A die-casting anti-thermal cracking and heat-treatment-free aluminum alloy and its preparation method

Abstract

The present invention provides a die-casting anti-thermal cracking heat-treatment-free aluminum alloy and a preparation method thereof. The preparation method of the present invention controls a certain alloy composition. Among them, a specific amount of Ti and V elements play a role in grain refinement on the one hand. After the alloy material is refined, higher strength and elongation can be obtained; on the other hand, AlTiV intermetallic compounds are formed by Ti and V in the alloy (energy spectrum shows that the atomic percentage is about Al 90 Ti4V4Ce2), which plays a role in second-phase strengthening, improves the heat resistance of the alloy, and maintains the high strength and toughness of the alloy; at the same time, AlMoFe intermetallic compounds are formed by Mo and Fe in the alloy (energy spectrum shows that the atomic percentage is about Al 74 Si 12 Mo 12 Fe2), which has a small thermal expansion coefficient and excellent volume stability, effectively preventing tiny dimensional deformation of parts; the present invention also controls certain process steps and parameters to improve the tissue uniformity, reduce the internal stress of the casting, and improve the casting performance of the alloy, etc.

Description

Technical Field

[0001] The present invention relates to the field of metal materials, and particularly to a die-casting formed heat crack-resistant and heat-treatment-free aluminum alloy and a preparation method thereof. Background Art

[0002] As is well known, when solution treating die-cast structural parts, the castings need to be heated to a temperature close to the solidus temperature. At this time, the strength of the castings drops sharply. During the subsequent cooling process, due to the large difference in the cooling rates of different parts, large thermal stresses are easily formed, inducing thermal deformation and reducing the dimensional and positional accuracy of the castings. To overcome this problem, multiple shaping processes need to be introduced into the production system, resulting in high manufacturing costs, low efficiency, and uncontrolled effects in the entire process. To meet the needs of the new energy vehicle large integrated die-casting parts market, domestic and foreign enterprises have successively developed various types of heat-treatment-free alloy materials.

[0003] Currently, the relatively mature heat-treatment-free alloys are mainly Al-Si series. The most representative ones are the high-strength and tough die-casting aluminum alloys Silafont-36, Magsimal-59, and Castasil-37 successively developed by Rheinmetall Aluminium of Germany, which mainly add alloying elements such as Cu, Mg, and Mn. In recent years, domestic automotive enterprises, die-casting enterprises, and aluminum alloy R & D enterprises have successively developed many Al-Si-Cu and Al-Si-Mg series heat-treatment-free alloys, including FAW-ZTHJ01 jointly developed by Tsinghua University and China FAW, TechCAST (JDA1b) jointly developed by Shanghai Jiao Tong University and Human Horizons, and LDHM-02 developed by Zhongwang Group, etc. These alloys have good strength and toughness without heat treatment and are widely used in new energy vehicle integrated parts, such as the front cabin and rear floor, etc.

[0004] One of the main challenges faced by the currently used heat-treatment-free material integrated die-casting parts products is to ensure the stable deformation and dimensional chain of the products. Even a deformation of only one-thousandth of the size of the integrated die-casting parts products directly affects the dimensional accuracy of the castings and subsequent processes such as assembly. How to make the castings deform stably and the deformation amount is within a predictable range. However, the currently mainstream heat-treatment-free alloy die-casting parts cannot completely eliminate the product deformation problem.

[0005] Currently, the mainstream heat-treatment-free die-casting aluminum alloy materials generally add main alloying elements such as Cu, Mg, and Mn. Although they have many performance advantages such as improving fluidity, increasing the tensile strength and hardness of the alloy, and improving machining performance. As is well known, according to relevant research: for hypoeutectic alloys, as the Cu content increases, the solubility of Cu in aluminum-silicon alloys at room temperature is very low, and the hot cracking tendency increases. When the Cu content reaches 4wt%, the hot cracking tendency is the largest; the Mg element causes large cooling shrinkage of the alloy, so it is easy to produce hot cracks and form porosity; the Mn element can effectively reduce the harmful effects of the Fe element, reduce sticking to the mold, and form Al74 Si 12 Mn 12 Fe2 compounds, but it is prone to composition segregation and form precipitates, affecting the shrinkage of the alloy wire.

[0006] On the one hand, during the air cooling process of the current integrated die-cast parts out of the mold, shrinkage deformation problems caused by uneven casting temperature will occur; on the other hand, the contour size of the integrated die-cast parts is more than 1m and it has a complex thin-wall structure. Even a very small thermal strain will cause a large warpage, and it cannot be corrected by subsequent straightening or machining, directly affecting the dimensional accuracy of the casting and subsequent assembly processes, reducing the qualified rate of the casting products.

[0007] How to ensure that the integrated die-cast part products have good strength and toughness and elongation, while ensuring stable deformation and dimensional chain of the products and improving the hot crack resistance of the alloy is also an urgent problem to be solved in the industry. Summary of the Invention

[0008] In view of this, the present invention provides a die-casting anti-hot-crack and heat-treatment-free aluminum alloy and its preparation method. The aluminum alloy prepared by the present invention has excellent hot crack resistance, and at the same time has high strength and toughness and good casting performance.

[0009] The present invention provides a preparation method of a die-casting anti-hot-crack and heat-treatment-free aluminum alloy, including the following steps:

[0010] A) Preheating:

[0011] Preheat the melting tools.

[0012] B) Batching:

[0013] Batch the raw materials according to the target alloy composition.

