Integrated die-casting forming method for aluminum alloy rear floor of new energy automobile

Abstract

The invention discloses an integrated die-casting forming method for an aluminum alloy rear floor of a new energy automobile. The integrated die-casting forming method sequentially comprises the following steps that (1) aluminum alloy liquid is smelted and prepared; (2) the molten aluminum alloy is subjected to injection refining purification and refining modification; (3) mounting a die-casting die and preheating; (4) spraying a release agent and closing the mold; (5) casting and vacuum die-casting forming; (6) opening the mold and taking out the aluminum alloy rear floor blank; (7) a runner and a cinder ladle of the blank are cut off; and (8) the blank is polished and machined, and a finished aluminum alloy floor product is obtained. Integrated die-casting forming of the aluminum alloy rear floor of the new energy automobile is achieved, refining purification and refining modification are conducted on the aluminum alloy liquid, the vacuum die-casting forming technology is optimized, and the mechanical property, quality stability and the product percent of pass of the aluminum alloy rear floor are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of die-casting of aluminum alloy parts, and specifically relates to an integrated die-casting method for an aluminum alloy rear floor of a new energy vehicle. Background Art

[0002] The production process of the rear floor of traditional new energy vehicles is to stamp metal materials into multiple parts first, and then weld the stamped parts into the rear floor. The traditional welded rear floor has many parts and processes, which makes the manufacturing cost of new energy vehicles high. Integrated die-casting is to die-cast multiple traditional parts into a whole at one time through a large die-casting machine. The integrated die-casting aluminum alloy rear floor of new energy vehicles not only greatly reduces the number of parts, but also greatly shortens the production process and production cycle, thereby significantly improving the production efficiency of new energy vehicles and reducing production costs.

[0003] The Chinese patent document with publication number CN117867305A discloses a high elongation Al-Si alloy integrated die casting and its microstructure control method and use. The microstructure control method of the high elongation Al-Si alloy integrated die casting comprises first adding an Al-Ti-B master alloy containing a specific titanium-boron ratio into the die-cast Al-Si alloy, causing it to completely melt in a short time through an auxiliary process, then quickly adding an Al-Sr master alloy for smelting and modification, and finally die-casting to obtain an Al-Si alloy integrated die casting with a high elongation.

[0004] The Chinese patent document with publication number CN117026020A discloses an aluminum alloy ingot for integrated die casting produced from recycled aluminum and a production method thereof. The aluminum alloy ingot production method comprises: (1) charging, laying industrial silicon flat on the bottom of a smelting furnace and baking it, adding waste aluminum into the smelting furnace to melt into aluminum liquid, and then adding aluminum manganese master alloy, aluminum zirconium master alloy, aluminum molybdenum master alloy, aluminum boron master alloy and aluminum rare earth master alloy into the aluminum liquid to fully melt; (2) refining, refining at a temperature of 720-760°C for 30-45 minutes; (3) casting: casting at 720-760°C. The aluminum alloy ingot has a yield strength of 130-150MPa, a tensile strength of 250-280MPa, an elongation of 10-14%, and an Fe content of less than 0.15wt.%.

[0005] The Chinese patent document with publication number CN117920971A discloses a cooling mechanism and die-casting mold for an integrated die-casting mold for new energy vehicles. The cooling mechanism includes: a cooling module with at least one surface in close contact with the side wall of the accommodating cavity facing the fixed mold assembly, and a cooling water circuit is provided in the cooling module. The cooling water circuit is used to circulate cooling water that takes away the heat of the cooling module. The invention increases the cooling area of ​​the movable mold assembly and improves the cooling effect by cooling the surface of the cooling module in close contact with the side wall of the accommodating cavity, shortens the cooling time of the casting in the die-casting mold, and thus reduces the manufacturing cost of the casting.

[0006] A Chinese patent document with publication number CN117113528A discloses a finite element modeling method for an integrated die-cast mid-rear floor, including geometric cleaning, using second-order tetrahedrons for finite element modeling; performing process simulation on the die-casting process; dividing the integrated die-cast mid-rear floor into regions according to the simulation results; based on the regional division results, sampling the integrated die-cast mid-rear floor in different regions and performing material tensile tests to obtain material properties in different regions; defining the finite element model attributes of the integrated die-cast mid-rear floor in different regions; performing vehicle body stiffness and strength performance analysis and structural optimization; and comparing with the test results to obtain the simulation analysis accuracy.

[0007] From the results of literature retrieval and production practice experience, although integrated die-casting can significantly reduce the number of parts and processes in the production of aluminum alloy rear floors for new energy vehicles, the integrated die-cast aluminum alloy rear floors are relatively large, so the integrated die-cast aluminum alloy materials and processes are extremely demanding. However, the existing integrated die-cast aluminum alloy rear floors for new energy vehicles still have problems such as low mechanical properties, poor quality stability, and low product qualification rate. Therefore, the existing integrated die-casting molding method for aluminum alloy rear floors for new energy vehicles still needs to be improved and developed. Summary of the invention

[0008] In view of the problems and shortcomings mentioned in the background technology, the present invention provides an integrated die-casting method for an aluminum alloy rear floor of a new energy vehicle. By scientifically designing the composition of the aluminum alloy, optimizing the refining and purification of the aluminum alloy liquid and the vacuum die-casting molding process, the mechanical properties, quality stability and product qualification rate of the integrated die-cast aluminum alloy rear floor of a new energy vehicle are improved.

