the requirements for aircraft are getting higher and higher, and their service environment is more severe. In addition to the basic high strength requirements, there are higher requirements for fatigue damage resistance and fracture toughness. However, Al-Cu-Mg alloys prepared by traditional processes such as casting and powder metallurgy have traditional defects such as low strength and toughness, uneven microstructure, and difficult structure regulation, making it difficult to meet the service requirements under harsh working conditions such as high-temperature ablation and explosion shock, which restricts the further development and application of this alloy.

[0003] At present, the key performance index for Al-Cu-Mg series alloy plates is the fatigue crack propagation rate, and the uneven grain size and stress concentration caused by different types of second-phase particles are the two main reasons for the fatigue crack propagation of Al-Cu-Mg alloy plates. First, coarse grains are prone to generate short fatigue cracks at grain boundaries during deformation at low strain rates, and the cracks are prone to propagate during deformation. Second, the "genetic effect" of as-cast microstructure defects leads to stress concentration or defects, and uneven deformation and uneven heating during deformation and heat treatment will also cause stress concentration to result in defects. The defects of stress concentration caused by grain size and second-phase particles in Al-Cu-Mg alloys restrict the development of Al-Cu-Mg alloy plates. As a material for aircraft skins, it cannot meet the performance requirements of aircraft service.

[0004] In addition, aluminum alloys have high requirements for surface quality. Alloys with poor surface quality are prone to defects such as scratches, corrosion, and incorrect coloring. During the hot deformation process, various microstructural properties of aluminum alloys such as texture, grain size, and grain distribution change, and these microstructures will show "inheritance", which has a significant impact on the surface quality of the alloy.

[0005] Therefore, how to improve the fatigue resistance of Al-Cu-Mg alloys and take into account the control of their surface quality has become an urgent technical problem in this field. Summary of the Invention

[0006] The object of the present invention is to provide an Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish, a preparation method and an application thereof. The Al-Cu-Mg alloy provided by the present invention has excellent mechanical properties and fatigue resistance. At the same time, the Al-Cu-Mg alloy has high surface finish, small surface roughness and good surface quality.

[0007] In order to achieve the above object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides an Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish, which comprises the following chemical components by mass percentage: Cu: 5.0-8.0%, Mg: 1.2-3.0%, Mn: 0.5-1.0%, Zr: 0.08-0.2%, Sc+RE: 0.2-2.0% and the balance Al.

[0009] Preferably, the mass ratio of Cu to Mg is 3.5-6.5.

[0010] Preferably, the RE is one or more of Y, Ce and La.

[0011] The present invention provides a preparation method of the Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish as described in the above technical solution, which comprises the following steps:

[0012] (1) Preparing an aluminum alloy ingot by a spray deposition process;

[0013] (2) Sequentially performing hot extrusion and hot rolling on the aluminum alloy ingot obtained in the step (1) to obtain a hot-rolled aluminum alloy;

[0014] (3) Sequentially performing pre-annealing and cold rolling on the hot-rolled aluminum alloy obtained in the step (2) to obtain a cold-rolled aluminum alloy;

[0015] (4) Sequentially performing recrystallization annealing, solution treatment, quenching treatment and aging treatment on the cold-rolled aluminum alloy obtained in the step (3) to obtain an Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish.

[0016] Preferably, the parameters of the spray deposition process in the step (1) include: using two-stage atomization, the atomizing gas is nitrogen; the main gas path pressure is 0.5-0.75 MPa; the atomizing temperature is 780-830 °C; the atomizing distance is 400-500 mm; the rotation frequency of the deposition disk is 5-6 Hz.

[0017] Preferably, the temperature of the hot extrusion in the step (2) is 420-450 °C, the speed of the hot extrusion is 3.5-4.0 mm / s, and the extrusion ratio of the hot extrusion is (10-20):1.

[0018] Preferably, in the step (2), the starting rolling temperature of hot rolling is 450-490 °C, the reduction rate per pass of hot rolling is 12-30%, the total deformation rate of hot rolling > 70%, the finishing rolling temperature of hot rolling > 400 °C, and the hot rolling method is longitudinal rolling.

[0019] Preferably, in the step (3), the total deformation rate of cold rolling is 40-60%, and the reduction rate per pass of cold rolling is 10-25%.

[0020] Preferably, in the step (4), the temperature of recrystallization annealing is 360-400 °C, and the holding time of recrystallization annealing is 1-2 h.

[0021] The present invention provides the application of the Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish described in the above technical solution or the Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish prepared by the preparation method described in the above technical solution in the skins for aerospace and military applications and the materials for interior decoration of transportation vehicles.

[0022] The present invention provides an Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish, which, by mass percentage, comprises the following chemical components: Cu: 5.0-8.0%, Mg: 1.2-3.0%, Mn: 0.5-1.0%, Zr: 0.08-0.2%, Sc+RE: 0.2-2.0% and the balance Al. By adding a relatively large amount of Cu element in the present invention, the number of precipitation phases inside the aluminum alloy is greatly increased, and it is more difficult for dislocations to cut through or bypass the fine-sized precipitation phases, thereby improving the strength of the aluminum alloy; at the same time, the contents of Cu and Mg are higher than those of conventional Al-Cu-Mg alloys. The high Cu and high Mg contents are beneficial to the formation of "atomic clusters". The Cu-Mg clusters are completely coherent with the matrix and have a positive effect on the alloy. On the one hand, the formation of a large number of Cu-Mg solute "atomic clusters" in the Al-Cu-Mg alloy has a significant effect of pinning dislocations; on the other hand, the solute "atomic clusters" are in a "metastable state" thermodynamically, and the binding between atoms within the clusters is not strong enough. When interacting with dislocations, energy can be dissipated through atomic rearrangement, separation and re-dissolution, etc. The clusters can be repeatedly cut by dislocations, which is more conducive to the slip of dislocations and is not easy to cause stress / strain concentration, making the alloy have better fatigue resistance; by adding Sc and RE, the effect of refining grains can be achieved, so that the average grain size of the Al-Cu-Mg alloy is mainly concentrated within 10 μm, thereby further improving the fatigue resistance of the alloy. The results of the examples show that the fatigue crack propagation rate of the Al-Cu-Mg alloy provided by the present invention is 6.34×10 -5 ~6.12×10 -4mm / cycle, the microhardness value of the Al-Cu-Mg alloy is 135 - 142 HV, with excellent mechanical properties and fatigue resistance. At the same time, the small (less than 10 μm) and uniform grains and texture regulation result in a high surface finish of the Al-Cu-Mg alloy, a small surface roughness, and good surface quality. Description of the Drawings

[0023] Figure 1 DSC curve of the aluminum alloy ingot obtained in step (1) of Example 1;

[0024] Figure 2 Grain size map of the hot-rolled aluminum alloy obtained in step (2) of Example 1;

