A 7075 aluminum alloy additive manufacturing structural part and its manufacturing method and application

Abstract

The present invention discloses a 7075 aluminum alloy additive manufacturing structural part and its manufacturing method and application, belonging to the field of aluminum alloy technology. The 7075 aluminum alloy additive manufacturing structural part is obtained by depositing a 7075 aluminum alloy raw material on a substrate by laser melting deposition. The chemical composition of the 7075 aluminum alloy raw material includes 4-7wt% Zn, 1.5-3wt% Mg, 1-2.5wt% Cu, 0.35-0.5wt% Fe, 0.03-0.07wt% Si and 0.1-0.3wt% Cr, with the balance being Al. The surface morphology of the structural part is relatively flat, the surface roughness profile is small, and it has certain hardness, tensile strength, yield strength, elongation and low friction coefficient. It can be used as a structural part in aerospace, transportation, automobile manufacturing, military equipment or tooling fixtures.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloys, and in particular to a 7075 aluminum alloy additively manufactured structural part, a manufacturing method thereof, and applications thereof. Background Art

[0002] As the most widely used non-ferrous metal structural material in industrial applications, aluminum alloy is gradually developing towards high comprehensive performance, large specifications, and material structure integration, providing strong support for high-performance manufacturing in aerospace, transportation, and high-end equipment.

[0003] Al-Zn-Mg-Cu alloys are ultra-high-strength aluminum alloys that have rapidly developed since their initial application in aerospace technology in the 1940s. Their low density, high specific strength, excellent toughness, and corrosion resistance have made them highly sought after in the aerospace, transportation, and military sectors. Over nearly 80 years of continuous research and development, aluminum alloys have, to a certain extent, met the development requirements of aerospace and cutting-edge equipment across the ages. Continuous innovation in aerospace product design has led to higher demands for the manufacture of large structures and complex components, particularly those driven by the pursuit of high reliability, lightweight design, long life, and low cost. This has further fueled the booming development of high-strength aluminum alloys.

[0004] Traditional aluminum alloy processing techniques primarily rely on smelting, casting, and forging. However, with the continuous improvement of product technology and the continuous shortening of development cycles, new requirements have been put forward for the manufacture of aluminum alloy components with complex and precise structures. These requirements require not only efficient and rapid manufacturing technology, but also the ability to quickly respond to changes in equipment design and flexible adaptability to the production of complex and precise components. Aluminum alloy components manufactured using traditional smelting, casting, and forging methods are increasingly unable to meet the requirements for the current large-scale and complex aluminum alloy product requirements in terms of microstructure and mechanical properties.

[0005] In view of this, this application is hereby filed. Summary of the Invention

[0006] One of the purposes of the present invention is to provide a 7075 aluminum alloy additively manufactured structural part that can meet the high performance requirements of some current large-sized and complex-structured aluminum alloy products.

[0007] A second object of the present invention is to provide a method for manufacturing the above-mentioned 7075 aluminum alloy additive manufacturing structural parts.

[0008] A third object of the present invention is to provide an application of the above-mentioned 7075 aluminum alloy additive manufacturing structural parts.

[0009] This application can be implemented as follows:

[0010] In a first aspect, the present application provides a 7075 aluminum alloy additively manufactured structural part, which is obtained by depositing a 7075 aluminum alloy raw material on a substrate by laser melting deposition, wherein the chemical composition of the 7075 aluminum alloy raw material includes 4-7wt% Zn, 1.5-3wt% Mg, 1-2.5wt% Cu, 0.35-0.5wt% Fe, 0.03-0.07wt% Si and 0.1-0.3wt% Cr, and the balance is Al.

[0011] In a preferred embodiment, the chemical composition of the 7075 aluminum alloy raw material includes 5-6 wt% Zn, 2-3 wt% Mg, 1.5-2 wt% Cu, 0.4-0.45 wt% Fe, 0.04-0.06 wt% Si and 0.15-0.25 wt% Cr, with the balance being Al.

[0012] In a more preferred embodiment, the chemical composition of the 7075 aluminum alloy raw material includes: 5.56wt% Zn, 2.46wt% Mg, 1.64wt% Cu, 0.42wt% Fe, 0.05wt% Si and 0.20wt% Cr, with the balance being Al.

[0013] In an optional embodiment, the 7075 aluminum alloy raw material is a spherical powder with a particle size of 45-106 μm.

[0014] In a preferred embodiment, the 7075 aluminum alloy raw material is vacuum atomized 7075 aluminum alloy spherical powder.

[0015] In an optional embodiment, the chemical composition of the substrate includes 4.5-6.5 wt % Zn, 1.5-3.5 wt % Mg, 0.5-1.5 wt % Cu, 0.15-0.35 wt % Fe, 0.08-0.2 wt % Si, and 0.15-0.3 wt % Cr, with the balance being Al.

[0016] In a preferred embodiment, the chemical composition of the substrate includes 5-6 wt% Zn, 2-3 wt% Mg, 1-2 wt% Cu, 0.2-0.3 wt% Fe, 0.1-0.15 wt% Si, and 0.2-0.25 wt% Cr, with the balance being Al.

[0017] In a more preferred embodiment, the chemical composition of the substrate includes 5.65 wt % Zn, 2.61 wt % Mg, 1.46 wt % Cu, 0.25 wt % Fe, 0.11 wt % Si, and 0.22 wt % Cr, with the balance being Al.

[0018] In an optional embodiment, the substrate is a 7075 aluminum alloy rolled plate in T6 state.

[0019] In an optional embodiment, the density of the 7075 aluminum alloy additively manufactured structural component is 0.84-0.88%, preferably 0.86-0.88%.

[0020] In an optional embodiment, in the structure of the 7075 aluminum alloy additively manufactured structural part, columnar crystals are formed at the bottom and middle, and equiaxed crystals are formed at the top, and the structure shows preferential orientation growth.

[0021] In an optional embodiment, the phases contained in the 7075 aluminum alloy additively manufactured structural component mainly include α-Al phase as the matrix phase and Mg(Zn, Cu, Al)2 as the precipitation phase.

[0022] In an optional embodiment, the average hardness of the 7075 aluminum alloy additively manufactured structural part is not less than 120HV 0.1 .

[0023] In an optional embodiment, the average friction coefficient of the 7075 aluminum alloy additively manufactured structural component is 0.4678-0.5134.

[0024] In an optional embodiment, the tensile strength of the 7075 aluminum alloy additively manufactured structural component is not less than 158 MPa, the yield strength is not less than 122 MPa, and the elongation is not less than 2.2%.

[0025] In an optional embodiment, the fracture mechanism of the 7075 aluminum alloy additively manufactured structural component is a mixed failure mode of brittle fracture, ductile fracture and intergranular fracture.

[0026] In a second aspect, the present application provides a method for manufacturing a 7075 aluminum alloy additively manufactured structural part as described in any of the aforementioned embodiments, comprising the following steps: depositing a 7075 aluminum alloy raw material on a substrate by laser melting deposition.

[0027] In an optional embodiment, the process conditions of laser melting deposition include: laser power of 1-1.2 kW, scanning speed of 4-6 m / s, powder feeding rate of 2-4 r / min, carrier gas volume of 18-22 L / min, and spot diameter of 0.3-0.5 mm.