[0009] The present invention achieves the above-mentioned purpose by adopting the following technical solutions:

[0010] A method for integrated die-casting of an aluminum alloy rear floor of a new energy vehicle is characterized in that it comprises the following steps in sequence:

[0011] (1) smelting and preparing aluminum alloy liquid, and controlling the temperature of the aluminum alloy liquid at 700-720° C.;

[0012] (2) performing refining agent spray refining and mixed gas spray refining degassing and deslagging on the aluminum alloy liquid;

[0013] (3) Installing the die-casting mold on the die-casting machine and preheating the die-casting mold;

[0014] (4) Spray a release agent on the inner cavity of the die-casting mold, and then start the die-casting machine to close the mold;

[0015] (5) pouring aluminum alloy liquid into the injection cylinder and vacuum die-casting it into a rear floor blank;

[0016] (6) Open the die-casting mold and take out the rear floor blank;

[0017] (7) Cut off the runners and slag bags of the floor blank;

[0018] (8) Grinding and machining the rear floor blank to obtain the aluminum alloy rear floor of the new energy vehicle.

[0019] Furthermore, the aluminum alloy liquid in step (1) is composed of the following components in mass percentage: Si 12.8-13.2%, Cu 1.8-2.2%, Zn 1.6-2.1%, Mn 0.6-0.9%, Fe≤0.2%, and the balance is Al and other inevitable impurity elements, the individual content of other impurity elements is ≤0.05%, and the total amount of other impurity elements is ≤0.15%.

[0020] Integrated die-casting has high requirements on die-cast aluminum alloy materials, requiring both higher fluidity and higher mechanical properties, so as to obtain a fully filled rear floor and excellent mechanical properties of the rear floor in a non-heat-treated state. Based on the traditional die-cast aluminum alloy, the present invention re-optimizes the composition of the aluminum alloy, wherein the main function of Si is to improve the fluidity of the aluminum alloy liquid. During the solidification process of the aluminum alloy, Si and Al can form an Al+Si eutectic liquid phase to improve the fluidity of the aluminum alloy liquid. Low Si content will lead to insufficient fluidity of the aluminum alloy liquid, and it is impossible to obtain a fully filled rear floor. However, the Si content cannot be too high, otherwise it will cause the plasticity of the aluminum alloy to decrease, resulting in insufficient plasticity of the integrated die-cast rear floor.

[0021] The main function of Cu is to enhance the strength of the rear floor. Cu has a strong solid solution strengthening effect in aluminum alloys and can significantly enhance the strength of aluminum alloys. The Cu content cannot be lower than 1.8%, otherwise it will lead to insufficient strength of the rear floor. The higher the Cu content, the higher the strength of the rear floor. However, too high a Cu content will also increase the thermal cracking tendency of the rear floor, causing thermal crack defects in the integrated die-cast rear floor, resulting in the rear floor being unqualified and scrapped. In addition, too high a Cu content will also reduce the corrosion resistance of the rear floor.

[0022] The main function of Zn is to enhance the fluidity of aluminum alloy liquid and the strength of the rear floor. Zn can also form Al+Zn alloy liquid during the solidification process of aluminum alloy liquid to enhance the fluidity of aluminum alloy liquid, and at the same time produce obvious solid solution strengthening effect, enhancing the strength of the rear floor. However, the Zn content should not be too high, otherwise it will also increase the thermal cracking tendency of the rear floor.

[0023] The main function of Mn is to enhance the strength of the rear floor through dispersion strength. Mn can form MnAl6 particles in aluminum alloy. MnAl6 particles dispersed in aluminum alloy can not only enhance the strength of the rear floor, but also improve the high temperature resistance of the rear floor.

[0024] Fe is an inevitable impurity element in aluminum alloys, usually existing in the form of coarse needle-like Fe-rich phases. Coarse needle-like Fe-rich phases will split the aluminum alloy matrix, causing local stress concentration in the rear floor, becoming the crack source and crack extension direction of the rear floor, and reducing the strength and plasticity of the rear floor. Therefore, the content of impurity element Fe must be strictly controlled, and the integrated die-casting of the rear floor requires that the content of impurity element Fe be less than 0.2%.

[0025] Furthermore, the carrier gas for the refining agent spraying in step (2) is argon with a purity of ≥99.99%, the amount of the refining agent is 0.1-0.2% of the weight of the aluminum alloy liquid, the spraying refining time is 15-20 minutes, and the aluminum alloy liquid is left to stand for 30-40 minutes.

