High-toughness die-casting aluminum alloy and waste aluminum regeneration method thereof

Abstract

The invention discloses a high-toughness die-casting aluminum alloy and a waste aluminum regeneration method thereof. The die-casting aluminum alloy is composed of, by mass, 11.5%-12.5% of Si, 1.6%-2.5% of Cu, 1.1%-2.2% of Zn, 0.6%-0.8% of Mn, 0.04%-0.08% of Ti, 0.003%-0.006% of Sr, 0.001%-0.003% of P, smaller than or equal to 0.2% of Fe and the balance Al and inevitable impurity elements. The waste aluminum regeneration method sequentially comprises the following steps: carrying out sorting pretreatment on waste aluminum, heating and melting the waste aluminum into molten aluminum alloy, carrying out online detection and adjustment on components of the molten aluminum alloy, carrying out powder spraying refining and blowing refining on the molten aluminum alloy, and finally carrying out hydraulic casting on the aluminum alloy to obtain the aluminum alloy. The die-casting aluminum alloy is regenerated through the waste aluminum, the production cost of the die-casting aluminum alloy is reduced, low-carbon production of the die-casting aluminum alloy is achieved, and the die-casting aluminum alloy has excellent casting fluidity and mechanical performance and meets the die-casting requirement of a large aluminum alloy structural part.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy preparation, and in particular relates to a high-strength and toughness die-casting aluminum alloy and a waste aluminum regeneration method thereof. Background Art

[0002] Aluminum alloy die casting is the process of injecting aluminum alloy hydraulically into a metal mold under high pressure to cool and solidify it into aluminum alloy parts. Aluminum alloy die casting has high production efficiency and is suitable for the production of aluminum alloy parts with complex shapes. It is widely used in the production of automotive parts. Automobiles have become the largest application market for aluminum alloy die castings. According to statistics from the China Foundry Industry Association, the output of automotive aluminum alloy die castings in my country will reach more than 6 million tons in 2023. With the rapid development of new energy vehicles in my country, a large number of new energy vehicles have begun to use large-tonnage die casting to produce large aluminum alloy structural parts in recent years, integrating dozens of traditional parts into one die casting, which is called integrated die casting. In order to achieve integrated die casting of large aluminum alloy structural parts, new requirements are put forward for die-casting aluminum alloy materials, requiring die-casting aluminum alloys to have high strength and plasticity without heat treatment to avoid deformation of large aluminum alloy structural parts caused by heat treatment. In addition, with the implementation of the dual carbon policy, it is required to achieve low-carbon production of die-casting aluminum alloy automotive parts to reduce carbon taxes and production costs.

[0003] The Chinese patent document with publication number CN117845107A discloses a heat-treatment-free die-cast aluminum alloy, which is composed of the following components by mass percentage: Si 6.3-9%, Mg 0.15-0.5%, Cu 0.15-0.6%, Fe 0.1-0.25%, Mn 0.5-0.75%, Ti0.05-0.25%, Sr 0.02-0.06%, Zr≤0.15%, Sb≤0.3%, other impurity elements≤0.05%, and the balance is Al. The tensile strength of the die-cast aluminum alloy is 287-312MPa, the yield strength is 130-153MPa, and the elongation at break is 11.0-14.5%.

[0004] The Chinese patent document with publication number CN117684053A discloses a near-eutectic die-casting aluminum-silicon alloy material free of heat treatment, which is composed of the following components by mass percentage: Si 9.6-11.8%, Fe≤0.15%, Cu≤0.03%, Mn 0.3-0.8%, Mg 0-0.2%, Zn≤0.05%, Ti 0-0.15%, Zr 0-0.25%, rare earth 0-0.2%, Sr 0.01-0.05%, Pb≤0.1%, Sn≤0.01%, Cd≤0.01%, seed or modifier 0.05%-0.5%, and the rest is Al, the seed is TCB seed, and the modifier is Al-Sr-RE composite alloy. The tensile strength of the die-cast state is 270-300MPa, the yield strength is 120-145MPa, and the elongation is 10-16%.

[0005] The Chinese patent document with publication number CN117737522A discloses a Nb-containing heat-free aluminum-silicon alloy for new energy vehicles and a preparation method thereof. The aluminum-silicon alloy has the following mass fraction composition: Si 7.5-9.5%, Mg 0.15-0.25%, Co 0.1-0.3%, Mn 0.3-0.5%, V 0.01-0.1%, Ti 0.05-0.1%, Nb 0.03-0.1%, B0.01-0.03%, Sr0.01-0.02%, RE 0.01-0.1%, Fe≤0.2%, other uncontrollable impurity elements ≤0.5%, and the balance is Al. The tensile strength of the aluminum-silicon alloy is 306.49-310.17MPa, the yield strength is 201.7-208.45MPa, and the elongation at break is 7.88-8.04%.

