Extrusion casting piston device containing ceramic fiber reinforcement and forming method

Abstract

The invention discloses an extrusion casting piston device containing a ceramic fiber reinforcement, which comprises a fixed die and a movable die, the fixed die and the movable die are closed to form a cavity space for pouring a piston blank, the movable die is provided with a placing groove for placing the ceramic fiber reinforcement, and the fixed die is provided with an overflow groove I and an exhaust block I; the movable die is provided with a second overflow groove matched with the first overflow groove for use and further provided with a second exhaust block matched with the first exhaust block for use, the second overflow groove is directly connected with a slag collecting bag, the other end of the slag collecting bag is communicated with the second exhaust block, and a cooling unit is arranged in an inner die punch of the movable die; a hydraulic unit is arranged at the upper end of the movable mold; the lower end of the cavity space is connected with a low-pressure quantitative liquid conveying unit; the invention further provides a forming method of the squeeze casting piston containing the ceramic fiber reinforcement. According to the method, the ceramic fiber reinforcement and the matrix aluminum alloy can be well combined, the tissue density of a piston casting is improved, the quality and production efficiency of the extruded piston skirt are improved, and the cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of piston casting, in particular to an extrusion casting piston device containing a ceramic fiber reinforcement and a molding method. Background Art

[0002] The piston is the key moving part that transmits the main and auxiliary power of various equipment. It is the "heart" component of the equipment power. The piston is mainly composed of the piston top, wear-resistant ring and piston skirt. The piston top is a component of the combustion chamber, forming a closed space with the cylinder wall, and is subjected to high temperature and high pressure; the wear-resistant ring fits tightly with the piston ring, sealing gas, heat conduction and oil control; the piston skirt mainly plays a guiding role and bears side pressure. Its shape maintains a uniform and appropriate gap to ensure that the piston has sufficient bearing area in the cylinder. The piston is mainly subjected to high temperature, high pressure, complex friction and thermal-mechanical coupling loads. In recent years, with the development of technical indicators, diesel engine equipment has put forward higher requirements for high power and high explosion pressure technologies of power diesel engines, and the requirements for piston performance have also been increased accordingly. At present, the maximum explosion pressure of diesel engine power design target has been increased to 22MPa. The piston will work at a higher temperature and bear higher thermal and mechanical loads. The high temperature strength and heat fatigue resistance of the existing piston can no longer meet the requirements, and failures such as piston cracking and melting are difficult to avoid.

[0003] Squeeze casting is a combination of casting and forging processes, also known as liquid die forging, which is a process method that enables liquid or semi-solid metal melts to solidify and form under high mechanical pressure. Its basic working principle: Inject the molten or semi-solid metal liquid into the mold cavity that has been preheated to a certain temperature, and make the alloy liquid crystallize and solidify by applying a certain extrusion pressure to obtain castings with fine grains, good surface formability, high dimensional accuracy, and excellent performance. Traditional aluminum alloy pistons mainly use gravity casting, and a small number of pistons are produced by forging methods. Since the cross-sectional dimensions of general pistons vary greatly and the shape is complex, in gravity casting, the casting structure is coarse, and defects such as porosity occur in thick and large parts, resulting in low performance. When using the forging method to produce pistons, the forging streamline inside the piston is distributed according to the forging contour, thereby improving the mechanical properties and service life of the piston. However, pistons produced by forging cannot produce internal cooling oil channels in the piston and add wear-resistant inserts, and can only adopt combined forming, with complex production processes, very high product costs, and limited application scope. At present, almost all the equipment for producing pistons by squeeze casting at home and abroad is obtained by transforming four-column hydraulic presses. Such equipment has a simple squeeze casting mold with only a simple guiding device and a mechanism for ejecting castings, and cannot accurately control the vacuum degree, extrusion parameters, etc. The ceramic fiber reinforcement cannot form a good metallurgical bond with the aluminum alloy melt, and there are obvious stratifications in the thick and large parts of the piston skirt, with a high product rejection rate, limited performance improvement, high costs, and inability to produce in large quantities. Currently, the new squeeze casting pistons mainly have the following problems: (1) Due to the thick and large piston skirt of the diesel engine piston, which is far from the gate (feed port), the existing squeeze casting process causes obvious stratification and peeling phenomena in the skirt, and there are many shrinkage cavities, porosity and other defects; (2) The existing squeeze casting process has poor metallurgical bonding between the wear-resistant ceramic fiber reinforcement and the matrix alloy, with disadvantages such as poor wettability and low bonding strength of the ceramic fiber reinforcement. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a squeeze casting piston device and forming method containing ceramic fiber reinforcement. In terms of structure, the piston skirt, slag trap and overflow groove structures are optimized, and at the same time, a vacuum pumping auxiliary system is set for the exhaust block and a water cooling system is set for the inner mold; in terms of process, a double-layer vacuum pumping auxiliary system is adopted, combined with a low-pressure liquid-lifting method and a slow injection to first remove the gas and then quantitatively transport the aluminum alloy melt, so that the ceramic fiber reinforcement and the matrix aluminum alloy are well combined, reducing shrinkage porosity or shrinkage cavities existing in the piston casting, reducing segregation, refining grains, improving the density of the piston casting structure, improving the quality and production efficiency of the squeeze piston skirt, reducing costs.

