CN113430432B - Preparation method of high-Zn light high-strength aluminum alloy - Google Patents
Preparation method of high-Zn light high-strength aluminum alloy Download PDFInfo
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- C22C—ALLOYS
- C22C21/00—Alloys based on aluminium
- C22C21/10—Alloys based on aluminium with zinc as the next major constituent
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
- B22F10/20—Direct sintering or melting
- B22F10/28—Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
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- B33—ADDITIVE MANUFACTURING TECHNOLOGY
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- B33Y10/00—Processes of additive manufacturing
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B33Y70/00—Materials specially adapted for additive manufacturing
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- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/0408—Light metal alloys
- C22C1/0416—Aluminium-based alloys
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- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
- B22F2009/043—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling by ball milling
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Abstract
The invention discloses a preparation method of a high-Zn light high-strength aluminum alloy, which relates to the field of material processing engineering. The invention designs Al-Zn-Mg-Zr alloy powder suitable for a selective laser melting technology, and proposes that the burning loss of Zn is reduced to the maximum extent on the basis of realizing effective connection by controlling the lap joint rate between adjacent melting channels to be-5%. Meanwhile, different from preheating the substrate in other aluminum alloy forming processes, the invention further reduces the temperature of the substrate, and increases the temperature gradient by introducing cooling liquid to the bottom and the side surface of the substrate to reduce the temperature, thereby further increasing the supersaturated solid solution capacity of Zn. The invention is applied to the field of material processing.
Description
Technical Field
The invention belongs to the field of material processing engineering, and particularly relates to a preparation method of a high-Zn light high-strength aluminum alloy.
Background
The characteristics of rich aluminum alloy reserves, small density and high specific strength perfectly fit with the requirement of light weight, and the application prospect is wide, wherein the Al-Zn-Mg alloy is taken as a heat-treatment-reinforced ultrahigh-strength aluminum alloy, and is widely applied to the fields of aerospace, rail transit and the like due to the advantages of good fatigue property, high specific strength and the like. The defects of macro segregation, cracking, grain coarsening and the like easily occur in the traditional casting due to slow cooling in the preparation process, and a large amount of cracks and pore defects occur in a formed sample due to the fact that Zn is a low-melting-point element and is directly added with high-content Zn in the casting process, so that the sample cannot be used; and because the solidification speed in the casting process is limited, the solid solubility of Zn atoms in the aluminum alloy at room temperature is limited, the mass fraction of Zn in the common Al alloy is 7% or less, the solid solution strengthening effect cannot be fully exerted, and the quantity of particles precipitated in the later aging treatment process is limited, thereby limiting the further improvement of the mechanical property of the Al-Zn-Mg alloy. Further increasing the Zn content is an effective method for realizing the performance strengthening of the alloy.
Selective Laser Melting (SLM) is an additive technology based on a powder laying technology, and compared with the traditional processing modes such as casting, forging and welding, the SLM is difficult to prepare complex and tiny structural parts, has the defect of long manufacturing period, and has the characteristics of free forming and high-precision forming. The metal powder is completely melted under the high energy input action of selective laser melting, and the liquid phase is solidified after full contact, thus obtaining a metallurgically bonded high-density solid with less internal defects and a cooling rate of 103-107K/s, which is easy to form supersaturated solid solution and is helpful for refining crystal grains, and a formed piece with fine and uniform microstructure and good comprehensive performance is obtained. While the alloy components corresponding to the traditional Al-Zn-Mg alloy plate have a large number of crack defects in the sample after the selective laser melting processing, and basically have no use performance, some researches can reduce cracks through rare earth modification, but the performance of the formed alloy has larger loss compared with that of a forged state, for example, the sample is cracked after the 7075 aluminum alloy is directly subjected to selective laser melting forming, and the tensile strength loss exceeds 100MPa after the rare earth element is added and the selective laser melting forming is carried out. Therefore, based on the characteristics of the Al-Zn-Mg alloy and the advantage of high-speed cooling of the selective laser melting technology, the high-strength Al-Zn-Mg alloy suitable for the selective laser melting technology is designed, and has important application value.
Patent 110172620A discloses Al-Si-Mg alloy for selective laser melting technology and a method for preparing a product thereof, which designs an aluminum alloy powder, but needs further heat treatment after forming, and the plasticity of the sample is poor. Patent 112008076a discloses a method for optimizing the composition design of a selective laser melting aluminum alloy, but the method mainly focuses on the compactness of a sample and lacks the inspection of the mechanical properties of the formed sample.