[0006] The Chinese patent document with publication number CN116987936A discloses an Al-Si series heat-treatment-free aluminum alloy, which is composed of the following components by mass fraction: Si 6-9%, Cu 0-0.3%, Mn 0.4-0.8%, Fe 0-0.25%, Mg 0.1-0.4%, Zn 0-0.1%, Ni 0-0.1%. The aluminum alloy has a tensile strength of 300-320 MPa, a yield strength of 142-158 MPa, and an elongation at break of 12.5-17%.

[0007] Based on the results of literature retrieval and production practice experience, the existing aluminum alloys used for die-casting of large aluminum alloy structural parts still have the following problems: (1) The existing die-casting aluminum alloys are mainly aluminum-silicon alloys, and still have the problem of low yield strength or plasticity, which makes it difficult to meet the needs of large aluminum alloy automotive structural parts. (2) The existing die-casting aluminum alloys are mainly made of primary aluminum ingots as raw materials and are prepared by adding alloying elements. As we all know, primary aluminum ingots are obtained by electrolysis of alumina, and electrolytic aluminum is energy-intensive, which makes the preparation and production of die-casting aluminum alloys still have high carbon emissions and do not meet the requirements of low-carbon production. Therefore, the existing die-casting aluminum alloys and their preparation methods still need 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 a high-strength and toughness die-cast aluminum alloy and a method for regenerating waste aluminum thereof, and adopts waste aluminum to prepare the die-cast aluminum alloy. By optimizing the component composition and preparation method of the die-cast aluminum alloy, the strength and plasticity of the die-cast aluminum alloy are improved, the production cost of the die-cast aluminum alloy is reduced, the low-carbon production of the die-cast aluminum alloy is realized, and the die-casting production requirements of large aluminum alloy structural parts are met.

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

[0010] The first aspect of the present invention provides a high-strength and toughness die-casting aluminum alloy, which is characterized in that the die-casting aluminum alloy is composed of the following components in mass percentage: Si 11.5-12.5%, Cu 1.6-2.5%, Zn 1.1-2.2%, Mn 0.6-0.8%, Ti 0.04-0.08%, Sr 0.003-0.006%, P 0.001-0.003%, 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 ≤ 0.2%.

[0011] Among them, the main function of Si is to enhance the filling fluidity of die-cast aluminum alloys. Die-cast aluminum alloys must have excellent filling fluidity to meet the die-casting filling requirements of large, complex, thin-walled aluminum alloy structural parts. Si can form an Al+Si eutectic phase with Al during the solidification process of the die-cast aluminum alloy, thereby enhancing the filling fluidity of the die-cast aluminum alloy. A Si content lower than 11.5% will result in insufficient filling fluidity, and it will be impossible to obtain large, complex, thin-walled aluminum alloy structural parts that are fully filled. Too high a Si content will cause the plasticity of the die-cast aluminum alloy to drop significantly. Preferably, the Si content is 11.5-12.5%.

[0012] The main function of Cu is to enhance the strength of die-cast aluminum alloy. Cu has a good solid solution strengthening effect in die-cast aluminum alloy, which can significantly enhance the strength of die-cast aluminum alloy. However, too high Cu content will also increase the hot cracking tendency of die-cast aluminum alloy and reduce the corrosion resistance of die-cast aluminum alloy. Preferably, the Cu content is 1.6-2.5%.

[0013] The main function of Zn is to further enhance the filling fluidity of die-cast aluminum alloy and enhance the strength of die-cast aluminum alloy. However, the Zn content should not be too high, otherwise it will increase the thermal cracking tendency of die-cast aluminum alloy, which is easy to cause thermal cracking defects in large and complex thin-walled aluminum alloy structural parts. Preferably, the Zn content is 1.1-2.2%.

[0014] The main function of Mn is to enhance the strength of die-cast aluminum alloys through dispersion strength. Mn can form MnAl 6 Particles, MnAl 6 The particles dispersed in the die-cast aluminum alloy can not only enhance the strength of the die-cast aluminum alloy but also improve the high temperature resistance of the die-cast aluminum alloy. Preferably, the Mn content in the die-cast aluminum alloy is 0.6-0.8%.

[0015] The main function of Ti is to refine the α-Al grains and improve the filling fluidity of the die-casting aluminum alloy. When Ti is not added, the α-Al grains are coarse and dendritic when the die-casting aluminum alloy solidifies, which will hinder the flow of the eutectic liquid phase and cause the filling fluidity of the die-casting aluminum alloy to decrease. When the α-Al grains are refined and transformed from coarse and dendritic to granular or spherical, the filling fluidity of the die-casting aluminum alloy is greatly improved. If the Ti content is too low, the refining effect is not obvious. However, if the Ti content is too high, it will not significantly improve the grain refining effect, but will increase the production cost. Preferably, the Ti content is 0.04-0.08%.

[0016] The main function of Sr is to refine the modified eutectic Si phase. In die-cast aluminum alloys, the eutectic Si phase is usually distributed in the aluminum alloy matrix in the form of coarse flakes, which not only reduces the mold filling fluidity of the die-cast aluminum alloy, but also splits the die-cast aluminum alloy matrix, reducing the strength and plasticity of the die-cast aluminum alloy. Adding 0.003-0.006% Sr can change the morphology of the eutectic Si phase from coarse flakes to fine and uniform particles or fibers, which can significantly improve the mold filling fluidity, strength and plasticity of the die-cast aluminum alloy.