[0005] The technical solutions provided by the present invention are as follows: An extrusion casting piston device containing ceramic fiber reinforcements, comprising a fixed mold and a movable mold. After the fixed mold and the movable mold are closed, a cavity space for pouring the piston blank is formed. A placement groove for placing the ceramic fiber reinforcements is provided on the movable mold. An overflow groove I and an exhaust block I are provided on the fixed mold. An overflow groove II, which is used in cooperation with the overflow groove I, is provided on the movable mold. An exhaust block II, which is used in cooperation with the exhaust block I, is also provided on the movable mold. The overflow groove I and the overflow groove II are both arranged on the inner side wall of the cavity space near the upper part of the piston skirt. The overflow groove II is directly connected to a slag trap, and the other end of the slag trap is communicated with the exhaust block II. A cooling unit is arranged in the inner die punch of the movable mold. A hydraulic unit for driving the inner die punch of the movable mold is provided at the upper end of the movable mold. A low-pressure quantitative liquid injection unit is connected to the lower end of the cavity space.

[0006] Preferably, the volume ratio of the slag trap to the volume of the piston skirt is 0.8 - 1.5.

[0007] Preferably, a vacuum pipeline is connected to the gate on the fixed mold.

[0008] Preferably, it further includes a pin seat ejecting push rod and a gate ejecting push rod. The pin seat ejecting push rod and the gate ejecting push rod are located on the same side and are arranged in parallel, one above the other.

[0009] Preferably, a vacuum pipe orifice is arranged in the exhaust block I and / or the exhaust block II.

[0010] Preferably, the low-pressure quantitative liquid injection unit includes an infusion pipe and a riser pipe connected to a side-insulation furnace with a sealed structure for storing aluminum alloy melt. An inert gas inlet pipe is communicated with the side-insulation furnace. An electromagnetic pump is arranged on the infusion pipe. The upper end of the riser pipe is communicated with the cavity space. An extrusion punch is arranged at the lower end of the riser pipe. The extrusion punch is connected to a shot sleeve through an extrusion rod. The riser pipe is arranged in a barrel. An induction heating pipe is arranged on the barrel. A liquid level sensor is arranged at the upper part of the barrel.

[0011] Preferably, the cooling unit includes a plurality of cooling water pipes.

[0012] A forming method for an extrusion casting piston containing ceramic fiber reinforcements includes the following operating steps: S1. Preheating of the ceramic fiber reinforcements: The ceramic fiber reinforcements are preheated and heat-insulated. S2. Preparation for modification, refining and degassing of the aluminum alloy melt: The aluminum alloy used for extrusion casting is charged, melted and modified according to the piston matrix ratio, and then poured into the side-insulation furnace for rotary degassing. S3. Mold preparation, spraying, mold closing, debugging and heating: Use the squeeze casting piston device containing ceramic fiber reinforcement described above as the casting mold. Then, spray and brush the release agent at the corresponding positions of the fixed mold and the moving mold respectively. Place the preheated ceramic fiber reinforcement into the placement groove on the moving mold. Close the moving mold and the fixed mold to form a closed cavity. Then, debug and heat the closed mold to heat the mold temperature to 250 - 300 °C; S4. Filling of aluminum alloy melt: Squeeze the aluminum alloy melt into the closed cavity from the lower end of the mold through the low-pressure quantitative infusion unit; S5. Boosting and pressure holding: After filling, perform boosting and pressure holding. The boosting pressure is 115 - 145 MPa, and the pressure holding time is 18.5 - 23.5 s; S6. Pressure relief and part removal, heat treatment: Separate the moving mold from the fixed mold, take out the piston blank, and then perform heat treatment on the piston blank.

