A method for precision manufacturing of small parts

Abstract

The application relates to a precision preparation method of small parts, which comprises the following steps: preheating a compression chamber to 300-400 DEG C, adding liquid alloy above the liquidus by 20-40 DEG C into the compression chamber, adding alloy powder with an average particle size of 5-20 mu m and applying ultrasonic action to the liquid alloy to form a mixed melt above the liquidus by 5-10 DEG C, performing low-speed compression shooting on the mixed melt within 5S, then performing high-speed compression shooting on the mixed melt, and obtaining the small parts after pressure holding and cooling; wherein the mass of the alloy powder is 2-10% of the mass of the liquid alloy, the speed of the low-speed compression shooting is 0.05-0.1 m / s, the speed of the high-speed compression shooting is 2-10 m / s, the time of the low-speed compression shooting is 4-8S, and the heat conductivity coefficient of the inner surface of the compression chamber is <5 W / m*K.

Description

Technical Field

[0001] The invention relates to the technical field of semi-solid alloy materials, in particular to a precision preparation method for small parts. Background Art

[0002] At present, semi-solid forming technology is mainly used for medium and large-volume castings. This is because the common semi-solid slurry preparation methods, such as mechanical stirring, double-helix stirring, cooling chute, electromagnetic stirring, etc., are not suitable for the preparation of small-volume semi-solid slurries. The preparation process of small-volume semi-solid slurries is prone to air entrainment, oxidation and pre-crystallization. In addition, during the transfer of the slurry, local overcooling is likely to occur when the slurry contacts the wall of the transfer container, resulting in the formation of coarse crystals.

[0003] During the semi-solid casting process of small parts such as mobile phone frames, mid-plates and tablet computer frames, the solid phase fraction and crystal structure of large-volume slurry are prone to change during the long pouring process, resulting in large differences between batches, which affects the application of semi-solid technology on small parts.

[0004] Therefore, it is necessary to provide a method for the precise preparation of small parts. Summary of the Invention

[0005] In order to prepare small parts with high strength, it is necessary to provide a precise preparation method for small parts.

[0006] A precision preparation method for small parts, characterized in that it includes the following steps: preheating a pressure chamber to 0-10°C above the liquidus of a liquid alloy, adding a liquid alloy 20-40°C above the liquidus into the pressure chamber, adding an alloy powder with an average particle size of 5-20 μm into the pressure chamber and applying ultrasound to the liquid alloy to form a mixed melt 5-10°C above the liquidus, low-speed injection molding the mixed melt within 5 seconds, and then high-speed injection molding the mixed melt, and obtaining the small parts after pressure-maintaining cooling; wherein the mass of the alloy powder is 2-10% of the mass of the liquid alloy, the rate of the low-speed injection molding is 0.05-0.1 m / s, the rate of the high-speed injection molding is 2-10 m / s, the time of the low-speed injection molding is 4-8 seconds, and the thermal conductivity of the inner surface of the pressure chamber is less than 5 W / m·K.

[0007] This solution uses a pressure chamber with an inner surface thermal conductivity of less than 5W / m·K to prevent the liquid alloy from being locally overcooled and forming pre-crystallization after contacting the inner wall of the pressure chamber. In the process of adding liquid alloy to the pressure chamber, alloy powder is added and ultrasonic action is applied to make the alloy powder evenly distributed in the liquid alloy to form a mixed melt 5-10°C above the liquidus line. At this time, the alloy powder and the liquid alloy have not yet fully exchanged heat. First, low-speed injection is used to avoid air entrainment in the mixed melt with a low solid phase fraction. During low-speed injection, under the shear force provided by the injection and the local supercooling provided by the alloy powder, The liquid phase components in the mixed melt form new crystal nuclei, and the evenly distributed alloy powder provides a uniform temperature field for the mixed melt. The liquid phase components nucleate around the alloy powder, so the mixed melt as a whole has a relatively uniform material field. The uniform temperature field and material field and the heterogeneous nucleation effect provided by the alloy powder form a refined primary phase and inhibit the rosetting and dendrite formation of the primary phase, forming equiaxed crystals, thereby obtaining a semi-solid slurry with high fluidity; during high-speed injection, the semi-solid slurry with high fluidity can fully fill the interior of the mold, and ultimately obtain high-strength precision small parts.