[0017] The main function of P is to refine the modified primary Si phase. In addition to forming the eutectic Si phase, Si also forms the primary Si phase in the die-cast aluminum alloy. The primary Si phase is usually in a coarse block shape, which not only reduces the mold filling fluidity of the die-cast aluminum alloy, but also reduces the strength and plasticity of the die-cast aluminum alloy. Adding 0.001-0.003% P can change the morphology of the primary Si phase from coarse blocks to fine and uniform particles, which can significantly improve the mold filling fluidity, strength and plasticity of the die-cast aluminum alloy.

[0018] Fe is an inevitable impurity element in die-cast aluminum alloys. It usually exists in the form of coarse needle-like Fe-rich phases, which will seriously split the matrix of the die-cast aluminum alloy and reduce the strength and plasticity of the die-cast aluminum alloy. Therefore, the content of impurity element Fe must be strictly controlled to make the Fe content ≤0.2%.

[0019] A second aspect of the present invention provides a method for recycling waste aluminum of high-strength and toughness die-cast aluminum alloy, which is characterized by comprising the following steps in sequence:

[0020] Step 1: sorting and pre-treating the scrap aluminum to obtain scrap aluminum that can be recycled;

[0021] Step 2: heating and melting the pre-processed scrap aluminum into aluminum alloy liquid;

[0022] Step 3: Online detection and adjustment of the chemical composition of the aluminum alloy liquid;

[0023] Step 4: using argon gas and refining agent to spray and refine the aluminum alloy liquid;

[0024] Step 5: Using mixed gas to spray and refine the aluminum alloy liquid;

[0025] Step six: hydraulically casting the aluminum alloy into an aluminum alloy to obtain the die-cast aluminum alloy.

[0026] Furthermore, the sorting and pretreatment of the scrap aluminum described in step one is to sort out and remove the iron, rubber, plastic, wood, stone, mud and other inclusions carried or embedded in the scrap aluminum to obtain scrap aluminum that can be recycled. The iron includes iron wire, iron nails, iron blocks, etc. The sorting and pretreatment method can be manual picking and removal, or mechanical. The mechanical method usually uses a crusher to crush the scrap aluminum, and then removes the inclusions in the scrap aluminum by magnetic separation, wind separation or water separation. For scrap aluminum without inclusions, it can be directly recycled without sorting, but scrap aluminum containing inclusions must be sorted and pretreated. The cost of manual sorting and pretreatment is low, but the disadvantage is that the labor intensity is relatively high. The mechanical method is suitable for mass production, but the disadvantage is that the investment is large and the cost is high. Manual and mechanical methods each have their own advantages and disadvantages. It can be decided whether to use manual sorting or mechanical sorting according to the specific circumstances of the scrap aluminum and the enterprise.

[0027] Furthermore, in step 2, heating and melting the waste aluminum into aluminum alloy liquid is to put the waste aluminum into an aluminum melting furnace and heat it at 720-760°C to melt it into aluminum alloy liquid. The heating temperature should not be lower than 720°C, otherwise the melting rate of the waste aluminum is too slow. The heating temperature should not be higher than 760°C, as too high a temperature will aggravate the oxidation and burning of the waste aluminum. The aluminum melting furnace can be a regenerative gas-fired aluminum melting furnace or a medium frequency induction furnace, among which the regenerative gas-fired aluminum melting furnace has high thermal utilization efficiency, which is conducive to reducing energy consumption and production costs, and is currently a widely used aluminum melting furnace for die-casting aluminum alloy enterprises. The medium frequency induction furnace has a high heating and melting speed and high production efficiency, but it consumes a lot of electricity, which is not conducive to reducing energy consumption and production costs. Therefore, a regenerative gas-fired aluminum melting furnace is preferably used to heat and melt the waste aluminum.

[0028] Furthermore, the online detection of the chemical composition of the aluminum alloy liquid described in step three is to cast the aluminum alloy liquid into an aluminum alloy sample, and after turning and flattening, use a desktop direct-reading spectrometer or a handheld spectrometer to detect the chemical composition of the aluminum alloy sample on site. The online adjustment of the chemical composition of the aluminum alloy liquid is to compare the chemical composition of the aluminum alloy sample with the chemical composition requirements of the target die-casting aluminum alloy. If the content of a chemical element is lower than the chemical composition requirements of the target die-casting aluminum alloy, the content of the chemical element in the aluminum alloy liquid is increased by adding pure metal or alloy of the chemical element. If the content of a chemical element exceeds the chemical composition requirements of the target die-casting aluminum alloy, the content of the element in the aluminum alloy liquid is diluted by adding aluminum ingots, so that the chemical composition of the aluminum alloy liquid meets the chemical composition of the target die-casting aluminum alloy.