[0026] During the smelting and preparation process, aluminum alloy liquid will inevitably be involved in inclusions and gas absorption, the inclusions are mainly aluminum oxide, and the gas absorption is mainly hydrogen absorption. If the aluminum alloy liquid is not refined and purified, the inclusions and hydrogen absorption involved in the aluminum alloy liquid will remain inside the rear floor to form defects such as pores, inclusions and looseness, which will become the crack source and crack extension direction of the rear floor, which will seriously reduce the strength, plasticity and fatigue resistance of the rear floor. Therefore, in order to obtain a high-strength and high-plasticity integrated die-casting rear floor, the aluminum alloy liquid must be refined, dehydrogenated and deslaged.

[0027] The refining agent spray refining adopts a powder spraying tank and a stainless steel pipe, and uses argon as a carrier to spray a solid powdered refining agent into the aluminum alloy liquid, so that the refining agent contacts and reacts with the aluminum alloy liquid, and then the inclusions and hydrogen are taken out of the aluminum alloy liquid. The deslagging and degassing effect of the refining agent spray refining is first related to the purity of the argon gas, the amount of the refining agent and the spray refining time. The higher the purity of the argon gas, the greater the amount of the refining agent, the longer the spray refining time, the better the deslagging and dehydrogenation effect, but the corresponding production cost will also increase. If the spray refining time is too long, the oxidation and burning of the aluminum alloy liquid will also increase. After the spray refining is completed, after the scum on the surface of the aluminum alloy liquid is removed, a covering agent should be sprinkled on the surface of the aluminum alloy liquid in time to avoid oxidation and burning of the aluminum alloy liquid and re-absorption of hydrogen. After sprinkling the covering agent, the aluminum alloy liquid needs to be left to stand for a period of time, and the standing time cannot be less than 30 minutes, so that the inclusions and bubbles in the aluminum alloy liquid have sufficient time to escape.

[0028] Furthermore, the refining agent in step (2) is composed of the following components in mass percentage: NaCl 35.12%, NaF 19.84%, TiCl3 16.51%, SrSO4 10.06%, KPO3 11.45%, and Na2B4O7 7.02%. The preparation method of the refining agent comprises the following steps in sequence: (1) according to the composition and mass percentage of the refining agent, NaCl, NaF, TiCl3, SrSO4, KPO3, and Na2B4O7 with a purity of ≥99.8% are selected as raw materials for batching; (2) the ingredients are added into water at a temperature of 70°C and stirred to dissolve into an aqueous solution, the mass ratio of water to ingredients being 1.2, and then the aqueous solution is heated to 100°C to evaporate to obtain solid crystals; (3) the solid crystals are crushed into powders with a particle size of less than 2 mm, and the powders are dried and dehydrated at 160°C for 4 hours to obtain the refining agent.

[0029] The deslagging and dehydrogenation effect of refining agent spray refining is also closely related to the composition and preparation method of the refining agent. The existing refining agent is mainly obtained by crushing and mixing fluoride salt and chloride salt. The components of the refining agent exist independently of each other, resulting in a high melting point of the refining agent and low deslagging and dehydrogenation efficiency, which is difficult to meet the requirements of rear floor integrated die casting for high clean aluminum alloy liquid. In order to improve the deslagging and dehydrogenation effect of powder spray refining, the present invention develops a high-efficiency multifunctional powder refining agent, and adopts an evaporation recrystallization method to prepare the refining agent. Through solution evaporation, the components are re-solidified and recrystallized to form a eutectic with a lower melting point. For example, the melting point of NaCl is usually 801°C, and the melting point of NaF is usually 993°C. When the two form a NaCl·NaF eutectic, the melting point drops to 698°C, thereby greatly reducing the melting point of the refining agent, making the refining agent more easily dissolved in the aluminum alloy liquid, and playing a synergistic role during refining, significantly enhancing the deslagging and dehydrogenation capabilities of the refining agent, wherein NaCl reacts with the aluminum alloy liquid to generate AlCl3 with a boiling point of only 180°C, and the AlCl3 bubbles adsorb and capture inclusions and hydrogen in the aluminum alloy liquid during the floating process, and then escape from the aluminum alloy liquid together, playing a role in deslagging and dehydrogenation. The main function of NaF is to destroy the alumina film by forming molten salt, dissolve inclusions such as alumina into the molten salt, increase the surface tension between inclusions and aluminum alloy liquid, promote the separation of inclusions such as alumina from aluminum alloy liquid, and enhance the slag removal function of the refining agent. TiCl3 reacts with aluminum alloy liquid to generate AlCl3 bubbles, which absorb and capture inclusions and hydrogen in the aluminum alloy liquid during the floating process, enhancing the slag removal and hydrogen removal ability of the refining agent. The Ti element obtained by the reaction can enhance the grain refinement effect on the aluminum alloy and improve the strength and plasticity of the rear floor. SrSO4 reacts with aluminum alloy liquid to generate SO2 bubbles, which absorb and capture inclusions and hydrogen in the aluminum alloy liquid during the floating process, enhancing the slag removal and hydrogen removal ability of the refining agent. The Sr element obtained by the reaction can enhance the refinement and modification effect on the eutectic Si phase in the aluminum alloy and improve the strength and plasticity of the rear floor. KPO3 reacts with aluminum alloy liquid to generate P element, which can enhance the refinement and modification of the primary Si phase in the aluminum alloy, and improve the strength, plasticity and wear resistance of the rear floor. Na2B4O7 reacts with aluminum alloy liquid to generate B element, which can refine the coarse Fe-rich phase of the modified aluminum alloy, eliminate the harm of the coarse Fe-rich phase to the strength and plasticity of the aluminum alloy, and improve the strength and plasticity of the rear floor.