[0013] Preferably, in step S1, the preheating temperature of the ceramic fiber reinforcement is 300 °C ± 10 °C, and the heat preservation time is 1.5 - 2 h.

[0014] Preferably, in step S1, the ceramic fiber reinforcement by mass fraction includes 15 - 35 wt% silicon carbide short fibers, 5 - 11 wt% boron powder, and 54 - 80 wt% carbon fibers as the matrix.

[0015] Preferably, in step S4, before the filling of the aluminum alloy melt, evacuate the gate position, and the vacuum degree is 220 - 260 mbar; The filling speed parameters of the aluminum alloy melt adopt double-stage regulation. The punch speed is 0.11 - 0.23 m / s from 0 - 0.8 s, and the punch speed is 0.42 - 0.48 mm / s from 0.9 - 2 s; After the injection filling, start to evacuate the exhaust groove, and the vacuum degree is 80 - 120 mbar.

[0016] The present invention has the following advantages over the prior art: 1. Aiming at the disadvantages of poor wettability and bonding performance of wear-resistant ceramic fiber reinforcements in the existing squeeze casting process, the novel ceramic fiber reinforcement of the present invention by mass fraction includes 15 - 35 wt% silicon carbide short fibers, 5 - 11 wt% boron powder, and 54 - 80 wt% carbon fibers as the matrix. The present invention selects a certain proportion of lightweight and high-modulus boron powder (boron atoms have a layered structure similar to graphite) for mixing with the matrix carbon / silicon carbide fibers to reduce the defect sensitivity of the matrix carbon / silicon carbide fibers to the matrix alloy. Through the coupling effect between the phase interface and the interface, and between the phases, a more excellent performance than that of the single-reinforcement composite material is obtained; At the same time, a small amount of AlB is generated by the reaction of boron powder in the aluminum alloy melt 2 , during the squeeze casting aluminizing process, the in-situ self-generated AlB 2The wettability and compatibility between the reinforcing phase and the aluminum matrix are extremely excellent, which can optimize the interfacial bonding between the matrix carbon / silicon carbide fiber reinforcement and the aluminum matrix, improve the wettability, and effectively increase the bonding strength between the ceramic fiber reinforcement and the aluminum alloy. At the same time, a certain proportion of matrix carbon / silicon carbide short fibers are selected to endow the ceramic fiber reinforcement with characteristics such as high strength, excellent oxidation resistance, high modulus, and low density.

[0017] 2. Aiming at the obvious delamination and peeling phenomenon in the skirt part caused by the existing squeeze casting process and the defects such as a large amount of gas entrapment, shrinkage porosity, and porosity, the squeeze casting piston device of the present invention optimizes the structure of the piston skirt. The skirt is directly connected to the slag trap and the overflow groove. By setting the ratio between the volume of the slag trap and the volume of the piston skirt, the piston skirt can be fully compensated for shrinkage, and turbulence can be eliminated, so that the position where the liquid flows converge moves to the slag trap. At the same time, a vacuum-assisted system (vacuum pipe orifice) is provided in the exhaust block one and / or two, which is conducive to exhausting air from the cavity. By setting the internal mold cooling water channel of the moving mold, since the slag trap is close to the internal mold, the cooling water channel can control the temperature of the internal mold. During the solidification process of the casting, the piston skirt area is cooled by passing water, and at the same time, the melt in the slag trap can also be rapidly cooled, meeting the bottom-up solidification sequence of the piston squeeze casting, reducing the risk of shrinkage porosity and other defects in the piston skirt, eliminating defects such as gas entrapment, eddy current, and inclusion in the skirt, improving the casting quality of the piston blank, thereby realizing the refinement of the piston matrix structure, improving the mechanical properties of the piston, and achieving the purpose of improving the high-strengthening and high-reliability of the piston.

[0018] 3. The squeeze casting piston device containing ceramic fiber reinforcement of the present invention uses a low-pressure liquid-lifting method to transport the melted aluminum alloy liquid into the die-casting type conveying pipeline, and realizes the quantitative transportation and pouring process of the aluminum alloy liquid by controlling the operation time of the hydraulic piston through a set control program. In addition, the metal liquid is transported into the mold cavity by a bottom-pouring method. During the entire filling process, the liquid level rises smoothly, natural convection is not easily generated, gas entrapment does not easily occur, and closed-mold pouring can be realized, thereby improving the quality and production efficiency of the squeeze casting parts and reducing the transformation cost, and further promoting the application of the squeeze casting process in actual production.