[0029] Furthermore, the purity of the argon gas in step 4 is ≥99.99%, the amount of the refining agent is 0.1-0.2% of the weight of the aluminum alloy liquid, the temperature of the aluminum alloy liquid during spray refining is 700-720°C, and the spray refining time is 15-20 minutes.

[0030] Since the surface of scrap aluminum is inevitably covered or adhered with paint, coating, oil and water vapor, these coverings and water vapor enter the aluminum melting furnace with the scrap aluminum, and after heating and melting, the aluminum alloy liquid is involved in the inclusions, and the water vapor decomposes and causes the aluminum alloy liquid to absorb hydrogen, so that the aluminum alloy contains a large amount of slag and hydrogen. If the slag and hydrogen removal treatment is not carried out, the slag hydrogen will remain in the aluminum alloy to form defects such as pores, inclusions and looseness, reduce the quality of the aluminum alloy, and deteriorate the mechanical properties and corrosion resistance of the aluminum alloy. Therefore, in order to obtain die-cast aluminum alloy that meets the requirements, the aluminum alloy liquid must be refined, deslaged and dehydrogenated.

[0031] The 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 in the aluminum alloy liquid are taken out of the aluminum alloy liquid. The deslagging and degassing effect of spray refining is related to the purity of argon, the amount of refining agent, the quality of refining agent, the temperature of the aluminum alloy liquid and the spray refining time. The higher the purity of argon, the greater the amount of refining agent, the longer the spray refining time, the better the deslagging and dehydrogenation effect, but the production cost will also increase accordingly. If the temperature of the aluminum alloy liquid is too high or 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 removing the scum on the surface of the aluminum alloy liquid, 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 standing for a period of time so that inclusions and bubbles in the aluminum alloy liquid have sufficient time to escape. The standing time of the aluminum alloy liquid is not less than 30 minutes, and preferably the standing time of the aluminum alloy liquid is 30-40 minutes.

[0032] Furthermore, the refining agent in step 4 is composed of the following components in mass percentage: 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%.

[0033] The deslagging and dehydrogenation effect of powder spray refining is closely related to the composition of the refining agent. The existing refining agent is mainly obtained by crushing and mixing fluoride salts and chloride salts, which leads to low deslagging and dehydrogenation efficiency of the refining agent, large emission of irritating smoke and single function, which makes it difficult to meet the needs of high-performance die-casting aluminum alloys. In order to improve the deslagging and dehydrogenation effect of powder spray refining, the present invention has developed a highly efficient and environmentally friendly multifunctional powder refining agent, in which NaCl reacts with aluminum liquid to generate AlCl with a boiling point of only 180°C. 3 , AlCl 3 During the floating process, the bubbles absorb and capture inclusions and hydrogen in the aluminum alloy liquid, and then escape from the aluminum alloy liquid together, playing a role in removing slag and hydrogen. 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 the inclusions and the aluminum alloy liquid, promote the separation of inclusions such as alumina from the aluminum alloy liquid, and enhance the slag removal function of the refining agent. TiCl 3 Reacts with aluminum alloy liquid to form AlCl 3 Bubbles, AlCl 3During the floating process, the bubbles absorb and capture inclusions and hydrogen in the aluminum alloy liquid, enhancing the slag and hydrogen removal capabilities of the refining agent. The Ti element obtained by the reaction can refine the grains of the aluminum alloy and improve the strength and plasticity of the aluminum alloy. 4 Reacts with aluminum alloy liquid to generate SO 2 Bubbles, SO 2 During the floating process, the bubbles can absorb and capture inclusions and hydrogen in the aluminum liquid, enhancing the slag and hydrogen removal capabilities of the refining agent. The Sr element obtained by the reaction can refine the eutectic Si phase of the modified aluminum alloy and improve the strength and plasticity of the aluminum alloy. 3 It reacts with aluminum alloy liquid to generate P element, which can refine the primary Si phase of the modified aluminum alloy and improve the strength, plasticity and wear resistance of the aluminum alloy. 2 B 4 O 7 By reacting with aluminum liquid to generate element B, the coarse Fe-rich phase of the modified aluminum alloy can be refined, eliminating the harm of the coarse Fe-rich phase to the strength and plasticity of the aluminum alloy, and improving the strength and plasticity of the die-cast aluminum alloy.

[0034] Furthermore, the preparation method of the refining agent in step 4 comprises the following steps in sequence:

[0035] (1) According to the composition and mass percentage of the refining agent, select NaCl, NaF, TiCl with a purity of ≥99.8% 3 、SrSO 4 , KPO 3 、Na 2 B 4 O 7 The invention relates to a method for preparing raw materials; (2) adding the ingredients into water at a temperature of 70° C. and stirring to dissolve the ingredients 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 powders with a particle size of less than 2 mm, and drying and dehydrating the powders at 160° C. for 4 hours to obtain the refining agent.