[0030] Furthermore, the amount of mixed gas used in the mixed gas blowing refining in step (2) is 2-3 cubic meters per ton of aluminum alloy liquid, and the pressure of the mixed gas is (0.3-0.5)×10 5 Pa, the blowing refining time is 10-15 minutes, and the aluminum alloy liquid standing time is 20-30 minutes.

[0031] Although the refining agent spray refining greatly reduces the slag hydrogen content of the aluminum alloy liquid, the aluminum alloy liquid still contains slag hydrogen because the refining agent spray refining can only remove part of the slag. In addition, although powder spray refining also has a dehydrogenation effect, the dehydrogenation effect is limited because the refining agent inevitably contains moisture, which will be brought into the powder spray refining, causing the aluminum alloy liquid to absorb hydrogen again, so that the dehydrogenation is always in a dynamic equilibrium process. It is difficult for powder spray refining to reduce the hydrogen content of the aluminum alloy liquid to below 0.2ml / 100gAl. Therefore, in order to obtain a highly clean aluminum alloy liquid, gas spray refining is also required to further reduce the slag hydrogen content in the aluminum alloy liquid.

[0032] The mixed gas spray refining adopts a stainless steel pipe or a degasser to spray the mixed gas into the aluminum alloy liquid, so that the mixed gas forms fine bubbles to contact and react with the aluminum alloy liquid, and the hydrogen and inclusions in the aluminum alloy liquid are brought out of the liquid surface by the floating of the bubbles. The dehydrogenation and slag removal effect of the mixed gas spray refining is first related to the amount of the mixed gas and the spray refining time. The greater the amount of the mixed gas, the longer the spray refining time, and the better the deslag and hydrogen removal effect of the spray refining, but the production cost will also increase accordingly. If the spray refining time is too long, the oxidation and burning of the aluminum alloy liquid will also increase. After the spray refining is completed, after the scum on the surface of the aluminum alloy liquid is removed, a covering agent should be sprinkled on the surface of the aluminum alloy liquid in time to avoid oxidation and burning of the aluminum alloy liquid and hydrogen absorption. After sprinkling the covering agent, the aluminum alloy liquid needs to be left to stand for a period of time so that the bubbles in the aluminum alloy liquid have sufficient time to escape.

[0033] Furthermore, the mixed gas in step (2) is composed of argon gas with a purity of ≥99.99%, sulfur hexafluoride and carbon monoxide, the volume percentage of sulfur hexafluoride in the mixed gas is 9-11%, and the volume percentage of carbon monoxide is 3-5%.

[0034] The slag removal and hydrogen removal effect of gas injection refining is also closely related to the composition of the gas. The existing gas injection refining technology usually injects inert gas nitrogen or argon, or a mixture of inert gas and chlorine into the aluminum alloy liquid. The relative molecular mass of nitrogen is 28.01 and the density is 1.25kg / m 3 The relative molecular mass of argon is 39.94 and the density is 1.78 kg / m 3 The relative molecular mass of chlorine is 70.91 and the density is 3.21kg / m 3 . Due to the small relative molecular mass and low density of nitrogen, argon and chlorine, the bubbles rise faster in the aluminum alloy liquid, and the contact time between the bubbles and the aluminum alloy liquid is shorter, which limits the time for the bubbles to capture and adsorb hydrogen and inclusions, greatly affecting the dehydrogenation and deslagging effect of gas injection refining. In addition, although the relative density of chlorine is relatively large, chlorine is a toxic gas with a strong pungent odor, which will not only corrode the smelting furnace and smelting tools, but also cause serious environmental pollution.

[0035] Aiming at the problems and shortcomings of the existing gas injection refining technology, in order to obtain a highly clean aluminum alloy liquid, the present invention injects a mixed gas consisting of argon with a purity of ≥99.99%, sulfur hexafluoride with a purity of ≥99.99% and carbon monoxide with a purity of ≥99.99% into the aluminum alloy liquid, wherein sulfur hexafluoride is a high-density, high-stability gas with a relative molecular mass of 146.05 and a density of 6.5kg / m 3 , and sulfur hexafluoride is non-toxic, non-flammable and non-corrosive. Adding 9-11% by volume of sulfur hexafluoride to the mixed gas can significantly slow down the floating speed of bubbles in the aluminum alloy liquid, increase the contact time between the bubbles and the aluminum alloy liquid, and enable the bubbles to capture and absorb more hydrogen and inclusions, thereby improving the dehydrogenation and deslagging effect of gas injection refining. Adding 3-5% by volume of carbon monoxide to the mixed gas is to use carbon monoxide to capture oxygen in the aluminum alloy liquid to form carbon dioxide, avoid oxygen and aluminum forming an aluminum oxide film on the bubble surface, enhance the ability of the bubbles to capture and absorb hydrogen and inclusions, and improve the deslagging and dehydrogenation effect of gas injection refining.