[0025] Figure 3 Orientation distribution function ODF map of the hot-rolled aluminum alloy obtained in step (2) of Example 1;

[0026] Figure 4 Grain size map of the cold-rolled aluminum alloy obtained in step (3) of Example 1;

[0027] Figure 5 Orientation distribution function ODF map of the cold-rolled aluminum alloy obtained in step (3) of Example 1;

[0028] Figure 6 Geometrically necessary dislocation density map of the cold-rolled aluminum alloy obtained in step (3) of Example 1;

[0029] Figure 7 Grain size map of the Al-Cu-Mg alloy obtained in Examples 1 - 4;

[0030] Figure 8 Orientation distribution function ODF map of the Al-Cu-Mg alloy obtained in Example 1;

[0031] Figure 9 Orientation distribution function ODF map of the Al-Cu-Mg alloy obtained in Example 2;

[0032] Figure 10 Orientation distribution function ODF map of the Al-Cu-Mg alloy obtained in Example 3;

[0033] Figure 11 Orientation distribution function ODF map of the Al-Cu-Mg alloy obtained in Example 4;

[0034] Figure 12 Geometrically necessary dislocation density of the Al-Cu-Mg alloy obtained in Examples 1 - 4;

[0035] Figure 13 Grain boundary distribution map of the Al-Cu-Mg alloy obtained in Examples 1 - 4;

[0036] Figure 14 SEM images of the Al-Cu-Mg alloys obtained in Examples 1 to 4;

[0037] Figure 15 EDS spectrum of the Al-Cu-Mg alloy obtained in Example 4;

[0038] Figure 16 Electron probe image of the Al-Cu-Mg alloy obtained in Example 4;

[0039] Figure 17 Legend of the fatigue crack growth da / dN-ΔK specimen data for the Al-Cu-Mg alloy obtained in Example 1;

[0040] Figure 18 Legend of the fatigue crack growth da / dN-ΔK specimen data for the Al-Cu-Mg alloy obtained in Example 2;

[0041] Figure 19 Legend of the fatigue crack growth da / dN-ΔK specimen data for the Al-Cu-Mg alloy obtained in Example 3;

[0042] Figure 20 Legend of the fatigue crack growth da / dN-ΔK specimen data for the Al-Cu-Mg alloy obtained in Example 4;

[0043] Figure 21 Physical image of the Al-Cu-Mg alloy obtained in Example 1;

[0044] Figure 22 Physical image of the Al-Cu-Mg alloy obtained in Example 2;

[0045] Figure 23 Physical image of the Al-Cu-Mg alloy obtained in Example 3;

[0046] Figure 24 Physical image of the Al-Cu-Mg alloy obtained in Example 4;

[0047] Figure 25 Surface roughness of the Al-Cu-Mg alloy obtained in Example 1;

[0048] Figure 26 Surface roughness of the Al-Cu-Mg alloy obtained in Example 2;

[0049] Figure 27 Surface roughness of the Al-Cu-Mg alloy obtained in Example 3;

[0050] Figure 28The surface roughness of the Al-Cu-Mg alloy obtained in Example 4. Detailed implementation manners

[0051] The present invention provides an Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish. By mass percentage, it includes the following chemical components: Cu: 5.0 - 8.0%, Mg: 1.2 - 3.0%, Mn: 0.5 - 1.0%, Zr: 0.08 - 0.2%, Sc + RE: 0.2 - 2.0%, and the balance Al.

[0052] By mass percentage, the Al-Cu-Mg alloy provided by the present invention with high resistance to fatigue crack propagation and high surface finish includes Cu: 5.0 - 8.0%. As an implementation manner of the present invention, the mass percentage of Cu in the Al-Cu-Mg alloy can be 5.2%, 5.5%, 5.8%, 6.0%, 6.2%, 6.5%, 6.8%, 7.0%, 7.2%, 7.5% or 7.8%. By adding more Cu elements in the present invention, the number of precipitation phases inside the aluminum alloy is greatly increased, and it is more difficult for dislocations to cut through or bypass the precipitation phases with small sizes, thereby improving the strength of the aluminum alloy.

[0053] By mass percentage, the Al-Cu-Mg alloy provided by the present invention with high resistance to fatigue crack propagation and high surface finish includes Mg: 1.2 - 3.0%. As an implementation manner of the present invention, the mass percentage of Mg in the Al-Cu-Mg alloy can be 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6% or 2.8%.

[0054] In the present invention, the mass ratio of Cu to Mg is preferably 3.5 - 6.5. As an implementation manner of the present invention, the mass ratio of Cu to Mg can be 4.0, 4.5, 5.0, 5.5 or 6.0.

[0055] In the present invention, the contents of Cu and Mg are higher than those of conventional Al-Cu-Mg alloys. The high Cu and high Mg contents are beneficial to the formation of "atomic clusters". The Cu-Mg clusters are completely coherent with the matrix and have a positive effect on the alloy. On the one hand, the formation of a large number of Cu-Mg solute "atomic clusters" in the Al-Cu-Mg alloy has a significant effect of pinning dislocations; on the other hand, the solute "atomic clusters" are in a "metastable state" thermodynamically, and the binding between atoms in the clusters is not strong enough. When interacting with dislocations, energy can be dissipated through atomic rearrangement, separation and re-dissolution, etc. The clusters can be repeatedly cut by dislocations, which is more conducive to the slip of dislocations and is not easy to cause stress / strain concentration, making the alloy have better fatigue resistance; by controlling the mass ratio of Cu to Mg in the present invention, the fatigue resistance of the alloy can be further improved.

[0056] By mass percentage, the Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish provided by the present invention comprises Mn: 0.5 to 1.0%. As an embodiment of the present invention, the mass percentage of Mn in the Al-Cu-Mg alloy may be 0.6%, 0.7%, 0.8% or 0.9%. By adding Mn element to the alloy, the present invention can increase the recrystallization temperature of the alloy, refine the recrystallized grains, and contribute to improving the mechanical properties of the alloy.

[0057] By mass percentage, the Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish provided by the present invention comprises Zr: 0.08 to 0.2%. As an embodiment of the present invention, the mass percentage of Zr in the Al-Cu-Mg alloy may be 0.1%, 0.12%, 0.14%, 0.16% or 0.18%. By adding a small amount of Zr element, the present invention can eliminate the dendritic structure in the alloy, refine the grains, and inhibit recrystallization, thereby improving the mechanical properties of the alloy.

