CN101629272B - Method for preparing continuous-fiber partially-reinforced aluminum alloy parts - Google Patents

Abstract

The invention relates to the preparation technology of aluminum alloy precision castings, in particular to a method for preparing continuous fiber locally reinforced aluminum alloy parts. It is placed on the corresponding part of the wax model of the part, and then the wax model of the part with reinforced fiber is directly produced on the wax injection machine, and then welded and assembled with the wax model of the casting system to become a complete wax model system; after several dipping coatings , Hanging sand circulation, a ceramic mold shell will be formed outside the wax mold system. After the ceramic mold shell is fully dried, it will be dewaxed and roasted; the ceramic mold shell will be cast with liquid aluminum alloy, and immediately after the casting is completed, it will be cast on the mold shell The cavity is pressurized with argon gas, and after complete solidification and cooling, the continuous fiber locally reinforced aluminum alloy parts are obtained. The invention does not need to make a fiber prefabricated mold specially, and solves the problems of processing, arranging and placing in the casting mold and the like of the fiber filaments better.

Description

A method for preparing continuous fiber locally reinforced aluminum alloy parts

technical field

The invention relates to the preparation technology of aluminum alloy precision castings, in particular to a method for preparing continuous fiber locally reinforced aluminum alloy parts. This method combines the preparation of the part wax mold and the reinforced fiber preform in the traditional investment casting process, uses gas pressurization to fill and solidify the liquid metal under pressure, and utilizes the characteristics of investment casting to directly produce continuous castings. (Long) fiber locally reinforced aluminum alloy parts.

Background technique

Continuous fiber locally reinforced aluminum alloy precision castings, using high-strength fibers to reinforce the high tensile stress area during service, has the incomparable bearing capacity, fatigue resistance and serviceability of ordinary aluminum alloy castings, as well as the incomparable specific strength and performance of steel parts. Lightweight advantages, used as structural parts can be widely used in aviation, automobiles, sports equipment and other fields, and has broad market prospects. The industrial production method of continuous fiber locally reinforced aluminum alloy structural parts has been one of the research hotspots in the field of material science for many years.

At present, a variety of methods have been developed in the preparation of continuous fiber reinforced metal matrix composite parts at home and abroad, mainly including laminated hot pressing diffusion bonding, vapor deposition hot isostatic pressing, powder metallurgy, casting method and directional solidification method, etc. . The casting method uses some special liquid forming processes to prepare composite materials, which can directly produce parts blanks, which is far more economical and convenient to process than other methods. At present, the continuous fiber reinforced aluminum matrix composite parts produced by casting method mostly adopt prefabricated impregnation technology. The reinforcing fiber is first made into a preform of a certain shape according to the required direction and volume fraction. The prefabricated form is placed in the reinforced part of the casting in the mold cavity and fixed by special structures on the metal mold. The liquid metal is usually poured under pressure through a casting system into the mold, impregnating the preform and filling the spaces between the reinforcing filaments. After solidification and cooling, a continuous fiber-reinforced metal matrix composite casting blank can be obtained. However, filamentous reinforcing fiber filaments are usually small in diameter and flexible, and it is difficult to control their arrangement and distribution, making the preparation of preforms difficult and costly. Therefore, research and development of non-prefabricated casting technology for continuous fiber reinforced aluminum matrix composites and low-cost direct production of composite castings are of great significance to the popularization and application of this advanced material.

Contents of the invention

The object of the present invention is to provide a new method for directly producing continuous (long) fiber-reinforced aluminum alloy matrix composite parts without using prefabricated infiltration technology. This method combines traditional investment precision casting technology with liquid metal pressure infiltration, does not need to make special fiber prefabricated molds, and better solves the problems of fiber filament handling, arrangement and placement in the mold. And it can make full use of the characteristics of investment precision casting with high precision and high degree of shape freedom to directly produce various near-net-shape composite material castings.

The whole process consists of three parts, namely: fiber treatment and wax mold making, mold shell preparation, casting and pressure solidification, specifically: passing the fiber bundle through a high-temperature liquid wax pool, and after the wax layer is completely cooled to room temperature, the fiber bundle is It is placed on the corresponding part of the wax model of the part, and then the wax model of the part with reinforced fiber is directly produced on the wax injection machine, and then welded and assembled with the wax model of the casting system to become a complete wax model system; after several dipping coatings , Hanging sand circulation, a ceramic mold shell will be formed outside the wax mold system. After the ceramic mold shell is fully dried, it will be dewaxed and roasted; the ceramic mold shell will be cast with liquid aluminum alloy, and immediately after the casting is completed, it will be cast on the mold shell The cavity is pressurized with argon gas, and after complete solidification and cooling, the continuous fiber locally reinforced aluminum alloy parts can be obtained.