[0036] The deslagging and dehydrogenation effects of the refining agent are closely related to its preparation method. Existing refining agents are usually obtained by directly mixing chloride salts and fluoride salts after mechanical crushing. The components of this refining agent exist independently of each other, the melting point of the refining agent is high, and there is a lack of synergy between the components, resulting in low deslagging and dehydrogenation efficiency of the refining agent. The present invention breaks through the traditional preparation method and adopts a solution evaporation 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 easier to dissolve in the aluminum alloy liquid, and playing a synergistic role during refining, which can significantly enhance the deslagging and dehydrogenation capabilities of the refining agent.

[0037] Furthermore, the mixed gas in step five 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%.

[0038] In the existing gas injection refining technology, inert gas nitrogen or argon, or a mixture of inert gas and chlorine, is usually injected 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.

[0039] 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.

[0040] Furthermore, the amount of the mixed gas in step 5 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 temperature of the aluminum alloy liquid during spray refining is 700-720℃, and the spray refining time is 10-15 minutes.

[0041] Although the slag hydrogen content of aluminum alloy liquid is greatly reduced by powder spray refining, 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, making the dehydrogenation always in a dynamic equilibrium process. It is difficult for powder spray refining to reduce the hydrogen content of aluminum alloy liquid to below 0.2ml / 100gAl. Therefore, in order to obtain highly clean aluminum alloy liquid, air blowing refining dehydrogenation and slag removal treatment is also required.

[0042] 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 also related to the amount of the mixed gas, the temperature of the aluminum alloy liquid and the spray refining time. The greater the amount of the mixed gas, the longer the spray refining time, the better the deslag and hydrogen removal effect of the spray refining, but the production cost will also increase accordingly. If the temperature of the aluminum alloy liquid is too high or 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 removing the scum on the surface of the aluminum alloy liquid, 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 the coating agent is applied, 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. The standing time of the aluminum alloy liquid cannot be less than 20 minutes. As a preferred embodiment, the standing time of the aluminum alloy liquid is 20-30 minutes. Through mixed gas spray refining, the hydrogen content of the aluminum alloy liquid can be reduced to less than 0.15ml / 100gAl, and the inclusion content can be reduced to 0.1mm2 / kgAl or less, thereby greatly improving the cleanliness of the die-casting aluminum alloy liquid.

[0043] Further, the aluminum alloy is hydraulically cast into aluminum alloy in step 6 under the conditions that the pouring temperature of the aluminum alloy liquid is 710-730°C, the mold temperature is 200-250°C, the vacuum degree is 200-300mbar, the filling 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 710°C, the mold temperature cannot be lower than 200°C, the vacuum degree cannot be less than 200mbar, the filling speed cannot be lower than 20m / s, and the boost pressure cannot be lower than 700bar, otherwise it is possible to cause incomplete filling of large aluminum alloy parts or surface cold shut defects, and it is impossible to obtain large aluminum alloy parts with dense organization. However, the pouring temperature and mold 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.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The die-cast aluminum alloy of the present invention has a tensile strength of not less than 350MPa, a yield strength of not less than 300MPa, and an elongation after fracture of not less than 10% in a non-heat-treated state. It also has excellent filling fluidity and meets the requirements of integrated die-casting of large aluminum alloy structural parts. (2) The present invention realizes the recycling of waste aluminum of high-strength and toughness die-cast aluminum alloy, improves the utilization value of waste aluminum, reduces the production cost of die-cast aluminum alloy, and realizes the low-carbon die-casting production of large aluminum alloy structural parts. (3) The high-efficiency, environmentally friendly and multifunctional powder refining agent developed by the present invention overcomes the problems of low degassing and slag removal efficiency and single function of traditional refining agents, and can not only greatly improve the cleanliness of die-cast aluminum alloy liquid, but also refine and modify the die-cast aluminum alloy to improve the mechanical properties of the die-cast aluminum alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is the microstructure of the die-cast aluminum alloy in Example 1 of the present invention.

[0047] Figure 2 This is the microstructure of the die-cast aluminum alloy of Comparative Example 4. DETAILED DESCRIPTION

[0048] 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.

[0049] Embodiment 1:

[0050] The die-casting aluminum alloy is composed of the following components in mass percentage: Si 11.89%, Cu 2.12%, Zn 1.67%, Mn 0.72%, Ti 0.06%, Sr 0.005%, P 0.002%, Fe≤0.2%, the balance is Al and other unavoidable impurity elements, the individual content of other impurity elements is ≤0.05%, and the total amount of other impurity elements is ≤0.2%. The waste aluminum recycling method comprises the following steps in sequence:

[0051] Step 1: Pre-process the scrap aluminum by sorting it to remove the iron, rubber, plastic, wood, stone, mud and other impurities carried or embedded in the scrap aluminum to obtain scrap aluminum that can be recycled;

