Powder metallurgy piston and preparation method thereof

Abstract

The invention discloses a powder metallurgy piston and a preparation method thereof. The powder metallurgy piston comprises, by weight, 63.5%-89% of aluminum-silicon alloy powder, 1.5%-5% of electrolytic copper powder, 1.0%-3.5% of nickel powder, 0.6%-1.5% of magnesium powder, 0.05%-0.1% of zirconium powder, 0.05%-0.1% of vanadium powder, 0.1%-0.15% of titanium powder, 0.05%-0.11% of scandium powder, 0.05%-0.1% of chromium powder and the balance gas atomization aluminum powder. And the weight ratio of the aluminum-silicon alloy powder to the atomized aluminum powder is greater than or equal to 2.2. The powder metallurgy piston is made of aluminum alloy materials, has the advantages of being high in heat-resistant strength, excellent in welding performance, light in weight, good in abrasion resistance, low in thermal expansion coefficient, good in thermal conductivity and the like, and has important application prospects in the field of automobile engine piston materials.

Description

Technical Field

[0001] The present application relates to the technical field of powder metallurgy, and in particular to a powder metallurgy piston and a preparation method thereof. Background Art

[0002] The piston is one of the most important parts in a car engine and is known as the "heart" of the engine. The function of the piston is to withstand the gas pressure and transmit energy to the connecting rod through the piston pin to drive the crankshaft to move. Therefore, the piston is one of the important factors that determine the overall quality of the engine. At present, with the continuous improvement of technical indicators such as diesel engine power and explosion pressure, the working environment of the piston has become quite harsh. It is subjected to high pressure, high speed, high temperature mechanical load and thermal load at the same time. The piston in this working environment also has special requirements for its material.

[0003] At present, diesel engine pistons at home and abroad are formed by gravity casting, and most of the piston materials are eutectic Al-Si alloys. The representative Al-Si alloy piston material is ZL109. At the same time, in order to further improve the heat resistance of the material, the composition of ZL109 material is optimized, the content of strengthening elements such as Cu and Ni is increased, and the piston alloy AlSiCuMgNi material is improved. The pistons of National I to National V diesel engines are mainly made of aluminum alloy materials.

[0004] With the demand for high reliability and high reinforcement of vehicle power systems, higher requirements are placed on technologies such as high power and high explosion pressure of diesel engines. The piston will work under higher temperature and higher friction and wear conditions, and bear higher thermal and mechanical loads. Traditional piston aluminum alloy materials can no longer meet the high technical index requirements of diesel engines, so the piston materials of National VI and above diesel engines are mainly steel materials, such as 42CrMo4, 34CrNiMo6, 38MnVS6, etc.

[0005] Steel pistons can withstand explosion pressures of up to 25MPa and have a small thermal expansion coefficient, so all-steel pistons have lower fuel consumption, higher strength, longer life and less noise. However, the density of the steel piston material is high, which is three times that of aluminum alloy materials, and the thermal conductivity is low, which is 1 / 3 of that of aluminum alloy piston materials. This causes the steel piston to be heavy, have high inertia, and have poor heat dissipation capacity, resulting in high surface temperature and rust on the steel piston, which seriously affects the development of lightweight and high mobility of vehicles. Summary of the invention

[0006] The present invention provides a powder metallurgy piston and a preparation method thereof, so as to solve the technical problem in the prior art that steel material pistons have heavy weight, large inertia and poor heat dissipation capacity, which seriously affect the development of lightweight and high mobility of vehicles.

[0007] To achieve the above object, the technical solution provided by the present invention is as follows:

[0008] The first aspect of the present invention provides a powder metallurgy piston, whose raw materials include the following components in weight percentage: 63.5% to 89% aluminum silicon alloy powder, 1.5% to 5% electrolytic copper powder, 1.0% to 3.5% nickel powder, 0.6% to 1.5% magnesium powder, 0.05% to 0.1% zirconium powder, 0.05% to 0.1% vanadium powder, 0.1% to 0.15% titanium powder, 0.05% to 0.11% scandium powder, 0.05% to 0.11% chromium powder, and the rest is atomized aluminum powder; the weight ratio of the aluminum silicon alloy powder to the atomized aluminum powder is greater than or equal to 2.2.

[0009] Furthermore, the raw materials include the following components in weight percentage: 65% aluminum silicon alloy powder, 4.5% electrolytic copper powder, 3% nickel powder, 1.5% magnesium powder, 0.05% zirconium powder, 0.05% vanadium powder, 0.12% titanium powder, 0.1% scandium powder, 0.05% chromium powder, and the rest is atomized aluminum powder.

[0010] 4. Furthermore, the powder metallurgy piston comprises the following components in weight percentage: Si 12.7% to 17.8%, Cu 1.5% to 5.0%, Ni 1.0% to 3.5%, Mg 0.6% to 1.5%, Ti 0.11% to 0.15%, Sc 0.05% to 0.11%, Cr 0.05% to 0.1%, Zr 0.05% to 0.1%, V 0.05% to 0.1%, iron and oxygen are inevitable impurity elements, iron is not more than 0.7%, oxygen is not more than 0.5%, and the balance is Al.

[0011] Furthermore, the powder metallurgy piston includes the following components in weight percentage: Si 15%, Cu 1.5%, Ni 1.0%, Mg 0.6%, Ti 0.13%, Sc 0.07%, Cr 0.08%, Zr 0.08%, V 0.05%, Fe 0.68%, O 0.29%, and the balance is Al.

[0012] A second aspect of the present invention provides a method for preparing the above-mentioned powder metallurgy piston, comprising the following steps:

[0013] S1, mixing the raw materials according to the proportion, loading into a ball mill, adding additives and ball milling to obtain a mixed powder;

[0014] S2, hot pressing and sintering the mixed powder to obtain a blank, the hot pressing and sintering includes 5 stages: the first stage is to heat up to 450℃~505℃ and keep it warm for 25min~35min; the second stage is to heat up to 511℃~545℃ and keep it warm for 41min~53min, and apply a pressure of 25MPa~30MPa at the same time; the third stage is to heat up to 552℃~566℃ and keep it warm for 62min~78min; the fourth stage is to heat up to 573℃~593℃ and keep it warm for 81min~106min, and apply a pressure of 30MPa~40MPa after the end of the heat preservation; the fifth stage is to heat up to 597℃~608℃ and keep it warm for 254min~329min, and apply a pressure of 50MPa~60MPa after the end of the heat preservation;

[0015] S3, forging the blank obtained in step S2 to obtain a piston top blank and / or a piston skirt blank; welding the piston top blank and the piston skirt blank to obtain the powder metallurgy piston.