[0028] In a preferred embodiment, the process conditions of laser melting deposition include: laser power of 1.1 kW, scanning speed of 5 m / s, powder feeding rate of 3 r / min, carrier gas volume of 20 L / min, and spot diameter of 0.4 mm.

[0029] In a third aspect, the present application provides an application of 7075 aluminum alloy additively manufactured structural parts as described in any of the aforementioned embodiments, which can be used as structural parts in aerospace, transportation, automobile manufacturing, military equipment or tooling fixtures.

[0030] In an optional embodiment, 7075 aluminum alloy additively manufactured structural parts are used to make automobile chassis.

[0031] The beneficial effects of this application include:

[0032] This application uses a combination of specific raw materials and manufacturing process parameters to make it possible to produce 7075 aluminum alloy structural parts using a laser melting deposition method. The produced 7075 aluminum alloy structural parts have a relatively flat surface morphology, a small surface roughness profile, and have certain hardness, tensile strength, yield strength, elongation and a low friction coefficient. They meet the current high performance requirements of some large-sized and complex-structured aluminum alloy products and can be used in aerospace, transportation, automobile manufacturing, military equipment or tooling fixtures and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 Deposition samples and surface profiles corresponding to different laser powers in the macro-molding morphology analysis of the experimental example;

[0035] Figure 2 This is the roughness profile of the deposited sample corresponding to different laser powers in the macro-molding morphology analysis of the experimental example;

[0036] Figure 3 This is the density result diagram of the deposited sample corresponding to different laser powers in the density test of the experimental example;

[0037] Figure 4 This is the microstructure morphology of the deposited sample corresponding to different laser powers in the microstructure analysis of the experimental example;

[0038] Figure 5 The microstructure morphology of the deposited sample at different positions when the laser power is 1.1 kW in the microstructure analysis of the experimental example;

[0039] Figure 6 This is the SEM analysis result of the middle part of the deposited sample at a laser power of 1.1 kW in the microstructure analysis of the experimental example;

[0040] Figure 7 This is the EDS analysis result of the deposited sample at a laser power of 1.1 kW in the microstructure analysis of the experimental example;

[0041] Figure 8 This is the phase diagram of the Al-Zn-Mg-Cu quaternary alloy when the Zn content is 6 wt.% and the sum of the copper and magnesium contents is 5 wt.% in the experimental example DSC test;

[0042] Figure 9 The DSC curve and XRD diffraction pattern of the deposited sample when the laser power is 1.1 kW in the DSC test of the experimental example;

[0043] Figure 10 Bright field images, nanoscale EDS line scan results, and SAED patterns of the second phase at different locations of the deposited sample in the experimental phase structure at a laser power of 1.1 kW.

[0044] Figure 11 The phase diagram and selected area electron diffraction pattern of micron precipitates with different morphologies in the deposited sample at a laser power of 1.1 kW in the experimental phase structure;

[0045] Figure 12 This is the microhardness result diagram of the deposited sample corresponding to different laser powers in the mechanical properties analysis of the test example;

[0046] Figure 13 This is the wear resistance result diagram of the deposited sample corresponding to different laser powers in the mechanical properties analysis of the test example;

[0047] Figure 14 This is the tensile stress-strain curve of the deposited sample at a laser power of 1.1 kW in the mechanical properties analysis of the experimental example;

[0048] Figure 15 This is the SEM image of the fracture morphology after the tensile test in the mechanical properties analysis of the experimental example. DETAILED DESCRIPTION

[0049] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0050] The following is a detailed description of the 7075 aluminum alloy additive manufacturing structural parts provided in this application, as well as their production methods and applications.

[0051] At present, the application of laser melting deposition in aluminum alloys is mainly concentrated in Al 10 SiMg and Al 12Si and other high-Si content alloys, but rarely used in 2-series and 7-series aluminum alloy applications. The reason is that the solidification temperature range of high-Si content alloys is small and the solidification shrinkage rate is relatively low, while high-strength aluminum alloys, such as 2-series and 7-series aluminum alloys, are prone to solidification cracking. During the solidification process of such aluminum alloys, the thermal contraction difference between the semi-solid molten pool and the adjacent solid material will generate tensile stress on the solidifying material; if the remaining liquid in the molten pool flows into the interdendritic region and is not sufficient to compensate for the solidification shrinkage and thermally induced strain, pores or voids will form between the growing grains and develop into cracks.

[0052] Based on this, the inventors creatively proposed an effective and feasible method for manufacturing 7075 aluminum alloy additive manufacturing structural parts. By combining specific raw materials and manufacturing process parameters, it effectively overcomes the problem that the laser melting deposition process in the existing technology is difficult to apply to 2 series and 7 series aluminum alloys.

[0053] The present application proposes a 7075 aluminum alloy additively manufactured structural part, which is obtained by depositing a 7075 aluminum alloy raw material on a substrate by laser melting deposition. The chemical composition of the 7075 aluminum alloy raw material includes 4-7wt% Zn, 1.5-3wt% Mg, 1-2.5wt% Cu, 0.35-0.5wt% Fe, 0.03-0.07wt% Si and 0.1-0.3wt% Cr, and the balance is Al.

[0054] For reference, the Zn content may be 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt% or 7 wt%, or any other value within the range of 4-7 wt%.

[0055] The Mg content may be 1.5 wt%, 2 wt%, 2.5 wt% or 3 wt%, or any other value within the range of 1.5-3 wt%.

[0056] The content of Cu may be 1 wt%, 1.5 wt%, 2 wt% or 2.5 wt%, or any other value within the range of 1-2.5 wt%.

[0057] The content of Fe may be 0.35 wt%, 0.4 wt%, 0.45 wt% or 0.5 wt%, or any other value within the range of 0.35-0.5 wt%.

[0058] The Si content may be 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt% or 0.07 wt%, or any other value within the range of 0.03-0.07 wt%.

[0059] The Cr content may be 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt% or 0.3 wt%, or any other value within the range of 0.1-0.3 wt%.

[0060] It is worth noting that the chemical components of the 7075 aluminum alloy raw material in this application, Zn, Mg, Cu, Fe, Si and Cr, can be freely combined within the above ranges, and the remainder is Al.

[0061] In some preferred embodiments, the chemical composition of the 7075 aluminum alloy raw material illustratively includes 5-6 wt% Zn, 2-3 wt% Mg, 1.5-2 wt% Cu, 0.4-0.45 wt% Fe, 0.04-0.06 wt% Si and 0.15-0.25 wt% Cr, with the balance being Al.

[0062] In some more preferred embodiments, the chemical composition of the 7075 aluminum alloy raw material illustratively includes: 5.56wt% Zn, 2.46wt% Mg, 1.64wt% Cu, 0.42wt% Fe, 0.05wt% Si and 0.20wt% Cr, with the balance being Al.

[0063] Among the above chemical components, Zn primarily plays a role in solid solution strengthening, improving alloy strength. When the Zn content is below 4wt%, it can easily lead to significant regression and re-aging, with only partial remelting of the GP zone. Above 7wt%, it can easily lead to severe macrosegregation, poor ductility, and increased hot cracking.

[0064] Mg mainly plays a role in forming a strengthening phase through aging, that is, precipitation strengthening. When the Mg content is less than 1.5wt%, the effect is not obvious, and when it is higher than 3wt%, the formability is poor.