Disclosure of Invention
The invention aims to overcome the defects of the existing alloy preparation technology, and provides a novel method, namely a preparation method of high-strength aluminum alloy based on selective laser melting, which is suitable for the processing characteristics of selective laser melting and realizes further strengthening of the performance of the aluminum alloy.
The invention relates to a preparation method of a high-Zn light high-strength aluminum alloy, which is carried out according to the following steps:
weighing and mixing powder for selective laser melting, wherein the mass fraction of Zn is 12-15%, the mass fraction of Mg is 1-2%, the mass fraction of Zr is 0.5-2%, and the balance is Al;
mechanically mixing the powder mixed in the last step by adopting a planetary ball milling powder mixer, introducing inert gas into a mixing tank to protect the powder from oxidation, and then rotating at the rotation speed of 200-400rpm for 5-10min and stopping rotating for 5-10min for cooling for 4-8 h;
drawing a model through three-dimensional drawing software, and drawing the three-dimensional model according to a pre-designed part structure and size; spreading the powder mixed in the last step according to the thickness of 0.03-0.05mm, spreading the powder layer by layer, transversely cutting the model into a plurality of continuous equal-thickness slices (as shown in figure 7) with the thickness of 0.03-0.05mm by three-dimensional drawing software;
fourthly, pre-clamping the substrate on a forming platform, adjusting the levelness of the substrate to +/-0.025 mm, and introducing cooling liquid at the temperature of-20 to 0 ℃ into a fixed cooling cavity at the bottom and the periphery of the substrate at the flow speed of 5 to 10L/min;
fifthly, setting process parameters, operating a model data file, introducing argon for protection, and starting equipment after the oxygen content in a forming bin is less than 0.1%;
fully cooling the formed block sample, taking out, performing wire cut electrical discharge machining, and performing ultrasonic cleaning to recover unused powder; thus completing the preparation method of the high-Zn light high-strength aluminum alloy;
wherein, the set process parameters in the fifth step are as follows: the diameter of the laser spot is 0.1-0.12mm, the laser scanning interval is 0.09-0.13mm, the laser power is 320W plus 120W, the scanning speed is 800mm/s plus 200W plus, and the overlapping rate between adjacent melt channels is controlled at-5%.
Further, the grain sizes of Al powder, Zn powder and Mg powder in the weighed Al-Zn-Mg-Zr alloy powder are all 60-80 mu m; the grain size of the Zr powder is 80-100 μm.
Furthermore, the mass fraction of Zn in the Al-Zn-Mg-Zr alloy powder is 13-14%, the mass fraction of Mg is 1.5-2%, the mass fraction of Zr is 1-2%, and the balance is Al.
Further, the rotation speed of 300-400rpm in the step two is rotated for 6-8min and then stopped for 6-8min for cooling.
Further, the thickness of the powder laid in the third step is 0.04 mm.
Further, the ultrasonic cleaning time in the sixth step is 30 min.
Further, the process parameters set in the fifth step are as follows: the diameter of the laser spot is 0.1-0.12mm, the laser scanning interval is 0.1-0.13mm, the laser power is 150-280W, the scanning speed is 300-600mm/s, and the overlapping rate between adjacent melt channels is controlled at-3%.
Further, the process parameters set in the fifth step are as follows: the diameter of the laser spot is 0.1-0.12mm, the laser scanning interval is 0.1-0.12mm, the laser power is 180-250W, the scanning speed is 300-500mm/s, and the overlapping rate between adjacent melt channels is controlled at-2%.
Further, the process parameters set in the fifth step are as follows: the diameter of the laser spot is 0.1-0.12mm, the laser scanning interval is 0.1-0.11mm, the laser power is 200-.
Further, the process parameters set in the fifth step are as follows: the diameter of a laser spot is 0.1mm, the laser scanning interval is 0.11mm, the laser power is 200W, the scanning speed is 400mm/s, and the overlapping rate between adjacent melting channels is controlled to be 0%.