[0019] 4. The squeeze casting piston device with ceramic fiber reinforcement of the present invention adopts the methods of vacuum extraction at the gate position and vacuum extraction at the exhaust groove, and combines the double-stage regulation of the filling speed parameter of the upward movement of the squeeze punch to squeeze the aluminum alloy liquid into the closed cavity. (The starting point is the upward movement of the squeeze punch) From 0 to 0.8 s, the punch speed is 0.11 - 0.23 m / s, and from 0.9 to 2 s, the punch speed is 0.42 - 0.48 mm / s, reducing the heat loss of the molten metal in the runner, and the speed of the molten metal slows down before reaching the inner gate, ensuring the smooth movement of the front liquid level, enabling all the air to be exhausted from the cavity, allowing the aluminum alloy matrix solution to penetrate into the ceramic fiber reinforcement, forming a good metallurgical bond between the two, eliminating pores and looseness inside the piston, and improving the bonding strength between the wear-resistant insert and the matrix; 5. The double-ejection mechanism composed of the pin boss ejection push rod and the gate ejection push rod of the squeeze casting piston device with ceramic fiber reinforcement of the present invention solves the problem of poor ejection during mold opening of the squeeze casting piston and eliminates the risks such as mold opening scratches of the piston blank.

[0020] 6. Aiming at the disadvantages such as poor metallurgical bonding between the wear-resistant ceramic fiber reinforcement and the matrix alloy in the existing squeeze casting process, the forming method of the squeeze casting piston with ceramic fiber reinforcement of the present invention combines methods such as a new type of ceramic fiber reinforcement + a quantitative gating system + double-layer vacuum extraction + double-stage regulation of injection speed, further enabling a good metallurgical bond between the ceramic fiber reinforcement and the matrix aluminum alloy melt, improving the casting quality, bonding rate and bonding strength of the bonding area between the ceramic fiber reinforcement and the aluminum matrix, reducing shrinkage porosity or shrinkage cavities in the piston casting, reducing segregation, refining grains, improving the tissue density of the piston casting, and improving the quality and production efficiency of the squeeze piston skirt. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0022] Figure 1 It is a schematic structural diagram of the squeeze casting piston device with ceramic fiber reinforcement in the embodiment of the present invention; Figure 2 It is a schematic structural diagram of the moving mold in the embodiment of the present invention; Figure 3 It is a schematic structural diagram of the fixed mold in the embodiment of the present invention; Figure 4 It is a microstructural diagram of the piston matrix in the embodiment of the present invention; Figure 5This is the microstructure diagram of the piston ceramic fiber reinforced insert ring in the embodiment of the present invention; Figure 6 This is the microstructure diagram formed by the combination of the piston ceramic fiber reinforced insert ring and the aluminum alloy matrix in the embodiment of the present invention; Figure 7 This is the structural schematic diagram of the piston blank obtained after casting in the embodiment of the present invention.

[0023] Reference numerals: 1, fixed mold; 11, overflow groove 1; 12, exhaust block 1; 13, vacuum pipeline; 2, moving mold; 21, placement groove; 22, overflow groove 2; 23, exhaust block 2; 24, slag collecting pocket; 25, cooling unit; 26, hydraulic unit; 3, low-pressure quantitative infusion unit; 31, in-line holding furnace; 32, infusion pipe; 33, riser pipe; 34, inert gas inlet pipe; 35, electromagnetic pump; 36, extrusion punch; 37, extrusion rod; 38, injection cylinder; 39, barrel; 391, induction heating pipe; 392, liquid level sensor; 4, pin seat ejection push rod; 5, gate ejection push rod; 6, vacuum pipe orifice; 7, piston skirt; 8, piston pin seat; 9, piston gate; 10, ceramic fiber reinforcement. Detailed implementation manners