[0058] By mass percentage, the Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish provided by the present invention comprises Sc + RE: 0.2 to 2.0%. As an embodiment of the present invention, the mass percentage of Sc + RE in the Al-Cu-Mg alloy may be 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6% or 1.8%. In the present invention, the RE is preferably one or more of Y, Ce and La. As an embodiment of the present invention, when the RE is Y, Ce and La, the mass ratio of Y, Ce and La may be 1:1:1; when the RE is Y and La, the mass ratio of Y and La may be 1:2; when the RE is Y and Ce, the mass ratio of Y and Ce may be 1:2. By adding Sc and RE, the present invention can play a role in refining the grains, so that the average grain size of the Al-Cu-Mg alloy is mainly concentrated within 10 μm, thereby further improving the fatigue resistance of the alloy.

[0059] The present invention has no special limitation on the dosage relationship between the Sc and RE, and they can be mixed in any proportion. As an embodiment of the present invention, the mass ratio of Sc and RE may be 1:(0.01 to 10), and may also be 1:0.01, 1:0.05, 1:0.1, 1:0.2, 1:0.5, 1:0.8, 1:1, 1:1.5, 1:2, 1:3, 1:4, 1:5 or 1:10.

[0060] By mass percentage, the Al-Cu-Mg alloy provided by the present invention that resists fatigue crack propagation and has high surface finish includes the balance of Al. In the present invention, Al is the matrix component of the alloy.

[0061] In the present invention, the average grain size of the Al-Cu-Mg alloy is preferably <10 μm; the second-phase particles of the Al-Cu-Mg alloy are preferably Al2Cu, Al2CuMg, and Al3(Sc,Y) composite rare-earth phases. In the present invention, the small average grain size of the Al-Cu-Mg alloy can further improve the fatigue resistance of the alloy; while the composite rare-earth phase particles have strong resistance to recrystallization and stronger coarsening resistance than Al3Zr, Al3Sc, and Al3Y, and their distribution is also more dispersed, which can endow the aluminum alloy with more excellent comprehensive properties.

[0062] The Al-Cu-Mg alloy provided by the present invention regulates the alloy composition, can eliminate defects such as low strength and toughness, uneven structure, and large grain size, and obtains an aluminum alloy sheet with fine grains, uniform structure, high strength, excellent fatigue resistance, and good surface quality (finish).

[0063] The present invention also provides a preparation method of the Al-Cu-Mg alloy that resists fatigue crack propagation and has high surface finish according to the above technical solution, including the following steps:

[0064] (1) Prepare an aluminum alloy ingot by spray deposition process;

[0065] (2) Successively perform hot extrusion and hot rolling on the aluminum alloy ingot obtained in step (1) to obtain a hot-rolled aluminum alloy;

[0066] (3) Successively perform pre-annealing and cold rolling on the hot-rolled aluminum alloy obtained in step (2) to obtain a cold-rolled aluminum alloy;

[0067] (4) Successively perform recrystallization annealing, solution treatment, quenching treatment, and aging treatment on the cold-rolled aluminum alloy obtained in step (3) to obtain an Al-Cu-Mg alloy that resists fatigue crack propagation and has high surface finish.

[0068] The present invention prepares an aluminum alloy ingot by spray deposition process.

[0069] The present invention has no special limitation on the raw materials used in the preparation of aluminum alloy ingots, which are determined according to the common technical knowledge of those skilled in the art, as long as the chemical composition of the aluminum alloy ingots meets the requirements. As an implementation manner of the present invention, the raw materials used in the preparation of aluminum alloy ingots may include a Cu source, a Mg source, a Mn source, a Zr source, a Sc source, a RE source, and an Al source; the Cu source, the Mg source, the Mn source, the Zr source, the Sc source, and the RE source may be elemental substances or master alloys, and may also be Al-50Cu master alloy, Al-50Mg master alloy, Al-50Mn master alloy, Al-4Zr master alloy, Al-2Sc master alloy, and Al-10RE master alloy; the Al-10RE master alloy may be Al-10Y master alloy, Al-10Ce master alloy, or Al-10La master alloy; the Al source may be high-purity aluminum; the purity of the high-purity aluminum may be ≥99.995%. The present invention has no special limitation on the specific sources of the raw materials, and commercially available products well-known to those skilled in the art can be used.

[0070] In the present invention, the parameters of the spray deposition process preferably include: using secondary atomization, and the atomizing gas is nitrogen; the main gas path pressure is 0.5 - 0.75 MPa; the atomizing temperature is 780 - 830 °C; the atomizing distance is 400 - 500 mm; the rotation frequency of the deposition disk is 5 - 6 Hz. As an implementation manner of the present invention, the nitrogen may be high-pressure pipeline industrial nitrogen; the main gas path pressure may be 0.55 MPa, 0.6 MPa, 0.65 MPa, or 0.7 MPa; the atomizing temperature may be 790 °C, 800 °C, 810 °C, or 820 °C; the atomizing distance may be 410 mm, 420 mm, 430 mm, 440 mm, 450 mm, 460 mm, 470 mm, 480 mm, or 490 mm; the rotation frequency of the deposition disk may be 5.1 Hz, 5.2 Hz, 5.3 Hz, 5.4 Hz, 5.5 Hz, 5.6 Hz, 5.7 Hz, 5.8 Hz, or 5.9 Hz. By preparing aluminum alloy ingots through the spray deposition process, the present invention can endow them with many advantages such as uniform structure, fine grains, low composition segregation, low oxidation degree, and high mechanical properties, thereby improving the comprehensive properties of aluminum alloys.

[0071] By adopting the spray deposition rapid solidification process, under the condition of high alloying, the solute diffusion and solute segregation in the alloy solidification process are in a "non-equilibrium" solidification state, resulting in significant changes in nucleation, growth, and interface morphology, inhibiting the formation of coarse grain phases, thereby refining the microstructure, inhibiting or eliminating segregation, and obtaining a supersaturated solid solution, reducing the number of crack nucleations from the source of preparation; at the same time, the spray deposition process can increase the solid solution content of Cu elements in the Al-Cu-Mg alloy. The aluminum alloy ingot obtained by the spray deposition process of the present invention undergoes a "solute diffusion" process different (opposite) from that of the conventional casting process during subsequent hot working, filling the solute into the grain boundaries and uniforming the internal stress, which can effectively improve the surface finish, plasticity, and fatigue resistance of the aluminum alloy.

[0072] After obtaining the aluminum alloy ingot, the present invention sequentially subjects the aluminum alloy ingot to hot extrusion and hot rolling to obtain hot-rolled aluminum alloy.

[0073] In the present invention, the temperature of the hot extrusion is preferably 420 - 450 °C; the speed of the hot extrusion is preferably 3.5 - 4.0 mm / s; the extrusion ratio of the hot extrusion is preferably (10 - 20):1. As an embodiment of the present invention, the temperature of the hot extrusion can be 430 - 440 °C; the speed of the hot extrusion can be 3.6 - 3.9 mm / s, and can also be 3.7 - 3.8 mm / s; the extrusion ratio of the hot extrusion can be 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, or 19:1. By hot extrusion, the present invention can improve the density of the aluminum alloy, reduce or eliminate defects such as pores, looseness, and microcracks in the aluminum alloy, and significantly improve the mechanical properties and fatigue strength of the aluminum alloy.