The fiber bundle contains 500-1000 fibers with a diameter of 10-50 μm. Because the diameter is small and flexible, the fiber bundle can be pulled by the reel, immersed in and passed through the liquid wax pool. The temperature of the wax liquid is 70-90°C, and it has good wettability with the fiber filaments. The liquid wax material can penetrate into the gaps between the fiber filaments and form a wax layer with a certain thickness on the surface of the fiber filaments. The fiber tow with the wax layer just pulled out from the wax pool, because the wax layer still has a certain temperature, has a certain flexibility and deformation ability, and can be processed into a certain shape by a reel or cut into a certain length for future use.

Depending on the shape of the part and the location of the fiber-reinforced area, the placement of fiber bundles can be considered on the part wax mold. After the wax layer is completely cooled to room temperature, it has a certain strength, which makes the fiber filaments with the wax layer have a certain rigidity, which greatly facilitates the directional arrangement of the fiber filaments and placement in the mold. In addition, the wax mold molding of the reinforced area can also be specially designed, and the fibers with the wax layer are arranged in the molding according to the required direction, and the wax mold of the fiber reinforced part of the part is prepared in advance through molding, and then welded and assembled with other parts Into a complete wax model of parts with reinforced fibers.

The preparation of the ceramic mold shell is the same as the traditional investment casting process. Usually, after 6 to 8 cycles of dipping paint and hanging sand, a ceramic mold shell will be formed outside the wax mold, and the thickness of the mold shell is 10-20mm. A ceramic mold shell with a certain thickness and strength will be formed outside the wax pattern, and the two ends of the fiber filaments have also been firmly stuck by the ceramic mold shell. Dewaxing is carried out in a high-pressure steam kettle, and the pressure during dewaxing is about 0.6MPa. The firing temperature of the shell after dewaxing is mainly based on the material of the shell, usually 700-1000°C.

During the solidification process of molten aluminum after casting, argon gas is used to pressurize, and the pressure is usually controlled at 0.6-1.0MPa. In order to fully ensure the filling and impregnation of the aluminum liquid between the fiber filaments, at the same time, the liquid metal solidifies under pressure, which can make the structure of the casting dense and have better mechanical properties. Casting and pressurized solidification can also be carried out on low-pressure casting machines to realize semi-mechanized production.

After the casting is completely solidified and cooled, the mold is cleaned, the sprue riser is cut off, and the necessary surface cleaning is carried out, so that the required continuous fiber reinforced aluminum alloy casting can be obtained.

The process method developed by the invention can be used to produce composite materials composed of different aluminum alloy matrixes and fiber materials. The volume percentage of fibers in the reinforcement area can vary between 40-60% according to different application requirements; gas pressurization is used during the filling and solidification process, and the pressure is usually controlled at 0.6-1.0MPa. Casting and pressurized solidification can also be carried out on low-pressure casting machines to realize semi-mechanized production.

Description of drawings

Fig. 1. the flow chart of process of the present invention

a. The fiber is immersed in the wax pool through the roller; b. The preparation of the wax model of the part; c. The coating (circulation); d. The hanging sand (circulation); ;h. Demoulding and cleaning; i. Cutting the riser and cleaning the surface

The photo of the continuous fiber reinforced aluminum alloy sample of Fig. 2 Example 1

a. blank; b. processed sample

Section structure of the sample of Fig. 3 Example 1

Detailed ways

Example 1:

According to the process of the above invention, 50% volume fraction γ-Al ₂ O ₃ fiber (produced by Japan Sumitomo Chemical Company, model Altex SN, fiber filament diameter 15 μm, tensile strength 1.8GPa) reinforced aluminum alloy (Al-6% Zn-1%Mg-0.1%Cu) test bar, test block and continuous fiber locally reinforced aluminum alloy test block. Figure 2a is the blank photo of these three samples, and Figure 2b is the processed sample. Test rods and small test pieces are integrally reinforced with continuous fibers and are used for performance testing. The large test block is locally reinforced by continuous fibers, the middle of the test block is a reinforced area, and the two sides are non-reinforced areas. Using this test block can verify the process feasibility of the present invention, and can measure the macroscopic internal stress of the reinforced area and the non-reinforced area. The measured tensile strength and elastic modulus of the 50% fiber-reinforced aluminum alloy composite material are shown in Table 1 along the fiber direction and perpendicular to the fiber direction. In addition, the distribution of fibers in the test bar was also observed. Figure 3 is a photo of the cross-sectional structure of the sample. It can be seen that the fibers can be evenly distributed throughout the cross-section.