[0016] Furthermore, in step S1, the auxiliary agent is stearic acid, the weight of the stearic acid is 1.2wt% to 1.6wt% of the total weight of the raw material, the ball-to-material ratio is 5 to 6, the ball milling speed is 223rpm to 427rpm, and the ball milling time is 6h to 8h.

[0017] Furthermore, the die forging step in step S3 includes: pre-heating the blank to 501°C to 552°C and keeping it warm for 6.5h to 9.5h; fixing the die on the die forging equipment, upsetting the blank after the insulation, and then performing three forging processes to obtain the piston top blank and / or piston skirt blank.

[0018] Furthermore, the longitudinal upsetting ratio of the blank is 1.2 to 1.8, and the transverse deformation is 23% to 65%.

[0019] Furthermore, in the three forging steps, the speed of the first hammer is 821-867 m / min, the speed of the second hammer is 714-754 m / min, and the speed of the third hammer is 596-621 m / min.

[0020] Furthermore, before the welding step described in step S3, the piston top blank and / or the piston skirt blank are subjected to heat treatment, specifically including: primary solution treatment at a temperature of 475°C to 485°C and a holding time of 0.5h to 1h; secondary solution treatment at a temperature of 505°C to 525°C and a holding time of 3h to 4h; aging treatment at a temperature of 175°C to 185°C and a holding time of 7h to 8h.

[0021] The powder metallurgy piston provided by the present invention is made of aluminum alloy material, and has the advantages of high heat resistance, excellent weldability, light weight, good wear resistance, low thermal expansion coefficient, good thermal conductivity, etc., and has important application prospects in the field of automobile engine piston materials.

[0022] The powder metallurgy piston provided by the present invention is prepared by powder metallurgy, and the piston top blank and / or piston skirt blank are prepared by ball milling powder mixing, five-stage sintering and die forging process, which improves the densification degree of the alloy, effectively reduces the porosity, refines the grains, makes the material structure more uniform, and improves the strength, toughness and fatigue resistance of the piston blank, making it superior to the performance level of traditional pistons and meeting the current and future use requirements of high-performance diesel engine pistons. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 This is a schematic diagram of the piston structure in an embodiment of the present invention;

[0025] Figure 2 The XRD diffraction pattern of the mixed powder in Example 1 of the present invention;

[0026] Figure 3 This is a DSC curve of the mixed powder in Example 1 of the present invention;

[0027] Figure 4 This is the metallographic structure diagram of the sintered blank in Example 1 of the present invention;

[0028] Figure 5 This is the metallographic structure diagram of the piston blank in the forged state in Example 1 of the present invention.

[0029] Reference numerals:

[0030] 1. Piston top blank; 2. Piston skirt blank; 3. Internal cooling oil channel. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0032] It should be noted that when an element is referred to as being "fixed on" or "set on" another element, it can be directly on the other element or indirectly set on the other element; when an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0033] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0034] 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 technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, "multiple" and "several" mean two or more, unless otherwise clearly and specifically defined.

[0035] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions under which this application can be implemented. Therefore, they have no substantive technical significance. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in this application without affecting the effects and purposes that can be achieved by this application.

[0036] In a first aspect of an embodiment of the present application, a powder metallurgy piston is provided, wherein the raw materials thereof include the following components in weight percentage: 63.5% to 89% aluminum-silicon alloy powder, 1.5% to 5% electrolytic copper powder, 1.0% to 3.5% nickel powder, 0.6% to 1.5% magnesium powder, 0.05% to 0.1% zirconium powder, 0.05% to 0.1% vanadium powder, 0.1% to 0.15% titanium powder, 0.05% to 0.11% scandium powder, 0.05% to 0.11% chromium powder, and the rest is atomized aluminum powder; the weight ratio of the aluminum-silicon alloy powder to the atomized aluminum powder is greater than or equal to 2.2.

[0037] With the continuous improvement of diesel engine technical indicators, the working environment of the piston has also changed. The piston needs to have the characteristics of low density, light weight, good thermal conductivity, poor heat absorption, and small thermal expansion coefficient. It also needs to have sufficient high temperature strength, wear resistance, corrosion resistance and good dimensional stability.

[0038] Although steel pistons can withstand explosion pressures of up to 25 MPa and have a small thermal expansion coefficient, lower fuel consumption and higher strength, they have a high density (7.8 g / cm 3 ), which is 3 times the density of aluminum alloy pistons and 1 / 3 of the thermal conductivity of aluminum alloy pistons, resulting in problems such as heavy weight and high inertia of steel pistons. In addition, the increase in the weight of steel pistons directly increases the reciprocating inertia force of the engine when it is working, thereby increasing the volume and weight of the engine, which seriously hinders the development of vehicle power towards lightweight and high mobility. At the same time, the thermal conductivity of steel pistons is small (40-45W / mK), the heat dissipation capacity is poor, and there are problems such as high surface temperature and severe rust, which cause defects such as engine cylinder scuffing.

[0039] Although the traditional aluminum alloy piston is light in weight, its high temperature mechanical properties are poor and it can no longer withstand the increasingly high mechanical and thermal loads. At present, the material used for forged aluminum pistons in China is 4032 aluminum alloy, which has poor welding performance. During the welding process, welding defects such as pores and cracks are easily generated. At the same time, its forging temperature range is narrow, the deformation temperature range is small, and it is difficult to form. It requires greater impact force to form, which easily causes forgings to crack. The high temperature performance of 4032 aluminum alloy is limited. When the temperature exceeds 200C, the strength of the material will drop significantly.

[0040] The powder metallurgy piston in the embodiment of the present application is made of aluminum alloy material, and has the advantages of high heat resistance, excellent welding performance, light weight, good wear resistance, low thermal expansion coefficient, good thermal conductivity, etc., and has important application prospects in the field of automobile engine piston materials.

[0041] In the embodiment of the present application, the aluminum silicon alloy powder is spherical. Compared with silicon powder, the aluminum silicon alloy powder has a lower melting point, which makes the alloy powder more fluid during hot pressing and sintering, and can improve the filling rate. At the same time, the shrinkage rate is small during solidification, which helps to reduce the internal stress during hot pressing and sintering and improve the density. Therefore, the weight ratio of the aluminum silicon alloy powder to the atomized aluminum powder is greater than or equal to 2.2. In the embodiment of the present application, the aluminum silicon alloy powder is Al20Si.