[0014] In terms of mass percentage, the composition of the target alloy is as follows:

[0015] Si: 6% - 11%;

[0016] V: 0.3% - 1.2%;

[0017] Ti: 0.4% - 1.2%;

[0018] Mo: 0.2% - 0.8%;

[0019] Ce: 0.2% - 0.6%;

[0020] Sr: 0.01% - 0.07%;

[0021] Fe: ≤0.2%;

[0022] Al: the balance;

[0023] The raw materials include: aluminum ingots, crystalline silicon, aluminum-molybdenum master alloy, aluminum-titanium master alloy, aluminum-vanadium master alloy, aluminum-strontium master alloy, and aluminum-cerium master alloy;

[0024] C) Melting:

[0025] Add aluminum ingots, crystalline silicon, and aluminum-molybdenum master alloy into the melting furnace, heat up to 800 - 820 °C and hold the temperature, then cool down to 760 - 780 °C, and add aluminum-titanium master alloy, aluminum-vanadium master alloy, and aluminum-cerium master alloy into the melting furnace, and hold the temperature for melting;

[0026] D) Refining and degassing:

[0027] When the temperature of the aluminum liquid in the melting furnace drops to 720 - 740 °C, add aluminum-strontium master alloy and an environmentally friendly refining agent into the melting furnace for on-line degassing and refining;

[0028] E) Die casting:

[0029] Pour the aluminum liquid into the shot chamber of the die-casting machine, the punch advances at the set injection speed, the aluminum liquid passes through the gating system until the cavity is filled, start vacuum pumping, after filling is completed, perform pressure casting to obtain an aluminum alloy die-casting;

[0030] The process conditions for the above die casting are as follows:

[0031] Die-casting mold temperature: 180 - 220 °C;

[0032] Aluminum liquid pouring temperature: 680 - 710 °C;

[0033] Injection: low speed 0.10 - 0.18 m / s, high speed 3.5 - 6.5 m / s, punch high-speed switching point 420 - 500 mm, total injection stroke 750 - 800 mm;

[0034] Filling time: 110 - 162 s;

[0035] Vacuum degree: ≤150 mbar;

[0036] Casting pressure: 800 - 1200 bar.

[0037] Preferably, in step A), the preheating temperature is 150 - 200 °C and the time is ≥2 h.

[0038] Preferably, in step B), the aluminum-molybdenum master alloy is AlMo5;

[0039] The aluminum-titanium master alloy is AlTi10;

[0040] The aluminum-vanadium master alloy is AlV4;

[0041] The aluminum-strontium master alloy is AlSr10;

[0042] The aluminum-cerium master alloy is AlCe10.

[0043] Preferably, in step C):

[0044] The time for holding the temperature at 800 - 820 °C is 0.5 - 1 h;

[0045] The time for holding the temperature after adding the aluminum-titanium master alloy, aluminum-vanadium master alloy and aluminum-cerium master alloy is 1.5 - 2.5 h.

[0046] Preferably, in step D), the refining time is 8 - 12 min, the gas injection flow rate is 0.8 - 1.2 m 3 / h, and the rotor speed is 850 - 950 r / min.

[0047] Preferably, in step D), the main components of the environmentally friendly refining agent are 35 wt% - 45 wt% of NaCl and 35 wt% - 45 wt% of KCl.

[0048] Preferably, in step D), the dosage of the environmentally friendly refining agent is 0.5% - 1% of the total mass of the raw materials.

[0049] Preferably, in step E), the die-casting forming process specifically includes:

[0050] E1) Cleaning the installed die-casting mold;

[0051] E2) Debugging the installed die-casting mold;

[0052] E3) Preheating the die-casting mold;

[0053] E4) Spraying and brushing die-casting release agent on the die-casting mold, and setting the condition parameters during die-casting through the control cabinet;

[0054] E5) Taking molten aluminum and pouring it into the shot sleeve, and starting vacuum pumping;

[0055] E6) The punch advances at the set injection speed until the pouring gate is completely closed;

[0056] E7) The molten aluminum passes through the gating system until the cavity is filled;

[0057] E8) After filling is completed, perform pressure boosting and solidification;

[0058] E9) Separating the moving die from the fixed die, taking out the die-casting part, and obtaining the alloy die-casting part.

[0059] Preferably, in step E3), the preheating temperature is 180 - 220 °C.

[0060] The present invention also provides a die-casting anti-thermal-cracking heat-treatment-free aluminum alloy prepared by the preparation method described in the above technical solution.

[0061] At present, most of the heat-treatment-free materials used in integrated die-casting adopt the addition of Cu or Mg or Mn elements, which increases the thermal cracking tendency of alloy parts, and the castings are prone to bending deformation, reducing the qualified rate of castings. The preparation method of the present invention controls a certain alloy composition. Among them, a specific amount of Ti and V elements play a role in grain refinement on the one hand. After the alloy material is refined, higher strength and elongation can be obtained; on the other hand, Ti and V form AlTiV intermetallic compounds in the alloy (the energy spectrum shows that the atomic percentage is about Al 90 Ti4V4Ce2), which plays a role in second-phase strengthening, improves the heat resistance of the alloy, and maintains the high-strength and high-toughness performance of the alloy; at the same time, Mo and Fe form AlMoFe intermetallic compounds in the alloy (the energy spectrum shows that the atomic percentage is about Al 74 Si 12 Mo 12 Fe2), which has a small thermal expansion coefficient and excellent volume stability, effectively preventing small dimensional deformation of parts; moreover, the present invention also controls certain process steps, especially controlling certain process parameters in die-casting forming (including the injection speed, punch high-speed switching point, total injection stroke, filling time, casting pressure, vacuum degree, die-casting mold temperature, and aluminum liquid pouring temperature mentioned above), improving the casting performance, improving the tissue uniformity of the alloy, reducing the internal stress of the casting, etc., and further improving the anti-thermal-cracking performance and high-strength and high-toughness performance of the product. That is, the present invention simultaneously controls the huge influence of the deformation and stress of the casting on the casting through both alloy composition and preparation process, improving the performance of the alloy product.

