Thermal cracking resistant die casting aluminum alloy and preparation method thereof

Abstract

This invention discloses a hot-cracking resistant die-cast aluminum alloy and its preparation method, relating to the field of aluminum alloy technology. Step 1: Melt a high-zinc base aluminum alloy, add a slag remover for refining and slag removal; obtain an aluminum melt; Step 2: Perform electromagnetic levitation melting on the aluminum melt, add a refining agent and a modifier, and continue melting to obtain a modified aluminum melt; Step 3: Die-cast the modified aluminum melt under pulsed electric field assistance, and then heat-treat it to obtain a die-cast aluminum alloy; the refining agent is Al-Ti-C; the modifier includes lanthanum and ytterbium. This application utilizes Al-Ti-C as a refining agent and a combination of lanthanum and ytterbium as modifiers to modify a high-zinc base aluminum alloy, while simultaneously employing electromagnetic levitation melting, pulsed electric field-assisted die casting, and specific heat treatment processes for synergistic effects. This effectively improves the hot-cracking resistance of zinc content >1%, and also enhances the mechanical properties and corrosion resistance of the die-cast aluminum alloy.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, specifically to a hot-crack resistant die-cast aluminum alloy and its preparation method. Background Technology

[0002] Aluminum-silicon-copper die-casting aluminum alloys exhibit excellent casting performance and low susceptibility to hot cracking, making them one of the most widely used materials in cast aluminum alloys. Among them, ADC12 aluminum alloys, due to their good fluidity and airtightness, are widely used in die-casting materials for automotive parts, electronic structural components, and communication components. Meanwhile, with the development of the recycled aluminum industry, recycling waste aluminum can effectively reduce raw material costs. However, in actual recycling, the zinc content generally exceeds 1.0% due to the mixing of galvanized steel stamping scrap, waste zinc-aluminum die-casting parts, and repeated remelting of gate remelting materials. Strictly adhering to the standard composition of conventional ADC12 aluminum alloy (zinc ≤ 1%) requires diluting the zinc content with more than 50% aluminum ingots, making it difficult to increase the waste aluminum ratio and resulting in high costs. To address this, existing research has expanded the zinc content in ADC12 aluminum alloys to >1%. For example, in the study "Research on the Properties of High-Zinc Die-cast ADC12ZS Alloy," the upper limit of zinc content was expanded from 1% to 2.5%. This increased the proportion of scrap aluminum from 40-50% to 70-80%. However, with the increased zinc content, the limited solid solubility of zinc (>1%) in aluminum leads to segregation. The zinc-rich second phase crosses the grain interior in a strip-like form, disrupting the metallurgical bond at the grain boundaries and significantly increasing the tendency for hot cracking under solidification shrinkage stress. Simultaneously, under high zinc conditions, the grain boundary precipitates exhibit a continuous network distribution, greatly increasing the tendency for intergranular corrosion and significantly reducing the alloy's corrosion resistance.

[0003] Therefore, overcoming the above-mentioned defects and preparing a hot-crack resistant die-cast aluminum alloy is of great industrial significance. Summary of the Invention

[0004] The purpose of this invention is to provide a hot-crack resistant die-cast aluminum alloy and its preparation method, so as to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for preparing a hot-cracking resistant die-cast aluminum alloy includes the following steps: Step 1: Melt the high-zinc base aluminum alloy, add a slag remover, and refine and remove slag to obtain molten aluminum; Step 2: Electromagnetically levitate the aluminum melt, add refining agent and modifier, and continue smelting to obtain modified aluminum melt; Step 3: The modified aluminum melt is die-cast under the assistance of a pulsed electric field, and then heat-treated to obtain a die-cast aluminum alloy; The refining agent is Al-Ti-C; the modifying agent includes lanthanum and ytterbium.

[0006] More preferably, the refining agent is an Al-5Ti-0.2C master alloy; the amount of the refining agent added accounts for 2 to 3 wt% of the base aluminum alloy.

[0007] In a more optimized manner, the modifier is composed of Al-20La master alloy and Al-20Yb master alloy in a mass ratio of 1:1; the amount of modifier added accounts for 2 to 3 wt% of the base aluminum alloy.