[0065] Cu primarily contributes to the potential difference between grain boundaries and the interior of the grains, significantly improving the alloy's stress corrosion resistance. A Cu content below 1wt% is likely to have little effect, while a Cu content above 2.5wt% can actually worsen the alloy's corrosion resistance. In addition to affecting the potential difference between grain boundaries and the interior of the grains, the element also influences phase transformations within the alloy. For example, Cu can combine with impurity elements to form impurity phases.

[0066] Fe and Si are impurity elements that can form Al6Fe, FeAl3 phases and eutectic compounds, reducing the toughness and plasticity of the alloy.

[0067] Cr mainly plays the role of grain refinement and improving the alloy's stress corrosion resistance. When the Cr content is less than 0.1wt%, the effect is not obvious, and when it is higher than 0.3wt%, it tends to increase quenching sensitivity.

[0068] The laser melting deposition method used in this application is formed by overlapping melt channels. The quality characteristics of the powder material directly determine the quality of the melt channel formation. Therefore, laser melting deposition has strict requirements on the particle size distribution, particle shape, fluidity and oxygen content of the powder.

[0069] In an optional embodiment, the 7075 aluminum alloy raw material used in the present application can be a spherical powder with a particle size of 45-106 μm, preferably with an average particle size of 54.78±8.25 μm. For reference, the 7075 aluminum alloy spherical powder can be specifically vacuum atomized 7075 aluminum alloy spherical powder.

[0070] This application uses spherical particles, which have better flowability than powders of other shapes. Powders with irregular shapes, small sizes, and rough surfaces have poor flowability. Furthermore, this application uses vacuum-atomized spherical powders, which are oxygen-free and facilitate subsequent laser melting deposition.

[0071] The 7075 aluminum alloy spherical powder with the above-mentioned particle size distribution, particle shape, fluidity and oxygen content is used as the raw material. It has good sphericity and fluidity, and low oxygen content, which is conducive to obtaining a good deposition effect and improving product performance.

[0072] In an alternative embodiment, the chemical composition of the substrate may include 4.5-6.5 wt % Zn, 1.5-3.5 wt % Mg, 0.5-1.5 wt % Cu, 0.15-0.35 wt % Fe, 0.08-0.2 wt % Si, and 0.15-0.3 wt % Cr, with the balance being Al.

[0073] In a preferred embodiment, the chemical composition of the substrate includes 5-6 wt% Zn, 2-3 wt% Mg, 1-2 wt% Cu, 0.2-0.3 wt% Fe, 0.1-0.15 wt% Si, and 0.2-0.25 wt% Cr, with the balance being Al.

[0074] In a more preferred embodiment, the chemical composition of the substrate includes 5.65 wt % Zn, 2.61 wt % Mg, 1.46 wt % Cu, 0.25 wt % Fe, 0.11 wt % Si, and 0.22 wt % Cr, with the balance being Al.

[0075] For reference, the substrate may be, for example, a T6 state 7075 aluminum alloy rolled plate, and its size may be, for example, 300 mm×100 mm×6 mm (length×width×height).

[0076] Correspondingly, the present application also provides a method for manufacturing the above-mentioned 7075 aluminum alloy additive manufacturing structural parts, comprising the following steps: depositing 7075 aluminum alloy raw material on a substrate by laser melting deposition.

[0077] In an optional embodiment, the process conditions of laser melting deposition may include: laser power of 1-1.2 kW, scanning speed of 4-6 m / s, powder feeding rate of 2-4 r / min, carrier gas volume of 18-22 L / min, and spot diameter of 0.3-0.5 mm.

[0078] For reference, the laser power may be 1 kW, 1.05 kW, 1.1 kW, 1.15 kW or 1.2 kW, or any other value within the range of 1-1.2 kW.

[0079] The scanning speed may be 4 m / s, 4.5 m / s, 5 m / s, 5.5 m / s or 6 m / s, or any other value within the range of 4-6 m / s.

[0080] The powder feeding rate may be 2 r / min, 2.5 r / min, 3 r / min, 3.5 r / min or 4 r / min, or any other value within the range of 2-4 r / min.

[0081] The carrier gas volume can be 18 L / min, 19 L / min, 20 L / min, 21 L / min or 22 L / min, or any other value within the range of 18-22 L / min.

[0082] The diameter of the light spot may be 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm or 0.5 mm, or any other value within the range of 0.3-0.5 mm.

[0083] Among them, laser power has a direct impact on the roughness, density, microstructure, microhardness, wear resistance and tensile properties of structural parts. A power lower than 1kw or higher than 1.2kw will lead to a decrease in the above-mentioned properties of the structural parts.

[0084] Scanning speed primarily affects density, defects, and pores. A scanning speed below 4 m / s increases the amount of laser energy absorbed by the alloy powder per unit time, but also creates spheroidization defects, which in turn affects the density of the selective laser melted sample. A speed above 6 m / s results in insufficient laser energy and some alloy particles remaining unmelted or in a semi-molten state due to excessive laser scanning speed. Consequently, there is insufficient liquid alloy to fill the pores between the particles.

[0085] The powder feeding rate primarily affects formability. A powder feeding rate below 2 r / min can easily prevent the powder from melting and forming, resulting in a sample block with many defects and low density. A rate above 4 r / min can easily lead to incomplete melting of the metal particles, resulting in defects such as pores and inclusions in the molten pool, and the presence of incompletely melted alloy particles.

[0086] The carrier gas volume primarily affects the effectiveness of air isolation and oxidation prevention. When the carrier gas volume is less than 18 L / min, the gas shielding effect is likely to be ineffective, oxidation may occur, and problems such as pores and defects may occur. When the carrier gas volume is greater than 22 L / min, it is likely to cause irregular solidification of the molten pool, low surface flatness, and uneven quality and strength.

[0087] The spot diameter mainly affects the molding quality. When the spot diameter is less than 0.3mm, it is easy for the metal powder to not be completely melted. When it is greater than 0.5mm, it is easy for the metal powder to be melted again.

[0088] In some preferred embodiments, the process conditions of laser melting deposition exemplarily include: laser power of 1.1 kW, scanning speed of 5 m / s, powder feeding rate of 3 r / min, carrier gas volume of 20 L / min, and spot diameter of 0.4 mm.

[0089] Preferably, before laser deposition, the surface of the base material may be polished with a grinder to remove oxides and impurities, then cleaned with acetone to remove organic matter, and then vacuum dried before laser deposition.

[0090] As mentioned above, the above-mentioned laser melting deposition conditions adopted in the present application, firstly, can prevent the aluminum alloy from being oxidized during the laser melting deposition process, and avoid affecting the mechanical properties of the sample due to the oxidation of the aluminum alloy during the laser melting deposition process; secondly, the aluminum alloy powder used has good fluidity. During the laser melting deposition of the aluminum alloy, the aluminum alloy powder is sent out from the powder barrel through a carrier gas powder feeder, and then output coaxially with the laser beam at the nozzle. Therefore, the aluminum alloy powder with high fluidity used in the present application can be sprayed out smoothly, avoiding clogging of the nozzle or even damage to the entire deposition system; thirdly, since the reflectivity of the aluminum alloy to the laser is very high (about 91%), the laser used in the present application can output sufficiently high energy to ensure that the energy absorbed by the aluminum alloy powder can melt it.