Example 2:

The crankshaft connecting rod of the aluminum alloy sports bicycle produced by the invention can replace the original high-strength forged steel parts, and the weight can be reduced by about 69%. The force arm section in the middle of the connecting rod is locally reinforced with 45% volume percentage γ-Al ₂ O ₃ fiber (produced by Sumitomo Chemical Company, Japan, model Altex SN, fiber diameter 15μm, tensile strength 1.8GPa), and the matrix material is cast aluminum silicon alloy. Zircon powder refractory material and silica sol binder are used for ceramic slurry, zircon powder (particle size 0.25mm) is used for surface layer (two layers) hanging sand material, and mullite powder (particle size 0.8-1.4mm) is used for reinforcement layer , a total of 8 layers of mold shell, about 20mm thick. Dewaxing is carried out in a steam kettle with a pressure of 0.6MPa and a holding time of 90 seconds. The shell firing is carried out in an electric furnace at a firing temperature of 850°C. Since the mold shell was not cast immediately after firing, the mold shell was preheated before casting, and the preheating temperature was 750°C. The aluminum alloy is melted in a resistance crucible furnace, and the casting temperature is 700°C. After casting, pressurize the molten aluminum in the mold shell with argon gas, the pressure is 0.8MPa, and the holding time is 5 minutes. After the casting is cooled and solidified and cooled to room temperature, the mold shell is removed, the sprue riser is cut off, and the finished product is obtained after grinding and cleaning. Parts have a high surface finish with the same cosmetic quality as forged steel bellcrank links. The middle arm is reinforced with fiber, which greatly improves the bearing capacity and service life of the parts.

Table 1. Mechanical properties of 50% γ-Al ₂ O ₃ fiber reinforced aluminum alloy samples

performance Test value Tensile strength along fiber direction, σ _b0° (MPa) 1003 Tensile strength perpendicular to fiber direction, σ _b90° (MPa) 220 Modulus of elasticity along fiber direction, E _0° (GPa) 135 Modulus of elasticity perpendicular to the fiber direction, E _90° (GPa) 80

Claims (1)

1. A method for preparing continuous fiber locally reinforced aluminum alloy parts, including fiber treatment and wax mold making, mold shell preparation, casting and pressurized solidification, specifically: passing the fiber bundle through a high-temperature liquid wax pool, and waiting for the wax layer to cool completely After reaching room temperature, the fiber bundles are placed on the corresponding parts of the part wax model, and then the part wax model with reinforced fibers is directly produced on the wax injection machine, and then welded and assembled with the casting system wax model to become a complete wax model system; after several cycles of immersing paint and hanging sand, a ceramic mold shell will be formed outside the wax pattern system. After the ceramic mold shell is fully dried, it will be dewaxed and roasted; After that, immediately use argon to pressurize the cavity of the mold shell, and after it is completely solidified and cooled, the continuous fiber locally reinforced aluminum alloy parts can be obtained. If the ceramic mold shell is not cast immediately after firing, the ceramic mold shell should be cleaned before casting Preheating; the fiber bundle is composed of 500-1000 fibers with a diameter of 10-50 μm, the fibers are γ-Al ₂ O ₃ fibers, and the volume percentage of the fibers can be between 40-60% according to different usage requirements Change; the aluminum alloy is Al-6%Zn-1%Mg-0.1%Cu; the temperature of the high-temperature liquid wax pool wax liquid is 70-90°C; the preparation process of the ceramic formwork is as follows: after 6～ 8 cycles of soaking paint and hanging sand will form a ceramic mold shell on the outside of the wax mold, and the thickness of the mold shell is 10-20mm; the dewaxing of the ceramic mold shell is carried out in a high-pressure steam kettle, and the pressure during dewaxing is 0.6mm. Mpa, the firing temperature of the ceramic formwork after dewaxing is 700-1000°C; liquid aluminum alloy casting is carried out on the ceramic formwork, and during the solidification process of the molten aluminum after casting, argon gas is used to pressurize the pressure and the pressure is controlled at 0.6-1.0Mpa .

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