[0042] In the embodiments of the present application, the main alloy raw materials such as aluminum silicon alloy powder, electrolytic copper powder, nickel powder, and magnesium powder can form a second phase Mg2Si (which plays a role in solid solution strengthening) and Al7Cu4Ni, Al5Cu2Mg8Si6 metal compounds (which play a role in dispersion strengthening), which can improve the high temperature performance and heat resistance strength performance of the alloy.

[0043] In the embodiments of the present application, the main functions of titanium powder, vanadium powder, zirconium powder and scandium powder are to refine the grains and improve the welding performance and toughness of the alloy. Titanium and vanadium can refine the grains of aluminum alloys. During the welding process, the fine grain structure helps to reduce the crack tendency of the heat affected zone of the weld. Because finer grains can make the material deform more evenly under thermal stress, thereby improving the crack resistance of the welding material and the toughness of the alloy. Zirconium (Zr) is also an effective grain refiner. Adding zirconium can improve the welding solidification structure of aluminum alloys, reduce the sensitivity of welding hot cracks, and make the quality of welded joints higher. Scandium (Sc) can form a highly dispersed compound Al3Sc in aluminum alloys, which has a refining and strengthening effect on the structure of aluminum alloys. During welding, these dispersed phases can inhibit grain growth, improve welding performance, and significantly improve its high temperature strength.

[0044] 5. Further, the powder metallurgy piston includes the following components in weight percentage: Si 12.7% to 17.8%, Cu 1.5% to 5.0%, Ni 1.0% to 3.5%, Mg 0.6% to 1.5%, Ti 0.11% to 0.15%, Sc 0.05% to 0.11%, Cr 0.05% to 0.1%, Zr 0.05% to 0.1%, V 0.05% to 0.1%, iron and oxygen are inevitable impurity elements, iron is not more than 0.7%, oxygen is not more than 0.5%, and the balance is Al. The powder metallurgy piston of the embodiment of the present application includes the above components after molding.

[0045] A second aspect of the embodiment of the present application provides a method for preparing the above-mentioned powder metallurgy piston, comprising the following steps:

[0046] S1, mixing the raw materials according to the proportion, loading into a ball mill, adding additives and ball milling to obtain a mixed powder;

[0047] S2. Hot pressing and sintering the mixed powder to obtain a blank. The hot pressing and sintering includes 5 stages:

[0048] The first stage is to heat up to 450℃~505℃ and keep it for 25min~35min;

[0049] The second stage is to raise the temperature to 511℃~545℃ and keep it at this temperature for 41min~53min, while applying a pressure of 25MPa~30MPa;

[0050] The third stage is to heat up to 552℃~566℃ and keep it at that temperature for 62min~78min;

[0051] The fourth stage is to heat up to 573℃~593℃ and keep it at this temperature for 81min~106min, and then apply a pressure of 30MPa~40MPa after the end of the heat preservation;

[0052] The fifth stage is to heat up to 597℃~608℃ and keep it at this temperature for 254min~329min, and then apply a pressure of 50MPa~60MPa after the end of the heat preservation;

[0053] S3, forging the blank obtained in step S2 to obtain a piston top blank 1 and / or a piston skirt blank 2; welding the piston top blank 1 and the piston skirt blank 2 to obtain the powder metallurgy piston.

[0054] In the embodiment of the present application, the first stage is to raise the temperature to 450° C. to 505° C. and keep the temperature for 25 min to 35 min to fully volatilize the additives added during the mixing ball milling process.

[0055] The second stage is to heat up to 511℃~545℃ and keep it for 41min~53min, while applying a pressure of 25MPa~30MPa. At the above temperature, the aluminum-silicon alloy powder and the atomized aluminum powder have softened. Under the pressure of 25MPa~30MPa, the aluminum-silicon alloy powder and the atomized aluminum powder are more tightly combined, which is conducive to the occurrence of the reaction and the mass transfer process, and is also conducive to increasing the density of the alloy.

[0056] The third stage is to heat up to 552℃~566℃ and keep it at this temperature for 62min~78min. This process is not pressurized to prevent the liquid phase components from being squeezed out, which will change the overall composition of the alloy and destroy the organizational structure. The squeezed liquid will also contaminate the mold.

[0057] The fourth stage is to heat up to 573℃~593℃ and keep it warm for 81min~106min, and then apply 30MPa~40MPa of pressure after the end of the heat preservation. This stage is the pressurized densification stage. The temperature is raised to 556℃~582℃ and kept warm for 81min~106min, which can make the liquid completely solidify, and then apply 30MPa~40MPa of pressure to increase the density of the alloy. Shrinkage cavities will appear during the liquid phase solidification process, making it difficult to ensure the density of the alloy, so this step is one of the keys to ensure the density of the alloy. At this stage, the density of the alloy reaches 85.2%~90.5%.

[0058] The fifth stage is the pressurized densification stage, where the temperature is raised to 597℃~608℃ and kept for 254min~329min, and then a pressure of 50MPa~60MPa is applied to give the alloy enough time and energy to fully react the various powder elements in the raw materials, ensure that the alloy liquid is completely solidified and forms the expected phase composition, and improve the density of the alloy. The purpose is the same as the fourth stage, which is to further improve the density of the alloy to 92.7%~96.2%.

[0059] In the embodiment of the present application, the metal compound and the primary silicon crystal in the blank prepared by the liquid phase multi-stage hot pressing sintering method are relatively coarse. Figure 4 As shown, they are in the form of coarse plates or overlapped with each other to form irregular shapes, and are unevenly distributed in the matrix, resulting in certain pores in the alloy, reducing the density, and having an adverse effect on the mechanical properties and thermophysical properties of the alloy.

[0060] In order to solve the above-mentioned problems, the billet is forged by forging to improve the density. At the same time, the size, shape and distribution of the metal compound and primary silicon are optimized to make the metal compound and primary silicon refined, the sharp corners blunted and the distribution more uniform.

[0061] The pistons of diesel engines of National VI and above all include 3 internal cooling oil passages. In addition, the pistons also include a top and a skirt. Figure 1 The powder metallurgy piston preparation method of the embodiment of the present application can be used to make one or both of the piston top blank 1 and the piston skirt blank 2, which can be selected according to actual conditions. The piston top blank 1 and the piston skirt blank 2 are formed by welding, such as electron beam welding, laser welding, stir friction welding, etc.