[0091] The 7075 aluminum alloy additive manufacturing structural parts produced by the above method have a density of 0.84-0.88% (preferably 0.86-0.88%) and an average hardness of not less than 120HV 0.1 The average friction coefficient is 0.4678-0.5134, the tensile strength is not less than 158 MPa, the yield strength is not less than 122 MPa, and the elongation is not less than 2.2%. The microstructure of this 7075 aluminum alloy additively manufactured structural component shows columnar crystals at the bottom and middle, and equiaxed crystals at the top, with the structure showing preferentially oriented growth. The phases contained mainly include α-Al as the matrix phase and Mg(Zn,Cu,Al)2 as the precipitation phase. The fracture mechanism is a mixed failure mode of brittle fracture, ductile fracture, and intergranular fracture.

[0092] Furthermore, this application also provides applications for additively manufactured structural parts made from the aforementioned 7075 aluminum alloy, such as structural parts in fields such as aerospace, transportation, automotive manufacturing, military equipment, or fixtures. As a specific example, the aforementioned 7075 aluminum alloy additively manufactured structural parts can be used to manufacture automotive chassis, such as the aluminum alloy chassis of unmanned vehicles.

[0093] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0094] Example 1

[0095] This embodiment provides a 7075 aluminum alloy additive manufacturing structural component, which is obtained by depositing a 7075 aluminum alloy raw material on a substrate by laser melting deposition.

[0096] The chemical composition of the 7075 aluminum alloy raw material includes 5.56 wt% Zn, 2.46 wt% Mg, 1.64 wt% Cu, 0.42 wt% Fe, 0.05 wt% Si and 0.20 wt% Cr, with the balance being Al.

[0097] The chemical composition of the substrate includes 5.65 wt % Zn, 2.61 wt % Mg, 1.46 wt % Cu, 0.25 wt % Fe, 0.11 wt % Si, and 0.22 wt % Cr, with the balance being Al.

[0098] The 7075 aluminum alloy raw material is vacuum-atomized spherical powder with a particle size of 45-106 μm. The average particle size of the spherical powder is 54.78 ± 8.25 μm. The substrate is a T6-tempered 7075 aluminum alloy rolled plate with dimensions of 300 mm × 100 mm × 6 mm.

[0099] The manufacturing method of the 7075 aluminum alloy additive manufacturing structural part includes:

[0100] Pre-treatment of the substrate: Grind the surface of the base material with a grinding wheel to remove oxides and impurities, then clean it with acetone to remove organic matter, and then vacuum dry it.

[0101] 7075 aluminum alloy raw material was deposited on the substrate surface. The laser melting deposition process conditions included a laser power of 1.1 kW, a scanning speed of 5 m / s, a powder feed rate of 3 r / min, a carrier gas volume of 20 L / min, and a spot diameter of 0.4 mm. As the powder material flowed from the laser cladding head, it was deposited and melted along a pre-set path. After the first layer was deposited, the cladding head returned to its origin to continue depositing the second layer. This process was repeated 15 times to obtain a rectangular block.

[0102] The fiber laser used in the above process is RC-LMC-6000-R, equipped with a KUKA robot (KR60HA). The equipment consists of a laser, a robot system, a powder feeding system, a control system, a water cooler, an air compressor, and an inert gas protection system.

[0103] Example 2

[0104] The only difference between this embodiment and embodiment 1 is that the laser power during the laser melting deposition process is 1.0 kW.

[0105] Example 3

[0106] The only difference between this embodiment and embodiment 1 is that the laser power during the laser melting deposition process is 1.2 kW.

[0107] Example 4

[0108] The difference between this embodiment and embodiment 1 is that the chemical composition of the 7075 aluminum alloy raw material includes 5wt% Zn, 3wt% Mg, 1.5wt% Cu, 0.45wt% Fe, 0.04wt% Si and 0.25wt% Cr, with the balance being Al.

[0109] Example 5

[0110] The difference between this embodiment and embodiment 1 is that the chemical composition of the 7075 aluminum alloy raw material includes 6wt% Zn, 2wt% Mg, 2wt% Cu, 0.4wt% Fe, 0.06wt% Si and 0.15wt% Cr, with the balance being Al.

[0111] Example 6

[0112] The difference between this embodiment and embodiment 1 is that the chemical composition of the 7075 aluminum alloy raw material includes 4wt% Zn, 1.5wt% Mg, 1wt% Cu, 0.35wt% Fe, 0.03wt% Si and 0.1wt% Cr, with the balance being Al.

[0113] Example 7

[0114] The difference between this embodiment and embodiment 1 is that the chemical composition of the 7075 aluminum alloy raw material includes 7wt% Zn, 3wt% Mg, 2.5wt% Cu, 0.5wt% Fe, 0.07wt% Si and 0.3wt% Cr, with the balance being Al.

[0115] Example 8

[0116] The difference between this embodiment and embodiment 1 is that the process conditions of laser melting deposition include: laser power of 1.1 kW, scanning speed of 4 m / s, powder feeding rate of 2 r / min, carrier gas volume of 18 L / min, and spot diameter of 0.3 mm.

[0117] Example 9

[0118] The difference between this embodiment and embodiment 1 is that the process conditions of laser melting deposition include: laser power of 1.1 kW, scanning speed of 6 m / s, powder feeding rate of 4 r / min, carrier gas volume of 22 L / min, and spot diameter of 0.5 mm.

[0119] Comparative Example 1

[0120] The difference between this comparative example and Example 1 is that the chemical composition of the aluminum alloy powder raw material used is: 8wt% Zn, 5wt% Mg, 1wt% Cu, 0.35wt% Fe, 0.03wt% Si, and 0.1wt% Cr, with the balance being Al. The average grain size of the aluminum alloy laser additively manufactured part obtained is 95μm, and the average hardness is 82HV. 0.1, , the tensile strength is 120.2MPa and the yield strength is 88.5MPa.

[0121] Comparative Example 2

[0122] The difference between this comparative example and Example 1 is that the particle size of the 7075 aluminum alloy raw material used is 120 μm. The average grain size of the aluminum alloy laser additive manufacturing part obtained is 103 μm and the average hardness is 81 HV. 0.1, , the tensile strength is 110.3MPa and the yield strength is 79.3MPa.

[0123] Comparative Example 3

[0124] The difference between this comparative example and Example 1 is that the laser melting deposition process conditions are: laser power of 1.1 kW, scanning speed of 3.5 m / s, powder feeding rate of 1.5 r / min, carrier gas volume of 15 L / min, and spot diameter of 0.2 mm. The average grain size of the aluminum alloy laser additively manufactured part obtained is 110 μm and the average hardness is 75 HV. 0.1, , the tensile strength is 103.6MPa and the yield strength is 75.5MPa.

[0125] Comparative Example 4

[0126] The difference between this comparative example and Example 1 is that the process conditions of laser melting deposition are: laser power of 1.1 kW, scanning speed of 6.5 m / s, powder feeding rate of 4.5 r / min, carrier gas volume of 25 L / min, and spot diameter of 0.6 mm. The average grain size of the aluminum alloy laser additively manufactured part obtained is 80 μm and the average hardness is 98 HV. 0.1, , the tensile strength is 137.56MPa and the yield strength is 98.3MPa.