[0074] The present invention preferably further includes cutting the product of the hot extrusion. The present invention has no special limitation on the specific operation of the cutting, as long as the thickness of the cutting product meets the requirements. As an embodiment of the present invention, the thickness of the cutting product can be 40 mm, 45 mm, 50 mm, 55 mm, or 60 mm.

[0075] In the present invention, the starting rolling temperature of the hot rolling is preferably 450 - 490°C; the reduction ratio per pass of the hot rolling is preferably 12 - 30%; the total deformation rate of the hot rolling is preferably > 70%; the finishing rolling temperature of the hot rolling is preferably > 400°C; the hot rolling method is preferably longitudinal rolling. As an embodiment of the present invention, the starting rolling temperature of the hot rolling can be 460 - 480°C, and can also be 470°C; the reduction ratio per pass of the hot rolling can be 14%, 16%, 18%, 20%, 22%, 24%, 26% or 28%; the total deformation rate of the hot rolling can be 72%, 74%, 75%, 76%, 78% or 80%. The present invention can refine the grains and eliminate the defects of the microstructure through hot rolling, thereby making the alloy structure dense and improving the mechanical properties.

[0076] In the present invention, the thickness of the hot-rolled aluminum alloy is preferably 5 - 6 mm.

[0077] After obtaining the hot-rolled aluminum alloy, the present invention sequentially performs pre-annealing and cold rolling on the hot-rolled aluminum alloy to obtain a cold-rolled aluminum alloy.

[0078] In the present invention, the temperature of the pre-annealing is preferably 300 - 340°C; the time of the pre-annealing is preferably 2 - 4 h. As an embodiment of the present invention, the temperature of the pre-annealing can be 305°C, 310°C, 315°C, 320°C, 325°C, 330°C or 335°C; the time of the pre-annealing can be 2.5 - 3.5 h, and can also be 3 h. The present invention can eliminate the internal stress generated during the hot rolling process of the alloy through pre-annealing, improve the plasticity of the alloy, and facilitate subsequent cold rolling.

[0079] In the present invention, the total deformation rate of the cold rolling is preferably 40 - 60%; the reduction ratio per pass of the cold rolling is preferably 10 - 25%; the cold rolling preferably uses a single-stand reversible rolling mill for multi-pass cold rolling. As an embodiment of the present invention, the total deformation rate of the cold rolling can be 42%, 45%, 48%, 50%, 52%, 55% or 58%; the reduction ratio per pass of the cold rolling can be 12%, 15%, 18%, 20% or 23%. The present invention can elongate the grains in the alloy along the rolling direction through cold rolling and form many fine grains, and the sizes of these fine grains are mainly distributed within 20 μm, thereby improving the mechanical properties of the alloy; at the same time, the texture formed by the cold-rolled aluminum alloy is mainly deformation textures such as Brass and S, its texture strength is relatively high, there is still a small amount of recrystallization texture remaining, and the dislocation density of the aluminum alloy increases, which can further improve the mechanical properties of the alloy.

[0080] In the present invention, the thickness of the cold-rolled aluminum alloy is preferably 2 - 3 mm.

[0081] After obtaining the cold-rolled aluminum alloy, the present invention sequentially subjects the cold-rolled aluminum alloy to recrystallization annealing, solution treatment, quenching treatment, and aging treatment to obtain an Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish.

[0082] In the present invention, the temperature of the recrystallization annealing is preferably 360 - 400 °C; the holding time of the recrystallization annealing is preferably 1 - 2 h. As an embodiment of the present invention, the temperature of the recrystallization annealing can be 365 °C, 370 °C, 375 °C, 380 °C, 385 °C, 390 °C, or 395 °C. Through recrystallization annealing, new grains can cover the matrix, and the grains are mainly equiaxed grains. At the same time, the higher the temperature of the recrystallization annealing, the greater the recrystallization driving force, and the higher the degree of recrystallization completion within the same holding time; also, after the recrystallization annealing treatment, the proportion of the Goss texture, which is beneficial to the fatigue resistance performance, in the Al-Cu-Mg alloy is the highest, which can significantly improve the fatigue resistance performance of the Al-Cu-Mg alloy.

[0083] In the present invention, the temperature of the solution treatment is preferably 480 - 500 °C; the holding time of the solution treatment is preferably 20 - 60 min; the heating rate to the solution treatment temperature is preferably > 50 °C / s. As an embodiment of the present invention, the temperature of the solution treatment can be 485 °C, 490 °C, or 495 °C; the holding time of the solution treatment can be 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, or 55 min. Through the solution treatment, the plasticity and toughness of the aluminum alloy can be improved.

[0084] In the present invention, the quenching treatment method is preferably water quenching; the transfer time of the alloy during the quenching treatment is preferably < 20 s, more preferably < 15 s. By performing quenching treatment after solution treatment, the strength and hardness of the aluminum alloy can be significantly reduced.

[0085] In the present invention, the aging treatment method is preferably natural aging; the temperature of the aging treatment is preferably room temperature; the time of the aging treatment is preferably 3 - 5 days. Through the aging treatment, the atoms in the aluminum alloy can diffuse sufficiently, and discontinuous precipitation and continuous precipitation of the second-phase particles occur in the aluminum alloy. The former forms strip-shaped and block-shaped second phases at the grain boundaries, and the latter forms non-directional particles or short rod-shaped second phases inside the grains, which significantly improves the hardness of the aluminum alloy matrix. The microhardness value of the finally obtained Al-Cu-Mg alloy is 135 - 142 HV.

[0086] The present invention prepares an Al-Cu-Mg alloy ingot blank by using spray deposition technology, and successively subjects the ingot blank to hot extrusion, hot rolling, pre-annealing, cold rolling, recrystallization annealing, and solution aging treatments. The obtained Al-Cu-Mg alloy has fine and uniformly distributed grains, mainly concentrated below 10 μm, with an average grain size of about 8 μm. The Al-Cu-Mg alloy has excellent anti-fatigue performance, good surface quality, and high strength.

[0087] The chemical composition design of the Al-Cu-Mg alloy provided by the present invention is reasonable, the preparation process is simple and controllable, and the obtained product has excellent performance, which is convenient for large-scale industrial applications.

[0088] The present invention adopts the spray deposition technology, a rapid solidification technology, adds rare earths, and complexly regulates the second phase, grain size, and grain orientation, and develops corresponding processing and preparation technologies. While ensuring the high strength of the Al-Cu-Mg alloy, the anti-fatigue performance and surface quality of the alloy are improved, which is of great significance for the application of this alloy in the aerospace field and transportation vehicles such as automobiles.