[0062] In some embodiments, the die forging step includes: pre-heating the blank to 501°C to 552°C and keeping it warm for 6.5h to 9.5h; fixing the die on the die forging equipment, upsetting the blank after the insulation, and then performing three forging processes to obtain a piston top blank 1 and / or a piston skirt blank 2.

[0063] In the embodiment of the present application, the blank is preheated in a box-type electric furnace before forging. When the blank temperature is heated to 501°C to 552°C, in order to evenly heat the inside of the material, eliminate the stress caused by the heat, and make the material structure uniform, the temperature is kept for 6.5h to 9.5h. Then the mold is fixed on the die forging equipment. After the blank is kept warm for a preset time, the blank is upset. Upsetting at a higher temperature can reduce the deformation resistance of the base material and improve its plastic deformation capacity, thereby reducing the load required for forging and reducing the possibility of cracks, so that the material can be forged into well-formed and high-density parts at a lower pressure.

[0064] In the embodiment of the present application, an electric screw press is used for three-stage forming forging. In the early stage of forging, the density of the blank is relatively low, and the forming load increases slowly as the downward pressure of the upper die increases. Towards the end of forging, the blank is constrained by the die wall and densified, resulting in increased deformation resistance and a rapid increase in the load. As the strain rate increases, the initial deformation resistance increases. Therefore, three-stage forming forging is performed, the forging speed is reduced in stages, and the density is increased to 98.1% to 99.2%.

[0065] During the forging process, after each piece is forged, another piece of blank is hooked out from the furnace. It is not allowed to hook out multiple pieces of blanks at one time. After every 20 pieces are forged, the forgings are checked and adjusted in time if abnormalities are found. After each piece is forged, the mixed lubricant of graphite and engine oil is sprayed on the die cavity. The blank after forging needs to be polished. The inner cavity and the surrounding area of ​​the blank are polished with a pneumatic grinder, and the blank is piled in the frame for cooling.

[0066] Furthermore, the longitudinal upsetting ratio of the blank is 1.2 to 1.8, and the transverse deformation is 23% to 65%. In the three forging steps, the speed of the first hammer is 821 to 867 m / min, the speed of the second hammer is 714 to 754 m / min, and the speed of the third hammer is 596 to 621 m / min.

[0067] In some embodiments, before the welding step in step S3, the piston top blank 1 and / or the piston skirt blank 2 are heat treated, specifically including: primary solution treatment at a temperature of 475°C to 485°C and a holding time of 0.5h to 1h; secondary solution treatment at a temperature of 505°C to 525°C and a holding time of 3h to 4h; aging treatment at a temperature of 175°C to 185°C and a holding time of 7h to 8h.

[0068] In the embodiment of the present application, the forged blank needs to be heat treated, namely, solid solution strengthening and aging treatment, to strengthen the blank performance. The heat treatment process parameters are shown in Table 1.

[0069] Table 1 Heat treatment process parameters

[0070]

[0071] All reagents in the following examples are commercially available.

[0072] Example 1

[0073] The raw materials of the powder metallurgy piston include the following components: 3250g of aluminum silicon alloy powder, 1281.5g of atomized aluminum powder, 225g of electrolytic copper powder, 150g of nickel powder, 75g of magnesium powder, 2.5g of zirconium powder, 2.5g of vanadium powder, 6g of titanium powder, 5g of scandium powder, and 2.5g of chromium powder. The weight ratio of aluminum silicon alloy powder to atomized aluminum powder is 2.5. The particle size range and purity of the above raw materials are shown in Table 2.

[0074] Table 2 Raw material particle size range and purity

[0075] name Particle size range (μm) and purity Aerosol Aluminum Powder 10-30, purity>99.8% Aluminum Silicon Alloy Powder (Al20Si) 50-100, purity>99.8% Electrolytic copper powder 30-60, purity>99% Nickel powder 20-50, purity>99% Magnesium powder 50-100, purity>99% Zirconium powder 15-45, purity>99% Vanadium powder 20-50, purity>99% Titanium powder 50-100, purity>99% Chrome powder 50-100, purity>99% Scandium powder 50-100, purity>99%

[0076] The method for preparing the powder metallurgy piston comprises the following steps:

[0077] Weigh the raw materials according to the above weight, put the powder into a ball mill in a vacuum glove box for ball milling. Fill the ball mill with argon, mix the raw materials on the ball mill, add 62g of stearic acid as an auxiliary agent to improve the powder yield, the ball milling time is 6.2h, the ball milling speed is 398rpm, and the ball-to-material ratio is 5.8 to obtain a mixed powder.

[0078] The mixed powder was sintered by hot pressing to obtain a green body. The mixed powder was analyzed by XRD (refer to Figure 2 ) and DSC analysis (refer to Figure 3 ). Figure 3 In the DSC curve, the endothermic peak appears at around 582°C, which indicates that the melting point of the mixed powder is 582°C. 556°C is the temperature at which eutectic silicon is formed; 539°C and 546°C are the formation temperatures of Mg2Si and Al7Cu4Ni metal compounds respectively; and 501°C is the formation temperature of Al5Cu2Mg8Si6 metal compound.

[0079] The mixed powder after ball milling is hot pressed and sintered to obtain the blank. The metallographic structure diagram of the sintered state is shown in Figure 4 , hot pressing sintering includes 5 stages:

[0080] The first stage is to heat up to 455℃ and keep it for 26min;

[0081] The second stage was to raise the temperature to 501°C and keep it at that temperature for 42 min, while applying a pressure of 26 MPa;

[0082] The third stage is to increase the temperature to 546°C and keep it at that temperature for 65 minutes;

[0083] The fourth stage is to heat up to 556℃ and keep it for 87min, and then apply a pressure of 32MPa after the end of the heat preservation;

[0084] The fifth stage is to raise the temperature to 582°C and keep it at this temperature for 267 minutes, and then apply a pressure of 53 MPa.

[0085] The sintered billet is heated for pretreatment, heated to 507°C and kept warm for 7.5 hours; the die is fixed on the die forging equipment, and the billet after the insulation is upset, the longitudinal upsetting ratio of the billet is 1.3, and the transverse deformation is 31%, and the temperature after upsetting is 507°C. The billet is forged three times using an electric screw press. In the three forging steps, the speed of the first hammer is 863m / min, the speed of the second hammer is 752m / min, and the speed of the third hammer is 618m / min. Different dies are used to obtain the piston top blank and the piston skirt blank. For the metallographic structure diagram of the forged state, see Figure 5 .