[0062] The test results show that the aluminum alloy provided by the present invention has a room-temperature tensile strength of more than 280 MPa, a room-temperature yield strength of more than 134 MPa, a liquid-solid phase temperature difference of less than 68, a latent heat of crystallization of more than 341 KJ / kg, a linear shrinkage rate of less than 0.50%, an anti-thermal-cracking force value of more than 678 N, a linear expansion coefficient of less than 20.7×10 -6 m / m·K, and a volume stability value of less than 0.012%. It does not require heat treatment process and also exhibits excellent high-strength toughness, stable deformability, and anti-thermal-cracking property. Description of the Drawings

[0063] 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 the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0064] Figure 1 Schematic diagrams of the test die used in the die-casting process for a 2000T high-vacuum cold chamber die-casting machine and die-cast products; among them, Figure 1 (a)-(b) are schematic diagrams of the test die, and 1(c) is a schematic diagram of the die-cast product;

[0065] Figure 2 Microstructure diagrams (500X) of the aluminum-silicon alloy castings obtained in Example 1 at different magnifications;

[0066] Figure 3 Microstructure diagrams (2000X) of the aluminum-silicon alloy castings obtained in Example 1 at different magnifications;

[0067] Figure 4 EDS layer images (2000X) of the aluminum-silicon alloy castings obtained in Example 1;

[0068] Figure 5 Microstructure diagram (500X) of the aluminum-silicon alloy castings obtained in Example 2;

[0069] Figure 6 Surface scan microstructure diagram (500X) of the aluminum-silicon alloy castings obtained in Example 3;

[0070] Figure 7 DSC curve of the aluminum-silicon alloy castings obtained in Example 1. Detailed implementation manners

[0071] The present invention provides a preparation method for a die-cast heat crack-resistant and heat-treatment-free aluminum alloy, comprising the following steps:

[0072] A) Preheating:

[0073] Preheat the metal charge and melting tools;

[0074] B) Batching:

[0075] Batch the raw materials according to the target alloy composition;

[0076] In terms of mass percentage, the composition of the target alloy is as follows:

[0077] Si: 6% - 11%;

[0078] V: 0.3% - 1.2%;

[0079] Ti: 0.4% - 1.2%;

[0080] Mo: 0.2% - 0.8%;

[0081] Ce: 0.2% - 0.6%;

[0082] Sr: 0.01% - 0.07%;

[0083] Fe: ≤0.2%;

[0084] Al: the balance;

[0085] The raw materials include: aluminum ingots, crystalline silicon, aluminum-molybdenum master alloy, aluminum-titanium master alloy, aluminum-vanadium master alloy, aluminum-strontium master alloy, and aluminum-cerium master alloy;

[0086] C) Melting:

[0087] Add aluminum ingots, crystalline silicon, and aluminum-molybdenum master alloy into the melting furnace, heat up to 800 - 820 °C and keep warm, then cool down to 760 - 780 °C, and add aluminum-titanium master alloy, aluminum-vanadium master alloy, and aluminum-cerium master alloy into the melting furnace for holding and melting;

[0088] D) Refining and degassing:

[0089] When the temperature of the aluminum liquid in the melting furnace drops to 720 - 740 °C, add aluminum-strontium master alloy and an environmentally friendly refining agent into the melting furnace for on-line degassing and refining;

[0090] E) Die casting:

[0091] Pour the aluminum liquid into the shot chamber of the die casting machine, the punch advances at the set injection speed, the aluminum liquid passes through the gating system until the cavity is filled, and vacuum is drawn. After filling, pressure casting is carried out to obtain aluminum alloy die castings;

[0092] The process conditions for the above die casting are as follows:

[0093] Die casting mold temperature: 180 - 220 °C;

[0094] Aluminum liquid pouring temperature: 680 - 710 °C;

[0095] Injection: low speed 0.10 - 0.18 m / s, high speed 3.5 - 6.5 m / s, punch high speed switching point 420 - 500 mm, total injection stroke 750 - 800 mm;

[0096] Filling time: 110 - 162 s;

[0097] Vacuum degree: ≤150 mbar;

[0098] Casting pressure: 800 - 1200 bar.

[0099] Regarding step A) : Preheating

[0100] According to the present invention, preheat the melting tools.

[0101] In the present invention, before melting, the melting tools are preheated. The melting tools are conventional melting tools, including: bell jars, ladles, slag skimmers, stirring spoons, etc. Specifically, the preheating method can be placing the object to be preheated on the high-temperature melting furnace cover for preheating. In the present invention, the preheating temperature is preferably 150-200°C; the preheating time is preferably ≥2 h. In the present invention, before preheating, it is preferred to first apply a coating on the surface of the melting tool to prevent the introduction of Fe impurities. Specifically, the coating can be applied 2-3 times. The coating preferably comprises the following components in mass ratio: red coating powder 10% + water glass 2% + water 90%.

[0102] In the present invention, in addition to preheating the melting tools, it is preferred to also preheat the refining agent and the metal charge to be used subsequently. The preheating method can also specifically be placing the object to be preheated on the high-temperature melting furnace cover for preheating. The preheating temperature is preferably 150-200°C; the preheating time is preferably ≥2 h. The preheating treatment in step A) of the present invention is beneficial to controlling the impurities in the cast aluminum-silicon alloy.

[0103] Regarding step B) : Batching

[0104] According to the present invention, the raw materials are batched according to the target alloy composition.

[0105] In the present invention, by mass percentage, the composition of the target alloy is as follows:

[0106] Si: 6% - 11%;

[0107] V: 0.3% - 1.2%;

[0108] Ti: 0.4% - 1.2%;

[0109] Mo: 0.2% - 0.8%;

[0110] Ce: 0.2% - 0.6%;

[0111] Sr: 0.01% - 0.07%;

[0112] Fe: ≤0.2%;

[0113] Al: the balance.

[0114] Among them, the content of Si can specifically be 6%, 7%, 8%, 9%, 10%, 11%. The content of V can specifically be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%. The content of Ti can specifically be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%. The content of Mo can specifically be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%. The content of Ce can specifically be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%. The content of Sr can specifically be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%.