The principle of the invention for realizing the large-scale strengthening of the performance of the aluminum alloy is as follows: (1) when the Zn content in the aluminum alloy is increased to 10% or more, Zn can form a large amount of solid solution in the alloy, the solid solution exists in a supersaturated solid solution form, the lattice distortion effect is exerted, and a stress field is formed to hinder dislocation movement; meanwhile, the generation of a T phase without a strengthening effect can be avoided, and the precipitation of a GP zone and an eta' phase is promoted, wherein the two phases are the most effective strengthening phases in the aluminum alloy and can greatly strengthen the mechanical property of the alloy; (2) meanwhile, part of Zn and Mg can react to generate a strengthening phase, and the strengthening phase is precipitated at a grain boundary to strengthen the grain boundary and further strengthen the alloy performance.
The solubility of Zn in Al at high temperatures is about 30% and at room temperature is extremely low, which makes it difficult to achieve solid solution with high Zn content in conventional casting, and thus further strengthening. And because Zn is a low-melting-point element, burning loss easily occurs in melt forming, and a large number of cracks and holes are easily formed, when the Zn content is too high, on one hand, solid solution cannot be realized, and on the other hand, cracks which cannot be inhibited appear under high-temperature cooling, so that the effective strengthening is realized by controlling the Zn content, and the heat input is controlled and the cracks are inhibited.
Based on the above principle, the invention: (1) Al-Zn-Mg-Zr alloy powder for a selective laser melting technology is designed, the solid solution effect, strengthening phase precipitation, crack and air hole tendency and the like of Zn added into the aluminum alloy are considered, the mass fraction of Zn is 12-15% (2), and by calculating lattice parameters and matching phases, Zr is added to play the role of nucleation and fine-grain strengthening, so that cracks are effectively inhibited. The contents of other elements comprise: 1-2% of Mg, 0.5-2% of Zr and the balance of Al, wherein the total mass ratio is 100%. (3) Different from the method of adopting 30-60% of lap joint rate in the selective laser melting process of other aluminum alloys, the invention provides that the burning loss of Zn is reduced to the maximum extent on the basis of realizing effective connection by controlling the lap joint rate between adjacent melting channels to be-5%. (4) Meanwhile, different from preheating of the substrate in the forming process of other aluminum alloys, the invention provides the step of further cooling the substrate, and the temperature gradient is increased by introducing cooling liquid of-20-0 ℃ into the bottom and the side surfaces of the substrate at the flow rate of 5-10L/min for cooling, so that the supersaturated solid solution capacity of Zn in the aluminum matrix is further increased.
The material of the invention is not limited to aluminum alloy with high Zn content, but also can be used for designing and forming preparation of selective laser melting powder of aluminum alloy added with high Mg content or other low-melting-point alloy elements.
Compared with the preparation method of the high-strength aluminum alloy in other inventions, the aluminum alloy prepared by adopting the powder components and the method has the following advantages:
(1) the special powder is not required to be prepared by an air atomization method, the powder is easy to obtain, the mixing efficiency is high, the powder which is not used up can be treated and recycled, the powder utilization rate is close to 100 percent, and the cost can be greatly reduced.
(2) The heat input is controlled, the power consumption is low, the energy utilization rate is high, dense connection can be realized while the Zn loss is reduced to the maximum extent, and the defect that a large amount of Zn is evaporated to cause air holes and the defect that the heat input is insufficient to cause unfused connection are avoided.
(3) The temperature gradient is further increased by cooling the formed substrate with cooling liquid, so that the solid solution of high-content Zn in the aluminum alloy, the grain refinement and the uniform distribution of the structure are realized.
(4) The used alloy elements have simple components and good strengthening effect, and the combination of the element proportion of Zn and Zr inhibits the crack defect, so that the mechanical property and the plasticity of the finally formed alloy are good.
(5) The prepared aluminum alloy does not need to be subjected to heat treatment, has fine and uniform crystal grains, and high surface precision of a formed sample, does not need to be subjected to subsequent processing, and can be directly put into use.
Drawings
FIG. 1 is an electron microscope image of the morphology of mixed powder, wherein a is a picture of the whole mixing situation and b is a picture of partial powder;
FIG. 2 is a photograph of a selected area laser fusion molded sample;
FIG. 3 is a morphology chart of a high-strength aluminum alloy forming sample prepared in example 1, wherein a is a metallographic morphology and b is a grain morphology and distribution map;
FIG. 4 is a topographical view of a high-strength aluminum alloy formed sample of comparative example 1;
FIG. 5 is a topographical view of a high-strength aluminum alloy formed sample of comparative example 2;
FIG. 6 is a topographical view of a high-strength aluminum alloy formed sample of comparative example 3;
fig. 7 is a schematic diagram of a model transversely cut into a plurality of continuous equal-thickness slices by three-dimensional drawing software.