[0036] Furthermore, the preheating of the die-casting mold described in step (3) is to heat the die-casting mold to 250-270°C by a mold temperature controller. The rear floor is an ultra-large aluminum alloy structural part. In order to ensure that an integrated die-cast rear floor with complete mold filling and dense structure can be obtained, the preheating temperature of the die-casting mold must be strictly controlled. If the preheating temperature of the die-casting mold is lower than 250°C, it will cause difficulty in filling the rear floor, and defects such as cold shut will occur on the surface, making it impossible to obtain a rear floor with complete mold filling and dense structure. However, the preheating temperature of the die-casting mold cannot be too high, otherwise it will increase the cooling speed of the rear floor in the mold, which will not only reduce production efficiency, but also deteriorate the mechanical properties of the rear floor, resulting in unqualified products.

[0037] Furthermore, in step (4), the release agent is sprayed on the inner cavity of the die-casting mold by using a sprayer to evenly spray the release agent on the inner cavity surface of the die-casting mold so that the rear floor can be separated from the die-casting mold. The clamping force of the die-casting machine for starting the mold is not less than 7500 tons. The rear floor is an ultra-large aluminum alloy structural part. In order to ensure the integrated die-casting molding of the rear floor, it must have sufficient clamping force, which must not be less than 7500 tons, but the clamping force does not need to be greater than 9000 tons, otherwise it will cause excess clamping force, which will increase production costs.

[0038] Further, the pouring temperature of the aluminum alloy liquid described in step (5) is 690-700°C, the vacuum degree of vacuum die casting is 230-250mbar, the injection pressure is 80-90MPa, the injection speed is 20-25m / s, the boost pressure is 700-800bar, and the holding time is 15-20s. The pouring temperature of the aluminum alloy cannot be lower than 690°C, the vacuum degree cannot be less than 230mbar, the injection pressure cannot be lower than 80MPa, the injection speed cannot be lower than 20m / s, and the boost pressure cannot be lower than 700bar, otherwise it will cause defects such as incomplete filling of the rear floor and cold shut on the surface, and it is impossible to obtain a rear floor with dense structure and good surface quality. However, the pouring temperature of the aluminum alloy cannot be too high, otherwise it is easy to cause the aluminum alloy liquid to cool and solidify for too long in the mold, resulting in shrinkage cracks and reducing production efficiency.

[0039] Furthermore, the step (6) of opening the die-casting mold and removing the rear floor blank refers to starting the die-casting machine mold opening mechanism to open the die-casting mold after the rear floor blank is cooled and solidified, and then grasping the rear floor blank by a robot arm to remove the rear floor blank from the inner cavity of the die-casting mold.

[0040] Furthermore, the cutting off of the flow channel and slag bag of the rear floor blank in step (7) is performed by sawing off the injection flow channel and the slag bag around the rear floor by a robot saw.

[0041] Furthermore, the grinding of the rear floor blank in step (8) is to grind the saw cut and surface of the rear floor blank by an automatic grinder to obtain a rear floor with a smooth and complete surface. The machining of the rear floor blank is to drill holes, tap screw holes, and perform milling and other processes on the rear floor blank to obtain a finished rear floor. The grinding and machining of the rear floor are relatively mature production processes, and the equipment used is also conventional equipment, which will not be elaborated and described in detail here.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The present invention realizes the integrated die-casting of the aluminum alloy rear floor of new energy vehicles, shortens the production process of the rear floor, reduces the production process, and is conducive to improving the production efficiency and reducing the production cost of the rear floor. The present invention greatly improves the mechanical properties, quality stability and product qualification rate of the rear floor by scientifically designing the composition of the aluminum alloy, optimizing the aluminum alloy liquid refining and purification and vacuum die-casting process. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The present invention is a process flow chart of the integrated die-casting molding process of the aluminum alloy rear floor of a new energy vehicle. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] Embodiment 1:

[0047] The integrated die-casting method for the rear floor of an aluminum alloy for a new energy vehicle comprises the following steps in sequence: (1) preparing an aluminum alloy liquid according to a composition of Si 12.96%, Cu 2.03%, Zn 1.85%, Mn 0.74%, Fe ≤ 0.2%, the remainder being Al and other unavoidable impurity elements, the individual content of other impurity elements ≤ 0.05%, and the total amount of other impurity elements ≤ 0.15% by mass, and controlling the temperature of the aluminum alloy liquid at 710° C.; (2) using argon gas with a purity of 99.99% and a refining agent with a weight of 0.15% of the weight of the aluminum alloy liquid to spray and refine the aluminum alloy liquid for 18 minutes, allowing the aluminum alloy liquid to stand for 35 minutes, and then using a mixed gas consisting of argon gas with a purity of 99.99%, sulfur hexafluoride and carbon monoxide to spray and refine the aluminum alloy liquid for 12 minutes, wherein the amount of the mixed gas is 2.5 cubic meters per ton of the aluminum alloy liquid, and the pressure of the mixed gas is 0.4×10 5 Pa, the volume percentage of sulfur hexafluoride in the mixed gas is 10%, and the volume percentage of carbon monoxide is 4%. After refining, the aluminum alloy liquid is allowed to stand for 25 minutes; (3) the die-casting mold is installed on the die-casting machine, and the die-casting mold is preheated to 260°C; (4) a mold release agent is sprayed on the inner cavity of the die-casting mold, and then the die-casting machine is started to close the mold, and the clamping force is 8000 tons; (5) the 695°C aluminum alloy liquid is poured into the injection cylinder for vacuum die-casting into a rear floor blank, the vacuum degree is 240mbar, the injection pressure is 85MPa, the injection speed is 22m / s, the boost pressure is 750bar, and the holding time is 18s; (6) the die-casting machine's mold opening mechanism is started to open the die-casting mold, and the rear floor blank is taken out by a robot; (7) the runner and slag bag of the rear floor blank are cut off; (8) the rear floor blank is polished and machined to obtain the aluminum alloy rear floor of the new energy vehicle.