[0115] In the present invention, the raw materials (i.e., pre-melted materials) include: aluminum ingots, crystalline silicon, aluminum-molybdenum master alloy, aluminum-titanium master alloy, aluminum-vanadium master alloy, aluminum-strontium master alloy, and aluminum-cerium master alloy. Among them, the aluminum ingots are preferably industrial high-purity aluminum with an Al content of ≥ 99.90 wt%. The Si content in the crystalline silicon is ≥ 98.5 wt%. The aluminum-molybdenum master alloy is preferably AlMo5. The aluminum-titanium master alloy is preferably AlTi10. The aluminum-vanadium master alloy is preferably AlV4. The aluminum-strontium master alloy is preferably AlSr10. The aluminum-cerium master alloy is preferably AlCe10.

[0116] Regarding step C) : Melting

[0117] According to the present invention, aluminum ingots, crystalline silicon, and aluminum-molybdenum master alloy are added to a melting furnace, heated to 800 - 820 °C and held for heat preservation, then cooled to 760 - 780 °C, and aluminum-titanium master alloy, aluminum-vanadium master alloy, and aluminum-cerium master alloy are added to the melting furnace for heat-preserving melting.

[0118] In the present invention, aluminum ingots, crystalline silicon and aluminum-molybdenum master alloy are first added to a melting furnace for heating up and heat preservation. Among them, the heating rate of the heating up is preferably 145 - 150 °C / h, and specifically can be 145 °C / h, 146 °C / h, 147 °C / h, 148 °C / h, 149 °C / h, 150 °C / h. The target temperature of the heating up is 800 - 820 °C, and specifically can be 800 °C, 805 °C, 810 °C, 815 °C, 820 °C. After reaching the above target temperature, the heat preservation time is preferably 0.5 - 1 h, and specifically can be 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1.0 h. After the aluminum ingots, crystalline silicon and aluminum-molybdenum master alloy are fully melted and the temperature is kept stable during the above heat preservation, cooling is carried out. The cooling is to cool down to 760 - 780 °C, and specifically can be 760 °C, 765 °C, 770 °C, 775 °C, 780 °C. After cooling down to the above temperature, aluminum-titanium master alloy, aluminum-vanadium master alloy and aluminum-cerium master alloy are added into the melting furnace for heat preservation melting. The heat preservation time is preferably 1.5 - 2.5 h, and specifically can be 1.5 h, 2.0 h, 2.5 h.

[0119] In the present invention, according to the above specific feeding sequence (first add aluminum ingots, crystalline silicon and aluminum-molybdenum master alloy → then add aluminum-titanium master alloy, aluminum-vanadium master alloy and aluminum-cerium master alloy → next, i.e., step D, add aluminum-strontium master alloy), feeding and melting are carried out in temperature segments, which is beneficial to improving the uniformity of alloy components and preventing the component segregation of aluminum-molybdenum-iron-silicon phase, thereby improving the product performance; if the above feeding sequence is broken, for example, first add aluminum-titanium master alloy, aluminum-vanadium master alloy and aluminum-cerium master alloy, then add aluminum ingots, crystalline silicon and aluminum-molybdenum master alloy, or add all raw materials together, etc., the uniformity of alloy components will be reduced, component segregation will occur, and the product performance will become poor.

[0120] Regarding step D) : Refining and degassing

[0121] According to the present invention, when the temperature of the aluminum liquid in the melting furnace drops to 720 - 740 °C, aluminum-strontium master alloy and an environmental protection refining agent are added into the melting furnace for on-line degassing and refining.

[0122] In the present invention, after the melting in step C), cooling is carried out to make the temperature of the aluminum liquid in the melting furnace drop to 720 - 740 °C, specifically can be 720 °C, 725 °C, 730 °C, 735 °C, 740 °C. When the temperature drops to the above temperature, aluminum-strontium master alloy and an environmental protection refining agent are added, and on-line degassing and refining are carried out at the above temperature. Specifically: when the temperature drops to the above temperature, aluminum-strontium master alloy and an environmental protection refining agent are added, the degassing machine is started, the rotor and baffle automatically sink, and automatically enter the refining stage. The refining time is preferably 8 - 12 min, and specifically can be 8 min, 9 min, 10 min, 11 min, 12 min. The argon flow rate for the refining is preferably 0.8 - 1.2 m3 / h, specifically it can be 0.8 m 3 / h, 0.9 m 3 / h, 1.0 m 3 / h, 1.1 m 3 / h, 1.2 m 3 / h. The rotor speed is preferably 850 - 950 r / min, specifically it can be 850 r / min, 860 r / min, 870 r / min, 880 r / min, 890 r / min, 900 r / min, 910 r / min, 920 r / min, 930 r / min, 940 r / min, 950 r / min.

[0123] After degassing, the rotor rises. Immediately use tools to dredge the vent holes of the rotor and perform slag removal treatment. Specifically: According to the separation situation of the aluminum slag after refining and rotary degassing, use a slag ladle to stir the molten slag on the liquid surface for at least 2 - 4 min, then clean up the floating slag on the aluminum liquid surface. Pour the fished molten slag onto the slag frying platform or into the slag frying bucket, and try to spread the molten slag as much as possible.

[0124] In the present invention, the environmentally friendly refining agent is a commercially available traditional refining agent, and its main components are: 35 wt% - 45 wt% of NaCl and 35 wt% - 45 wt% of KCl. In the present invention, the dosage of the environmentally friendly refining agent is preferably 0.5% - 1% of the total mass of the raw materials, specifically it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%.

[0125] Regarding step E) : die casting

[0126] According to the present invention, pour the aluminum liquid into the pressure chamber of the die casting machine. The punch advances at the set injection speed. The aluminum liquid passes through the gating system until the cavity is filled, and at the same time, vacuum is pumped. After the filling is completed, pressure casting is carried out to obtain aluminum alloy die castings. Specifically, after the molten metal is refined to be qualified, the pouring temperature of the aluminum liquid is maintained at 680 - 710 °C, and die casting process is used to obtain castings. During the die casting process, the liquid metal fills the mold at high speed, and at the same time, vacuum is pumped to reduce the gas entrainment and slag production of the molten metal, and it solidifies under high pressure to ensure obtaining castings with dense structure and excellent performance.