Detailed Description
It will be understood by those of ordinary skill in the art that the foregoing embodiments are specific examples for carrying out the invention, and that various changes in form and details may be made therein without departing from the spirit and scope of the invention in practice.
To make the objects, aspects and advantages of the embodiments of the present invention more apparent, the following detailed description clearly illustrates the spirit of the disclosure, and any person skilled in the art, after understanding the embodiments of the disclosure, may make changes and modifications to the technology taught by the disclosure without departing from the spirit and scope of the disclosure.
The exemplary embodiments of the present invention and the description thereof are provided to explain the present invention and not to limit the present invention.
The beneficial effects of the present invention are demonstrated by the following examples:
example 1
This example uses Al-14Zn-2Mg-2Zr powder as an example, and is tested by ball milling and mixing and forming alloy samples by selective laser melting. The preparation method comprises the following steps:
respectively preparing Al powder, Zn powder, Mg powder and Zr powder, wherein the powder is spherical, the grain diameters of the Al powder, the Zn powder and the Mg powder are intensively distributed within the range of 60-80 mu m, and the grain diameter of the Zr powder is intensively distributed within the range of 80-100 mu m.
Weighing powder of different elements by using an electronic balance according to the powder proportion of the Al-14Zn-2Mg-2 Zr: namely, 2g of Zr powder, 2g of Mg powder, and 14gZn powder were weighed and mixed with 82g of Al powder.
And step three, mechanically mixing the materials by adopting a planetary ball milling powder mixer, introducing inert gas Ar gas into a mixing tank to protect the powder from oxidation at the rotating speed of 400rpm, stopping rotating for 5 minutes after rotating for 5 minutes, cooling and mixing for 6 hours.
The powder morphology after mixing is shown in FIG. 1. The larger particle size is about 50 μm, compared with the original particles, the particles after ball milling and mixing are obviously refined compared with the particles before ball milling. In addition, polygonal particles are basically not present in a visual field, and part of spheroidal particles with larger particle sizes are Zr powder which is spheroidized after full ball milling; wherein the spherical particle matrix is aluminum powder particles, a plurality of fine particles are adhered to the surfaces of the particles, and even uniform coating layers can be observed on partial particle surfaces when the particle morphology is observed under a high-power electron microscope. The observation shows that the distribution of various particles is more uniform and the powder mixing effect is good.
And fourthly, drawing the model through three-dimensional drawing software, and drawing the three-dimensional model according to the pre-designed part structure and size.
And step five, setting the thickness of the spread powder in the test to be 30 microns, and cutting the software into a plurality of continuous equal-thickness slices with the thickness of 30 microns from the bottom plane according to the height of the planned forming component.
Step six, pre-clamping the substrate on a forming platform, adjusting the levelness of the substrate to +/-0.025 mm, fixing a cooling cavity at the bottom of the substrate and nearby, and introducing 0 ℃ cooling liquid with the flow rate of 6L/min.
Setting process parameters, wherein the diameter of a laser spot adopted in the scanning process is 0.1mm, the laser scanning interval is 0.11mm, the laser power is 200W, the laser scanning speed is 400mm/s, the lap joint rate between adjacent melting channels is 0, remelting does not occur in the forming process of the same layer, and the scanning direction is rotated by 67 degrees layer by layer. Repeating the steps until the whole workpiece is finished; and (5) operating the model data file of the bone-shaped tensile sample designed in the third step, introducing argon gas for protection, and starting the equipment after the oxygen content in the forming bin is less than 0.1%. The final formed sample shape is shown in fig. 2.
And step eight, fully cooling the formed block sample, taking out, performing wire cut electrical discharge machining, performing ultrasonic cleaning for 30min, and removing oil stains and other pollutants remained on the surface of the sample in the wire cutting process. The powder which is not used up is recovered.