[0008] In a more optimized manner, the process parameters for electromagnetic levitation melting in step 2 are: current of 50~90A and temperature of 730~760℃.

[0009] In a more optimized manner, in step 3, the process parameters of the die-casting process are: die-casting specific pressure of 70~100MPa; and the parameters of the pulse electric field are: current density of 10~18A / mm², pulse width of 18~22μs, and pulse frequency of 45~55Hz.

[0010] In a more optimized manner, step 3 includes heat treatment, primary aging treatment, and secondary aging treatment. The process parameters for the solution treatment are: heat treatment at 500~550℃ for 4~5 hours, followed by water cooling to room temperature; The process parameters for the first-stage aging treatment are: holding at 140~150℃ for 4~5 hours, then air-cooling to room temperature after removal from the furnace; The process parameters for the secondary aging treatment are: holding at 170~180℃ for 5~6 hours, and then cooling to room temperature with the furnace.

[0011] Ideally, the water cooling to room temperature is achieved using a 0.1-0.5 g / L sodium dodecyl sarcosinate aqueous solution at 25-30°C.

[0012] More optimally, the elemental composition of the high-zinc base aluminum alloy is as follows: by mass fraction, 9.0~12.0% silicon, 0.70~0.95% iron, 1.5~3.0% copper, 1.5~2.0% zinc, ≤0.30% magnesium, ≤0.50% nickel, ≤0.50% manganese, ≤0.10% tin, ≤0.005% calcium, ≤0.10% lead, with the balance being aluminum and unavoidable impurities.

[0013] In a more optimized manner, the slag remover is composed of sodium chloride, potassium chloride, cryolite, and sodium fluorosilicate in a mass ratio of 3~4:3~4:1~1.5:0.5~1.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: In this application, the high zinc base aluminum alloy is modified by using Al-Ti-C refining agent and lanthanum and ytterbium compound as modifiers, and at the same time, electromagnetic levitation melting, pulse electric field assisted die casting and specific heat treatment processes are used to achieve technical synergy, which effectively improves the hot cracking resistance of zinc content >1%, and at the same time improves the mechanical properties and corrosion resistance of die-cast aluminum alloy.

[0015] The grain refiner selected is an Al-5Ti-0.2C master alloy, in which the TiC particles have a face-centered cubic structure, low lattice mismatch with α-Al, good chemical stability in high-zinc, high-silicon melts, and will not react with zinc or silicon at the interface, thus serving as a stable heterogeneous nucleation core for a long time. After refinement, α-Al transforms from coarse dendrites to fine equiaxed crystals. On the one hand, the grain boundary area increases significantly, solidification shrinkage stress is evenly distributed, and zinc-rich phases cannot continuously distribute along the grain boundaries to form crack channels, directly improving the resistance to hot cracking. On the other hand, grain refinement can simultaneously improve strength and plasticity, and the increased grain boundaries can also block corrosion and improve corrosion resistance. In addition, compared with the common Al-Ti-B modifier, in this application, in addition to zinc, the silicon content is also high. If B is introduced, TiB2 particles will be generated, causing silicon atoms to accumulate on the surface of TiB2 particles to form titanium silicon compounds, resulting in silicon poisoning, inhibiting the nucleation ability of nucleation cores, and reducing the refinement effect.

[0016] The modifier consists of Al-20La master alloy and Al-20Yb master alloy in a 1:1 mass ratio. It is used to improve defects caused by the strip-like distribution of zinc-rich phases cutting the matrix and the hot cracking caused by the needle-like formation of eutectic silicon, which are resulting from high zinc content. Compared to the limitations of single rare earth modification, a composite formulation achieves synergy. The Al3Yb generated by ytterbium, together with TiC, forms a dual heterogeneous nucleation core, further refining the grain size. Meanwhile, La segregates at the growth front of the eutectic silicon and zinc-rich phases, inhibiting the preferential growth of the second phase along a specific direction. This transforms the needle-like eutectic silicon and the strip-like zinc-rich phases that traverse the grains into dispersed particles, effectively improving the cutting effect of the second phase on grain boundaries. It also suppresses stress concentration at the tips of the second phase, inhibiting cracking and thus improving hot cracking resistance. Simultaneously, it inhibits the formation of continuous galvanic corrosion by the dispersed second phase, effectively improving corrosion resistance.