[0008] Furthermore, the average particle size of the alloy powder is 5-10 μm. Alloy powders with an average particle size that is too large have a small specific surface area, poor heat transfer efficiency, and difficulty achieving a large degree of supercooling to promote crystal nucleation. Furthermore, crystal nuclei tend to adhere to the alloy powder, further affecting heat transfer efficiency. Alloy powders with an average particle size that is too small are difficult to disperse evenly, resulting in uneven distribution of the alloy powder and thus affecting the generation of crystal nuclei.

[0009] Furthermore, the mass of the alloy powder is 5%-10% of the mass of the liquid alloy. If the mass of the alloy powder is too low, it will be difficult to achieve a large degree of undercooling, and it may even be impossible to lower the temperature of the mixed melt to the semi-solid range. If the mass of the alloy powder is too high, the mixed melt may cool to the semi-solid range during the mixing process, which may easily produce coarsened grains due to the weak shear force provided by the mixing.

[0010] Furthermore, the temperature of the alloy powder is 20-100° C. If the temperature of the alloy powder is too high, it is difficult to provide a faster heat exchange effect and form a larger supercooling degree; if the temperature of the alloy powder is too low, additional costs will be incurred.

[0011] Furthermore, the high-speed injection rate is 5-8 m / s. The above injection rate can better fill the mold.

[0012] Furthermore, the inner surface of the pressure chamber is coated with a thermal insulation ceramic material. Thermal insulation ceramic materials, such as TBCs and ZrO2-based ceramic materials, have a thermal conductivity of less than 10W / m·K, or even less than 1W / m·K, and can withstand high temperatures and high pressures.

[0013] Furthermore, the frequency of the ultrasound is 15-35kHz, and the power of the ultrasound is 1000-2000W.

[0014] Furthermore, the holding pressure is 150-200 MPa, and the holding time is 10-20 seconds. The above holding pressure parameters can allow the mixed melt to fully fill the mold.

[0015] Furthermore, the liquid alloy comprises 6.5-7.5% silicon, 0.3-0.45% magnesium, 0-0.12% iron, 0-0.05% manganese, 0-0.1% copper, 0-0.05% zinc, 0-0.2% titanium, and the balance aluminum. The material exhibits excellent fluidity at semi-solid temperatures and can fully fill a mold.

[0016] Furthermore, the alloy powder contains 1-3% by mass of a refiner. The alloy powder containing the refiner can not only play a heterogeneous nucleation role, but also partially dissolve the refiner in the mixed melt to inhibit grain growth. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Fig. 1 Schematic diagram of the metallographic structure of the casting prepared in Example 1.

[0018] Fig. 2 Schematic diagram of the metallographic structure of the casting prepared in Comparative Example 1. DETAILED DESCRIPTION

[0019] For ease of understanding of the present application, the present application will be described more fully below. The present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0020] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the description of this application, the meaning of "several" is at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0023] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0024] Unless otherwise specified, the percentage contents mentioned in this application refer to mass percentage for solid-liquid mixture and solid-solid mixture, and refer to volume percentage for liquid-liquid mixture.

[0025] The percentage concentrations mentioned in this application, unless otherwise specified, refer to the final concentration, which refers to the percentage of the added component in the system after the addition of the component.

[0026] The temperature parameters in this application, unless otherwise specified, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows for temperature fluctuations within the precision range of instrument control.

[0027] The "particles" mentioned in this application, or materials with a defined particle size distribution, are not necessarily spherical in shape but may be irregular, primary or secondary. The particle size of irregular particles is the average of their maximum and minimum diameters.

[0028] Example 1: The composition of the liquid alloy (percentages in the Examples and Comparative Examples are by weight) is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, strontium: 0.0001%, and the remainder is aluminum. The various metals were weighed according to the liquid alloy composition, mixed, heated to 650°C, deslagging and degassing to form a liquid alloy, and then cooled to 40°C above the liquidus and held at that temperature.