The density of the formed part obtained by the embodiment is 98.5%, the surface roughness Ra is 3.6, the surface precision is extremely high, and no obvious cracks and air hole defects exist in the sample, as shown in fig. 3 (a); the grain structure of the obtained sample is very fine, and many grains are fine submicron grains, and the grain distribution is shown in fig. 3 (b). The mechanical property indexes are as follows: the average value of the surface hardness of the directly formed sample exceeds 170HV, and the hardness is extremely high; under the normal temperature stretching rate of 2mm/min, the maximum yield strength of the sample is 510MPa, the maximum tensile strength is 605MPa, and the plastic deformation rate is 10.6 percent. In the embodiment, the comprehensive mechanical property of the sample prepared by adopting the powder components and the corresponding process is far greater than that of the Al-Zn-Mg alloy prepared by traditional casting and laser melting.
Comparative example 1
In this example, 7075 aluminum alloy powder (Al-5.6Zn-2Mg) is used as an example, and selective laser melting is used to form an aluminum alloy sample as follows:
drawing a model through three-dimensional drawing software, and drawing the three-dimensional model according to a pre-designed part structure and size.
And step two, setting the thickness of the spread powder in the test to be 30 microns, and cutting the software into a plurality of continuous equal-thickness slices with the thickness of 30 microns from the bottom plane according to the height of the planned forming component.
And step three, pre-clamping the substrate on a forming platform, adjusting the levelness of the substrate to +/-0.025 mm, fixing a cooling cavity at the bottom of the substrate and nearby, and introducing 0 ℃ cooling liquid with the flow rate of 5L/min.
Setting process parameters, wherein the diameter of a laser spot adopted in the scanning process is 0.1mm, the laser scanning interval is 0.1mm, the laser power is 360W, the laser scanning rate is 1200mm/s, the lap joint rate of adjacent melting channels is 30%, and the scanning direction is that the laser spot rotates 90 degrees layer by layer. Repeating the steps until the whole workpiece is finished; and (5) operating the model data file of the sample designed in the third step, introducing argon for protection, and starting the equipment after the oxygen content in the forming bin is less than 0.1%.
And fifthly, taking out the formed block sample after fully cooling, and using electric spark wire cutting and ultrasonic cleaning for 30min to remove oil stains and other pollutants remained on the surface of the sample in the wire cutting process. The powder which is not used up is recovered.
The density of the formed part obtained by this example was 95%, and a large number of cracks parallel to the forming direction were distributed over the surface of the sample, as shown in fig. 4. The mechanical property indexes are as follows: the surface hardness of the directly formed sample is about 130HV on average; at the normal temperature stretching rate of 2mm/min, because a large number of cracks exist in the sample, the sample is broken and fractured at about 30MPa, and the practical use value is not realized.
Comparative example 2
In this example, Al-14Zn-2Mg-2Zr powder designed and prepared by the present invention was used as an example, and ball milling and mixing were performed and an alloy sample test was performed by selective laser melting. The implementation effect of preparing the sample without adopting the process set by the invention is as follows:
respectively preparing Al powder, Zn powder, Mg powder and Zr powder, wherein the powder is spherical, the grain diameters of the Al powder, the Zn powder and the Mg powder are intensively distributed within the range of 60-80 mu m, and the grain diameter of the Zr powder is intensively distributed within the range of 80-100 mu m.
Weighing powder of different elements by using an electronic balance according to the powder proportion of the Al-14Zn-2Mg-2 Zr: namely, 2g of Zr powder, 2g of Mg powder, and 14gZn powder were weighed and mixed with 82g of Al powder.
And step three, mechanically mixing the materials by adopting a planetary ball milling powder mixer, introducing inert gas Ar gas into a mixing tank to protect the powder from oxidation at the rotating speed of 400rpm, stopping rotating for 5 minutes after rotating for 5 minutes, cooling and mixing for 6 hours.
And fourthly, drawing the model through three-dimensional drawing software, and drawing the three-dimensional model according to the pre-designed part structure and size.
And step five, setting the thickness of the spread powder in the test to be 30 microns, and cutting the software into a plurality of continuous equal-thickness slices with the thickness of 30 microns from the bottom plane according to the height of the planned forming component.
Step six, pre-clamping the substrate on a forming platform, adjusting the levelness of the substrate to +/-0.025 mm, fixing a cooling cavity at the bottom of the substrate and nearby, and introducing 0 ℃ cooling liquid with the flow rate of 5L/min.