[0089] The present invention also provides the application of the Al-Cu-Mg alloy with anti-fatigue crack propagation and high surface finish described in the above technical solution or the Al-Cu-Mg alloy with anti-fatigue crack propagation and high surface finish prepared by the preparation method described in the above technical solution in the skins for aerospace military use and the materials for interior decoration of transportation vehicles.

[0090] In the present invention, the transportation vehicle preferably includes an automobile.

[0091] The present invention has no special limitation on the specific manner of the above application, and the application manner well-known to those skilled in the art can be adopted.

[0092] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0093] Example 1

[0094] An Al-Cu-Mg alloy with anti-fatigue crack propagation and high surface finish, by mass percentage, consists of the following chemical components: Cu: 7.8%, Mg: 2.2%, Mn: 0.5%, Zr: 0.1%, Sc and RE: 1.8% and the balance Al; the mass ratio of Sc and RE is 1:10, RE is Y and La, and the mass ratio of Y and La is 1:2; the mass ratio of Cu and Mg is 3.55;

[0095] The preparation method of the Al-Cu-Mg alloy with anti-fatigue crack growth and high surface finish is as follows:

[0096] (1) Prepare an aluminum alloy ingot from raw materials by spray deposition process; the raw materials are Al-50Cu master alloy, Al-50Mg master alloy, Al-50Mn master alloy, Al-4Zr master alloy, Al-2Sc master alloy, Al-10Y master alloy, Al-10La master alloy and high-purity aluminum; the purity of the high-purity aluminum is ≥99.995%; the parameters of the spray deposition process are: using two-stage atomization, the atomizing gas is high-pressure pipeline industrial nitrogen; the main gas path pressure is 0.6 MPa; the atomizing temperature is 790 °C; the atomizing distance is 430 mm; the rotation frequency of the deposition disk is 5.4 Hz;

[0097] (2) Hot-extrude the aluminum alloy ingot obtained in step (1), then cut it to an alloy thickness of 50 mm, and finally perform hot rolling to obtain a hot-rolled aluminum alloy with a thickness of 6 mm; the temperature of the hot extrusion is 420 °C, the speed of the hot extrusion is 3.5 mm / s, and the extrusion ratio of the hot extrusion is 15:1; the starting rolling temperature of the hot rolling is 460 °C, the single-pass reduction rate of the hot rolling is 15%, the total deformation rate of the hot rolling is 80%, the final rolling temperature of the hot rolling is 400 °C, and the hot rolling method is longitudinal rolling;

[0098] (3) Pre-anneal the hot-rolled aluminum alloy obtained in step (2), and then perform cold rolling using a single-stand reversible rolling mill to obtain a cold-rolled aluminum alloy with a thickness of 3 mm; the temperature of the pre-annealing is 310 °C, and the time of the pre-annealing is 3 h; the total deformation rate of the cold rolling is 50%, and the single-pass reduction rate of the cold rolling is 10%;

[0099] (4) Perform recrystallization annealing, solution treatment, quenching treatment and aging treatment on the cold-rolled aluminum alloy obtained in step (3) in sequence to obtain the Al-Cu-Mg alloy with anti-fatigue crack growth and high surface finish; the temperature of the recrystallization annealing is 370 °C, and the holding time of the recrystallization annealing is 2 h; the temperature of the solution treatment is 485 °C, the holding time of the solution treatment is 40 min, and the heating rate to the solution treatment temperature is 60 °C / s; the quenching treatment method is water quenching, and the transfer time of the alloy during quenching treatment is 12 s; the aging treatment is natural aging at room temperature for 5 days.

[0100] Example 2

[0101] An Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish, by mass percentage, consists of the following chemical components: Cu: 6.8%, Mg: 1.2%, Mn: 0.6%, Zr: 0.12%, Sc and RE: 1.2%, and the balance Al; the mass ratio of Sc and RE is 1:5, RE is Y and Ce, and the mass ratio of Y and Ce is 1:2; the mass ratio of Cu and Mg is 5.67;

[0102] The preparation method of the Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish comprises the following steps:

[0103] (1) Prepare an aluminum alloy ingot from raw materials by spray deposition process; the raw materials are Al-50Cu master alloy, Al-50Mg master alloy, Al-50Mn master alloy, Al-4Zr master alloy, Al-2Sc master alloy, Al-10Y master alloy, Al-10Ce master alloy and high-purity aluminum; the purity of the high-purity aluminum is ≥99.995%; the parameters of the spray deposition process are: adopt secondary atomization, and the atomizing gas is high-pressure pipeline industrial nitrogen; the main gas path pressure is 0.65 MPa; the atomizing temperature is 800 °C; the atomizing distance is 450 mm; the rotation frequency of the deposition disk is 5.6 Hz;

[0104] (2) Hot extrude the aluminum alloy ingot obtained in step (1), then cut it to an alloy thickness of 50 mm, and finally perform hot rolling to obtain a hot-rolled aluminum alloy with a thickness of 6 mm; the temperature of the hot extrusion is 430 °C, the speed of the hot extrusion is 3.6 mm / s, and the extrusion ratio of the hot extrusion is 15:1; the starting rolling temperature of the hot rolling is 465 °C, the single-pass reduction rate of the hot rolling is 15%, the total deformation rate of the hot rolling is 80%, the final rolling temperature of the hot rolling is 405 °C, and the hot rolling method is longitudinal rolling;

[0105] (3) Pre-anneal the hot-rolled aluminum alloy obtained in step (2), and then perform cold rolling using a single-stand reversible rolling mill to obtain a cold-rolled aluminum alloy with a thickness of 3 mm; the temperature of the pre-annealing is 320 °C, and the time of the pre-annealing is 3 h; the total deformation rate of the cold rolling is 50%, and the single-pass reduction rate of the cold rolling is 10%;

[0106] (4) The cold-rolled aluminum alloy obtained in step (3) is successively subjected to recrystallization annealing, solution treatment, quenching treatment, and aging treatment to obtain an Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish. The temperature of the recrystallization annealing is 380 °C, and the holding time of the recrystallization annealing is 2 h. The temperature of the solution treatment is 485 °C, the holding time of the solution treatment is 40 min, and the heating rate to the solution treatment temperature is 60 °C / s. The quenching treatment method is water quenching, and the transfer time of the alloy during quenching treatment is 13 s. The aging treatment is natural aging at room temperature for 5 days.