[0127] Test example

[0128] The 7075 aluminum alloy additively manufactured structural parts obtained in Examples 1-3 above were subjected to macro-molding morphology analysis, density testing, DSC testing, microstructure analysis, phase analysis, and mechanical property analysis (microhardness, wear resistance, and tensile properties).

[0129] The analysis and test methods and results are as follows:

[0130] ① Macro-molding morphology analysis

[0131] Surface roughness is an important parameter to measure the surface molding quality of parts, which directly affects the service performance and service life of the molded parts.

[0132] In this experiment, the surface roughness of the molded samples produced by different additive manufacturing methods was tested using an Olympus LEXT OLS5000 laser confocal scanning microscope (3D MEASURING LASER MICROSCOPE OLS5000).

[0133] The results are as follows:

[0134] Deposition samples and surface profiles at different laser powers are shown in Figure 2. Figure 1 As shown, Figure 1 (a) to Figure 1 (c) The corresponding powers are 1.0 kW, 1.1 kW, and 1.2 kW, respectively. From the external macroscopic morphology, it can be seen that the samples formed at three different laser powers all have good forming effects, with no obvious macroscopic cracks or pores. The length, width, and height are 100 mm × 50 mm × 15 mm.

[0135] The roughness profiles of the three laser powers are shown in Figure 2. Figure 2 As shown, Figure 2 (a) to Figure 2 (c) corresponds to powers of 1.0 kW, 1.1 kW, and 1.2 kW, respectively. It can be seen from the figure that when the laser power is 1.0 kW, the surface roughness profile is 473.774 μm; when the laser power is 1.1 kW, the surface roughness profile is 434.092 μm; when the laser power is 1.2 kW, the surface roughness profile is 566.705 μm.

[0136] It can be seen from this that when the laser power is 1.1 kW, the surface roughness profile is minimized. When the laser power is reduced, incomplete melting of the powder causes the molten pool to rise significantly above the horizontal plane. When the power is increased, powder splashing during laser processing becomes more severe. Molten slag falls on both sides of the melt channel and on the upper surface, increasing the surface roughness profile. Properly increasing the laser power can fully melt the metal powder, improve wettability, and enhance surface quality. However, excessive power can cause surface spheroidization and voids, making the surface rougher. Therefore, appropriate laser power parameters can effectively improve surface roughness.

[0137] ②Density test

[0138] Density is the ratio of a molded part's actual density to its theoretical standard density. Also known as the packing ratio or maximum space utilization, it refers to the volume fraction occupied by atoms in a unit cell and is a key indicator of a part's mechanical properties. Defects such as incomplete melting, pores, and cracks within a molded part directly impact its density. Therefore, density is the most fundamental indicator of the quality of an AM molded part.

[0139] In this test, an MH-120C Solid Electronic densimeter was used to measure alloy density. This method follows Archimedes' principle. Samples were weighed in air and then in distilled water, and the density was automatically calculated using the following formula. To ensure measurement accuracy, each sample was weighed three times and the average value was calculated. The difference between the actual density and the reference density was the density.

[0140] The formula is as follows: ρ 致密度 = 样品 ÷ρ 理论 ×100%.

[0141] Where m 空气 and m 水 are the weight of the sample in air and water, respectively, 水 is the density of water, ρ 理论 is the standard theoretical density.

[0142] The results are as follows:

[0143] Figure 3 The density after laser deposition at different powers is shown. The results show that at 1.1 kW, the density is the highest. When the laser power is reduced, the melting of the alloy powder is incomplete, which affects the formability and the density is also reduced. When the laser power is increased, the gasification of the alloy powder is more serious, so the density will be reduced.

[0144] ③Microstructure

[0145] Methods: JEOL JSM-7500 field scanning electron microscope (SEM) was used to analyze the microstructure and elemental composition distribution of powder and deposited samples.

[0146] The results are as follows:

[0147] Figure 4 is the microstructure of the deposited sample at different powers, Figure 4 (a) to Figure 4 (c) Corresponding to laser powers of 1.0 kW, 1.1 kW, and 1.2 kW, respectively. As can be seen from this figure, at a laser power of 1.1 kW, microstructure defects are minimized. At a power of 1.2 kW, the number of pores increases and the pore diameter becomes larger. When the laser power is relatively low, due to insufficient powder melting, some partially melted powder enters the molten pool, forming a large number of pores. As the laser power gradually increases, the powder melts more fully, and the pores and inclusions in the deposited layer are significantly reduced. As the laser power continues to increase, the temperature in the molten pool rises sharply, the molten pool moves violently, and the disturbance increases. During this process, gas may be mixed into the molten pool, unable to escape during the cooling and solidification of the molten pool, and thus remain in the deposited layer, resulting in pores in the deposited layer. Initially, the volume fraction of equiaxed crystals is much smaller than that of columnar crystals. In the liquid phase region at the leading edge of the columnar crystals, the density of equiaxed crystals is relatively low. The columnar crystals engulf the equiaxed crystals that first come into contact with them, making them the raw material for their own growth. As the transformation continues, the columnar crystals continue to grow, the temperature gradient at their front continues to decrease, the solidification rate continues to increase, more equiaxed crystal nuclei grow in the liquid phase, and their density continues to increase. When competing with the columnar crystals for growth, their competitive advantage gradually increases, and the growth advantage of the columnar crystals gradually disappears. When the growth advantage of the columnar crystals in the competitive growth completely disappears, they slowly stop growing and transform into equiaxed crystals that completely dominate, continuing to grow and develop, and eventually all the liquid metal in the molten pool solidifies and crystallizes.

[0148] In order to further analyze the characteristics of tissue evolution, different positions of the tissue were analyzed at a laser power of 1.1 kW, such as Figure 5 As shown in (a), (b), and (c), Figure 5(d) The grains were counted using Nanomeasurer 1.2 software. The average grain size was 53.36 μm. Rapid laser heating and rapid solidification were the main reasons for grain refinement. The growth of grains during fusion welding is caused by the epitaxial solidification of the base material and the growth toward the center line of the weld. Similarly, under conditions of overheating of the melt, there is almost no uniform nucleation during laser deposition and melting, and the grains always enhance nucleation at the solid-liquid interface between the substrate surface and the liquid metal. Crystallization begins at the boundary of the molten pool, and the grains continue to grow into columnar crystals and enter the melt. The most favorable crystal orientation for α-Al grain growth is (001). When perpendicular to the isotherm of the molten pool boundary, the heat dissipation at this isotherm is the fastest, and the α-Al grains can continue to grow into the molten pool. But in <001> Directionally, grain growth in the direction of the grain boundary isotherms is suppressed, growing only over a short distance. This phenomenon is known as preferred orientation. It is due to the inconsistent thermal cycling from the bottom to the top of the sample during LMD deposition. At the bottom, the deposition of the substrate accelerates heat dissipation, and the substrate grains serve as nucleation particles for deposition, forming an equiaxed structure at the bottom. As the number of layers increases, the heat dissipation of the substrate decreases, forming coarse columnar grains in the middle and top of the substrate. The top is not remelted, which directly reflects the structural characteristics of the deposited layer. At the bottom of the molten pool, the upper layer remelts under a certain temperature gradient and grows epitaxially, resulting in a columnar crystal structure in most of the middle part. On the other hand, due to the CET transition, equiaxed crystals form at the top. Under the action of the upper heat treatment, the intermediate columnar crystals grow and form coarse columnar crystals.