[0086] From the comparison diagram of the metallographic structures of the sintered and forged states, it can be seen that the forging process has a significant improvement on the reduction of porosity and the increase of density. The pores of the powder forging alloy are uniform and small, and most areas are completely dense. At the same time, the coarse metal compounds and silicon phases are significantly reduced, and the average size of the silicon phase is reduced from 15μm to below 3μm. The density of the blank is increased from 93.4% in the sintered state to 98.9% in the forged state.

[0087] The piston top blank and the piston skirt blank are heat treated, specifically including: primary solution treatment at a temperature of 475°C and a holding time of 0.5h; secondary solution treatment at a temperature of 505°C and a holding time of 3h; water cooling to 52°C; aging treatment at a temperature of 175°C and a holding time of 7h, and air cooling.

[0088] After heat treatment, the piston top blank and the piston skirt blank are welded to obtain a powder metallurgy piston.

[0089] Example 2

[0090] The raw materials of the powder metallurgy piston include the following components: 4250g of aluminum silicon alloy powder, 388g of atomized aluminum powder, 125g of electrolytic copper powder, 150g of nickel powder, 65g of magnesium powder, 4.5g of zirconium powder, 4.5g of vanadium powder, 3.5g of titanium powder, 3g of scandium powder, and 4.5g of chromium powder. The weight ratio of aluminum silicon alloy powder to atomized aluminum powder is 1:1.

[0091] The method for preparing the powder metallurgy piston comprises the following steps:

[0092] Weigh the raw materials according to the above weight, put the powder into a ball mill in a vacuum glove box for ball milling. Fill the ball mill with argon gas, mix the raw materials on the ball mill, and add 68g of stearic acid as an auxiliary agent to improve the powder yield. The ball milling time is 6.8h, the ball milling speed is 421rpm, and the ball-to-material ratio is 6 to obtain a mixed powder.

[0093] The mixed powder after ball milling is hot pressed and sintered to obtain a blank. The hot pressing and sintering includes 5 stages:

[0094] The first stage is to heat up to 475℃ and keep it for 28min;

[0095] The second stage was to raise the temperature to 515°C and keep it at that temperature for 42 min, while applying a pressure of 26 MPa;

[0096] The third stage is to increase the temperature to 559°C and keep it for 65 minutes;

[0097] The fourth stage is to heat up to 583℃ and keep it for 86min, and then apply a pressure of 34MPa after the end of the heat preservation;

[0098] The fifth stage is to raise the temperature to 601°C and keep it at this temperature for 275 minutes, and then apply a pressure of 53 MPa.

[0099] The sintered blank was heated and pre-treated to 515°C and kept warm for 8.1h. The die was fixed on the die forging equipment, and the blank was upset after the insulation. The longitudinal upsetting ratio of the blank was 1.5, and the transverse deformation was 45%. The temperature after upsetting was 515°C. The blank was forged three times using an electric screw press. In the three forging steps, the speed of the first hammer was 851m / min, the speed of the second hammer was 741m / min, and the speed of the third hammer was 601m / min. Different dies were used to obtain the piston top blank and the piston skirt blank. The blank density increased from 94.2% in the sintered state to 99.1% in the forged state.

[0100] The piston top blank and the piston skirt blank are heat treated, specifically including: primary solution treatment at a temperature of 478°C and a holding time of 0.7h; secondary solution treatment at a temperature of 510°C and a holding time of 3.2h; water cooling to 58°C; aging treatment at a temperature of 177°C and a holding time of 7.2h, and air cooling.

[0101] After heat treatment, the piston top blank and the piston skirt blank are welded to obtain a powder metallurgy piston.

[0102] Example 3

[0103] The raw materials of the powder metallurgy piston include the following components: 3750g of aluminum silicon alloy, 1074g of atomized aluminum powder, 75g of electrolytic copper powder, 50g of nickel powder, 30g of magnesium powder, 4g of zirconium powder, 2.5g of vanadium powder, 6.5g of titanium powder, 3.5g of scandium powder, and 4g of chromium powder. The weight ratio of aluminum silicon alloy powder to atomized aluminum powder is 3.5.

[0104] The method for preparing the powder metallurgy piston comprises the following steps:

[0105] Weigh the raw materials according to the above weight, put the powder into a ball mill in a vacuum glove box for ball milling. Fill the ball mill with argon, mix the raw materials on the ball mill, add 70g of stearic acid as an auxiliary agent to improve the powder yield, the ball milling time is 7h, the ball milling speed is 325rpm, and the ball-to-material ratio is 5.5 to obtain a mixed powder.

[0106] The mixed powder after ball milling is hot pressed and sintered to obtain a blank. The hot pressing and sintering includes 5 stages:

[0107] The first stage is to heat up to 485℃ and keep it for 30min;

[0108] The second stage was to raise the temperature to 523°C and keep it at that temperature for 45 min, while applying a pressure of 27 MPa;

[0109] The third stage is to increase the temperature to 557°C and keep it at that temperature for 68 minutes;

[0110] The fourth stage is to heat up to 589℃ and keep it for 94min, and then apply a pressure of 35MPa after the end of the heat preservation;

[0111] The fifth stage is to raise the temperature to 604°C and keep it at this temperature for 291 minutes, and then apply a pressure of 55 MPa.

[0112] The sintered blank was heated and pre-treated to 521°C and kept warm for 8.5 hours. The die was fixed on the die forging equipment, and the blank was upset after the insulation. The longitudinal upsetting ratio of the blank was 1.6, and the transverse deformation was 51%. The temperature after upsetting was 521°C. The blank was forged three times using an electric screw press. In the three forging steps, the speed of the first hammer was 846m / min, the speed of the second hammer was 734m / min, and the speed of the third hammer was 615m / min. Different dies were used to obtain the piston top blank and the piston skirt blank. The blank density increased from 92.9% in the sintered state to 98.3% in the forged state.

[0113] The piston top blank and the piston skirt blank are heat treated, specifically including: primary solution treatment at a temperature of 480°C and a holding time of 0.8h; secondary solution treatment at a temperature of 515°C and a holding time of 3.5h; water cooling to 65°C; aging treatment at a temperature of 180°C and a holding time of 7.5h, and air cooling.

[0114] After heat treatment, the piston top blank and the piston skirt blank are welded to obtain a powder metallurgy piston.