[0024] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0025] As shown in Figures 1 - 3 Figures 6 and 7, the embodiment of the present invention provides an squeeze casting piston device containing a ceramic fiber reinforcement, including a fixed mold 1 and a moving mold 2. After the fixed mold 1 and the moving mold 2 are closed, a cavity space for pouring the piston blank is formed. The moving mold 2 is provided with a placement groove 21 for placing the ceramic fiber reinforcement 10. The fixed mold 1 is provided with an overflow groove 11 and an exhaust block 12. The moving mold 2 is provided with an overflow groove 22 that is used in cooperation with the overflow groove 11, and the moving mold 2 is further provided with an exhaust block 23 that is used in cooperation with the exhaust block 12. Both the overflow groove 11 and the overflow groove 22 are arranged on the inner side wall of the cavity space near the upper part of the piston skirt 7. The overflow groove 22 is directly connected to a slag collecting pocket 24, and the other end of the slag collecting pocket 24 is communicated with the exhaust block 23. A cooling unit 25 is arranged inside the inner mold punch of the moving mold 2; a hydraulic unit 26 for driving the inner mold punch of the moving mold is arranged at the upper end of the moving mold 2, and the lower end of the cavity space is connected to a low-pressure quantitative infusion unit 3.

[0026] In this embodiment, the volume ratio of the slag trap 24 to the volume of the piston skirt 7 is 0.8 - 1.5, which can fully compensate for the shrinkage of the piston skirt 7 and eliminate turbulence, causing the location where the liquid flows converge to move to the slag trap 24.

[0027] In this embodiment, a vacuum pipeline 13 is connected to the gate on the fixed mold 1, which is conducive to exhausting the air from the cavity at the piston gate 9 and eliminating air entrainment.

[0028] The squeeze casting piston device with ceramic fiber reinforcement in this embodiment further includes a pin boss ejecting push rod 4 and a gate ejecting push rod 5. The pin boss ejecting push rod 4 and the gate ejecting push rod 5 are located on the same side and are arranged in parallel, one above the other. The pin boss ejecting push rod 4 and the gate ejecting push rod 5 work together to facilitate the demolding of the piston blank after pouring.

[0029] In this embodiment, a vacuum pipe orifice 6 is provided in the exhaust block one 12 and / or the exhaust block two 23, which is conducive to exhausting the air from the thick part of the piston skirt 7 from the cavity, making it not easy to generate air entrainment, and enabling closed mold pouring, thereby improving the quality and production efficiency of the squeeze casting parts.

[0030] In this embodiment, the low-pressure metering infusion unit 3 includes an infusion pipe 32 and a lift pipe 33 connected to the side machine holding furnace 31 with a sealed structure for storing aluminum alloy melt. An inert gas inlet pipe 34 is connected to the side machine holding furnace 31. The aluminum alloy melt in the side machine holding furnace 31 is pressed into the infusion pipe 32 and the lift pipe 33 through air pressure. An electromagnetic pump 35 is provided on the infusion pipe 32 to facilitate controlling the flow rate of the aluminum alloy melt in the infusion pipe 32. The upper end of the lift pipe 33 is connected to the cavity space, and a squeeze punch 36 is provided at the lower end of the lift pipe 33. The squeeze punch 36 is connected to a shot sleeve 38 through a squeeze rod 37. By pushing the squeeze rod 37 with the shot sleeve 38, the squeeze rod 37 pushes the squeeze punch 36, and the squeeze punch 36 pushes upward to squeeze the aluminum alloy melt in the lift pipe 33 into the cavity space. The lift pipe 33 is arranged in a barrel 39, and an induction heating pipe 391 is provided on the barrel 39. A liquid level sensor 392 is provided at the upper part of the barrel 39.

[0031] In this embodiment, the cooling unit 24 includes a plurality of cooling water pipes.

[0032] A forming method for a squeeze casting piston with ceramic fiber reinforcement includes the following operating steps: S1. Preheating of the ceramic fiber reinforcement 10: The ceramic fiber reinforcement 10 is preheated and heat-insulated to prevent the matrix aluminum liquid from solidifying due to cooling before infiltrating into the pores and blocking the infiltration channels. S2. Preparation for modification, refining, and degassing of the aluminum alloy melt: After charging, melting, and modifying the aluminum alloy for squeeze casting according to the piston matrix ratio, it is poured into the side machine holding furnace 31 for rotary degassing. S3. Mold preparation, spraying, mold clamping, debugging and heating: Use the above squeeze casting piston device containing ceramic fiber reinforcement as the pouring mold. Then, spray and brush the mold release agent at the corresponding positions of the fixed mold 1 and the moving mold 2 respectively. Place the preheated ceramic fiber reinforcement 10 into the placement groove 21 on the moving mold 2. Clamp the moving mold 1 and the fixed mold 2 to form a closed cavity (the inner mold punch moves to a fixed position, the moving mold and the fixed mold are clamped from left and right, and the left and right locking rings reach the locking position. The mold completes pre-clamping to form a closed cavity). Then, debug and heat the clamped mold to heat the temperature of the mold to 250 - 300 °C; S4. Filling of aluminum alloy melt: Squeeze the aluminum alloy melt into the closed cavity from the lower end of the mold through the low-pressure quantitative infusion unit 3; S5. Boosting and pressure holding: After filling is completed, perform boosting and pressure holding to avoid gas mixing into the molten metal, and at the same time ensure obtaining dense castings. The boosting pressure is 115 - 145 MPa, and the pressure holding time is 18.5 - 23.5 s; S6. Pressure relief and part removal, heat treatment: Separate the moving mold and the fixed mold, take out the piston blank, and then perform heat treatment on the piston blank.