[0029] The alloy powder composition is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, calcium: 1%, and the remainder is aluminum. The various metals are weighed according to the alloy powder composition, mixed, heated to 650°C, and deslagging and degassing to form a liquid. The powder is then formed into a powder by spraying and sieved to obtain an alloy powder with an average particle size of 5μm.

[0030] The press chamber was preheated to 400°C (the interior of the press chamber was coated with a TBCs coating (yttria-stabilized zirconia YSZ coating) with a thermal conductivity of 0.93 W / m·K), 2 kg of liquid alloy and 0.1 kg of alloy powder were poured into the press chamber, and ultrasonic action was applied to the liquid alloy to form a mixed melt, wherein the frequency of the ultrasonic action was 35 kHz and the power was 1000 W. The mixed melt was quickly (within 5 seconds, wherein the conditions of the embodiment and the comparative example were the same) subjected to low-speed injection (at this time, the temperature of the mixed melt was 5°C above the liquidus line), and the mixed melt was subjected to low-speed injection. The rapid injection rate is 0.05m / s, the low-speed injection time is 8s, the high-speed injection rate is 10m / s, and the high-speed injection is performed until the mixed slurry fully fills the mold, and then the pressure is maintained. The holding pressure is 200MPa and the holding time is 10S to obtain small parts (the small parts in this embodiment and other embodiments and comparative examples are all mobile phone frames. Those skilled in the art can understand that this scheme can be applied to semi-solid casting of other small parts, such as mobile phone mid-plates, tablet computer frames, small medical devices and other small parts).

[0031] Example 2: The liquid alloy composition is: silicon: 6.5%, nickel: 0.02%, magnesium: 0.45%, copper: 0.01%, iron: 0.12%, zinc: 0.05%, titanium: 0.20%, manganese: 0.005%, strontium: 0.0001%, and the remainder is aluminum. The various metals are weighed according to the liquid alloy composition, mixed, heated to 650°C, deslagging and degassing to form a liquid alloy, and then cooled to 40°C above the liquidus and held at this temperature.

[0032] The alloy powder composition is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, calcium: 1%, and the remainder is aluminum. The various metals are weighed according to the alloy powder composition, mixed, heated to 650°C, and deslagging and degassing to form a liquid. The powder is then formed into a powder by spraying and sieved to obtain an alloy powder with an average particle size of 5μm.

[0033] Preheat the compression chamber to 400℃ (the compression chamber is coated with a TBCs coating (yttria-stabilized zirconia YSZ coating) with a thermal conductivity of 0.93 W / m·K), pour 2 kg of liquid alloy and 0.1 kg of alloy powder into the compression chamber, and apply ultrasonic action to the liquid alloy to form a mixed melt, wherein the frequency of the ultrasonic action is 15 kHz, the power is 2000 W, the mixed melt is quickly subjected to low-speed injection (at this time, the temperature of the mixed melt is 5℃ above the liquidus), the low-speed injection rate is 0.1 m / s, the low-speed injection time is 5 s, the high-speed injection rate is 2 m / s, the mixed slurry is fully filled into the mold by high-speed injection, and then pressure holding is performed, the pressure holding pressure is 200 MPa, and the pressure holding time is 10 s, thereby obtaining a small part.

[0034] In Example 3, the composition of the liquid alloy is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, strontium: 0.0001%, and the rest is aluminum. According to the composition of the liquid alloy, various metals are weighed and mixed, heated to 650℃, and then slagging and degassing to form a liquid alloy, which is cooled to 40℃ above the liquidus and held.

[0035] The composition of the alloy powder is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, calcium: 3%, and the rest is aluminum. According to the composition of the alloy powder, various metals are weighed and mixed, heated to 650℃, and then slagging and degassing to form a liquid, which is formed into a powder by a spray method, and sieved to obtain an alloy powder with an average particle size of 5 μm.