[0115] Example 4

[0116] The raw materials of the powder metallurgy piston include the following components: 3500g of aluminum silicon alloy powder, 1089g of atomized aluminum powder, 175g of electrolytic copper powder, 175g of nickel powder, 40g of magnesium powder, 3g of zirconium powder, 3g of vanadium powder, 7g of titanium powder, 4.5g of scandium powder, and 3.5g of chromium powder. The weight ratio of aluminum silicon alloy powder to atomized aluminum powder is 3.2.

[0117] The method for preparing the powder metallurgy piston comprises the following steps:

[0118] Weigh the raw materials according to the above weight, put the powder into a ball mill in a vacuum glove box for ball milling. Fill the ball mill with argon, mix the raw materials on the ball mill, add 75g of stearic acid as an auxiliary agent to improve the powder yield, the ball milling time is 7.5h, the ball milling speed is 298rpm, and the ball-to-material ratio is 5.7 to obtain a mixed powder.

[0119] The mixed powder after ball milling is hot pressed and sintered to obtain a blank. The hot pressing and sintering includes 5 stages:

[0120] The first stage is to heat to 491°C and keep it for 32 minutes;

[0121] The second stage was to raise the temperature to 531°C and keep it at that temperature for 47 min, while applying a pressure of 28 MPa;

[0122] The third stage is to increase the temperature to 562°C and keep it at that temperature for 73 minutes;

[0123] The fourth stage is to heat up to 576℃ and keep it for 101min, and then apply a pressure of 37MPa after the end of the heat preservation;

[0124] The fifth stage is to raise the temperature to 599°C and keep it at this temperature for 278 minutes, and then apply a pressure of 53 MPa.

[0125] The sintered blank was heated and pre-treated to 533°C and kept warm for 9 hours; the die was fixed on the die forging equipment, and the blank was upset after the insulation, with the longitudinal upset ratio of the blank being 1.7, and the transverse deformation being 55%, and the temperature after upsetting being 533°C. The blank was forged three times using an electric screw press, and in the three forging steps, the speed of the first hammer was 831m / min, the speed of the second hammer was 725m / min, and the speed of the third hammer was 607m / min. Different dies were used to obtain the piston top blank and the piston skirt blank, respectively. The blank density was increased from 94.5% in the sintered state to 99.2% in the forged state.

[0126] The piston top blank and the piston skirt blank are heat treated, specifically including: primary solution treatment at a temperature of 482°C and a holding time of 0.8h; secondary solution treatment at a temperature of 520°C and a holding time of 3.7h; water cooling to 75°C; aging treatment at a temperature of 182°C and a holding time of 7.8h, and air cooling.

[0127] After heat treatment, the piston top blank and the piston skirt blank are welded to obtain a powder metallurgy piston.

[0128] Example 5

[0129] The raw materials of the powder metallurgy piston include the following components: 4000g of aluminum silicon alloy powder, 703g of atomized aluminum powder, 100g of electrolytic copper powder, 125g of nickel powder, 50g of magnesium powder, 3.5g of zirconium powder, 3.5g of vanadium powder, 7.5g of titanium powder, 4g of scandium powder, and 3g of chromium powder. The weight ratio of aluminum silicon alloy powder to atomized aluminum powder is 5.7.

[0130] The method for preparing the powder metallurgy piston comprises the following steps:

[0131] Weigh the raw materials according to the above weight, put the powder into a ball mill in a vacuum glove box for ball milling. Fill the ball mill with argon, mix the raw materials on the ball mill, add 79g of stearic acid as an auxiliary agent to improve the powder yield, the ball milling time is 7.8h, the ball milling speed is 257rpm, and the ball-to-material ratio is 5.8 to obtain a mixed powder.

[0132] The mixed powder after ball milling is hot pressed and sintered to obtain a blank. The hot pressing and sintering includes 5 stages:

[0133] The first stage is to heat up to 500°C and keep it for 35 minutes;

[0134] The second stage was to raise the temperature to 538°C and keep it at that temperature for 49 min, while applying a pressure of 29 MPa;

[0135] The third stage is to heat up to 555°C and keep it at that temperature for 78 minutes;

[0136] The fourth stage is to heat up to 581℃ and keep it for 105min, and then apply a pressure of 40MPa after the end of the heat preservation;

[0137] The fifth stage is to raise the temperature to 602°C and keep it at this temperature for 322 minutes, and then apply a pressure of 60 MPa.

[0138] The sintered blank was heated and pre-treated to 550°C and kept warm for 9.5 hours. The die was fixed on the die forging equipment, and the blank was upset after the insulation. The longitudinal upsetting ratio of the blank was 1.8, and the transverse deformation was 63%. The temperature after upsetting was 550°C. The blank was forged three times using an electric screw press. In the three forging steps, the speed of the first hammer was 822m / min, the speed of the second hammer was 715m / min, and the speed of the third hammer was 597m / min. Different dies were used to obtain the piston top blank and the piston skirt blank. The blank density increased from 95.8% in the sintered state to 98.9% in the forged state.

[0139] The piston top blank and the piston skirt blank are heat treated, specifically including: primary solution treatment at a temperature of 485°C and a holding time of 1 hour; secondary solution treatment at a temperature of 525°C and a holding time of 4 hours; water cooling to 80°C; aging treatment at a temperature of 185°C and a holding time of 8 hours, and air cooling.

[0140] After heat treatment, the piston top blank and the piston skirt blank are welded to obtain a powder metallurgy piston.

[0141] Comparative Example 1

[0142] The raw materials of the powder metallurgy piston include the following components: 3250g of aluminum silicon alloy powder, 1281.5g of atomized aluminum powder, 225g of electrolytic copper powder, 150g of nickel powder, 75g of magnesium powder, and 2.5g of chromium powder. The weight ratio of aluminum silicon alloy powder to atomized aluminum powder is 2.5.

[0143] The method for preparing the powder metallurgy piston comprises the following steps:

[0144] Weigh the raw materials according to the above weight, put the powder into a ball mill in a vacuum glove box for ball milling. Fill the ball mill with argon, mix the raw materials on the ball mill, add 62g of stearic acid as an auxiliary agent to improve the powder yield, the ball milling time is 6.2h, the ball milling speed is 398rpm, and the ball-to-material ratio is 5.8 to obtain a mixed powder.