[0149] The middle part of the deposited sample was analyzed by scanning electron microscopy. Figure 6 As shown, Figure 6 (a) and Figure 6 (c) is low magnification, Figure 6 (b) and Figure 6 (d) is low magnification. Figure 6 It can be seen that the precipitates at the grain boundaries and within the grains have been corroded away, with particles falling off and forming pores. A large number of precipitates are distributed throughout the sedimentary sample. These precipitates exist both within the grains and at the grain boundaries, appearing as discontinuous stripes and blocks.

[0150] In order to conduct a further quantitative analysis, EDS analysis was performed on the scanning electron microscope images to determine the chemical composition. The results are as follows Figure 7As shown, (a) is the overall surface scan, (b) is the line scan, and the rest are surface scan element distribution maps. The matrix phase is α-Al, resulting in a high Al content. The surface scan element distribution reveals that Zn, Mg, and Cu are enriched at grain boundaries and within the grains, with segregation in element distribution. Analysis of these grain boundary and intragranular phases reveals a series of precipitates rich in Zn, Mg, and Cu. Table 1 shows the point spectrum results for points A, B, and C. The Zn and Mg contents vary little, but at corrosion pit B, the Cu content increases significantly, while the Al content decreases sharply. O and C also vary significantly, likely due to the influx of oxygen during deposition and the presence of C due to elemental burnout. Line scan results show that the particles are primarily Al and Cu precipitates, distributed around the corrosion pits. During the LMD process, the rapid solidification rate easily leads to nonequilibrium solidification, resulting in dendritic segregation of solute atoms.

[0151] Table 1 EDS analysis results of elements in different regions (At.%)

[0152]

[0153] ④DSC test

[0154] In order to analyze the second phase precipitation law during the deposition process, differential scanning calorimetry measurements were performed on the deposited samples and atomized powders at a laser power of 1.1 kW.

[0155] Differential Scanning Calorimetry (DSC) measurement method: The center of the sample to be tested was cut into a 2 mm × 2 mm square, which was then polished smooth with sandpaper. Analysis was performed using a differential scanning calorimeter (Model Q2000). DSC was performed at a heating and cooling rate of 10°C / min from 40 to 500°C with a sample mass of 80 μg, with the dominant phase formation and dissolution sequence recorded.

[0156] Phase analysis method: The samples were cut into 10 × 10 × 6 mm squares along the deposition direction using a wire cutting machine. After being polished smooth with sandpaper, the phase composition was analyzed using a PANalytical X-ray diffractometer (XRD) in the Netherlands. A Cu target with a wavelength of 1.54060 nm was used, the scanning speed (2θ) was 5 deg / min, and the scanning range was 20 to 90 deg with a step size of 0.02 deg.

[0157] result: Figure 8The phase diagram of Al-Zn-Mg-Cu quaternary alloy with Zn content of 6wt.% and Cu and Mg content of 5wt.% was studied. The Al matrix is ​​supersaturated, and Al2CuMg (S phase), Al2Mg3Zn3 (T phase) and MgZn2 (S phase) are precipitated. The precipitation order of Al-Zn-Mg-Cu is: GP zone → η′ → η → T → S. First, the GP zone rich in Mg and Zn is formed, and then the η′ metastable phase is formed, and then it evolves into the stable η phase. Through further aging, T (Al2Mg3Zn3) and S (Al2CuMg) can be formed, from Figure 9 (a) A small exothermic peak was observed near 120°C for both the powder and the deposited sample, which may be the generation of the GP zone. A second peak was found near 220-230°C, the appearance of which may be related to the precipitation of the η′ phase. When the Mg / Zn ratio of the aluminum alloy is large, the T phase is the main phase, rather than the η phase and its precursor phase η′. The endothermic peak of the deposited sample around 410°C may be related to the precipitation of the η phase. It is worth noting that due to the kinetics of the diffusion-controlled reaction, using continuous heating DSC, all phase formation temperatures and phase dissolution temperatures are slightly higher than the corresponding equilibrium transformation temperature values. For the supersaturated solid solution α composed of two components A and B, the driving force for the precipitation of the B-rich component β phase is related to the matrix concentration. The higher the matrix concentration, the greater the driving force for precipitation. The relationship between the nucleation rate N and the activation energy can be expressed by the following formula:

[0158]

[0159]

[0160] Among them, Q * --nucleation activation energy, - Driving force for desolvation.

[0161] The main precipitates of aluminum-zinc-magnesium-copper alloys are magnesium-rich phases and zinc-rich phases. As can be seen from the above formula, the higher the Mg content, the higher the driving force for precipitation and the lower the nucleation activation energy, so the nucleation rate of Mg-rich and Zn-rich phases (GPI zones) also increases accordingly. As the aging time increases, most of the GPI zones gradually disappear, and only a very small number of large-sized GPI zones can exist stably throughout the aging process. Part of the disappeared GPI zones dissolves in the matrix, and the other part is converted into η' phase. Since alloys with high Mg content will produce more GPI zones at the beginning of aging, and the number of η' phases formed by the transformation of GPI zones will inevitably increase, alloys with high Mg content have higher hardness at the beginning of aging and peak aging.

[0162] Figure 9(b) shows the XRD diffraction pattern of the sample deposited at 1.1 kW laser power. As shown in the figure, after searching with a standard PDF card, only the matrix α-Al phase and the precipitated phase Mg(Zn,Cu,Al)2 were retrieved from the XRD pattern, as shown in the locally enlarged area of ​​the figure. The matrix α-Al phase has a significantly higher (111) diffraction peak than other diffraction peaks. Therefore, the laser-deposited 7075 aluminum alloy has a clear preferred orientation in the (111) direction, and the epitaxial growth characteristics in the structure correspond to this. In addition to these two phases, no other phases were observed. This may be because the content of the second phase or precipitated phase is too low to produce a clear X-ray diffraction peak.

[0163] ⑤ Phase structure

[0164] Transmission electron microscopy analysis method:

[0165] A 10 mm × 10 mm × 0.5 mm sheet sample was cut from the middle of the deposited sample and mechanically thinned to 35 μm for transmission electron microscopy observation. High-field, high-resolution and scanning transmission electron microscopy (STEM) observations were carried out using a FEI Talos 200X and a FEI Technai G2 F30 transmission electron microscope (TEM) and a FEI TALOS 200X and a FEI Technai G2 F30 transmission electron microscope (TEM) equipped with a high-angle annular dark field (HAADF) detector. Fast Fourier transform (FFT) of the high-resolution images was performed using Gatan Digital Micrograph software.

[0166] The phase structure test results are as follows:

[0167] Since the phase composition cannot be identified based on chemical element composition, in order to further determine the composition of the second phase in the sediment sample, the micromorphology of the organization was observed and analyzed using transmission electron microscopy, and the type of precipitated phase was determined by selected area electron diffraction. The analysis results are as follows: Figure 10 As shown, Figure 10 (a) and Figure 10 (d) is the bright field image of the second phase at different positions, Figure 10(b) and Figure 10 (e) is the nanoscale EDS line scan result, Figure 10 (c) and Figure 10 (f) is the corresponding SAED pattern.