[0036] Preheat the compression chamber to 300℃ (the compression chamber is coated with a TBCs coating (yttria-stabilized zirconia YSZ coating) with a thermal conductivity of 0.93 W / m·K), pour 2 kg of liquid alloy and 0.1 kg of alloy powder into the compression chamber, and apply ultrasonic action to the liquid alloy to form a mixed melt, wherein the frequency of the ultrasonic action is 35 kHz, the power is 1000 W, the mixed melt is quickly subjected to low-speed injection (at this time, the temperature of the mixed melt is 5℃ above the liquidus), the low-speed injection rate is 0.05 m / s, the low-speed injection time is 8 s, the high-speed injection rate is 10 m / s, the mixed slurry is fully filled into the mold by high-speed injection, and then pressure holding is performed, the pressure holding pressure is 150 MPa, and the pressure holding time is 20 s, thereby obtaining a small part.

[0037] Example 4: The composition of the liquid alloy is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, strontium: 0.0001%, and the remainder is aluminum. The various metals are weighed according to the liquid alloy composition, mixed, heated to 650°C, deslagging and degassing to form a liquid alloy, and then cooled to 40°C above the liquidus and held at this temperature.

[0038] The alloy powder composition is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, calcium: 1%, and the remainder is aluminum. The various metals are weighed according to the alloy powder composition, mixed, heated to 650°C, and deslagging and degassing to form a liquid. The powder is then formed into a powder by spraying and sieved to obtain an alloy powder with an average particle size of 20μm.

[0039] The press chamber is preheated to 400°C (the interior of the press chamber is coated with a TBCs coating (yttria-stabilized zirconia YSZ coating) with a thermal conductivity of 0.93W / m·K). 2kg of liquid alloy and 0.1kg of alloy powder are poured into the press chamber and ultrasonic action is applied to the liquid alloy to form a mixed melt. The frequency of the ultrasonic action is 35kHz and the power is 1000W. The mixed melt is quickly subjected to low-speed injection (at this time, the temperature of the mixed melt is 5°C above the liquidus line). The low-speed injection rate is 0.05m / s, the low-speed injection time is 8s, and the high-speed injection rate is 10m / s. The high-speed injection is performed until the mixed slurry fully fills the mold, and then the pressure is maintained at 200MPa for 10s to obtain a small part.

[0040] Example 5: The composition of the liquid alloy is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, strontium: 0.0001%, and the remainder is aluminum. The various metals are weighed according to the liquid alloy composition, mixed, heated to 650°C, deslagging and degassing to form a liquid alloy, and then cooled to 20°C above the liquidus and held at this temperature.

[0041] The alloy powder composition is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, calcium: 1%, and the remainder is aluminum. The various metals are weighed according to the alloy powder composition, mixed, heated to 650°C, and deslagging and degassing to form a liquid. The powder is then formed into a powder by spraying and sieved to obtain an alloy powder with an average particle size of 5μm.

[0042] Preheat the die to 400℃ (the die is coated with TBCs coating (yttria-stabilized zirconia YSZ coating) with thermal conductivity of 0.93 W / m·K), pour 2 kg of liquid alloy and 0.2 kg of alloy powder into the die, and apply ultrasonic action to the liquid alloy to form a mixed melt, wherein the frequency of the ultrasonic action is 35 kHz, and the power is 1000 W. The mixed melt is quickly subjected to low-speed injection (at this time, the temperature of the mixed melt is 5℃ above the liquidus line), the low-speed injection rate is 0.05 m / s, the low-speed injection time is 8 s, the high-speed injection rate is 10 m / s, and the mixed slurry is fully filled into the mold after high-speed injection, and then pressure holding is performed, the pressure holding pressure is 200 MPa, and the pressure holding time is 10 s, thereby obtaining a small part.

[0043] In Example 6, the composition of the liquid alloy is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, strontium: 0.0001%, and the rest is aluminum. According to the composition of the liquid alloy, various metals are weighed and mixed, heated to 650℃, and then slag and gas are removed to form a liquid alloy, which is cooled to 40℃ above the liquidus line and kept.