[0048] Embodiment 2:

[0049] The integrated die-casting molding method of the aluminum alloy rear floor of a new energy vehicle comprises the following steps in sequence: (1) smelting and preparing an aluminum alloy liquid according to a composition composition of Si 12.8%, Cu 2.2%, Zn 1.6%, Mn 0.9%, Fe ≤ 0.2%, the remainder being Al and other unavoidable impurity elements, the individual content of other impurity elements ≤ 0.05%, and the total amount of other impurity elements ≤ 0.15%, and controlling the temperature of the aluminum alloy liquid at 720°C; (2) using argon gas with a purity of 99.99% and a refining agent with a weight of 0.2% of the aluminum alloy liquid to spray and refine the aluminum alloy liquid for 20 minutes, after the aluminum alloy liquid is allowed to stand for 30 minutes, using a mixed gas consisting of argon gas with a purity of 99.99%, sulfur hexafluoride and carbon monoxide to spray and refine the aluminum alloy liquid for 10 minutes, the amount of the mixed gas used is 3 cubic meters / ton of aluminum alloy liquid, and the pressure of the mixed gas is 0.3×10 5 Pa, the volume percentage of sulfur hexafluoride in the mixed gas is 11%, and the volume percentage of carbon monoxide is 3%. After refining, the aluminum alloy liquid is allowed to stand for 20 minutes; (3) the die-casting mold is installed on the die-casting machine, and the die-casting mold is preheated to 270°C; (4) a mold release agent is sprayed on the inner cavity of the die-casting mold, and then the die-casting machine is started to close the mold, and the clamping force is 9000 tons; (5) the 700°C aluminum alloy liquid is poured into the injection cylinder for vacuum die-casting into a rear floor blank, the vacuum degree is 230mbar, the injection pressure is 90MPa, the injection speed is 20m / s, the boost pressure is 800bar, and the holding time is 15s; (6) the die-casting machine's mold opening mechanism is started to open the die-casting mold, and the rear floor blank is taken out by a robot; (7) the runner and slag bag of the rear floor blank are cut off; (8) the rear floor blank is polished and machined to obtain the aluminum alloy rear floor of the new energy vehicle.

[0050] Embodiment 3:

[0051] The integrated die-casting molding method of the aluminum alloy rear floor of a new energy vehicle comprises the following steps in sequence: (1) melting and preparing an aluminum alloy liquid according to a composition composition of Si 13.2%, Cu 1.8%, Zn 2.1%, Mn 0.6%, Fe ≤ 0.2%, the remainder being Al and other unavoidable impurity elements, the individual content of other impurity elements ≤ 0.05%, and the total amount of other impurity elements ≤ 0.15%, and controlling the temperature of the aluminum alloy liquid at 700°C; (2) using argon gas with a purity of 99.99% and a refining agent with a weight of 0.1% of the aluminum alloy liquid to spray and refine the aluminum alloy liquid for 15 minutes, after the aluminum alloy liquid is allowed to stand for 40 minutes, using a mixed gas composed of argon gas with a purity of 99.99%, sulfur hexafluoride and carbon monoxide to spray and refine the aluminum alloy liquid for 15 minutes, the amount of the mixed gas used is 2 cubic meters / ton of aluminum alloy liquid, and the pressure of the mixed gas is 0.5×10 5Pa, the volume percentage of sulfur hexafluoride in the mixed gas is 9%, and the volume percentage of carbon monoxide is 5%. After refining, the aluminum alloy liquid is allowed to stand for 30 minutes; (3) the die-casting mold is installed on the die-casting machine, and the die-casting mold is preheated to 250°C; (4) a mold release agent is sprayed on the inner cavity of the die-casting mold, and then the die-casting machine is started to close the mold, and the clamping force is 7500 tons; (5) the 690°C aluminum alloy liquid is poured into the injection cylinder for vacuum die-casting into a rear floor blank, the vacuum degree is 250mbar, the injection pressure is 80MPa, the injection speed is 25m / s, the boost pressure is 700bar, and the holding time is 20s; (6) the die-casting machine's mold opening mechanism is started to open the die-casting mold, and the rear floor blank is taken out by a robot; (7) the runner and slag bag of the rear floor blank are cut off; (8) the rear floor blank is polished and machined to obtain the aluminum alloy rear floor of the new energy vehicle.