[0168] The above results indicate that all of the above phases are ηMg(Zn,Cu,Al)₂ phases. The equilibrium chemical composition of the η phase is MgZn₂, with a hexagonal structure and belonging to the P63 / mmc space group. However, zinc atoms are easily substituted by copper and aluminum atoms, forming a continuous solid solution without affecting the lattice structure. In aluminum-zinc-magnesium-copper alloys, the η phase almost always contains copper and aluminum. Nanoscale EDS line scans reveal that the atomic percentages of Zn, Mg, and Cu in the second phase range from 25.30% to 40%, 20% to 35%, and 18% to 22%, respectively. The alloying element concentrations detected by nanoscale EDS are significantly higher than those detected by SEM characterization, and the concentration differences between these phases are significant. However, these are not necessarily distinct results. Since the electron beam interaction volume of a scanning electron microscope is larger than that of a transmission electron microscope, the higher alloying element content may be due to the greater contribution of the Al matrix to the EDS signal. The concentration differences between these phases may be due to their different orientations. Therefore, we used high-resolution transmission electron microscopy (HRTEM) to further search for structural evidence.

[0169] Micronized precipitates with different morphologies were found to exist in all alloy compositions, e.g. Figure 11 As shown, Figure 11 (a) is an irregular phase, Figure 11 (d) is a long rod-shaped phase, Figure 11 (b) and Figure 11 (e) is a high-resolution image, Figure 11 (c) and Figure 11 (f) is the selected area electron diffraction pattern corresponding to the length phase. Among them, the number of long strip-shaped second phase is the largest and the most common, with a length of about 30 to 40 nm. Another type of precipitated phase is spherical, elliptical or water droplet-shaped; the formation of the precipitated phase consumes the solute elements nearby, so there is a small area without precipitated phase in the surrounding area. The selected area electron diffraction patterns of the precipitated phase are shown in Figure 11 (c) and Figure 11(f) After calibration and analysis, it was determined that these precipitates are all η(MgZn2) phases. Since they lack a specific orientation relationship with the matrix, it can be inferred that the micron-scale precipitates are generated by liquid-phase reactions during solidification. Sparse nano-precipitates are uniformly distributed throughout the alloy matrix. These phases are mostly rod-shaped or spherical, with lengths ranging from approximately 100 to 200 nm. They are inferred to be precipitation products from the supersaturated matrix. Due to the large size of these precipitates, their lattice parameters are difficult to determine, but the energy spectrum results confirm that they are a series of precipitates rich in Zn, Mg, and Cu. Another type of nanoprecipitated phase differs significantly in shape and distribution. These fine dispersed phases are numerous, but their size and distribution are uneven, with higher density in certain areas of the matrix. Their appearance often resembles water marks or petals. The strain contrast of these petals is consistent with the morphology of the Mg2Si dispersed phase. This is due to the coherence of the Mg2Si dispersed phase with the matrix, which undergoes lattice distortion around the dispersed phase, resulting in strain contrast. Under specific orientation conditions, a line of no contrast is generated, dividing the spherical particle into two symmetrical petals. This contrast is also known as Ashby-Brown contrast. Four variants of the η′ phase precipitated during aging in Al-Zn-Mg-Cu alloys are found, all parallel to the four {111} Al crystal planes of the matrix. The orientation relationships of the four variants with the matrix are:

[2342] η′ / /

[110] Al,

[0303] η′ / /

[022] Al,

[0303] η′ / /

[022] Al;

[0110] η′ / /

[110] Al,

[8121] η′ / /

[022] Al;

[0110] η′ / /

[110] Al,

[1821] η′ / /

[022] Al. <011> When observing the Al crystal zone axis, two of the variants of the η′ phase have a rod-like projection shape, and the other has an elliptical projection shape.

[0170] ⑥ Mechanical properties analysis

[0171] A. Microhardness

[0172] Method: Microhardness analysis was performed on the specimens using an HV-50 low-load Vickers hardness tester with a loading force of 1.98 N and a spacing of 5 mm between each measuring point. Each hardness value was tested three times and the average value was taken.

[0173] Results: As Figure 12 As shown, the average hardness of the sinking samples under the three laser powers all reached 120HV 0.1As shown above, the hardness of the sample deposited at a laser power of 1.1 kW is higher than that of the samples deposited at 1.0 kW and 1.2 kW. For all three samples, the hardness is lower at the bottom, increasing with the number of deposited layers, and decreasing toward the top. The average hardness of the cross-deposition sample is higher than that of the parallel-deposition sample because the secondary phase in the cross-deposition sample is dispersed and evenly distributed, while the secondary phase in the parallel-deposition sample segregates and precipitates at grain boundaries, forming coarse secondary phases. The change in hardness distribution from bottom to top is due to the fact that the central portion undergoes a long heat treatment, resulting in a large amount of dispersed secondary phase precipitation. The bottom portion, due to the heat dissipation effect of the substrate, remains at a shorter high temperature, resulting in less dispersed precipitation. The top portion exhibits an equiaxed structure and undergoes no heat treatment. Therefore, under the continuous heat input of laser additive manufacturing, the hardness values ​​of the sample increase first and then decrease from bottom to top. This is primarily due to two reasons: first, the rapid heating and cooling solidification processes of laser additive manufacturing lead to grain refinement. On the other hand, nonequilibrium solidification increases the solubility of the solid solution. EDS shows that the solubility of Si in Al (mass percentage) reaches 5.45, far exceeding its maximum solubility of 1.56%, enhancing the solid solution strengthening effect. The combined influence of these factors inevitably leads to the hardness of laser-additive alloys being higher than that of cast alloys of the same composition.

[0174] B. Wear resistance

[0175] Method: The wear resistance was tested using an HSR-2M high-speed reciprocating friction testing machine. The grinding ball was made of GCr15, the load was 50N, the reciprocating stroke was 6mm, and the test time was 15min.

[0176] Results: As Figure 13 As shown, Figure 13 (a) Curves showing the time-dependent variation of the friction coefficient of 7075 alloy additively manufactured at different laser powers. In the initial dry sliding wear stage, the friction coefficient fluctuates significantly. As the wear progresses, the friction coefficient gradually stabilizes, but the fluctuations remain relatively large. The wear then enters the stable wear stage, but with significant fluctuations. Figure 13 (b) is the average value of the friction coefficient at each power. When the laser power is 1.0 kW, the average friction coefficient is 0.5134. When the laser power is 1.1 kW, the average friction coefficient is 0.4678. When the laser power is 1.2 kW, the average friction coefficient is 0.4837. For general metal materials, the higher the hardness, the better the wear resistance.

[0177] C. Tensile properties

[0178] Method: A microcomputer-controlled electronic universal testing machine model MTS810 (250 kN) was selected, and a laser extensometer was used to measure strain (elongation). The initial strain rate was set to 1 mm / min and the tensile force was 50 N.

[0179] Results: As Figure 14 As shown, Figure 14 (a) is the stress-strain curve of the tensile test of the sample deposited with a laser power of 1.1 kW at room temperature, which shows initial elastic deformation and obvious strain hardening until final failure. Figure 14 (b) is the tensile strength, yield strength and elongation of the above-mentioned deposited sample. It can be seen from the figure that the tensile strength of the deposited sample is 158.66MPa, the yield strength is 122.3MPa, and the elongation is 2.3%. The deposited sample has very low strength and poor ductility, which is mainly caused by the main porosity defects in the microstructure, as can be seen from the metallographic structure diagram.