[0052] Step 2: Put the scrap aluminum after sorting and pretreatment into a regenerative gas-fired aluminum melting furnace and heat it at 740°C to melt it into aluminum alloy liquid; Step 3: Use a direct reading spectrometer to perform online detection and adjustment on the chemical composition of the aluminum alloy liquid; Step 4: Use argon with a purity of 99.99% and a refining agent of 0.15% by weight of the aluminum alloy liquid to spray and refine the aluminum alloy liquid at 710°C for 18 minutes, sprinkle a covering agent after slagging, and then let it stand for 35 minutes; Step 5: Use a mixed gas composed of argon, sulfur hexafluoride and carbon monoxide to spray and refine the aluminum alloy liquid at 710°C for 12 minutes, the purity of argon, sulfur hexafluoride and carbon monoxide is 99.99%, the volume percentage of sulfur hexafluoride in the mixed gas is 10%, the volume percentage of carbon monoxide is 4%, the amount of the mixed gas is 2.5 cubic meters / ton of aluminum alloy liquid, and the pressure of the mixed gas is 0.4×10 5 Pa, sprinkle covering agent after slagging, and then let it stand for 25 minutes; step six: hydraulically cast the aluminum alloy into aluminum alloy under the conditions of a pouring temperature of the aluminum alloy liquid of 720°C, a mold temperature of 225°C, a vacuum degree of 250mbar, a filling speed of 23m / s, a boost pressure of 760bar, and a holding time of 18s to obtain the die-cast aluminum alloy.

[0053] Embodiment 2:

[0054] The die-casting aluminum alloy is composed of the following components in mass percentage: Si 11.5%, Cu 2.5%, Zn 1.1%, Mn 0.8%, Ti 0.04%, Sr 0.006%, P 0.001%, Fe ≤ 0.2%, the balance is Al and other unavoidable impurity elements, the individual content of other impurity elements is ≤ 0.05%, and the total amount of other impurity elements is ≤ 0.2%. The waste aluminum recycling method comprises the following steps in sequence:

[0055] Step 1: Pre-process the scrap aluminum by sorting it to remove the iron, rubber, plastic, wood, stone, mud and other impurities carried or embedded in the scrap aluminum to obtain scrap aluminum that can be recycled;

[0056] Step 2: Put the scrap aluminum after sorting and pretreatment into a regenerative gas-fired aluminum melting furnace and heat it at 760°C to melt it into aluminum alloy liquid; Step 3: Use a direct reading spectrometer to perform online detection and adjustment on the chemical composition of the aluminum alloy liquid; Step 4: Use argon with a purity of 99.99% and a refining agent of 0.2% by weight of the aluminum alloy liquid to spray and refine the 700°C aluminum alloy liquid for 20 minutes, sprinkle a covering agent after slagging, and then let it stand for 30 minutes; Step 5: Use a mixed gas composed of argon, sulfur hexafluoride and carbon monoxide to spray and refine the 700°C aluminum alloy liquid for 15 minutes, the purity of argon, sulfur hexafluoride and carbon monoxide is 99.99%, the volume percentage of sulfur hexafluoride in the mixed gas is 9%, the volume percentage of carbon monoxide is 5%, the amount of the mixed gas is 2 cubic meters / ton of aluminum alloy liquid, and the pressure of the mixed gas is 0.5×10 5 Pa, sprinkle the covering agent after slagging, and then let it stand for 20 minutes; step six: hydraulically cast the aluminum alloy into an aluminum alloy under the conditions of a pouring temperature of the aluminum alloy liquid of 710°C, a mold temperature of 250°C, a vacuum degree of 300mbar, a filling speed of 20m / s, a boost pressure of 800bar, and a holding time of 20s to obtain the die-cast aluminum alloy.

[0057] Embodiment 3:

[0058] The die-casting aluminum alloy is composed of the following components in mass percentage: Si 12.5%, Cu 1.6%, Zn 2.2%, Mn 0.6%, Ti 0.08%, Sr 0.003%, P 0.003%, Fe ≤ 0.2%, the balance is Al and other unavoidable impurity elements, the individual content of other impurity elements is ≤ 0.05%, and the total amount of other impurity elements is ≤ 0.2%. The waste aluminum recycling method comprises the following steps in sequence:

[0059] Step 1: Pre-process the scrap aluminum by sorting it to remove the iron, rubber, plastic, wood, stone, mud and other impurities carried or embedded in the scrap aluminum to obtain scrap aluminum that can be recycled;

[0060] Step 2: Put the scrap aluminum after sorting and pretreatment into a regenerative gas-fired aluminum melting furnace and heat it at 720°C to melt it into aluminum alloy liquid; Step 3: Use a direct reading spectrometer to perform online detection and adjustment on the chemical composition of the aluminum alloy liquid; Step 4: Use argon with a purity of 99.99% and a refining agent of 0.1% by weight of the aluminum alloy liquid to spray and refine the aluminum alloy liquid at 720°C for 15 minutes, sprinkle a covering agent after slagging, and then let it stand for 40 minutes; Step 5: Use a mixed gas composed of argon, sulfur hexafluoride and carbon monoxide to spray and refine the aluminum alloy liquid at 720°C for 10 minutes, the purity of argon, sulfur hexafluoride and carbon monoxide is 99.99%, the volume percentage of sulfur hexafluoride in the mixed gas is 11%, the volume percentage of carbon monoxide is 3%, the amount of the mixed gas is 3 cubic meters / ton of aluminum alloy liquid, and the pressure of the mixed gas is 0.3×10 5 Pa, sprinkle the covering agent after slag removal, and then let it stand for 30 minutes; step six: hydraulically cast the aluminum alloy into an aluminum alloy under the conditions of a pouring temperature of the aluminum alloy liquid of 730°C, a mold temperature of 200°C, a vacuum degree of 200mbar, a filling speed of 25m / s, a boost pressure of 700bar, and a holding time of 15s to obtain the die-cast aluminum alloy.