[0052] The refining agent in step (2) of Examples 1-3 of the present invention is composed of the following components in percentage by mass: NaCl 35.12%, NaF 19.84%, TiCl 3 16.51%, SrSO 4 10.06%, KPO 3 11.45%, Na 2 B 4 O 7 7.02%. The preparation method of the refining agent comprises the following steps in sequence:

[0053] (1) According to the composition and mass percentage of the refining agent, NaCl, NaF, TiCl3, SrSO4, KPO3, and Na2B4O7 with a purity of ≥99.8% are selected as raw materials for batching; (2) the ingredients are added into water at a temperature of 70° C. and stirred to dissolve into an aqueous solution, wherein the mass ratio of water to the ingredients is 1.2, and then the aqueous solution is heated to 100° C. to evaporate and obtain solid crystals; (3) the solid crystals are crushed into powders with a particle size of less than 2 mm, and the powders are dried and dehydrated at 160° C. for 4 hours to obtain the refining agent.

[0054] Comparative Example 1:

[0055] The integrated die-casting method for the aluminum alloy rear floor of a new energy vehicle in this comparative example is the same as that in Example 1, except that in step (1), the aluminum alloy liquid is smelted and prepared according to the composition composition by mass percentage of Si 12.96%, Cu 1.24%, Zn 1.85%, Mn 0.74%, Fe≤0.2%, the balance being Al and other inevitable impurity elements, the single content of other impurity elements ≤0.05%, and the total amount of other impurity elements ≤0.15%.

[0056] Comparative Example 2:

[0057] The integrated die-casting method for the aluminum alloy rear floor of a new energy vehicle in this comparative example is the same as that in Example 1, except that in step (1), the aluminum alloy liquid is smelted and prepared according to the composition composition by mass percentage of Si 12.96%, Cu 2.03%, Zn 1.05%, Mn 0.74%, Fe≤0.2%, the balance being Al and other inevitable impurity elements, the single content of other impurity elements ≤0.05%, and the total amount of other impurity elements ≤0.15%.

[0058] Comparative Example 3:

[0059] The integrated die-casting method of the aluminum alloy rear floor of a new energy vehicle in this comparative example is the same as that in Example 1, except that the refining agent used is an existing conventional refining agent, which is composed of the following components in percentage by mass: NaCl 36.13%, KCl 15.42%, CaF2 16.84%, NaF19.24%, and C2Cl6 12.37%. The refining agent is obtained by directly crushing and mixing the raw materials after drying and dehydration.

[0060] Comparative Example 4:

[0061] The integrated die-casting method for the aluminum alloy rear floor of a new energy vehicle in this comparative example is the same as that in Example 1, except that in step (2), instead of using a mixed gas consisting of argon, sulfur hexafluoride and carbon monoxide to spray and refine the aluminum alloy liquid, argon with a purity of 99.99% is used to spray and refine the aluminum alloy liquid.

[0062] Verification example:

[0063] The hydrogen content and slag content of the aluminum alloy liquid before die casting of Examples 1-3 and Comparative Examples 1-4 were detected by using a HDA-V hydrogen meter and an Analyze PoDFA slag meter. The results are shown in Table 1. As can be seen from Table 1, the hydrogen content of the aluminum alloy liquid before die casting of Examples 1-3 and Comparative Examples 1-2 is less than 0.14 ml / 100 gAl, and the slag content is less than 0.08 mm 2 / kgAl. Comparative Example 3 uses conventional refining agent spraying refining, and Comparative Example 4 does not use mixed gas spraying refining, resulting in a relatively high gas slag content in the aluminum alloy liquid. By comparison, it can be seen that the technical solution of the present invention can significantly reduce the gas slag content of the aluminum alloy liquid before die casting and improve the cleanliness of the floor after die casting of the aluminum alloy.

[0064] Table 1 Hydrogen content and slag content of aluminum alloy liquid

[0065]

[0066]

[0067] Samples were taken from the die-cast aluminum alloy rear floor panels obtained in Examples 1-3 and Comparative Examples 1-4 to test the room temperature tensile mechanical properties of the aluminum alloy samples in the non-heat-treated state, and the results are shown in Table 2. As can be seen from Table 2, the tensile strength of the aluminum alloy rear floor panels of Examples 1-3 is higher than 350MPa, the yield strength is higher than 300MPa, and the elongation after fracture is greater than 10%, which has the advantages of high strength and good plasticity, and meets the mechanical properties required by the integrated die-casting of the aluminum alloy rear floor panels of new energy vehicles. Due to the insufficient Cu content of the aluminum alloy in Comparative Example 1 and the insufficient Zn content of the aluminum alloy in Comparative Example 2, the tensile strength of the aluminum alloy rear floor panels of Comparative Examples 1 and 2 is lower than 320MPa, and the yield strength is lower than 270MPa, which does not meet the mechanical properties required by the integrated die-casting of the aluminum alloy rear floor panels of new energy vehicles. Since Comparative Example 3 uses commercially available conventional refining agents to spray refine the aluminum alloy liquid, and Comparative Example 4 does not use mixed gas to spray refine the aluminum alloy liquid, the tensile strength of the aluminum alloy rear floors of Comparative Examples 3 and 4 is lower than 330 MPa, the yield strength is lower than 280 MPa, and the elongation after fracture is lower than 8%, which also does not meet the mechanical properties required for the integrated die-casting of the aluminum alloy rear floor of new energy vehicles.