[0180] Furthermore, the fracture morphology of the above deposited samples was analyzed using a JEOL JSM-7500 field scanning electron microscope (SEM). Figure 15 The SEM image of the fracture surface after the tensile test is shown. Figure 15 (a) and Figure 15 (b) is the low-magnification morphology of different regions. Figure 15 (b) is the pore and crack area, Figure 15 (d) is the intergranular region. As shown in the figure, the presence of shallow dimples indicates ductile fracture. In addition, some low-ductility regions with lamellar features are observed. Some internal defects, such as porosity and incompletely melted particles, can be seen in the figure, which are also observed on the fracture surface of the laser-melted specimen. Unbonded powder particles are weak areas that impair the behavior of the specimen under load. In addition, porosity is considered to be a stress concentration point, and cracks are likely to nucleate and propagate in these areas, thereby initiating fracture. Some pores and unmelted powder are present in the tensile fracture. These are the main reasons for the low tensile strength during the deposition process. Fracture morphology analysis shows that cleavage, dimples, and columnar crystals are locally present on the fracture surface, indicating a mixed failure mode of brittle fracture, ductile fracture, and intergranular fracture.

[0181] In summary, this application effectively overcomes the problem in the prior art that the laser melting deposition process is difficult to apply to 7075 aluminum alloy by adopting a combination of specific raw materials and manufacturing process parameters. The resulting 7075 aluminum alloy structural parts have a relatively flat surface morphology, a small surface roughness profile, and have certain hardness, tensile strength, yield strength, elongation and a low friction coefficient. They can be used in aerospace, transportation, automobile manufacturing, military equipment or tooling fixtures and other fields.

[0182] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A 7075 aluminum alloy additive manufacturing structural part, characterized in that: The 7075 aluminum alloy additive manufacturing structural component is obtained by depositing a 7075 aluminum alloy raw material on a substrate by laser melting deposition, and the chemical composition of the 7075 aluminum alloy raw material includes 4-7wt% Zn, 1.5-3wt% Mg, 1-2.5wt% Cu, 0.35-0.5wt% Fe, 0.03-0.07wt% Si and 0.1-0.3wt% Cr, with the balance being Al; The 7075 aluminum alloy raw material is a vacuum atomized 7075 aluminum alloy spherical powder with a particle size of 45-106 μm; The chemical composition of the substrate includes 4.5-6.5 wt % Zn, 1.5-3.5 wt % Mg, 0.5-1.5 wt % Cu, 0.15-0.35 wt % Fe, 0.08-0.2 wt % Si and 0.15-0.3 wt % Cr, with the balance being Al; The method for preparing a 7075 aluminum alloy additively manufactured structural part comprises: depositing the 7075 aluminum alloy raw material on the substrate by laser melting deposition; the process conditions of the laser melting deposition include: laser power of 1-1.2 kW, scanning speed of 4-6 m / s, powder feeding rate of 2-4 r / min, carrier gas volume of 18-22 L / min, and spot diameter of 0.3-0.5 mm; In the structure of the 7075 aluminum alloy additively manufactured structural part, columnar crystals are formed at the bottom and middle, and equiaxed crystals are formed at the top, and the structure shows preferential orientation growth; the average hardness of the 7075 aluminum alloy additively manufactured structural part is not less than 120HV 0.1 ; The average friction coefficient of the 7075 aluminum alloy additively manufactured structural parts is 0.4678-0.5134; the tensile strength of the 7075 aluminum alloy additively manufactured structural parts is not less than 158MPa, the yield strength is not less than 122MPa, and the elongation is not less than 2.2%.

2. The 7075 aluminum alloy additive manufacturing structural component according to claim 1, characterized in that: The chemical composition of the 7075 aluminum alloy raw material includes 5-6wt% Zn, 2-3wt% Mg, 1.5-2wt% Cu, 0.4-0.45wt% Fe, 0.04-0.06wt% Si and 0.15-0.25wt% Cr, with the balance being Al.

3. The 7075 aluminum alloy additively manufactured structural component according to claim 2, characterized in that: The chemical composition of the 7075 aluminum alloy raw material includes: 5.56wt% Zn, 2.46wt% Mg, 1.64wt% Cu, 0.42wt% Fe, 0.05wt% Si and 0.20wt% Cr, with the balance being Al.

4. The 7075 aluminum alloy additively manufactured structural component according to any one of claims 1 to 3, characterized in that: The chemical composition of the substrate includes 5-6 wt % of Zn, 2-3 wt % of Mg, 1-2 wt % of Cu, 0.2-0.3 wt % of Fe, 0.1-0.15 wt % of Si and 0.2-0.25 wt % of Cr, with the balance being Al.

5. The 7075 aluminum alloy additively manufactured structural component according to claim 4, characterized in that: The chemical composition of the substrate includes 5.65 wt % Zn, 2.61 wt % Mg, 1.46 wt % Cu, 0.25 wt % Fe, 0.11 wt % Si, and 0.22 wt % Cr, with the balance being Al.

6. The 7075 aluminum alloy additively manufactured structural component according to claim 5, characterized in that: The substrate is a T6 state 7075 aluminum alloy rolled plate.

7. The 7075 aluminum alloy additively manufactured structural component according to claim 1, characterized in that: The density of the 7075 aluminum alloy additively manufactured structural parts is 0.84-0.88%.

8. The 7075 aluminum alloy additively manufactured structural component according to claim 7, characterized in that: The density of the 7075 aluminum alloy additively manufactured structural parts is 0.86-0.88%.

9. The 7075 aluminum alloy additively manufactured structural component according to claim 1, characterized in that: The phases contained in the 7075 aluminum alloy additively manufactured structural component mainly include α-Al phase as a matrix phase and Mg(Zn, Cu, Al)2 as a precipitation phase.

10. The 7075 aluminum alloy additively manufactured structural component according to claim 1, characterized in that: The fracture mechanism of the 7075 aluminum alloy additively manufactured structural component is a mixed failure mode of brittle fracture, ductile fracture and intergranular fracture.

11. The method for manufacturing a 7075 aluminum alloy additively manufactured structural component according to any one of claims 1 to 10, wherein: The following steps are involved: Depositing the 7075 aluminum alloy raw material on the substrate by laser melting deposition; The process conditions of laser melting deposition include: laser power of 1-1.2 kW, scanning speed of 4-6 m / s, powder feeding rate of 2-4 r / min, carrier gas volume of 18-22 L / min, and spot diameter of 0.3-0.5 mm.

12. The manufacturing method according to claim 11, characterized in that: The process conditions of laser melting deposition include: laser power of 1.1 kW, scanning speed of 5 m / s, powder feeding rate of 3 r / min, carrier gas volume of 20 L / min, and spot diameter of 0.4 mm.

13. Application of 7075 aluminum alloy additive manufacturing structural parts according to any one of claims 1 to 10, characterized in that: 7075 aluminum alloy additive manufacturing structural parts are used as structural parts in aerospace, transportation, automobile manufacturing, military equipment or tooling fixtures.

14. The use according to claim 13, characterized in that The 7075 aluminum alloy additively manufactured structural parts are used to manufacture automobile chassis.

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