[0061] The refining agent described in Examples 1-3 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: (1) according to the composition and mass percentage of the refining agent, NaCl, NaF, TiCl with a purity of ≥99.8% are selected; 3 、SrSO 4 , KPO 3 、Na 2 B 4 O 7 The invention relates to a method for preparing raw materials; (2) adding the ingredients into water at a temperature of 70° C. and stirring to dissolve the ingredients 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 powders with a particle size of less than 2 mm, and drying and dehydrating the powders at 160° C. for 4 hours to obtain the refining agent.

[0062] Comparative Example 1:

[0063] The waste aluminum recycling method of the die-cast aluminum alloy in this comparative example is the same as that in Example 1, except that the die-cast aluminum alloy consists of the following components in mass percentage: Si 11.89%, Cu 1.48%, Zn 1.67%, Mn 0.72%, Ti0.06%, Sr 0.005%, P 0.002%, 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 ≤0.2%.

[0064] Comparative Example 2:

[0065] The waste aluminum recycling method of the die-cast aluminum alloy in this comparative example is the same as that in Example 2, except that the die-cast aluminum alloy consists of the following components in mass percentage: Si 11.5%, Cu 2.5%, Zn 0.8%, Mn 0.8%, Ti 0.04%, Sr0.006%, P 0.001%, 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 ≤0.2%.

[0066] Comparative Example 3:

[0067] The waste aluminum recycling method of the die-cast aluminum alloy in this comparative example is the same as that in Example 3, except that the die-cast aluminum alloy consists of the following components in mass percentage: Si 12.5%, Cu 1.6%, Zn 2.2%, Mn 0.4%, Ti 0.08%, Sr0.003%, P 0.003%, 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 ≤0.2%.

[0068] Comparative Example 4:

[0069] The composition of the die-cast aluminum alloy and the waste aluminum regeneration method of this comparative example are the same as those of Example 1, except that the refining agent used is an existing conventional refining agent, which is composed of the following components in mass percentage: NaCl 36.13%, KCl 15.42%, CaF 2 16.84%, NaF 19.24%, C 2 Cl 6 12.37%, the refining agent is obtained by directly crushing and mixing the raw materials after drying and dehydration.

[0070] Comparative Example 5:

[0071] The composition of the die-cast aluminum alloy in this comparative example and the method for regenerating waste aluminum are the same as those in Example 1, except that in step five, instead of using a mixed gas consisting of argon, sulfur hexafluoride and carbon monoxide, argon with a purity of 99.99% is used to spray and refine the aluminum alloy.

[0072] Verification example:

[0073] The hydrogen content and slag content of the aluminum alloy liquid before casting of Examples 1-3 and Comparative Examples 1-5 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 casting of Examples 1-3 and Comparative Examples 1-3 is less than 0.14 ml / 100 gAl, and the slag content is less than 0.08 mm 2 / kgAl. Comparative Example 4 uses commercially available conventional refining agent for refining by spraying, and Comparative Example 5 does not use mixed gas for refining by spraying, 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 and improve the cleanliness of the die-casting aluminum alloy liquid.

[0074] Table 1 Hydrogen content and slag content of aluminum alloy liquid

[0075]

[0076] Samples were taken from the die-cast aluminum alloys obtained in Examples 1-3 and Comparative Examples 1-5, and the room temperature tensile mechanical properties of the die-cast aluminum alloy samples in the non-heat-treated state were tested, and the results are shown in Table 2. As can be seen from Table 2, the tensile strength of the die-cast aluminum alloys of Examples 1-3 is not less than 350MPa, the yield strength is not less than 300MPa, and the elongation after fracture is not less than 10%, which has the advantages of high strength and good plasticity. Due to insufficient Cu content in the die-cast aluminum alloy of Comparative Example 1, insufficient Zn content in the die-cast aluminum alloy of Comparative Example 2, and insufficient Mn content in the die-cast aluminum alloy of Comparative Example 3, the tensile strength of the die-cast aluminum alloys of Comparative Examples 1-3 is lower than 325MPa, and the yield strength is lower than 280MPa. Comparative Example 4 uses commercially available conventional refining agent spray refining, while Comparative Example 5 does not use mixed gas spray refining. Due to the high gas slag content in the aluminum alloy liquid, the tensile strength of the die-cast aluminum alloys of Comparative Examples 4 and 5 is lower than 330 MPa, the yield strength is lower than 290 MPa, and the elongation after fracture is lower than 8%.