[0033] In this embodiment, in step S1, the ceramic fiber reinforcement 10 made of ceramic fiber to be used is placed into the muffle furnace. The ceramic fiber reinforcement 10 must be stacked neatly without breakage. The operator needs to wear clean gloves for operation to avoid oil stains on the ceramic fiber reinforcement 10. The ceramic fiber reinforcement 10 should be protected from bumps during transportation. In this embodiment, the ceramic fiber reinforcement 10 includes 15 - 35 wt% short silicon carbide fibers, 5 - 11 wt% boron powder, and 54 - 80 wt% carbon fibers as the matrix by mass fraction. The specifications of the used ceramic fiber reinforcement 10 are shown in Table 1 below. After the ceramic fiber reinforcement 10 is placed in the muffle furnace, close the furnace door tightly, adjust the furnace temperature to within 300 °C ± 10 °C, and keep it warm for 1.5 - 2 h before taking out the ceramic fiber reinforcement 10 for use. The furnace door of the muffle furnace should be closed immediately after loading and unloading the ceramic fiber reinforcement 10 each time. The ceramic fiber reinforcement 10 should not touch the furnace wall and the furnace door. Two muffle furnaces are used alternately to ensure that the baking temperature of the ceramic fiber reinforcement 10 reaches the specified requirements. It is prohibited to place the ceramic fiber reinforcement 10 outside the muffle furnace.

[0034] The ceramic fiber reinforcement 10 of this embodiment is formed by chemical vapor infiltration (CVI). Through CVI densification, not only can an excellent interfacial bond be formed between the matrix carbon and the silicon carbide fibers, but also by controlling the CVI process conditions, a high-density composite material with complete crystallization can be obtained. In the present invention, a certain proportion of light and high-modulus boron powder (boron atoms have a layered structure similar to that of graphite) is selected and mixed with the matrix carbon / silicon carbide fibers to reduce the defect sensitivity of the matrix carbon / silicon carbide fibers to the matrix alloy. Through the coupling effect between the phase interfaces and between the phases, a more excellent performance than that of the composite material reinforced by a single reinforcement is obtained. At the same time, a small amount of AlB is generated when the boron powder reacts in the aluminum alloy melt. 2 During the squeeze casting aluminizing process, the wettability and compatibility between the in-situ self-generated AlB 2 reinforcement phase and the aluminum matrix are very excellent, which can optimize the interfacial bond between the matrix carbon / silicon carbide fiber reinforcement and the aluminum matrix, improve the wettability, and effectively improve the bonding strength between the ceramic fiber reinforcement 10 and the aluminum alloy. At the same time, a certain proportion of matrix carbon / silicon carbide short fibers is selected to endow the ceramic fiber reinforcement 10 with characteristics such as high strength, excellent oxidation resistance, high modulus, and low density.

[0035] Table 1 Composition, proportion, and specification requirements of the ceramic fiber reinforcement parts

[0036] In this embodiment, the chemical composition of the aluminum alloy used in step S2 is shown in Table 2.

[0037] Table 2 Chemical composition of the aluminum alloy (wt%)

[0038] In this embodiment, the mold preparation in step S3 specifically includes: checking the states of the fixed mold and the moving mold of the mold, checking the water passing condition of the inner mold, not allowing waterway blockage, small water passing volume, or uncontrolled long water passing phenomenon, and not allowing leakage / dripping at the inner mold pipe joint; cleaning (hand sandblasting, polishing) the coatings, residual aluminum chips (blocks) on the moving mold, fixed mold, and inner mold of the mold at least once to ensure that the mold is tightly closed and flat, checking the cavity, parting surface, core-pulling slider, and cleaning the ejector rod, checking whether the vacuum system is unobstructed, and checking whether the core-pulling ejector rod moves smoothly; checking whether the ceramic fiber reinforcement parts are loose in cooperation with the inner mold and whether there are sundries on the mating surface; locking the whole set of molds for hoisting and installation, installing the ejector pull rod, tightening the screws of the dynamic and static pressure plates, connecting the sensor wires, connecting the vacuum pipe, sleeving the lift pipe, induction heating pipe, and asbestos gasket to make it airtight, connecting the mold temperature heating oil pipe and the cooling oil pipe, adjusting the injection support, installing the extrusion rod 37 and the extrusion hammer head, adjusting the clamping force, and checking whether the sensor indicator light is normal.