[0017] In conventional smelting, the large density difference between zinc and aluminum leads to segregation, resulting in excessively high zinc content in some areas, which in turn causes localized hot brittleness and a decline in performance. However, in electromagnetic levitation smelting, the Lorentz force generated by strong electromagnetic convection drives the melt, effectively eliminating zinc segregation and improving the hot brittleness caused by localized high zinc content. At the same time, strong stirring promotes the uniform dispersion of nucleation particles such as TiC and Al3Yb throughout the melt, preventing particle agglomeration and sedimentation, and promoting a finer refining effect.

[0018] Among them, pulsed electric field assistance is introduced in the die casting process. First, the electromigration effect drives the uniform distribution of solute atoms such as zinc and iron, further reducing microsegregation. Second, the Joule thermal pulse causes local micro-melting at the tip of the growing dendrite arm, breaking the dendrite and generating a large number of free crystal nuclei, further refining the grains. Third, the electroplastic effect reduces the solid-liquid interface energy and increases the nucleation rate.

[0019] In this way, electromagnetic levitation can be formed to achieve macroscopic uniformity of composition, and the refining agent and modifier can be modified to form the initial nucleation core, which is then solidified in the pulsed electric field to break the dendritic proliferation core and synergistically improve the overall performance.

[0020] Furthermore, a two-stage aging process is employed during heat treatment. First, aging at a lower temperature induces the precipitation of GP zones within the grains. Then, aging at a higher temperature results in the precipitation of fine, dispersed phases centered around these GP zones, achieving toughening and strengthening. Grain boundary precipitates aggregate into isolated particles, simultaneously improving mechanical properties and corrosion resistance. In addition, solution treatment is performed before aging, followed by water cooling in an aqueous solution containing sodium dodecyl sarcosinate. Compared to direct immersion in water, high-temperature aluminum reacts with water to form an oxide film and pitting. Introducing sodium dodecyl sarcosinate inhibits water corrosion without affecting the cooling rate or ensuring supersaturation, thus preventing surface oxidation and pitting, thereby improving corrosion resistance. Detailed Implementation

[0021] The present invention will now be described in detail with reference to specific embodiments. These embodiments are merely some, not all, of the embodiments described. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0022] Example 1: The preparation of die-cast aluminum alloy is as follows: Prepare a high-zinc base aluminum alloy with the following elemental composition by mass fraction: 10.5% silicon, 0.87% iron, 1.7% copper, 1.79% zinc, 0.2% magnesium, 0.32% nickel, 0.15% manganese, 0.05% tin, 0.002% calcium, 0.05% lead, with the balance being aluminum and unavoidable impurities. Sodium chloride, potassium chloride, cryolite, and sodium fluorosilicate are mixed in a mass ratio of 3.4:3.6:1.2:0.8 and dried at 200℃ until the moisture content is <0.1% to obtain a slag remover, which is then sealed for later use. Al-20La master alloy and Al-20Yb master alloy were mixed at a mass ratio of 1:1 to obtain a modifier, which was then preheated to 150℃ for later use. Al-5Ti-0.2C master alloy was used as a refining agent and preheated to 150℃ for later use; Step 1: Melt the high-zinc base aluminum alloy at 730℃, add a slag remover at a rate of 0.3 wt% of the base aluminum alloy; stir for 5 minutes, let stand for 10 minutes, remove the surface slag, and obtain the aluminum melt; Step 2: Transfer the aluminum melt obtained in Step 1 into a vacuum induction levitation melting furnace, evacuate the furnace to a vacuum level of 50 Pa and maintain it, set the induction output current to 70 A, and melt at 750 °C for 5 minutes; add Al-5Ti-0.2C, the amount of which accounts for 2.5 wt% of the base aluminum alloy; add a modifier, the amount of which accounts for 2.5 wt% of the base aluminum alloy; continue melting for 20 minutes. During the melting process, the alloy is suspended in a water-cooled copper crucible under the action of electromagnetic force and does not contact the crucible wall; thus obtaining modified aluminum melt. Step 3: Transfer the modified aluminum melt from Step 2 into the holding furnace of the die-casting machine and hold it at 750℃ for 15 minutes for high-pressure die casting. The die casting specific pressure is 80MPa. During pouring, a pulsed electric field is applied to both sides of the mold through graphite electrodes, with a current density of 15A / mm². 2 The pulse width is 20μs and the pulse frequency is 50Hz, which is continued until the casting is completely solidified. After demolding, the casting is placed in a box-type resistance furnace and held at 520℃ for 5 hours. It is then removed and immediately transferred to a 0.3g / L sodium dodecyl sarcosinate aqueous solution within 8 seconds and water-cooled to room temperature. It is then placed back into the furnace and held at 150℃ for 4 hours, and then air-cooled to room temperature. Finally, it is placed back into the furnace and held at 170℃ for 6 hours, and then cooled to room temperature with the furnace to obtain a thermal crack resistant die-cast aluminum alloy.