[0077] Table 2 Tensile mechanical properties of die-cast aluminum alloy

[0078]

[0079] Samples were taken from the die-cast aluminum alloys obtained in Example 1 and Comparative Example 4. After the samples were ground, polished and corroded, the microstructure of the die-cast aluminum alloys was observed under a microscope. Figure 1The microstructure of the die-cast aluminum alloy of Example 1 is shown in FIG. Figure 2 The microstructure of the die-cast aluminum alloy of Comparative Example 4. Figure 1 It can be seen that in Example 1, due to the refining agent used, the grain structure of the die-cast aluminum alloy is fine and uniform, and there are no coarse dendritic α-Al grains, needle-like Si phases, and Fe-rich phases. Figure 2 It can be seen that since Comparative Example 4 uses a conventional commercially available refining agent that does not have a refining and modification function, the grain structure of the die-cast aluminum alloy is coarse, the α-Al grains are coarse dendrites, and the Si phase and the Fe-rich phase are coarse needles or laths.

Claims

1. A high-strength and toughness die-cast aluminum alloy, characterized in that: The die-casting aluminum alloy consists of the following components in mass percentage: Si 11.5-12.5%, Cu 1.6-2.5%, Zn 1.1-2.2%, Mn 0.6-0.8%, Ti 0.04-0.08%, Sr0.003-0.006%, P 0.001-0.003%, 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 ≤0.2%.

2. A method for recycling waste aluminum of high-strength and toughness die-cast aluminum alloy as claimed in claim 1, characterized in that: The following steps are included in sequence: Step 1: sorting and pre-treating the scrap aluminum to obtain scrap aluminum that can be recycled; Step 2: heating and melting the pre-treated scrap aluminum into aluminum alloy liquid; Step 3: Online detection and adjustment of the chemical composition of the aluminum alloy liquid; Step 4: using argon gas and refining agent to spray and refine the aluminum alloy liquid; Step 5: Using mixed gas to spray and refine the aluminum alloy liquid; Step six: hydraulically casting the aluminum alloy into an aluminum alloy to obtain the die-cast aluminum alloy.

3. The method for recycling waste aluminum of high-strength and toughness die-cast aluminum alloy according to claim 2, characterized in that: The pretreatment of the scrap aluminum in step 1 is to sort out and remove the iron, rubber, plastic, wood, stone, mud and other inclusions carried or embedded in the scrap aluminum.

4. The method for recycling waste aluminum of high-strength and toughness die-cast aluminum alloy according to claim 2, characterized in that: The step 2 of heating and melting the waste aluminum into aluminum alloy liquid is to put the waste aluminum into an aluminum melting furnace and heat it at 720-760° C. to melt it into aluminum alloy liquid.

5. The method for recycling waste aluminum of high-strength and toughness die-cast aluminum alloy according to claim 2, characterized in that: The online adjustment of the chemical composition of the aluminum alloy liquid described in step three includes adding pure metal or alloy to increase the content of chemical elements in the aluminum alloy liquid and adding aluminum ingots to dilute the content of chemical elements in the aluminum alloy liquid, so that the chemical composition of the aluminum alloy liquid meets the chemical composition of the target die-casting aluminum alloy.

6. The method for recycling waste aluminum of high-strength and toughness die-cast aluminum alloy according to claim 2, characterized in that: The purity of the argon gas in step 4 is ≥99.99%, the amount of the refining agent used is 0.1-0.2% of the weight of the aluminum alloy liquid, the temperature of the aluminum alloy liquid during spray refining is 700-720°C, and the spray refining time is 15-20 minutes.

7. The method for recycling waste aluminum of high-strength and toughness die-cast aluminum alloy according to claim 2, characterized in that: The refining agent in step 4 is composed of the following components in mass percentage: NaCl 35.12%, NaF 19.84%, TiCl 3 16.51%, SrSO 4 10.06%, KPO 3 11.45%, and Na 2 B 4 O 7 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, TiCl 3, SrSO 4, KPO 3, and Na 2 B 4 O 7 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.

8. The method for recycling waste aluminum of high-strength and toughness die-cast aluminum alloy according to claim 2, characterized in that: The mixed gas in step 5 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%.

9. The method for recycling waste aluminum of high-strength and toughness die-cast aluminum alloy according to claim 2, characterized in that: The amount of the mixed gas in step 5 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 temperature of the aluminum alloy liquid during spray refining is 700-720℃, and the spray refining time is 10-15 minutes.

10. The method for recycling waste aluminum of high-strength and toughness die-cast aluminum alloy according to claim 2, characterized in that: The step six of hydraulically casting the aluminum alloy into aluminum alloy is performed under the conditions that the pouring temperature of the aluminum alloy liquid is 710-730°C, the mold temperature is 200-250°C, the vacuum degree is 200-300mbar, the filling speed is 20-25m / s, the boost pressure is 700-800bar, and the holding time is 15-20s.

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