[0039] In this embodiment, when spraying the mold release agent in step S3, since the casting adopts the sequential solidification method, when spraying the mold release agent, it should be noted that the coating should be thicker in the area near the gate and the thin-walled area, and thinner in the area far from the gate and the wide and thick parts of the casting.

[0040] In this embodiment, in step S4, the alloy in the in-line holding furnace 31 is melted to a preset temperature of 630 - 680 °C. The in-line holding furnace 31 starts to be slowly pressurized, and a certain amount of molten aluminum alloy is transported to the riser tube 33 in the barrel 39 through the electromagnetic pump 35 conveying system.

[0041] In this embodiment, in step S4, before the filling of the molten aluminum alloy, the gate position is evacuated first, and the vacuum degree is 220 - 260 mbar to reduce the gas entrainment and slag generation of the molten aluminum alloy; the filling speed parameter of the molten aluminum alloy adopts double-stage regulation, the punch speed of 0.11 - 0.23 m / s is adopted from 0 to 0.8 s, and the punch speed of 0.42 - 0.48 mm / s is adopted from 0.9 to 2 s; after the injection filling, the exhaust groove starts to be evacuated, and the vacuum degree is 80 - 120 mbar. The double-stage regulation of the speed can reduce the heat loss of the molten metal in the runner, and the speed of the molten metal slows down before reaching the inner gate, ensuring the stable movement of the front liquid surface. The specific squeeze casting process parameters are shown in Table 3.

[0042] Table 3 Squeeze casting process parameters

[0043] In this embodiment, the heat treatment process parameters in step S6 are shown in Table 4.

[0044] Table 4 Heat treatment process parameters

[0045] Using the forming method of the squeeze casting piston containing ceramic fiber reinforcements in this embodiment for casting can enable the ceramic fiber reinforcements 10 to form a good bond with the aluminum alloy matrix. As Figure 4 , Figure 5 , Figure 6 shown, from Figure 4 and Figure 5 it is found that gray long or short ceramic fiber matrices are evenly distributed in the silicon phase, strengthening phase, and matrix. From Figure 6 it can be seen that the ceramic fibers (the material composition of the ceramic fiber reinforcements 10) are well combined with the matrix alloy, without shrinkage porosity, shrinkage cavity and other defects. The ceramic fibers are randomly distributed in three dimensions. Since the fiber surface plays the role of crystal nuclei during solidification, the matrix structure in the composite area is finer than that in the non-composite area.

[0046] Table 5 Room temperature tensile strength, thermal conductivity and linear expansion coefficient of the composite material formed by ceramic fiber reinforcements and aluminum alloy matrix

[0047] As can be seen from Table 5, the bonding strength between the ceramic fiber and the matrix alloy is 356.7 - 395.6 MPa, the thermal conductivity is 157 - 171 W / m·K, and the linear expansion coefficient is 4.1 - 4.6×10 -6 m / mK. It shows that the ceramic fiber and the matrix alloy have a high bonding strength. At the same time, the ceramic fiber reinforcement 10 has properties such as high strength, excellent oxidation resistance, high modulus, and low density, meeting the requirements of the continuous improvement of the technical indicators of diesel engine pistons.

[0048] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An extrusion casting piston device containing a ceramic fiber reinforcement, comprising a fixed mold and a movable mold, wherein the fixed mold and the movable mold are combined to form a cavity space for casting a piston blank, characterized in that: The movable mold is provided with a placement groove for placing ceramic fiber reinforcements, the fixed mold is provided with an overflow groove 1 and an exhaust block 1, the movable mold is provided with an overflow groove 2 used in conjunction with the overflow groove 1, and the movable mold is also provided with an exhaust block 2 used in conjunction with the exhaust block 1. The overflow groove 1 and the overflow groove 2 are both arranged on the inner side wall of the cavity space near the upper part of the piston skirt, the overflow groove 2 is directly connected to a slag collecting bag, and the other end of the slag collecting bag is connected to the exhaust block 2, and a cooling unit is provided in the inner membrane punch of the movable mold; the upper end of the movable mold is provided with a hydraulic unit for driving the inner membrane punch of the movable mold, and the lower end of the cavity space is connected to a low-pressure quantitative infusion unit.