[0023] Example 2: The preparation of die-cast aluminum alloy is as follows: Prepare a high-zinc base aluminum alloy with the following elemental composition by mass fraction: 10.5% silicon, 0.87% iron, 1.7% copper, 1.79% zinc, 0.2% magnesium, 0.32% nickel, 0.15% manganese, 0.05% tin, 0.002% calcium, 0.05% lead, with the balance being aluminum and unavoidable impurities. Sodium chloride, potassium chloride, cryolite, and sodium fluorosilicate are mixed in a mass ratio of 3.4:3.6:1.2:0.8 and dried at 200℃ until the moisture content is <0.1% to obtain a slag remover, which is then sealed for later use. Al-20La master alloy and Al-20Yb master alloy were mixed at a mass ratio of 1:1 to obtain a modifier, which was then preheated to 150℃ for later use. Al-5Ti-0.2C master alloy was used as a refining agent and preheated to 150℃ for later use; Step 1: Melt the high-zinc base aluminum alloy at 730℃, add a slag remover at a rate of 0.3 wt% of the base aluminum alloy; stir for 5 minutes, let stand for 10 minutes, remove the surface slag, and obtain the aluminum melt; Step 2: Transfer the aluminum melt obtained in Step 1 into a vacuum induction levitation melting furnace, evacuate the furnace to a vacuum level of 50 Pa and maintain it, set the induction output current to 50 A, and melt at 760℃ for 5 minutes; add Al-5Ti-0.2C, the amount of which accounts for 2 wt% of the base aluminum alloy; add a modifier, the amount of which accounts for 2 wt% of the base aluminum alloy; continue melting for 20 minutes. During the melting process, the alloy is suspended in a water-cooled copper crucible under the action of electromagnetic force and does not contact the crucible wall; thus obtaining modified aluminum melt. Step 3: Transfer the modified aluminum melt from Step 2 into the holding furnace of the die-casting machine and hold it at 750℃ for 15 minutes for high-pressure die casting. The die casting specific pressure is 80MPa. During pouring, a pulsed electric field with a current density of 18A / mm is applied to both sides of the mold through graphite electrodes. 2 The pulse width is 22μs and the pulse frequency is 55Hz, which is continued until the casting is completely solidified. After demolding, the casting is placed in a box-type resistance furnace and held at 520℃ for 5 hours. It is then removed and immediately transferred to a 0.2g / L sodium dodecyl sarcosinate aqueous solution within 8 seconds and water-cooled to room temperature. It is then placed back into the furnace and held at 150℃ for 4 hours, and then air-cooled to room temperature. Finally, it is placed back into the furnace and held at 170℃ for 6 hours, and then cooled to room temperature with the furnace to obtain a thermal crack resistant die-cast aluminum alloy.