[0127] In the present invention, the process conditions in the above die casting are preferably as follows:

[0128] Die casting mold temperature: 180 - 220 °C;

[0129] Pouring temperature of aluminum liquid: 680 - 710 °C;

[0130] Injection: low speed 0.10 - 0.18 m / s, high speed 3.5 - 6.5 m / s, punch high speed switching point 420 - 500 mm, total injection stroke 750 - 800 mm;

[0131] Pouring time: 110 - 162 s;

[0132] Vacuum degree: ≤ 150 mbar;

[0133] Casting pressure: 800 - 1200 bar.

[0134] In the present invention, the die - casting machine used for die - casting is preferably a cold - chamber die - casting machine, specifically, it can be a 2000T cold - chamber die - casting machine. A die - casting machine generally includes a die - clamping mechanism, a shot - sleeve mechanism, a hydraulic system, an electrical control system, components and a machine base, etc. Among them, the shot - sleeve mechanism mainly includes a shot sleeve, a shot piston, a shot rod, a shot cylinder and a booster, etc. A die - casting die is a tool for casting metal parts, which cooperates with the die - casting machine to complete the die - casting process. The die - casting die is mainly composed of a moving die and a stationary die. Among them, the stationary die is connected to the shot - sleeve mechanism of the die - casting machine and is fixed on the stationary - die seat on the side of the shot sleeve of the die - casting machine's shot - sleeve mechanism. And the stationary die contains part of the die - casting die cavity, and there is a sprue on the stationary die directly connected to the shot sleeve or the nozzle of the die - casting machine. The moving die is fixed on the moving - die mounting plate of the die - casting machine and moves with the moving - die mounting plate. When the die is closed, the cavity and the gating system are formed. The liquid metal fills the cavity under high pressure; when the die is opened, the moving die and the stationary die are separated, and the casting is pushed out by means of the ejection mechanism provided on the moving die.

[0135] In the present invention, the process of die - casting preferably specifically includes:

[0136] E1) Clean the installed die - casting die;

[0137] E2) Debug the installed die - casting die;

[0138] E3) Preheat the die - casting die;

[0139] E4) Spray and brush die - casting release agent on the die - casting die, and set the condition parameters during die - casting through the control cabinet;

[0140] E5) Pour the aluminum liquid into the shot sleeve and start vacuum pumping;

[0141] E6) The piston advances at the set injection speed until the pouring gate is completely closed;

[0142] E7) The aluminum liquid passes through the gating system until the cavity is filled;

[0143] E8) After filling is completed, perform pressure boosting treatment and solidification;

[0144] E9) Separate the moving die and the stationary die, take out the die - cast part, and obtain the alloy die - cast part.

[0145] During the above die - casting process, the test die and die - casting products of the 2000T high - vacuum cold - chamber die - casting machine are asFigure 1 As shown, where Figure 1 (a)-(b) are test molds, and 1(c) is a die-cast product (length 450 mm × width 300 mm × thickness 1 - 3 mm).

[0146] Regarding step E1): Remove oil stains, rust stains, old coatings, etc. on the surface of the die-casting mold by cleaning.

[0147] Regarding step E3): In the present invention, preheating can be carried out by using an electric heating device. The electric heating device is preferably a low-voltage high-current electric heating device. In the present invention, the preheating temperature is preferably 180 - 220 °C, that is, the temperature of the die-casting mold reaches 180 - 220 °C, specifically 180 °C, 190 °C, 200 °C, 210 °C, 220 °C.

[0148] Regarding step E4): In the present invention, the type of the die-casting release agent is not particularly limited, and a conventional die-casting release agent in the art can be used. Since the casting adopts a sequential solidification method, when spraying and brushing the die-casting release agent, it should be noted that the coating should be thicker in the area near the riser and the thin-wall area, and thinner in the area far from the riser and the wide and thick parts of the casting. Controlling the condition parameters in the die-casting process mainly refers to controlling the injection process parameters. Specifically: low speed 0.10 - 0.18 m / s, high speed 3.5 - 6.5 m / s, punch high-speed switching point 420 - 500 mm, total injection stroke 750 - 800 mm. Among them, the low speed can specifically be 0.10 m / s, 0.11 m / s, 0.12 m / s, 0.13 m / s, 0.14 m / s, 0.15 m / s, 0.16 m / s, 0.17 m / s, 0.18 m / s. The high speed can specifically be 3.5 m / s, 4.0 m / s, 4.5 m / s, 5.0 m / s, 5.5 m / s, 6.0 m / s, 6.5 m / s. The punch high-speed switching point can specifically be 420 mm, 430 mm, 440 mm, 450 mm, 460 mm, 470 mm, 480 mm, 490 mm, 500 mm. The total injection stroke can specifically be 750 mm, 760 mm, 770 mm, 780 mm, 790 mm, 800 mm.

[0149] Regarding step E5): Specifically, a ladle can be used to quantitatively scoop up the molten aluminum from the crucible and then pour it into the shot chamber. At the same time, start the vacuum pumping system to pump vacuum to reduce the gas entrainment and slag generation of the molten metal. The vacuum degree is preferably ≤150 mbar.

[0150] Regarding step E7): This process is carried out under vacuum conditions. Specifically, it is maintained under the vacuum conditions described above. The pouring temperature of the molten aluminum is preferably 680 - 710 °C, specifically 680 °C, 685 °C, 690 °C, 695 °C, 700 °C, 705 °C, 710 °C.