2. The squeeze casting piston device containing ceramic fiber reinforcement according to claim 1, characterized in that: The volume ratio of the slag bag to the piston skirt is 0.8 to 1.

5.

3. The squeeze casting piston device containing ceramic fiber reinforcement according to claim 1, characterized in that: A vacuum pipeline is connected to the gate on the fixed mold.

4. The squeeze casting piston device containing ceramic fiber reinforcement according to claim 1, characterized in that: It also includes a pin seat ejector rod and a gate ejector rod, wherein the pin seat ejector rod and the gate ejector rod are located on the same side and are arranged in parallel in upper and lower parts.

5. The squeeze casting piston device containing ceramic fiber reinforcement according to claim 1, characterized in that: The exhaust block 1 and / or the exhaust block 2 is provided with a vacuum pipe opening.

6. The squeeze casting piston device containing ceramic fiber reinforcement according to any one of claims 1 to 5, characterized in that: The low-pressure quantitative infusion unit includes an infusion pipe and a riser pipe connected to a sealed machine-side insulation furnace for storing aluminum alloy solution. The machine-side insulation furnace is connected to an inert gas inlet pipe, an electromagnetic pump is provided on the infusion pipe, the upper end of the riser pipe is connected to the cavity space, an extrusion punch is provided at the lower end of the riser pipe, the extrusion punch is connected to a shot cylinder through an extrusion rod, the riser pipe is arranged in a barrel, an induction heating tube is provided on the barrel, and a liquid level sensor is provided on the upper part of the barrel.

7. A method for forming an extrusion casting piston containing a ceramic fiber reinforcement, characterized in that: The steps are as follows: S1. Preheating of ceramic fiber reinforcement: preheating and heat preservation of ceramic fiber reinforcement; S2. Preparation for modification, refining and degassing of aluminum alloy melt: melt and modify the aluminum alloy for extrusion casting according to the piston matrix ratio, and then pour it into the machine-side holding furnace for rotary degassing; S3, mold preparation, spraying, mold closing, debugging and heating: using the extrusion casting piston device containing ceramic fiber reinforcement according to any one of claims 1 to 6 as a casting mold, and then spraying a mold release agent on the corresponding positions of the fixed mold and the movable mold respectively, placing the preheated ceramic fiber reinforcement into the placement groove on the movable mold, closing the movable mold and the fixed mold to form a closed cavity, and then debugging and heating the mold after closing, so that the temperature of the mold is heated to 250-300°C; S4, aluminum alloy melt filling: the aluminum alloy melt is squeezed into the closed cavity from the lower end of the mold through a low-pressure quantitative infusion unit; S5, pressurization and pressure holding: after filling, pressurization and pressure holding are carried out, the pressurization pressure is 115~145MPa, and the pressure holding time is 18.5~23.5s; S6, pressure relief, part removal and heat treatment: the movable die is separated from the fixed die, the piston blank is taken out, and then the piston blank is heat treated.

8. The method for forming an extrusion casting piston containing ceramic fiber reinforcement according to claim 7, characterized in that: In the step S1, the preheating temperature of the ceramic fiber reinforcement is 300°C±10°C, and the heat preservation time is 1.5 to 2 hours.

9. The method for forming an extrusion casting piston containing ceramic fiber reinforcement according to claim 7, characterized in that: In the step S1, the ceramic fiber reinforcement comprises, by mass fraction, 15-35wt% of silicon carbide short fibers, 5-11wt% of boron powder, and 54-80wt% of carbon fibers as a matrix.

10. The method for forming an extrusion casting piston containing ceramic fiber reinforcement according to claim 7, characterized in that: In the step S4, the gate position is first evacuated before the aluminum alloy melt is filled, and the vacuum degree is 220-260 mbar; the aluminum alloy melt filling speed parameter adopts a two-stage control, 0.11-0.23 m / s is used for 0-0.8s, and 0.42-0.48 mm / s is used for 0.9-2s; the exhaust groove starts to be evacuated after injection filling, and the vacuum degree is 80-120 mbar.

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