[0044] The composition of the alloy powder is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, calcium: 1%, and the rest is aluminum. According to the composition of the alloy powder, various metals are weighed and mixed, heated to 650℃, and then slag and gas are removed to form a liquid, which is formed into a powder by a spray method, and sieved to obtain an alloy powder with an average particle size of 5 μm.

[0045] Preheat the die to 400℃ (the die is coated with TBCs coating (yttria-stabilized zirconia YSZ coating) with thermal conductivity of 0.93 W / m·K), pour 2 kg of liquid alloy and 0.2 kg of alloy powder into the die, and apply ultrasonic action to the liquid alloy to form a mixed melt, wherein the frequency of the ultrasonic action is 35 kHz, and the power is 1000 W. The mixed melt is quickly subjected to low-speed injection (at this time, the temperature of the mixed melt is 5℃ above the liquidus line), the low-speed injection rate is 0.05 m / s, the low-speed injection time is 8 s, the high-speed injection rate is 10 m / s, and the mixed slurry is fully filled into the mold after high-speed injection, and then pressure holding is performed, the pressure holding pressure is 200 MPa, and the pressure holding time is 10 s, thereby obtaining a small part.

[0046] Example 7: The composition of the liquid alloy is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, strontium: 0.0001%, and the remainder is aluminum. The various metals are weighed according to the liquid alloy composition, mixed, heated to 650°C, deslagging and degassing to form a liquid alloy, and then cooled to 40°C above the liquidus and held at that temperature.

[0047] The alloy powder composition is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, calcium: 1%, and the remainder is aluminum. The various metals are weighed according to the alloy powder composition, mixed, heated to 650°C, and deslagging and degassing to form a liquid. The powder is then formed into a powder by spraying and sieved to obtain an alloy powder with an average particle size of 5μm.

[0048] The press chamber is preheated to 400°C (the interior of the press chamber is coated with a TBCs coating (yttria-stabilized zirconia YSZ coating) with a thermal conductivity of 0.93W / m·K). 2kg of liquid alloy and 0.1kg of alloy powder are poured into the press chamber and ultrasonic action is applied to the liquid alloy to form a mixed melt. The frequency of the ultrasonic action is 35kHz and the power is 1000W. The mixed melt is quickly subjected to low-speed injection (at this time, the temperature of the mixed melt is 5°C above the liquidus line). The low-speed injection rate is 0.05m / s, the low-speed injection time is 8s, and the high-speed injection rate is 8m / s. The high-speed injection is performed until the mixed slurry fully fills the mold, and then the pressure is maintained. The holding pressure is 200MPa and the holding time is 10s to obtain a small part.

[0049] Comparative Example 1: The liquid alloy composition is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, strontium: 0.0001%, and the remainder is aluminum. The various metals were weighed according to the liquid alloy composition, mixed, heated to 650°C, deslagging and degassing to form a liquid alloy, and then cooled to 40°C above the liquidus and held at that temperature.

[0050] The alloy powder composition is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, calcium: 1%, and the remainder is aluminum. The various metals are weighed according to the alloy powder composition, mixed, heated to 650°C, and deslagging and degassing to form a liquid. The powder is then formed into a powder by spraying and sieved to obtain an alloy powder with an average particle size of 5μm.

[0051] The press chamber was preheated to 400°C (the interior of the press chamber was not coated with a thermal insulation coating, and the thermal conductivity was 45W / m·K). 2kg of liquid alloy and 0.1kg of alloy powder were poured into the press chamber, and ultrasonic action was applied to the liquid alloy to form a mixed melt. The frequency of the ultrasonic action was 35kHz, and the power was 1000W. The mixed melt was quickly shot at a low speed (at this time, the temperature of the mixed melt was 2°C above the liquidus line). The low-speed shot rate was 0.05m / s, the low-speed shot time was 8s, and the high-speed shot rate was 10m / s. The high-speed shot was continued until the mixed slurry fully filled the mold, and then the pressure was maintained. The holding pressure was 200MPa and the holding time was 10s to obtain a small part.