[0024] Example 3: The preparation of die-cast aluminum alloy is as follows: Prepare a high-zinc base aluminum alloy with the following elemental composition by mass fraction: 10.5% silicon, 0.87% iron, 1.7% copper, 1.79% zinc, 0.2% magnesium, 0.32% nickel, 0.15% manganese, 0.05% tin, 0.002% calcium, 0.05% lead, with the balance being aluminum and unavoidable impurities. Sodium chloride, potassium chloride, cryolite, and sodium fluorosilicate are mixed in a mass ratio of 3.4:3.6:1.2:0.8 and dried at 200℃ until the moisture content is <0.1% to obtain a slag remover, which is then sealed for later use. Al-20La master alloy and Al-20Yb master alloy were mixed at a mass ratio of 1:1 to obtain a modifier, which was then preheated to 150℃ for later use. Al-5Ti-0.2C master alloy was used as a refining agent and preheated to 150℃ for later use; Step 1: Melt the high-zinc base aluminum alloy at 730℃, add a slag remover at a rate of 0.3 wt% of the base aluminum alloy; stir for 5 minutes, let stand for 10 minutes, remove the surface slag, and obtain the aluminum melt; Step 2: Transfer the aluminum melt obtained in Step 1 into a vacuum induction levitation melting furnace, evacuate the furnace to a vacuum level of 50 Pa and maintain it, set the induction output current to 90 A, and melt at 730℃ for 3 minutes; add Al-5Ti-0.2C, the amount of which accounts for 3 wt% of the base aluminum alloy; add a modifier, the amount of which accounts for 3 wt% of the base aluminum alloy; continue melting for 20 minutes. During the melting process, the alloy is suspended in a water-cooled copper crucible under the action of electromagnetic force and does not contact the crucible wall; thus obtaining modified aluminum melt. Step 3: Transfer the modified aluminum melt from Step 2 into the holding furnace of the die-casting machine and hold it at 750℃ for 15 minutes for high-pressure die casting. The die casting specific pressure is 80MPa. During pouring, a pulsed electric field with a current density of 10A / mm is applied to both sides of the mold through graphite electrodes. 2 The pulse width is 18μs and the pulse frequency is 45Hz, continuing until the casting is completely solidified; after demolding, the casting is placed in a box-type resistance furnace and held at 520℃ for 5 hours. It is then removed and immediately transferred to a 0.4g / L sodium dodecyl sarcosinate aqueous solution within 8 seconds, and water-cooled to room temperature; it is then placed back into the furnace and held at 150℃ for 4 hours, and then air-cooled to room temperature; it is then placed back into the furnace and held at 170℃ for 6 hours, and then cooled to room temperature with the furnace to obtain a thermal crack resistant die-cast aluminum alloy.

[0025] Comparative Example 1: High-zinc base alloy, with the same composition as Example 1.

[0026] Comparative Example 2: Ordinary smelting was used, and the rest was the same as in Example 1; Prepare a high-zinc base aluminum alloy with the following elemental composition by mass fraction: 10.5% silicon, 0.87% iron, 1.7% copper, 1.79% zinc, 0.2% magnesium, 0.32% nickel, 0.15% manganese, 0.05% tin, 0.002% calcium, 0.05% lead, with the balance being aluminum and unavoidable impurities. Sodium chloride, potassium chloride, cryolite, and sodium fluorosilicate are mixed in a mass ratio of 3.4:3.6:1.2:0.8 and dried at 200℃ until the moisture content is <0.1% to obtain a slag remover, which is then sealed for later use. Al-20La master alloy and Al-20Yb master alloy were mixed at a mass ratio of 1:1 to obtain a modifier, which was then preheated to 150℃ for later use. Al-5Ti-0.2C master alloy was used as a refining agent and preheated to 150℃ for later use; Step 1: Melt the high-zinc base aluminum alloy at 730℃, add a slag remover at a rate of 0.3 wt% of the base aluminum alloy; stir for 5 minutes, let stand for 10 minutes, remove the surface slag, and obtain the aluminum melt; Step 2: Continue to melt the aluminum melt obtained in Step 1 at 750℃ for 5 minutes; add Al-5Ti-0.2C, the amount of which accounts for 2.5wt% of the base aluminum alloy; add a modifier, the amount of which accounts for 2.5wt% of the base aluminum alloy; continue to melt for 20 minutes to obtain modified aluminum melt; Step 3: Transfer the modified aluminum melt from Step 2 into the holding furnace of the die-casting machine and hold it at 750℃ for 15 minutes for high-pressure die casting. The die casting specific pressure is 80MPa. During pouring, a pulsed electric field is applied to both sides of the mold through graphite electrodes, with a current density of 15A / mm². 2 The pulse width is 20μs and the pulse frequency is 50Hz, which is continued until the casting is completely solidified. After demolding, the casting is placed in a box-type resistance furnace and held at 520℃ for 5 hours. It is then removed and immediately transferred to a 0.3g / L sodium dodecyl sarcosinate aqueous solution within 8 seconds and water-cooled to room temperature. It is then placed back into the furnace and held at 150℃ for 4 hours, and then air-cooled to room temperature. Finally, it is placed back into the furnace and held at 170℃ for 6 hours, and then cooled to room temperature with the furnace to obtain a thermal crack resistant die-cast aluminum alloy.