[0107] Example 3

[0108] An Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish is composed of the following chemical components by mass percentage: Cu: 6.0%, Mg: 1.5%, Mn: 0.7%, Zr: 0.14%, Sc and RE: 0.8%, and the balance Al. The mass ratio of Sc and RE is 1:1, RE is Y, La, and Ce, and the mass ratio of Y, La, and Ce is 1:1:1. The mass ratio of Cu and Mg is 4.0;

[0109] The preparation method of the Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish is the following steps:

[0110] (1) The raw materials are prepared into an aluminum alloy ingot by spray deposition process. The raw materials are Al-50Cu master alloy, Al-50Mg master alloy, Al-50Mn master alloy, Al-4Zr master alloy, Al-2Sc master alloy, Al-10Y master alloy, Al-10La master alloy, Al-10Ce master alloy, and high-purity aluminum. The purity of the high-purity aluminum is ≥99.995%. The parameters of the spray deposition process are: secondary atomization is adopted, and the atomizing gas is high-pressure pipeline industrial nitrogen. The main gas path pressure is 0.7 MPa. The atomization temperature is 470 °C. The atomization distance is 470 mm. The rotation frequency of the deposition disk is 5.8 Hz;

[0111] (2) The aluminum alloy ingot obtained in step (1) is hot extruded, then cut to an alloy thickness of 50 mm, and finally hot rolled to obtain a hot-rolled aluminum alloy with a thickness of 6 mm. The temperature of the hot extrusion is 440 °C, the speed of the hot extrusion is 3.8 mm / s, and the extrusion ratio of the hot extrusion is 15:1. The starting rolling temperature of the hot rolling is 470 °C, the single-pass reduction rate of the hot rolling is 15%, the total deformation rate of the hot rolling is 80%, the final rolling temperature of the hot rolling is 410 °C, and the hot rolling method is longitudinal rolling;

[0112] (3) Pre-anneal the hot-rolled aluminum alloy obtained in step (2), and then perform cold rolling using a single-stand reversible rolling mill to obtain a cold-rolled aluminum alloy with a thickness of 3 mm; the temperature of the pre-annealing is 330 °C, and the time of the pre-annealing is 3 h; the total deformation rate of the cold rolling is 50%, and the reduction rate per pass of the cold rolling is 10%;

[0113] (4) Subject the cold-rolled aluminum alloy obtained in step (3) to recrystallization annealing, solution treatment, quenching treatment, and aging treatment in sequence to obtain an Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish; the temperature of the recrystallization annealing is 390 °C, and the holding time of the recrystallization annealing is 2 h; the temperature of the solution treatment is 485 °C, the holding time of the solution treatment is 40 min, and the heating rate to the solution treatment temperature is 60 °C / s; the quenching treatment method is water quenching, and the transfer time of the alloy during the quenching treatment is 14 s; the aging treatment is natural aging at room temperature for 5 days.

[0114] Example 4

[0115] An Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish, by mass percentage, consists of the following chemical components: Cu: 5.2%, Mg: 1.4%, Mn: 0.8%, Zr: 0.16%, Sc and Y: 0.4%, and the balance is Al; the mass ratio of Sc to Y is 1:0.5; the mass ratio of Cu to Mg is 3.7;

[0116] The preparation method of the Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish is the following steps:

[0117] (1) Prepare an aluminum alloy ingot from raw materials using the spray deposition process; the raw materials are Al-50Cu master alloy, Al-50Mg master alloy, Al-50Mn master alloy, Al-4Zr master alloy, Al-2Sc master alloy, Al-10Y master alloy, and high-purity aluminum; the purity of the high-purity aluminum is ≥99.995%; the parameters of the spray deposition process are: using secondary atomization, the atomizing gas is high-pressure pipeline industrial nitrogen; the main gas path pressure is 0.75 MPa; the atomizing temperature is 820 °C; the atomizing distance is 490 mm; the rotation frequency of the deposition disk is 6 Hz;

[0118] (2) Hot-extrude the aluminum alloy ingot obtained in step (1), then cut it to an alloy thickness of 50 mm, and finally perform hot rolling to obtain a hot-rolled aluminum alloy with a thickness of 6 mm; the temperature of the hot extrusion is 450 °C, the speed of the hot extrusion is 4.0 mm / s, and the extrusion ratio of the hot extrusion is 15:1; the starting rolling temperature of the hot rolling is 480 °C, the reduction rate per pass of the hot rolling is 15%, the total deformation rate of the hot rolling is 80%, the final rolling temperature of the hot rolling is 420 °C, and the hot rolling method is longitudinal rolling;

[0119] (3) Pre-anneal the hot-rolled aluminum alloy obtained in step (2), and then perform cold rolling using a single-stand reversible rolling mill to obtain a cold-rolled aluminum alloy with a thickness of 3 mm; the temperature of the pre-annealing is 340 °C, and the time of the pre-annealing is 3 h; the total deformation rate of the cold rolling is 50%, and the reduction rate per pass of the cold rolling is 10%;

[0120] (4) Subject the cold-rolled aluminum alloy obtained in step (3) to recrystallization annealing, solution treatment, quenching treatment, and aging treatment in sequence to obtain an Al-Cu-Mg alloy with high resistance to fatigue crack propagation and high surface finish; the temperature of the recrystallization annealing is 400 °C, and the holding time of the recrystallization annealing is 2 h; the temperature of the solution treatment is 485 °C, the holding time of the solution treatment is 40 min, and the heating rate to the solution treatment temperature is 60 °C / s; the quenching treatment method is water quenching, and the transfer time of the alloy during the quenching treatment is 15 s; the aging treatment is natural aging at room temperature for 5 days.

[0121] Test the properties of the Al-Cu-Mg alloys prepared in Examples 1 to 4. Among them, the test parameters for the anti-fatigue performance (i.e., fatigue crack propagation rate) are: frequency 10 Hz, stress ratio 0.1, maximum load 800 N, and the results are shown in Table 1:

[0122] Table 1 Properties of the Al-Cu-Mg alloys prepared in Examples 1 to 4

[0123] Example Anti-fatigue performance (da / dN) Hardness Example 1 <![CDATA[3.41×10 -4 (mm / cycle)]]> 142HV Example 2 <![CDATA[6.12×10 -4 (mm / cycle)]]> 135HV Example 3 <![CDATA[6.34×10 -5 (mm / cycle)]]> 137HV Example 4 <![CDATA[2.48×10 -4 (mm / cycle)]]> 139HV

[0124] As can be seen from Table 1, the Al-Cu-Mg alloy obtained in the present invention has excellent anti-fatigue performance.

[0125] Use SEM and the supporting EBSD to examine the microstructure such as the second phase, grain size, and grain boundary of the Al-Cu-Mg alloys obtained in Examples 1 to 4. Among them, during the EBSD detection, the Al-Cu-Mg alloy sample is preheated to 60 °C and electromagnetic stress relief is performed.

[0126] Figure 1 is the DSC curve of the aluminum alloy ingot obtained in step (1) of Example 1. From Figure 1 it can be seen that a strong exothermic peak appears in the aluminum alloy ingot prepared in Example 1 at 510.3 °C, which means that the more Al solute atoms, to a certain extent, it can indicate that there are fewer second phases in the matrix of the aluminum alloy ingot. At the same time, according to the DSC curve of the aluminum alloy ingot, it shows that the subsequent formulated hot rolling temperature is reasonable.