[0145] The mixed powder after ball milling is hot pressed and sintered to obtain a blank. The hot pressing and sintering includes 5 stages:

[0146] The first stage is to heat up to 455℃ and keep it for 26min;

[0147] The second stage was to raise the temperature to 501°C and keep it at that temperature for 42 min, while applying a pressure of 26 MPa;

[0148] The third stage is to increase the temperature to 546°C and keep it at that temperature for 65 minutes;

[0149] The fourth stage is to heat up to 556℃ and keep it for 87min, and then apply a pressure of 32MPa after the end of the heat preservation;

[0150] The fifth stage is to raise the temperature to 582°C and keep it at this temperature for 267 minutes, and then apply a pressure of 53 MPa.

[0151] The sintered blank was heated for pretreatment, heated to 507°C and kept warm for 7.5 hours; the die was fixed on the die forging equipment, and the blank after the insulation was upset, the longitudinal upset ratio of the blank was 1.3, and the transverse deformation was 31%, and the temperature after upsetting was 507°C. The blank was forged three times using an electric screw press. In the three forging steps, the speed of the first hammer was 863m / min, the speed of the second hammer was 752m / min, and the speed of the third hammer was 618m / min. Different dies were used to obtain the piston top blank and the piston skirt blank.

[0152] The forging process has a significant improvement effect on reducing porosity and increasing density. The pores of the powder forging alloy are uniform and small, and most areas are completely dense. At the same time, the coarse metal compounds and silicon phases are significantly reduced, and the density is increased from 92.7% to 98.8%.

[0153] The piston top blank and the piston skirt blank are heat treated, specifically including: primary solution treatment at a temperature of 475°C and a holding time of 0.5h; secondary solution treatment at a temperature of 505°C and a holding time of 3h; water cooling to 52°C; aging treatment at a temperature of 175°C and a holding time of 7h, and air cooling.

[0154] After heat treatment, the piston top blank and the piston skirt blank are welded to obtain a powder metallurgy piston.

[0155] Comparative Example 2

[0156] The piston in this comparative example is made of AlSiCuMgNi material and is made by gravity casting. The weight percentage of each component in the piston is shown in Table 3. The specific production method is as follows:

[0157] (1) Melting of charge.

[0158] After loading according to the ingredient list, the temperature should be raised slowly. After keeping at 500℃ for 55 minutes, the temperature should be raised to 795℃ and kept at this temperature for 2.5 hours.

[0159] (2) Rotary refining and degassing

[0160] After the alloy is taken out of the furnace, the temperature is lowered to 770℃ and the degasser is turned on for 15 minutes. At the same time, the alloy melt is stirred; the rotor and baffle sink automatically and enter the refining stage automatically; after degassing, the rotor rises, and the air holes of the rotor are immediately unblocked with a tool, and the slag on the liquid surface is turned over with a slag spoon, and then the slag on the surface of the aluminum liquid is cleaned.

[0161] (3) Slag removal

[0162] According to the separation of aluminum slag after refining, 0.55wt% slag remover of the total weight of raw materials can be added to the surface of each furnace of aluminum liquid, and the slag on the liquid surface can be turned over with a slag spoon for 4 minutes, and then the floating slag on the surface of the aluminum liquid is cleaned up, and the removed slag is poured into the slag frying platform or slag frying bucket, and the slag is scraped as much as possible.

[0163] (4) Add magnesium blocks and phosphorus to modify the alloy

[0164] For the molten alloy, when the temperature drops to 750℃, use a preheated sample mold to scrape off the oxide film on the surface of the aluminum liquid, take a composition sample for spectral analysis, and add an appropriate amount of phosphorus alloy modifier and magnesium block after calculation and weighing. If necessary, other components can be adjusted by adding corresponding alloys.

[0165] (5) Composition inspection and blank (piston) casting

[0166] Use the preheated sample mold to remove the oxide film on the surface of the aluminum liquid, take the sample for pre-furnace spectral analysis, and compare the result with the corresponding material composition requirements. If the composition is unqualified, it needs to be adjusted, and then sampled for spectral analysis. After the composition is qualified, adjust the power of the medium frequency furnace so that the alloy liquid temperature reaches 772℃, and then it can be used for casting.

[0167] (6) Blank heat treatment process

[0168] The piston blank is heat treated, specifically including: solution treatment at a temperature of 520°C and a holding time of 6 hours; water cooling to 60°C; aging treatment at a temperature of 220°C and a holding time of 8 hours, and air cooling.

[0169] Comparative Example 3

[0170] The piston raw material in this comparative example is 4032 forging material, which is made by forging method. The weight percentage of each component in the piston is shown in Table 3. The specific production method is as follows:

[0171] The 4032 bar stock is cut into a certain proportion to obtain a bar blank, and the blank is pre-heated to 507°C and kept warm for 7.5 hours; the die is fixed on the die forging equipment, and the blank after the insulation is upset, the longitudinal upsetting ratio of the blank is 1.3, and the transverse deformation is 31%, and the temperature after upsetting is 507°C. The blank is forged three times by an electric screw press. In the three forging steps, the speed of the first hammer is 863m / min, the speed of the second hammer is 752m / min, and the speed of the third hammer is 618m / min. The piston blank is obtained by using the die.

[0172] The piston blank is heat treated, specifically including: primary solution treatment at a temperature of 475°C and a holding time of 0.5h; secondary solution treatment at a temperature of 505°C and a holding time of 3h; water cooling to 52°C; aging treatment at a temperature of 175°C and a holding time of 7h, and air cooling.

[0173] The weight percentage of each component in the powder metallurgy pistons of Examples 1 to 5 and the pistons of Comparative Examples 1 to 3 is shown in Table 3 (unit: %).

[0174] Table 3 Comparison of ingredients in Examples 1 to 5 and Comparative Examples 1 to 3

[0175]

[0176] The powder metallurgy pistons of Examples 1 to 5 and the pistons of Comparative Examples 1 to 3 were respectively subjected to performance tests, including hardness, tensile strength, yield strength, elongation at break, tensile strength of welded joints, fatigue strength, Young's modulus, thermal conductivity, thermal expansion coefficient, density and relative wear rate. The test results are shown in Table 4. Brinell hardness at room temperature shall be tested in accordance with GB / T231-2012 "Brinell hardness test method for metallic materials"; tensile strength, yield strength and elongation at break at room temperature shall be tested in accordance with GB / T228.1-2010 "Metal tensile test method"; high temperature tensile strength, yield strength and elongation at break shall be tested in accordance with GB / T228.2-2015 "High temperature tensile test method for metallic materials"; bending fatigue strength shall be tested in accordance with GB / T4337-2015 "Rotary bending method for fatigue test of metallic materials"; Young's modulus shall be tested in accordance with GB / T 22315-2008 "Test method for elastic modulus and Poisson's ratio of metallic materials"; thermal conductivity shall be tested in accordance with GB / T 22588-2008 "Flash method for measuring thermal diffusion coefficient or thermal conductivity"; thermal expansion coefficient shall be tested in accordance with GB / T 4339-2008 "Determination of characteristic parameters of thermal expansion of metallic materials"; density shall be tested in accordance with GB / T The relative wear rate is tested in accordance with GB / T 12444-2006 “Test methods for wear of metallic materials”.