[0027] Comparative Example 3: No pulsed electric field assistance, otherwise the same as Example 1; Prepare a high-zinc base aluminum alloy with the following elemental composition by mass fraction: 10.5% silicon, 0.87% iron, 1.7% copper, 1.79% zinc, 0.2% magnesium, 0.32% nickel, 0.15% manganese, 0.05% tin, 0.002% calcium, 0.05% lead, with the balance being aluminum and unavoidable impurities. Sodium chloride, potassium chloride, cryolite, and sodium fluorosilicate are mixed in a mass ratio of 3.4:3.6:1.2:0.8 and dried at 200℃ until the moisture content is <0.1% to obtain a slag remover, which is then sealed for later use. Al-20La master alloy and Al-20Yb master alloy were mixed at a mass ratio of 1:1 to obtain a modifier, which was then preheated to 150℃ for later use. Al-5Ti-0.2C master alloy was used as a refining agent and preheated to 150℃ for later use; Step 1: Melt the high-zinc base aluminum alloy at 730℃, add a slag remover at a rate of 0.3 wt% of the base aluminum alloy; stir for 5 minutes, let stand for 10 minutes, remove the surface slag, and obtain the aluminum melt; Step 2: Transfer the aluminum melt obtained in Step 1 into a vacuum induction levitation melting furnace, evacuate the furnace to a vacuum level of 50 Pa and maintain it, set the induction output current to 70 A, and melt at 750 °C for 5 minutes; add Al-5Ti-0.2C, the amount of which accounts for 2.5 wt% of the base aluminum alloy; add a modifier, the amount of which accounts for 2.5 wt% of the base aluminum alloy; continue melting for 20 minutes. During the melting process, the alloy is suspended in a water-cooled copper crucible under the action of electromagnetic force and does not contact the crucible wall; thus obtaining modified aluminum melt. Step 3: Transfer the modified aluminum melt from Step 2 into the holding furnace of the die casting machine, hold it at 750℃ for 15 minutes, and perform high-pressure die casting with a specific pressure of 80MPa. Demold the casting and place it in a box-type resistance furnace. Hold it at 520℃ for 5 hours, remove it, and immediately transfer it to a 0.3g / L sodium dodecyl sarcosinate aqueous solution within 8 seconds. Water cool it to room temperature. Put it back into the furnace and hold it at 150℃ for 4 hours. Remove it from the furnace and air cool it to room temperature. Put it back into the furnace and hold it at 170℃ for 6 hours. Cool it to room temperature with the furnace to obtain a hot-crack resistant die-cast aluminum alloy.