[0127] Figure 2 is the grain size diagram of the hot-rolled aluminum alloy obtained in step (2) of Example 1. FromFigure 2 It can be seen that many coarse grains in the hot-rolled aluminum alloy sheet are broken into fine grains, and many fine grains appear near the large grains, indicating that dynamic recrystallization occurs during the hot rolling process of the aluminum alloy.

[0128] Figure 3 It is the orientation distribution function (ODF) diagram of the hot-rolled aluminum alloy obtained in step (2) of Example 1. Figure 3 It can be seen that the texture formed in the hot-rolled aluminum alloy sheet is mainly Cube and Goss recrystallization textures, and there is also a small amount of deformation texture. The maximum texture strength of the hot-rolled aluminum alloy sheet is 2.97, and the volume fractions of its main textures are: (Cube: 1.47%, Goss: 0.89%, Brass: 0.49%, S: 0.28%, Copper: 0.15%).

[0129] Figure 4 It is the grain size diagram of the cold-rolled aluminum alloy obtained in step (3) of Example 1. Figure 4 It can be seen that for the sheet after multi-pass cold rolling, its grains are elongated along the rolling direction, and many fine grains appear. The sizes of these fine grains are mainly distributed within 20 μm.

[0130] Figure 5 It is the orientation distribution function (ODF) diagram of the cold-rolled aluminum alloy obtained in step (3) of Example 1. Figure 5 It can be seen that the texture formed in the cold-rolled aluminum alloy sheet is mainly deformation textures such as Brass and S, and there is still a small amount of recrystallization texture remaining. The maximum texture strength of the cold-rolled aluminum alloy sheet is 11. This is because the texture strength of deformation textures such as Brass is relatively high, and the volume fractions of its main textures are: (Cube: 0.22%, Goss: 0.22%, Brass: 3.17%, S: 1.02%, Copper: 0.28%).

[0131] Figure 6 It is the geometrically necessary dislocation density diagram of the cold-rolled aluminum alloy obtained in step (3) of Example 1. Figure 6 It can be seen that the dislocation density of the cold-rolled aluminum alloy sheet increases, which is related to the continuous generation of dislocations and the strong interaction between dislocations during the entire rolling process. The dislocation pile-up increases the deformation resistance of the aluminum alloy, and at this time, dislocation strengthening plays a major role in strengthening the aluminum alloy.

[0132] Figure 7 It is the grain size diagram of the Al-Cu-Mg alloy obtained in Examples 1 to 4; among them, (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is Example 4. Figure 7It can be seen that the grain size of the Al-Cu-Mg alloy provided by the present invention is generally small, and the grains are mainly distributed within 10 μm. The average grain sizes of Examples 1 to 4 are 7.96 μm, 8.43 μm, 7.56 μm, and 8.09 μm in sequence. Among them, the grain size of the Al-Cu-Mg alloy obtained in Example 3 is the smallest. After analysis, when the temperature of the recrystallization annealing is 390 °C, the recrystallization process proceeds relatively fully under the drive of the stored energy, and the new grains cover the matrix. The grains are mainly equiaxed grains, which indicates that the higher the temperature of the recrystallization annealing, the greater the recrystallization driving force, and the higher the degree of recrystallization completion within the same holding time. At different annealing temperatures, the new grains mainly nucleate and grow at the bowed grain boundaries. Therefore, the main softening mechanism of the aluminum alloy is "discontinuous dynamic recrystallization".

[0133] Figure 8 It is the orientation distribution function ODF diagram of the Al-Cu-Mg alloy obtained in Example 1; Figure 9 It is the orientation distribution function ODF diagram of the Al-Cu-Mg alloy obtained in Example 2; Figure 10 It is the orientation distribution function ODF diagram of the Al-Cu-Mg alloy obtained in Example 3; Figure 11 It is the orientation distribution function ODF diagram of the Al-Cu-Mg alloy obtained in Example 4. It can be seen from Figures 8 - 11 that the textures formed by the Al-Cu-Mg alloys obtained in Examples 1 to 4 are mainly Cube and Goss recrystallization textures, and there are also a small amount of deformation textures. Among them, the maximum texture intensities formed in the Al-Cu-Mg alloys obtained in Examples 1 to 4 are 2.19, 2.01, 2.12, and 1.96 in sequence. The volume fractions of their main textures are shown in Table 2. It can be seen that when the temperature of the recrystallization annealing is 390 °C, the proportion of the Goss texture, which is beneficial to the fatigue resistance performance, in the Al-Cu-Mg alloy is the highest.

[0134] Table 2 Texture composition and proportion in the Al-Cu-Mg alloys obtained in Examples 1 to 4

[0135]

[0136] Figure 12 It is the geometrically necessary dislocation density of the Al-Cu-Mg alloys obtained in Examples 1 to 4; among them, (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is Example 4. It can be seen from Figure 12It can be seen that the internal dislocation density of the Al-Cu-Mg alloys obtained in Examples 1 to 4 at different recrystallization annealing temperatures (370, 380, 390, and 400 °C) decreased significantly, indicating that the residual stress inside the alloy decreased significantly. At the same time, the aluminum alloy will generate dislocation pile-ups under the influence of rolling force, increasing the deformation resistance of the aluminum alloy. The recrystallization annealing treatment reduces the dislocation density of the alloy, reducing the contribution of dislocation strengthening to the mechanical properties of the alloy.

[0137] Figure 13 FIG. is the grain boundary distribution diagram of the Al-Cu-Mg alloys obtained in Examples 1 to 4; among them, (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is Example 4. From Figure 13 It can be seen that the proportion of high-angle grain boundaries in the Al-Cu-Mg alloys obtained in Examples 1 to 4 at different recrystallization annealing temperatures (370, 380, 390, 400 °C) is high, and those in Examples 1 to 4 are 0.831, 0.749, 0.841, and 0.858 in sequence. With the increase of the recrystallization annealing temperature, the high-angle grain boundaries mainly show an increasing trend, but when the recrystallization annealing temperature is 380 °C, the high-angle grain boundaries are relatively fewer because many recrystallization nuclei are formed during annealing at 380 °C, and high-angle grain boundaries can usually become potential nucleation sites for dynamic recrystallization, so the content decreases. High-angle grain boundaries have a significant impact on the strength and hardness of materials because they hinder the movement of dislocations and the slip of grains. Such grain boundaries act as obstacles in the material, inhibiting the growth of grains, thereby refining the grains, improving the strength of the material (i.e., fine grain strengthening), and also improving the creep resistance and high-temperature stability of the material. Research shows that small-angle grain boundaries have relatively little influence on the strength and hardness of materials, but can affect the deformation behavior and fatigue performance of materials.