[0151] Regarding step E8): The filling time is preferably 110 - 162 s, specifically it can be 110 s, 120 s, 130 s, 140 s, 150 s, 160 s, 162 s. The pressure boosting treatment is preferably boosting the pressure to 800 - 1200 bar (i.e., the casting pressure), specifically it can be 800 bar, 900 bar, 1000 bar, 1100 bar, 1200 bar. Through the above pressure boosting treatment, gas mixing into the molten metal is avoided, and at the same time, dense castings can be ensured to be obtained.

[0152] The present invention also provides a die-casting formed heat crack-resistant and heat treatment-free aluminum alloy prepared by the preparation method described in the above technical solution.

[0153] Currently, for the heat treatment-free materials used in integrated die-casting, most of them add Cu or Mg or Mn elements, which increases the hot cracking tendency of alloy components, the castings are prone to bending deformation, and the qualified rate of castings is reduced. In the preparation method of the present invention, a certain alloy composition is controlled. Among them, specific amounts of Ti and V elements, on the one hand, play a role in grain refinement. After the alloy material is refined, higher strength and elongation can be obtained; on the other hand, Ti and V form AlTiV intermetallic compounds in the alloy (the energy spectrum shows that the atomic percentage is about Al 90 Ti4V4Ce2), which play a role in second-phase strengthening, improve the heat resistance of the alloy, and maintain the high strength and toughness performance of the alloy; at the same time, Mo and Fe form AlMoFe intermetallic compounds in the alloy (the energy spectrum shows that the atomic percentage is about Al 74 Si 12 Mo 12 Fe2), which has a small thermal expansion coefficient and excellent volume stability, effectively preventing the tiny deformation of part dimensions; moreover, the present invention also controls certain process steps, especially controlling certain process parameters (including the injection speed, punch high-speed switching point, total injection stroke, filling time, casting pressure, vacuum degree, die-casting mold temperature, and aluminum liquid pouring temperature mentioned above) during casting, improving the casting performance, improving the tissue uniformity of the alloy, reducing the internal stress of the casting, etc., and further improving the heat crack resistance and high strength and toughness performance of the product. That is, the present invention simultaneously controls the huge influence of the deformation and stress of the casting on the casting through both alloy composition and preparation process, and improves the performance of the alloy product.

[0154] The test results show that for the aluminum alloy provided by the present invention, the room-temperature tensile strength reaches above 280 MPa, the room-temperature yield strength reaches above 134 MPa, the liquid-solid phase temperature difference is below 68, the latent heat of crystallization is above 341 KJ / kg, the linear shrinkage rate is below 0.50%, the hot crack resistance force value is above 678 N, and the linear expansion coefficient is at 20.7×10 -6Below m / m·K, the volume stability value is below 0.012%, no heat treatment process is required, and it also exhibits excellent high strength and toughness, stable deformability, and thermal crack resistance.

[0155] To further understand the present invention, the preferred embodiments of the present invention will be described below in conjunction with examples. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0156] Examples 1 - 9

[0157] A) Preheating:

[0158] Apply the coating 3 times on the surface of the melting tools (including bell jars, ladles, slag skimmers, stirring spoons, etc.) to prevent the introduction of Fe impurities. Preheat the melting tools, refining agents, and metal charge required for subsequent steps (place them on the lid of the high-temperature melting furnace for preheating), specifically dry them at 180°C for 2 h.

[0159] B) Batching:

[0160] Batch the raw materials according to the target alloy composition.

[0161] Among them, the raw materials are shown in Table 1:

[0162] Table 1: Raw Materials

[0163] Name Chemical composition Industrial high-purity aluminum Al≥99.90wt% Crystalline silicon Si≥98.5wt% Aluminum-molybdenum master alloy AlMo5 Aluminum-titanium master alloy AlTi10 Aluminum-vanadium master alloy AlV4 Aluminum-strontium master alloy AlSr10 Aluminum-cerium master alloy AlCe10

[0164] The alloy compositions of Examples 1 - 9 are shown in Table 2:

[0165] Table 2: Alloy Compositions

[0166]

[0167] C) Melting:

[0168] Add aluminum ingots, crystalline silicon, and aluminum-molybdenum master alloy to the melting furnace, heat it up to 810°C at a rate of 150°C / h and hold for 1 h. After ensuring that the aluminum ingots, crystalline silicon, and aluminum-molybdenum master alloy are melted and the temperature is stable, cool it down to 770°C, and add aluminum-titanium master alloy, aluminum-vanadium master alloy, and aluminum-cerium master alloy to the melting furnace, and hold for 2 h.

[0169] D) Refining and degassing:

[0170] When the temperature of the molten aluminum in the melting furnace drops to 730 °C, add aluminum-strontium master alloy and environmental protection refining agent (the main components are 35% - 45% NaCl and 35% - 45% KCl, and the addition amount of the refining agent is 0.8% of the total mass of the raw materials) into the melting furnace, turn on the degassing machine, and the rotor and baffle will automatically sink and enter the refining stage automatically. The rotor speed is 900 r / min, the refining time is 10 min, and the argon gas flow rate is 1.0 m 3 / h.

[0171] Skimming: After degassing, the rotor rises. Immediately use tools to dredge the vent holes of the rotor and perform skimming. Specifically: According to the separation of the aluminum slag after refining rotary degassing, use a slag ladle to stir the molten slag on the liquid surface for at least 3 min, then clean up the floating slag on the surface of the molten aluminum. Pour the fished molten slag onto the slag frying platform or into the slag frying bucket, and try to spread the molten slag as much as possible.

[0172] E) Die casting:

[0173] Pour the molten aluminum into the shot chamber of a 2000T cold chamber die casting machine. The punch advances at the set injection speed. The molten aluminum passes through the gating system until the cavity is filled, and at the same time, vacuum is pumped. After filling is completed, pressure casting is carried out to obtain aluminum alloy die castings. Specifically, the die casting process flow is as follows:

[0174] E1) Clean the installed die casting mold to remove oil stains, rust stains, old coatings, etc. on the surface of the die casting mold.