[0028] Comparative Example 4: Ordinary water was used, and a single-stage aging process was employed; otherwise, it was the same as Example 1. Prepare a high-zinc base aluminum alloy with the following elemental composition by mass fraction: 10.5% silicon, 0.87% iron, 1.7% copper, 1.79% zinc, 0.2% magnesium, 0.32% nickel, 0.15% manganese, 0.05% tin, 0.002% calcium, 0.05% lead, with the balance being aluminum and unavoidable impurities. Sodium chloride, potassium chloride, cryolite, and sodium fluorosilicate are mixed in a mass ratio of 3.4:3.6:1.2:0.8 and dried at 200℃ until the moisture content is <0.1% to obtain a slag remover, which is then sealed for later use. Al-20La master alloy and Al-20Yb master alloy were mixed at a mass ratio of 1:1 to obtain a modifier, which was then preheated to 150℃ for later use. Al-5Ti-0.2C master alloy was used as a refining agent and preheated to 150℃ for later use; Step 1: Melt the high-zinc base aluminum alloy at 730℃, add a slag remover at a rate of 0.3 wt% of the base aluminum alloy; stir for 5 minutes, let stand for 10 minutes, remove the surface slag, and obtain the aluminum melt; Step 2: Transfer the aluminum melt obtained in Step 1 into a vacuum induction levitation melting furnace, evacuate the furnace to a vacuum level of 50 Pa and maintain it, set the induction output current to 70 A, and melt at 750 °C for 5 minutes; add Al-5Ti-0.2C, the amount of which accounts for 2.5 wt% of the base aluminum alloy; add a modifier, the amount of which accounts for 2.5 wt% of the base aluminum alloy; continue melting for 20 minutes. During the melting process, the alloy is suspended in a water-cooled copper crucible under the action of electromagnetic force and does not contact the crucible wall; thus obtaining modified aluminum melt. Step 3: Transfer the modified aluminum melt from Step 2 into the holding furnace of the die-casting machine and hold it at 750℃ for 15 minutes for high-pressure die casting. The die casting specific pressure is 80MPa. During pouring, a pulsed electric field is applied to both sides of the mold through graphite electrodes, with a current density of 15A / mm². 2 The pulse width is 20μs and the pulse frequency is 50Hz, which is continued until the casting is completely solidified; after demolding, the casting is placed in a box-type resistance furnace and held at 520℃ for 5 hours. It is then taken out and immediately transferred to water within 8 seconds and cooled to room temperature; it is then placed back into the furnace and held at 170℃ for 10 hours, and then cooled to room temperature with the furnace to obtain a thermal crack resistant die-cast aluminum alloy.

[0029] Comparative Example 5: Al-5Ti-1B master alloy was used, and the rest was the same as in Example 1; Prepare a high-zinc base aluminum alloy with the following elemental composition by mass fraction: 10.5% silicon, 0.87% iron, 1.7% copper, 1.79% zinc, 0.2% magnesium, 0.32% nickel, 0.15% manganese, 0.05% tin, 0.002% calcium, 0.05% lead, with the balance being aluminum and unavoidable impurities. Sodium chloride, potassium chloride, cryolite, and sodium fluorosilicate are mixed in a mass ratio of 3.4:3.6:1.2:0.8 and dried at 200℃ until the moisture content is <0.1% to obtain a slag remover, which is then sealed for later use. Al-20La master alloy and Al-20Yb master alloy were mixed at a mass ratio of 1:1 to obtain a modifier, which was then preheated to 150℃ for later use. Al-5Ti-1B master alloy was used as a refining agent and preheated to 150℃ for later use. Step 1: Melt the high-zinc base aluminum alloy at 730℃, add a slag remover at a rate of 0.3 wt% of the base aluminum alloy; stir for 5 minutes, let stand for 10 minutes, remove the surface slag, and obtain the aluminum melt; Step 2: Transfer the aluminum melt obtained in Step 1 into a vacuum induction levitation melting furnace, evacuate the furnace to a vacuum level of 50 Pa and maintain it, set the induction output current to 70 A, and melt at 750 °C for 5 minutes; add Al-5Ti-1B, the amount of which accounts for 2.5 wt% of the base aluminum alloy; add a modifier, the amount of which accounts for 2.5 wt% of the base aluminum alloy; continue melting for 20 minutes. During the melting process, the alloy is suspended in a water-cooled copper crucible under the action of electromagnetic force and does not contact the crucible wall; thus obtaining modified aluminum melt. Step 3: Transfer the modified aluminum melt from Step 2 into the holding furnace of the die-casting machine and hold it at 750℃ for 15 minutes for high-pressure die casting. The die casting specific pressure is 80MPa. During pouring, a pulsed electric field is applied to both sides of the mold through graphite electrodes, with a current density of 15A / mm². 2 The pulse width is 20μs and the pulse frequency is 50Hz, which is continued until the casting is completely solidified. After demolding, the casting is placed in a box-type resistance furnace and held at 520℃ for 5 hours. It is then removed and immediately transferred to a 0.3g / L sodium dodecyl sarcosinate aqueous solution within 8 seconds and water-cooled to room temperature. It is then placed back into the furnace and held at 150℃ for 4 hours, and then air-cooled to room temperature. Finally, it is placed back into the furnace and held at 170℃ for 6 hours, and then cooled to room temperature with the furnace to obtain a thermal crack resistant die-cast aluminum alloy.