[0052] Comparative Example 2: The liquid alloy composition is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, strontium: 0.0001%, and the remainder is aluminum. The various metals according to the liquid alloy composition were weighed and mixed, heated to 650°C, and deslagging and degassing were performed to form a liquid alloy. The alloy was then cooled to 40°C above the liquidus and held at this temperature.

[0053] The press chamber is preheated to 400°C (the interior of the press chamber is coated with TBCs coating (yttria-stabilized zirconia YSZ coating), with a thermal conductivity of 0.93W / m·K), 2kg of liquid alloy is poured into the press chamber, and the liquid alloy is quickly injected at a low speed (the temperature of the mixed melt is 24°C above the liquidus at this time). The low-speed injection rate is 0.05m / s, the low-speed injection time is 8s, and the high-speed injection rate is 10m / s. The high-speed injection is performed until the mixed slurry fully fills the mold, and then the pressure is maintained at 200MPa and the pressure is maintained for 10s to obtain a small part.

[0054] Comparative Example 3: The liquid alloy composition is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, strontium: 0.0001%, and the remainder is aluminum. The various metals were weighed according to the liquid alloy composition, mixed, heated to 650°C, and deslagging and degassing were performed to form a liquid alloy. The alloy was then cooled to 80°C above the liquidus and held at that temperature.

[0055] The alloy powder composition is: silicon: 6.9%, nickel: 0.01%, magnesium: 0.30%, copper: 0.005%, iron: 0.10%, zinc: 0.015%, titanium: 0.10%, manganese: 0.003%, calcium: 1%, and the remainder is aluminum. The various metals are weighed according to the alloy powder composition, mixed, heated to 650°C, and deslagging and degassing to form a liquid. The powder is then formed into a powder by spraying and sieved to obtain an alloy powder with an average particle size of 5μm.

[0056] The press chamber is preheated to 400°C (the interior of the press chamber is coated with a TBCs coating (yttria-stabilized zirconia YSZ coating) with a thermal conductivity of 0.93W / m·K). 2kg of liquid alloy and 0.1kg of alloy powder are poured into the press chamber and ultrasonic action is applied to the liquid alloy to form a mixed melt. The frequency of the ultrasonic action is 35kHz and the power is 1000W. The mixed melt is quickly subjected to low-speed injection (at this time, the temperature of the mixed melt is 57°C above the liquidus line). The low-speed injection rate is 0.05m / s, the low-speed injection time is 8s, and the high-speed injection rate is 10m / s. The high-speed injection is performed until the mixed slurry fully fills the mold, and then the pressure is maintained at 200MPa for 10s to obtain a small part.

[0057] The small parts prepared in the above examples and comparative examples were subjected to tensile strength tests and metallographic identification, and the results are shown in Table 1. The tensile strength was measured according to the method disclosed in GB / T 228.1-2010 "Metallic materials tensile tests Part 1: Room temperature test methods".

[0058] Table 1: Tensile strength and metallographic results.

[0059]