[0175] E2) Debug the installed die casting mold.

[0176] E3) Preheat the die casting mold. Specifically, use an electric heating (low voltage and high current) device to preheat the mold so that the mold temperature is controlled at 200 °C.

[0177] E4) Spray and brush die casting release agent on the die casting mold, and set the condition parameters during die casting through the control cabinet.

[0178] E5) Use a pouring ladle to quantitatively ladle molten aluminum from the crucible and then pour it into the shot chamber. At the same time, start the vacuum pumping system to pump vacuum.

[0179] E6) The punch advances to completely seal the pouring gate at the set injection speed.

[0180] E7) The molten aluminum passes through the gating system until the cavity is filled, and this process is carried out under vacuum conditions.

[0181] E8) After filling is completed, perform pressure boosting treatment and solidification.

[0182] E9) Separate the moving mold from the fixed mold, take out the die casting, and obtain the alloy die casting.

[0183] Among them, the condition parameters of Examples 1-9 in the above die-casting process are shown in Table 3:

[0184] Table 3: Die-casting process parameters

[0185]

[0186] Comparative Examples 1-3

[0187] A) Preheating: The same as in Example 1.

[0188] B) Batching:

[0189] Batch the raw materials according to the target alloy composition.

[0190] Among them, the raw materials are shown in Table 4:

[0191] Table 4: Raw materials

[0192] Name Chemical composition Industrial high-purity aluminum Al≥99.90wt% Crystalline silicon Si≥98.5wt% Pure magnesium ingot Mg≥99.95wt% Pure copper plate Cu≥99.95wt% Aluminum-manganese master alloy AlMn20 Aluminum-strontium master alloy AlSr10

[0193] The alloy compositions of Comparative Examples 1-3 are shown in Table 5:

[0194] Table 5: Alloy compositions

[0195]

[0196] C) Melting:

[0197] Add aluminum ingots, crystalline silicon, pure copper plates and aluminum-manganese master alloy to the melting furnace, heat up to 810 °C at a rate of 150 °C / h and hold for 1 h, then cool down to 770 °C, add aluminum-strontium master alloy to the melting furnace, and hold for 2 h.

[0198] D) Refining and degassing:

[0199] When the temperature of the aluminum liquid in the melting furnace drops to 730 °C, add pure magnesium ingots and an environmental protection refining agent (the main components are 35% - 45% NaCl and 35% - 45% KCl, and the addition amount of the refining agent is 0.8% of the total mass of the raw materials) to the melting furnace, turn on the degassing machine, the rotor and the baffle will automatically sink and enter the refining stage automatically. The rotor speed is 900 r / min, the refining time is 10 min, and the argon flow rate is 1.0 m 3 / h.

[0200] Slagging: The same as in Example 1.

[0201] E) Die-casting forming:

[0202] Implement according to Examples 1-3 respectively to obtain the alloy casting products of Comparative Examples 1-3. That is, the condition parameters of Comparative Examples 1-3 in the die-casting process are the same as those of Examples 1-3 respectively (Comparative Example 1 corresponds to Example 1, Comparative Example 2 corresponds to Example 2, and Comparative Example 3 corresponds to Example 3).

[0203] Test examples:

[0204] 1. Metallographic analysis

[0205] Figure 2-3 They are the micrographs of the aluminum-silicon alloy castings obtained in Example 1 at different magnifications (500X and 2000X respectively). Figure 4 It is the EDS layered image (2000X) of the aluminum-silicon alloy casting obtained in Example 1. Analysis based on the above SEM micrographs combined with the EDS maps shows that Ti and V in the alloy of Example 1 play a role in grain refinement on the one hand. After the alloy material is refined, higher strength and elongation can be obtained; on the other hand, Ti and V form intermetallic compounds of AlTiV in the alloy (the energy spectrum shows that the atomic percentage is about Al 90 Ti4V4Ce2), playing a role in second-phase strengthening; at the same time, Mo and Fe form intermetallic compounds of AlMoFe in the alloy (the energy spectrum shows that the atomic percentage is about Al 74 Si 12 Mo 12 Fe2), with a small coefficient of thermal expansion and excellent volume stability, effectively preventing tiny dimensional deformation of parts; among them, the light gray blocks are AlMoFe compounds and the light white blocks are AlTiV compounds, covering the dark gray matrix aluminum matrix. The range of this three-phase region is very large, and it is also easy to distinguish each phase.

[0206] Figure 5 It is the micrograph (500X) of the aluminum-silicon alloy casting obtained in Example 2. Figure 6 It is the surface scanning microstructure diagram (500X) of the aluminum-silicon alloy casting obtained in Example 3.

[0207] 2. Tensile strength, yield strength and elongation

[0208] The alloy castings products obtained in each example and comparative example were respectively tested for tensile strength, yield strength and elongation. The results are shown in Table 6.

[0209] Table 6: Tensile strength, yield strength and elongation

[0210]

[0211] 3. Thermal crack resistance

[0212] The width of the effective crystallization temperature range of the alloy determines the absolute shrinkage amount of the alloy within the hot cracking temperature range. It can be seen that the smaller the effective crystallization interval from the linear shrinkage start temperature to the solidus line, the smaller the absolute shrinkage amount of the alloy within this temperature range, and the smaller the stress generated in the casting. Therefore, the tendency of the alloy to form hot cracks is smaller. So, the smaller the difference between the liquidus temperature and the solidus temperature or the larger the latent heat of crystallization, the greater the thermal crack resistance value.

[0213] The test results of each example and comparative example are shown in Table 7. Among them, the test of liquidus-solidus temperature refers to the standard of GB / T1425-1996. The test of linear shrinkage rate refers to the standard of JB / T4022.1-1999. The test of thermal crack resistance value refers to the standard of JB / T4022.2-1999. The linear expansion coefficient refers to the standard of QB / T 1321-2012, and the volume stability refers to the standard of GB / T 1148-2010. Among them, the DSC curve of the alloy obtained in Example 1 is as Figure 7 shown.