Seventhly, setting technological parameters, wherein the diameter of a laser spot adopted in the scanning process is 0.1mm, the laser scanning interval is 0.06mm, the laser power is 400W, the laser scanning speed is 1200mm/s, the lap joint rate between adjacent melting channels is 50%, and the scanning direction is that the laser spot rotates 67 degrees layer by layer. Repeating the steps until the whole workpiece is finished; and (5) operating the model data file of the sample designed in the third step, introducing argon for protection, and starting the equipment after the oxygen content in the forming bin is less than 0.1%.
And step eight, fully cooling the formed block sample, taking out, performing wire cut electrical discharge machining, performing ultrasonic cleaning for 30min, and removing oil stains and other pollutants remained on the surface of the sample in the wire cutting process. The powder which is not used up is recovered.
The density of the formed part obtained by the embodiment is 77.4%, the density is extremely low, and a large number of large-size holes left by evaporation of Zn element in the sample can be seen under a metallographic microscope, as shown in FIG. 5. As a large number of holes are formed in the sample, the hardness distribution of the sample is uneven, the maximum tensile strength of the sample is about 220MPa, the elongation is about 3.4 percent in a normal-temperature tensile test, and the performance is greatly reduced compared with the two examples. The sample formed in the embodiment is not good in compactness and mechanical property, and has no practical use value.
Comparative example 3:
this example illustrates the addition of 1.2% Zr (Al-5.6Zn-2 Mg-1.2% Zr) to 7075 aluminum alloy powder, using a selective laser melting to form aluminum alloy coupons as follows: powder components were taken as examples and ball milled for mixing and testing of alloy specimens formed by selective laser melting. The implementation effect of preparing the sample without adopting the process set by the invention is as follows:
respectively preparing 7075 aluminum alloy powder and Zr powder, wherein the powder is spherical, the particle sizes of the 7075 aluminum alloy powder are intensively distributed within the range of 60-80 mu m, and the particle sizes of the Zr powder are intensively distributed within the range of 80-100 mu m.
And step two, weighing and mixing the powder of different elements by using an electronic balance according to the powder proportion of the Al-5.6Zn-2Mg-1.2 percent Zr.
And step three, mechanically mixing the materials by adopting a planetary ball milling powder mixer, introducing inert gas Ar gas into a mixing tank to protect the powder from oxidation at the rotating speed of 400rpm, stopping rotating for 5 minutes after rotating for 5 minutes, cooling and mixing for 6 hours.
And fourthly, drawing the model through three-dimensional drawing software, and drawing the three-dimensional model according to the pre-designed part structure and size.
And step five, setting the thickness of the spread powder in the test to be 30 microns, and cutting the software into a plurality of continuous equal-thickness slices with the thickness of 30 microns from the bottom plane according to the height of the planned forming component.
Step six, pre-clamping the substrate on a forming platform, adjusting the levelness of the substrate to +/-0.025 mm, fixing a cooling cavity at the bottom of the substrate and nearby, and introducing 0 ℃ cooling liquid with the flow rate of 6L/min.
Setting process parameters, wherein the diameter of a laser spot adopted in the scanning process is 0.1mm, the laser scanning interval is 0.11mm, the laser power is 200W, the laser scanning speed is 400mm/s, the lap joint rate between adjacent melting channels is 0, remelting does not occur in the forming process of the same layer, and the scanning direction is rotated by 67 degrees layer by layer.
And step eight, fully cooling the formed block sample, taking out, performing wire cut electrical discharge machining, performing ultrasonic cleaning for 30min, and removing oil stains and other pollutants remained on the surface of the sample in the wire cutting process. The powder which is not used up is recovered.
The density of the formed part obtained by the embodiment is 97.6%, the density is higher, no obvious crack exists in the sample, the defect of the air hole is very little, and the adding and matching process of Zr realizes good crack inhibition, as shown in FIG. 6. The mechanical property indexes are as follows: the average value of the surface hardness of the directly formed sample exceeds 130 HV; under the normal temperature stretching rate of 2mm/min, the maximum yield strength of the sample is 260MPa, the maximum tensile strength is 330MPa, and the elongation is about 6 percent.
According to the embodiment and the proportion, the technical effect of the invention can be realized only by reasonably adjusting the Zn content in the powder to 12-15% and the matching lap joint rate to be close to 0, and introducing cooling liquid at the temperature of-20-0 ℃ at the flow rate of 5-10L/min to cool the bottom and the side surfaces of the substrate, and the like, so as to realize the aim of the invention.