[0060] According to the data in Table 1, the tensile strength and metallographic results of Examples 1-7 are better than those of Comparative Examples 1-3. This is because the present solution uses a pressure chamber with an inner surface thermal conductivity of less than 10W / m·K to prevent the liquid alloy from being locally overcooled and forming pre-crystallization after contacting the inner wall of the pressure chamber, and by adding alloy powder during the process of adding liquid alloy to the pressure chamber and applying ultrasonic action, the alloy powder is evenly distributed in the liquid alloy to form a mixed melt 5-10°C above the liquidus line. At this time, the alloy powder and the liquid alloy have not yet fully exchanged heat. First, low-speed injection is used to avoid air entrainment of the mixed melt with a low solid phase fraction. When the injection is performed at low speed, the mixed melt is heated to a temperature of 10°C above the liquidus line. Under the shear force provided by the alloy powder and the local supercooling provided by the alloy powder, the liquid phase components in the mixed melt form new crystal nuclei. The evenly distributed alloy powder provides a uniform temperature field for the mixed melt. The liquid phase components nucleate around the alloy powder. Therefore, the mixed melt as a whole has a relatively uniform material field. The uniform temperature field and material field, as well as the heterogeneous nucleation effect provided by the alloy powder, form a refined primary phase and inhibit the rosetting and dendrite formation of the primary phase, forming equiaxed crystals, thereby obtaining a semi-solid slurry with high fluidity. During high-speed injection, the semi-solid slurry with high fluidity can fully fill the interior of the mold, and finally obtain high-strength precision small parts. According to Figs. 1-2It can be seen from the results that Example 1 can produce equiaxed crystals, while Comparative Example 1 has a large number of coarsened dendrites. This is because Comparative Example 1 does not use a pressure chamber with a thermal insulation coating, and the mixed melt and the pressure chamber undergo heat exchange to produce a large number of dendrites; Comparative Example 2 does not add alloy powder, which is equivalent to ordinary liquid die casting, and it is difficult to obtain high-performance castings; Comparative Example 3 uses a liquid alloy with too high a temperature. The cooling effect provided by the alloy powder alone cannot reduce the mixed melt to the semi-solid temperature range, which is also equivalent to ordinary liquid die casting, and high-quality castings cannot be obtained.

[0061] Example 2 used alloy powder with a larger average particle size, resulting in a slightly lower tensile strength than Example 1. This is due to poor heat transfer efficiency and a smaller degree of undercooling. However, compared to the comparative example, high-performance semi-solid castings were still obtained. Example 6 used alloy powder with a lower mass ratio, providing fewer nucleation sites and a smaller degree of undercooling. The resulting crystal nuclei were relatively coarse, and the tensile properties were slightly lower than those of Example 1. Example 7 used a preferred high-speed injection rate, which fully filled the mold and produced fewer surface defects such as shrinkage cavities, resulting in higher tensile strength.

[0062] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0063] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for the precise preparation of small parts, characterized in that: The method comprises the following steps: preheating a pressure chamber to 300-400°C, adding a liquid alloy 20-40°C above the liquidus into the pressure chamber, adding alloy powder with an average particle size of 5-20 μm into the pressure chamber, applying ultrasound to the liquid alloy to form a mixed melt 5-10°C above the liquidus, subjecting the mixed melt to low-speed injection within 5 seconds, then subjecting the mixed melt to high-speed injection, and obtaining the small parts after pressure-maintaining cooling; wherein the mass of the alloy powder is 2-10% of the mass of the liquid alloy, the rate of the low-speed injection is 0.05-0.1 m / s, the rate of the high-speed injection is 2-10 m / s, the time of the low-speed injection is 4-8 seconds, and the thermal conductivity of the inner surface of the pressure chamber is less than 5 W / m·K.

2. The preparation method according to claim 1, characterized in that The average particle size of the alloy powder is 5-10 μm.

3. The preparation method according to claim 1, characterized in that The mass of the alloy powder is 5%-10% of the mass of the liquid alloy.

4. The preparation method according to claim 1, characterized in that The temperature of the alloy powder is 20-100°C.

5. The preparation method according to claim 1, characterized in that The speed of the high-speed injection is 5-8 m / s.

6. The preparation method according to claim 1, characterized in that The inner surface of the pressure chamber is coated with a heat-insulating ceramic material.

7. The preparation method according to claim 1, characterized in that The frequency of the ultrasound is 15-35 kHz, and the power of the ultrasound is 1000-2000 W.

8. The preparation method according to claim 1, characterized in that The holding pressure is 150-200 MPa, and the holding time is 10-20 seconds.

9. The preparation method according to claim 1, characterized in that The liquid alloy comprises, by weight, 6.5-7.5% silicon, 0.3-0.45% magnesium, 0-0.12% iron, 0-0.05% manganese, 0-0.1% copper, 0-0.05% zinc, 0-0.2% titanium, and the balance aluminum.

10. The preparation method according to claim 1, characterized in that The alloy powder contains 1-3% by mass of a refiner.

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