[0068] Table 2 Tensile mechanical properties of aluminum alloy rear floor

[0069]

Claims

1. A method for integrated die-casting of aluminum alloy rear floor of new energy vehicle, characterized in that: The following steps are included in sequence: (1) smelting and preparing aluminum alloy liquid, and controlling the temperature of the aluminum alloy liquid at 700-720° C.; (2) performing refining agent spray refining and mixed gas spray refining degassing and deslagging on the aluminum alloy liquid; (3) Installing the die-casting mold on the die-casting machine and preheating the die-casting mold; (4) Spray a release agent on the inner cavity of the die-casting mold, and then start the die-casting machine to close the mold; (5) pouring aluminum alloy liquid into the injection cylinder and vacuum die-casting it into a rear floor blank; (6) Open the die-casting mold and take out the rear floor blank; (7) Cut off the runners and slag bags of the floor blank; (8) Grinding and machining the rear floor blank to obtain the aluminum alloy rear floor of the new energy vehicle.

2. The integrated die-casting method for the aluminum alloy rear floor of a new energy vehicle according to claim 1, characterized in that: The aluminum alloy liquid in step (1) is composed of the following components in mass percentage: Si 12.8-13.2%, Cu 1.8-2.2%, Zn1.6-2.1%, Mn 0.6-0.9%, Fe≤0.2%, and the balance is Al and other inevitable impurity elements, the individual content of other impurity elements is ≤0.05%, and the total amount of other impurity elements is ≤0.15%.

3. The integrated die-casting method for the aluminum alloy rear floor of a new energy vehicle according to claim 1 is characterized in that: The carrier gas for the refining agent spraying in step (2) is argon with a purity of ≥99.99%, the amount of the refining agent is 0.1-0.2% of the weight of the aluminum alloy liquid, the spraying refining time is 15-20 minutes, and the aluminum alloy liquid is left to stand for 30-40 minutes.

4. The integrated die-casting method for the aluminum alloy rear floor of a new energy vehicle according to claim 1, characterized in that: The refining agent in step (2) is composed of the following components in mass percentage: NaCl 35.12%, NaF 19.84%, TiCl3 16.51%, SrSO4 10.06%, KPO3 11.45%, and Na2B4O7 7.02%.

5. The integrated die-casting method for the aluminum alloy rear floor of a new energy vehicle according to claim 1 or 4, characterized in that: The preparation method of the refining agent in step (2) comprises the following steps in sequence: (1) selecting NaCl, NaF, TiCl3, SrSO4, KPO3, and Na2B4O7 with a purity of ≥99.8% as raw materials for batching according to the composition and mass percentage of the refining agent; (2) adding the ingredients into water at a temperature of 70°C and stirring to dissolve them into an aqueous solution, wherein the mass ratio of water to the ingredients is 1.2, and then heating the aqueous solution to 100°C to evaporate the aqueous solution to obtain solid crystals; (3) crushing the solid crystals into powder with a particle size of less than 2 mm, and drying and dehydrating the powder at 160°C for 4 hours to obtain the refining agent.

6. The integrated die-casting method for the aluminum alloy rear floor of a new energy vehicle according to claim 1, characterized in that: The amount of mixed gas used in the mixed gas blowing refining in step (2) is 2-3 cubic meters per ton of aluminum alloy liquid, and the pressure of the mixed gas is (0.3-0.5)×10 5 Pa, the blowing refining time is 10-15 minutes, and the aluminum alloy liquid standing time is 20-30 minutes.

7. The integrated die-casting method for the aluminum alloy rear floor of a new energy vehicle according to claim 1, characterized in that: The mixed gas in step (2) is composed of argon gas with a purity of ≥99.99%, sulfur hexafluoride and carbon monoxide, wherein the volume percentage of sulfur hexafluoride in the mixed gas is 9-11%, and the volume percentage of carbon monoxide is 3-5%.

8. The integrated die-casting method for the aluminum alloy rear floor of a new energy vehicle according to claim 1, characterized in that: The preheating temperature of the die-casting mold in step (3) is 250-270°C.

9. The integrated die-casting method for the aluminum alloy rear floor of a new energy vehicle according to claim 1, characterized in that: The clamping force of the die-casting mold in step (4) is 7500-9000 tons.

10. The integrated die-casting method for the aluminum alloy rear floor of a new energy vehicle according to claim 1, characterized in that: The pouring temperature of the aluminum alloy liquid in step (5) is 690-700°C, the vacuum degree of vacuum die casting is 230-250mbar, the injection pressure is 80-90MPa, the injection speed is 20-25m / s, the boost pressure is 700-800bar, and the holding time is 15-20s.

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