Claims (10)
1. The preparation method of the high-Zn light high-strength aluminum alloy is characterized by comprising the following steps of:
weighing and mixing selective laser melting powder, wherein the selective laser melting powder comprises Al powder, Zn powder, Mg powder and Zr powder, the mass fraction of Zn is 12-15%, the mass fraction of Mg is 1-2%, the mass fraction of Zr is 0.5-2%, and the balance is Al;
mechanically mixing the powder mixed in the last step by adopting a planetary ball milling powder mixer, introducing inert gas into a mixing tank to protect the powder from oxidation, and then rotating at the rotation speed of 200-400rpm for 5-10min and stopping rotating for 5-10min for cooling for 4-8 h;
drawing a model through three-dimensional drawing software, and drawing the three-dimensional model according to a pre-designed part structure and size; spreading the powder mixed in the last step according to the thickness of 0.03-0.05mm, spreading the powder layer by layer, and transversely cutting the model into a plurality of continuous equal-thickness slices with the thickness of 0.03-0.05mm through three-dimensional drawing software;
fourthly, pre-clamping the substrate on a forming platform, adjusting the levelness of the substrate to +/-0.025 mm, and introducing cooling liquid at the temperature of-20 to 0 ℃ into a fixed cooling cavity at the bottom and the periphery of the substrate at the flow speed of 5 to 10L/min;
fifthly, setting process parameters, operating a model data file, introducing argon for protection, and starting equipment after the oxygen content in a forming bin is less than 0.1%;
fully cooling the formed block sample, taking out, performing wire cut electrical discharge machining, and performing ultrasonic cleaning to recover unused powder; thus completing the preparation method of the high-Zn light high-strength aluminum alloy;
wherein, the set process parameters in the fifth step are as follows: the diameter of the laser spot is 0.1-0.12mm, the laser scanning interval is 0.09-0.13mm, the laser power is 320W plus 120W, the scanning speed is 800mm/s plus 200W plus, and the overlapping rate between adjacent melt channels is controlled at-5%.
2. The method for preparing a high-Zn light-weight high-strength aluminum alloy according to claim 1, wherein the grain sizes of the Al powder, the Zn powder and the Mg powder are all 60-80 μm; the grain size of the Zr powder is 80-100 μm.
3. The method of claim 1, wherein the mass fraction of Zn is 13-14%, the mass fraction of Mg is 1.5-2%, the mass fraction of Zr is 1-2%, and the balance is Al.
4. The method as claimed in claim 1, wherein the rotation speed in step two is 400rpm, and the rotation is stopped for 6-8min after 6-8min for cooling.
5. The method for preparing the high-Zn light-weight high-strength aluminum alloy according to claim 1, wherein the powder spreading thickness in the third step is 0.04 mm.
6. The method for preparing a high-Zn light-weight high-strength aluminum alloy according to claim 1, wherein the ultrasonic cleaning time in the sixth step is 30 min.
7. The method for preparing the high-Zn light-weight high-strength aluminum alloy according to claim 1, wherein the set process parameters in the fifth step are as follows: the diameter of the laser spot is 0.1-0.12mm, the laser scanning interval is 0.1-0.13mm, the laser power is 150-280W, the scanning speed is 300-600mm/s, and the overlapping rate between adjacent melt channels is controlled at-3%.
8. The method for preparing the high-Zn light-weight high-strength aluminum alloy according to claim 1, wherein the set process parameters in the fifth step are as follows: the diameter of the laser spot is 0.1-0.12mm, the laser scanning interval is 0.1-0.12mm, the laser power is 180-250W, the scanning speed is 300-500mm/s, and the overlapping rate between adjacent melt channels is controlled at-2%.
9. The method for preparing the high-Zn light-weight high-strength aluminum alloy according to claim 1, wherein the set process parameters in the fifth step are as follows: the diameter of the laser spot is 0.1-0.12mm, the laser scanning interval is 0.1-0.11mm, the laser power is 200-.
10. The method for preparing the high-Zn light-weight high-strength aluminum alloy according to claim 1, wherein the set process parameters in the fifth step are as follows: the diameter of a laser spot is 0.1mm, the laser scanning interval is 0.11mm, the laser power is 200W, the scanning speed is 400mm/s, and the overlapping rate between adjacent melting channels is controlled to be 0%.
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