[0214] Table 7: Properties related to thermal cracking

[0215]

[0216] It can be seen from the test results in Tables 6-7 that the normal temperature tensile strength of Examples 1-9 of the present invention reaches above 280 MPa, the normal temperature yield strength reaches above 134 MPa, the liquidus-solidus temperature difference is below 68, the latent heat of crystallization is above 341 KJ / kg, the linear shrinkage rate is below 0.50%, the thermal crack resistance value is above 678 N, the linear expansion coefficient is below 20.7×10 -6 m / m·K, and the volume stability value is below 0.012%. No heat treatment process is required and it also exhibits excellent high strength and toughness, stable deformability and thermal crack resistance. The normal temperature tensile strength of Comparative Examples 1-3 is below 275 MPa, the normal temperature yield strength is below 128 MPa, the liquidus-solidus temperature difference is above 83, the latent heat of crystallization is below 335 KJ / kg, the linear shrinkage rate is above 0.58%, the thermal crack resistance value is below 657 N, the linear expansion coefficient is above 21.5×10 -6 m / m·K, and the volume stability value is above 0.015%. The strength and toughness, stable deformability and thermal crack resistance are all significantly deteriorated.

[0217] In this article, specific examples are used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention, including the best mode, and also enables any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The protection scope of the present invention patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to the literal description of the claims, or if they include equivalent structural elements that have no substantial difference from the literal description of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A preparation method of a die-casting anti-thermal-cracking and heat-treatment-free aluminum alloy, characterized in that, It includes the following steps: A) Preheating: Preheat the smelting tool. B) Batching: Batch the raw materials according to the target alloy composition. In terms of mass percentage, the composition of the target alloy is as follows: Si: 6% - 11%; V：0.3％～1.2％； Ti: 0.4% - 1.2%; Mo: 0.2% - 0.8%; Ce: 0.2% - 0.6%; Sr：0.01％～0.07％； Fe: ≤0.2%; Al: the balance; The raw materials include: aluminum ingots, crystalline silicon, aluminum-molybdenum master alloy, aluminum-titanium master alloy, aluminum-vanadium master alloy, aluminum-strontium master alloy, and aluminum-cerium master alloy; C) Melting: Add aluminum ingots, crystalline silicon, and aluminum-molybdenum master alloy into the melting furnace, heat up to 800 - 820°C and hold for a certain time, then cool down to 760 - 780°C, and add aluminum-titanium master alloy, aluminum-vanadium master alloy, and aluminum-cerium master alloy into the melting furnace, and hold for melting; D) Refining and degassing: When the temperature of the aluminum liquid in the melting furnace drops to 720 - 740°C, add aluminum-strontium master alloy and an environmentally friendly refining agent into the melting furnace for on-line degassing and refining; E) Die casting: Pour the aluminum liquid into the shot chamber of the die casting machine, the punch advances at the set injection speed, the aluminum liquid passes through the gating system until the cavity is filled, start vacuum pumping, after filling is completed, perform pressure casting to obtain aluminum alloy die castings; The process conditions for the above die casting are as follows: Die casting mold temperature: 180 - 220°C; Aluminum liquid pouring temperature: 680 - 710°C; Injection: low speed 0.10 - 0.18 m / s, high speed 3.5 - 6.5 m / s, punch high speed switching point 420 - 500 mm, total injection stroke 750 - 800 mm; Filling time: 110 - 162 s; Vacuum degree: ≤150 mbar; Casting pressure: 800 - 1200 bar.

2. The preparation method according to claim 1, wherein In step A), the temperature of the preheating is 150 - 200°C, and the time is ≥2 h.

3. The preparation method according to claim 1, characterized in that, In step B), the aluminum-molybdenum master alloy is AlMo5; The aluminum-titanium master alloy is AlTi10; The aluminum-vanadium master alloy is AlV4; The aluminum-strontium master alloy is AlSr10; The aluminum-cerium master alloy is AlCe10.

4. The preparation method according to claim 1, characterized in that, In step C): The time for heating up to 800 - 820°C and holding is 0.5 - 1 h; The time for holding after adding aluminum-titanium master alloy, aluminum-vanadium master alloy, and aluminum-cerium master alloy is 1.5 - 2.5 h.

5. The preparation method according to claim 1, characterized in that, In step D), the refining time is 8 to 12 minutes, the air compression flow rate is 0.8 to 1.2 m 3 / h, and the rotor speed is 850 to 950 r / min.

6. The preparation method according to claim 1, characterized in that, In step D), the main components of the environmentally friendly refining agent are 35 wt% - 45 wt% of NaCl and 35 wt% - 45 wt% of KCl.

7. The preparation method according to claim 1 or 6, characterized in that, In step D), the dosage of the environmentally friendly refining agent is 0.5% - 1% of the total mass of the raw materials.

8. The preparation method according to claim 1, wherein In step E), the process of die casting specifically includes: E1) Clean the installed die casting mold; E2) Debug the installed die casting mold; E3) Preheat the die casting mold; E4) Spray and brush die casting release agent on the die casting mold, and set the condition parameters during die casting through the control cabinet; E5) Take the aluminum liquid and pour it into the shot chamber, and start vacuum pumping; E6) The punch advances at the set injection speed until the pouring gate is completely closed; E7) The aluminum liquid passes through the gating system until the cavity is filled; E8) After the filling is completed, the pressure boosting treatment is carried out and solidification occurs; E9) The moving mold and the stationary mold are separated, and the die-cast part is taken out to obtain an alloy die-cast part.

9. The preparation method according to claim 8, wherein In step E3), the preheating temperature is 180 - 220 °C.

10. A die-cast anti-thermal cracking and heat-treatment-free aluminum alloy prepared by the preparation method according to any one of claims 1 to 9.

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