[0138] Figure 14 FIG. is the SEM image of the Al-Cu-Mg alloys obtained in Examples 1 to 4; among them, (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is Example 4.

[0139] Figure 15 FIG. is the EDS energy spectrum diagram of the Al-Cu-Mg alloy obtained in Example 4.

[0140] Figure 16 FIG. is the electron probe image of the Al-Cu-Mg alloy obtained in Example 4.

[0141] From Figures 14 - 16It can be seen that the second-phase particles in the Al-Cu-Mg alloys obtained in Examples 1 to 4 at different recrystallization annealing temperatures (370, 380, 390, 400 °C) are mainly Al2Cu, Al2CuMg, and rare-earth-containing composite phases. The Al2Cu and Al2CuMg phases are distributed both at grain boundaries and within grains, but mainly disperse within grains. These two second-phase particles are the main strengthening phases of the alloy. The rare-earth-containing composite phase mainly precipitates along grain boundaries. This composite phase has strong resistance to recrystallization and coarsening, and its dispersion distribution will endow the aluminum alloy with more excellent comprehensive properties.

[0142] Figure 17 It is the legend of the fatigue crack growth da / dN-ΔK specimen data of the Al-Cu-Mg alloy obtained in Example 1; Figure 18 It is the legend of the fatigue crack growth da / dN-ΔK specimen data of the Al-Cu-Mg alloy obtained in Example 2; Figure 19 It is the legend of the fatigue crack growth da / dN-ΔK specimen data of the Al-Cu-Mg alloy obtained in Example 3; Figure 20 It is the legend of the fatigue crack growth da / dN-ΔK specimen data of the Al-Cu-Mg alloy obtained in Example 4. Figures 17 - 20 It can be seen that the fatigue crack growth rates of the Al-Cu-Mg alloys obtained in Examples 1 to 4 at different recrystallization annealing temperatures (370, 380, 390, 400 °C) are generally small, that is, "excellent fatigue resistance". This is because when the specimen thickness is fixed, the annealing temperature has a great influence on the fatigue crack growth rate of the aged alloy. As the annealing temperature increases, the fatigue crack growth rate gradually decreases. When annealed at 390 °C, the fatigue crack growth rate of the alloy is the smallest. However, when the annealing temperature is 400 °C, the grain size and second-phase particles of the specimen coarsen, resulting in an increase in the fatigue crack growth rate. In addition, the mixed addition of rare-earth elements optimizes the comprehensive properties of the alloy and helps to improve the fatigue resistance.

[0143] Figure 21 It is the physical picture of the Al-Cu-Mg alloy obtained in Example 1; Figure 22 It is the physical picture of the Al-Cu-Mg alloy obtained in Example 2; Figure 23 It is the physical picture of the Al-Cu-Mg alloy obtained in Example 3; Figure 24 It is the physical picture of the Al-Cu-Mg alloy obtained in Example 4. Figures 21 - 24 It can be seen that the Al-Cu-Mg alloys obtained in Examples 1 to 4 at different recrystallization annealing temperatures (370, 380, 390, 400 °C) have high surface finish.

[0144] Figure 25 It is the surface roughness of the Al-Cu-Mg alloy obtained in Example 1; Figure 26The surface roughness of the Al-Cu-Mg alloy obtained in Example 2; Figure 27 The surface roughness of the Al-Cu-Mg alloy obtained in Example 3; Figure 28 The surface roughness of the Al-Cu-Mg alloy obtained in Example 4. From Figures 25 - 28 It can be seen that the roughness of the Al-Cu-Mg alloys obtained in Examples 1 to 4 at different recrystallization annealing temperatures (370, 380, 390, 400 °C) is relatively low, and the Ra values are 0.0104 μm, 0.0375 μm, 0.0291 μm, and 0.0109 μm respectively, indicating that the surface roughness of the Al-Cu-Mg alloy provided by the present invention is small and the surface quality of the aluminum alloy is good.

[0145] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An Al-Cu-Mg alloy with high surface finish and high fatigue crack growth resistance, comprising the following chemical components by mass percentage: Cu: 5.0-8.0%, Mg: 1.2-3.0%, Mn: 0.5-1.0%, Zr: 0.08-0.2%, Sc+RE: 0.2-2.0% and the balance Al.

2. The Al-Cu-Mg alloy according to claim 1, characterized in that: The mass ratio of Cu to Mg is 3.5 to 6.

5.

3. The Al-Cu-Mg alloy according to claim 1, characterized in that: The RE is one or more of Y, Ce and La.

4. The method for preparing the Al-Cu-Mg alloy having high surface finish and high fatigue crack growth resistance according to any one of claims 1 to 3, comprising the following steps: (1) Preparing aluminum alloy ingots by spray deposition process; (2) hot extruding and hot rolling the aluminum alloy ingot obtained in step (1) to obtain a hot-rolled aluminum alloy; (3) pre-annealing and cold-rolling the hot-rolled aluminum alloy obtained in step (2) to obtain a cold-rolled aluminum alloy; (4) The cold-rolled aluminum alloy obtained in step (3) is sequentially subjected to recrystallization annealing, solution treatment, quenching treatment and aging treatment to obtain an Al-Cu-Mg alloy that is resistant to fatigue crack propagation and has a high surface finish.

5. The preparation method according to claim 4, characterized in that: The parameters of the spray deposition process in step (1) include: two-stage atomization, the atomizing gas is nitrogen; the main gas line pressure is 0.5-0.75 MPa; the atomization temperature is 780-830° C.; the atomization distance is 400-500 mm; and the deposition disk rotation frequency is 5-6 Hz.

6. The preparation method according to claim 4, characterized in that: In the step (2), the temperature of the hot extrusion is 420-450° C., the speed of the hot extrusion is 3.5-4.0 mm / s, and the extrusion ratio of the hot extrusion is (10-20):

1.

7. The preparation method according to claim 4, characterized in that: In the step (2), the hot rolling start temperature is 450-490°C, the hot rolling single pass reduction rate is 12-30%, the total hot rolling deformation rate is greater than 70%, the hot rolling final rolling temperature is greater than 400°C, and the hot rolling method is longitudinal rolling.

8. The preparation method according to claim 4, characterized in that: In the step (3), the total deformation rate of cold rolling is 40-60%, and the single pass reduction rate of cold rolling is 10-25%.

9. The preparation method according to claim 4, characterized in that: The temperature of the recrystallization annealing in the step (4) is 360-400° C., and the holding time of the recrystallization annealing is 1-2 hours.

10. Use of the Al-Cu-Mg alloy having resistance to fatigue crack growth and high surface finish as described in any one of claims 1 to 3 or the Al-Cu-Mg alloy having resistance to fatigue crack growth and high surface finish prepared by the preparation method according to any one of claims 4 to 9 in aerospace and military skins and vehicle interior materials.

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