[0177] Table 4 Comparison of piston performance of Examples 1 to 5 and Comparative Examples 1 to 3

[0178]

[0179]

[0180] The powder metallurgy piston of the embodiment of the present application includes aluminum silicon alloy powder material, which has the advantages of high heat resistance, excellent welding performance, light weight, good wear resistance, low thermal expansion coefficient, good thermal conductivity, etc. At 300°C, the tensile strength is 110-145MPa, the yield strength is 71-85MPa, the elongation at break is 13-25%, the fatigue strength is 45-62MPa, the Young's modulus is 69000-72000MPa, and the thermal conductivity is 166-178W / mK; the relative wear rate is 0.7-1; at 300°C, the tensile strength of the welded joint is 88-116MPa, and the linear expansion coefficient of the aluminum alloy at 20-100°C is 19.2×10 -6 ~19.7×10 -6 m / m·K; the linear expansion coefficient of aluminum alloy at 20-200°C is 20.4×10 -6 ~20.6×10 -6 m / m K; the linear expansion coefficient of aluminum alloy at 20-300°C is 21×10 -6 ~21.5×10 -6 m / m·K.

[0181] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may 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 the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A powder metallurgy piston, characterized in that: The raw materials include the following components in weight percentage: 63.5% to 89% aluminum-silicon alloy powder, 1.5% to 5% electrolytic copper powder, 1.0% to 3.5% nickel powder, 0.6% to 1.5% magnesium powder, 0.05% to 0.1% zirconium powder, 0.05% to 0.1% vanadium powder, 0.1% to 0.15% titanium powder, 0.05% to 0.11% scandium powder, 0.05% to 0.11% chromium powder, and the rest is atomized aluminum powder; the weight ratio of the aluminum-silicon alloy powder to the atomized aluminum powder is greater than or equal to 2.

2.

2. The powder metallurgy piston according to claim 1, characterized in that: The raw materials include the following components in weight percentage: 65% aluminum silicon alloy powder, 4.5% electrolytic copper powder, 3% nickel powder, 1.5% magnesium powder, 0.05% zirconium powder, 0.05% vanadium powder, 0.12% titanium powder, 0.1% scandium powder, 0.05% chromium powder, and the rest is atomized aluminum powder.

3. The powder metallurgy piston according to claim 1 or 2, characterized in that: The powder metallurgy piston comprises the following components in percentage by weight: Si 12.7% to 17.8%, Cu 1.5% to 5.0%, Ni 1.0% to 3.5%, Mg 0.6% to 1.5%, Ti 0.11% to 0.15%, Sc 0.05% to 0.11%, Cr 0.05% to 0.1%, Zr 0.05% to 0.1%, V 0.05% to 0.1%, iron and oxygen are inevitable impurity elements, iron is not more than 0.7%, oxygen is not more than 0.5%, and the balance is Al.

4. The powder metallurgy piston according to claim 3, characterized in that: The powder metallurgy piston includes the following components in weight percentage: Si 15%, Cu 1.5%, Ni 1.0%, Mg 0.6%, Ti 0.13%, Sc 0.07%, Cr 0.08%, Zr 0.08%, V 0.05%, Fe 0.68%, O 0.29%, and the balance is Al.

5. The method for preparing a powder metallurgy piston according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, mixing the raw materials according to the proportion, loading into a ball mill, adding additives and ball milling to obtain a mixed powder; S2, hot pressing and sintering the mixed powder to obtain a blank, wherein the hot pressing and sintering includes 5 stages: The first stage is to heat up to 450℃~505℃ and keep it for 25min~35min; The second stage is to raise the temperature to 511℃~545℃ and keep it at this temperature for 41min~53min, while applying a pressure of 25MPa~30MPa; The third stage is to heat up to 552℃~566℃ and keep it at that temperature for 62min~78min; The fourth stage is to heat up to 573℃~593℃ and keep it at this temperature for 81min~106min, and then apply a pressure of 30MPa~40MPa after the end of the heat preservation; The fifth stage is to heat up to 597℃~608℃ and keep it at this temperature for 254min~329min, and then apply a pressure of 50MPa~60MPa after the end of the heat preservation; S3, forging the blank obtained in step S2 to obtain a piston top blank and / or a piston skirt blank; welding the piston top blank and the piston skirt blank to obtain the powder metallurgy piston.

6. The method for preparing a powder metallurgy piston according to claim 5, characterized in that: In step S1, the auxiliary agent is stearic acid, the weight of the stearic acid is 1.2wt% to 1.6wt% of the total weight of the raw materials, the ball-to-material ratio is 5 to 6, the ball milling speed is 223rpm to 427rpm, and the ball milling time is 6h to 8h.

7. The method for preparing a powder metallurgy piston according to claim 5, characterized in that: The step of die forging in step S3 includes: The blank is subjected to a heating pretreatment, the temperature is raised to 501° C. to 552° C. and kept at this temperature for 6.5 h to 9.5 h; The die is fixed on the die forging equipment, the blank after the heat preservation is upset, and then forged three times to obtain the piston top blank and / or piston skirt blank.

8. The method for preparing a powder metallurgy piston according to claim 7, characterized in that: The longitudinal upsetting ratio of the blank is 1.2 to 1.8, and the transverse deformation is 23% to 65%.

9. The method for preparing a powder metallurgy piston according to claim 7, characterized in that: In the three forging steps, the speed of the first hammer is 821-867 m / min, the speed of the second hammer is 714-754 m / min, and the speed of the third hammer is 596-621 m / min.

10. The method for preparing a powder metallurgy piston according to any one of claims 5 to 9, characterized in that: Before the welding step described in step S3, the piston top blank and / or the piston skirt blank are subjected to heat treatment, specifically including: primary solution treatment at a temperature of 475°C to 485°C and a holding time of 0.5h to 1h; secondary solution treatment at a temperature of 505°C to 525°C and a holding time of 3h to 4h; aging treatment at a temperature of 175°C to 185°C and a holding time of 7h to 8h.

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