[0030] Comparative Example 6: A single Al-20La master alloy was used, and the rest was the same as in Example 1; Prepare a high-zinc base aluminum alloy with the following elemental composition by mass fraction: 10.5% silicon, 0.87% iron, 1.7% copper, 1.79% zinc, 0.2% magnesium, 0.32% nickel, 0.15% manganese, 0.05% tin, 0.002% calcium, 0.05% lead, with the balance being aluminum and unavoidable impurities. Sodium chloride, potassium chloride, cryolite, and sodium fluorosilicate are mixed in a mass ratio of 3.4:3.6:1.2:0.8 and dried at 200℃ until the moisture content is <0.1% to obtain a slag remover, which is then sealed for later use. Al-20La master alloy was used as a modifier and preheated to 150℃ for later use. Al-5Ti-0.2C master alloy was used as a refining agent and preheated to 150℃ for later use; Step 1: Melt the high-zinc base aluminum alloy at 730℃, add a slag remover at a rate of 0.3 wt% of the base aluminum alloy; stir for 5 minutes, let stand for 10 minutes, remove the surface slag, and obtain the aluminum melt; Step 2: Transfer the aluminum melt obtained in Step 1 into a vacuum induction levitation melting furnace, evacuate the furnace to a vacuum level of 50 Pa and maintain it, set the induction output current to 70 A, and melt at 750 °C for 5 minutes; add Al-5Ti-0.2C, the amount of which accounts for 2.5 wt% of the base aluminum alloy; add a modifier, the amount of which accounts for 2.5 wt% of the base aluminum alloy; continue melting for 20 minutes. During the melting process, the alloy is suspended in a water-cooled copper crucible under the action of electromagnetic force and does not contact the crucible wall; thus obtaining modified aluminum melt. Step 3: Transfer the modified aluminum melt from Step 2 into the holding furnace of the die-casting machine and hold it at 750℃ for 15 minutes for high-pressure die casting. The die casting specific pressure is 80MPa. During pouring, a pulsed electric field is applied to both sides of the mold through graphite electrodes, with a current density of 15A / mm². 2 The pulse width is 20μs and the pulse frequency is 50Hz, which is continued until the casting is completely solidified. After demolding, the casting is placed in a box-type resistance furnace and held at 520℃ for 5 hours. It is then removed and immediately transferred to a 0.3g / L sodium dodecyl sarcosinate aqueous solution within 8 seconds and water-cooled to room temperature. It is then placed back into the furnace and held at 150℃ for 4 hours, and then air-cooled to room temperature. Finally, it is placed back into the furnace and held at 170℃ for 6 hours, and then cooled to room temperature with the furnace to obtain a thermal crack resistant die-cast aluminum alloy.

[0031] Performance testing: (1) Testing of thermal crack resistance: Using a thermal crack tester and a constraint rod casting thermal crack tester, the metal mold was preheated to 200°C. The diameter of the sample was 10 mm, and the lengths were 51 mm, 89 mm, 127 mm, and 165 mm, respectively. The maximum shrinkage stress during solidification was recorded, and the average value was calculated.

[0032] (2) Corrosion resistance test: The die-cast aluminum alloy was made into a 10mm×10mm×10mm sample, polished with 2000-grit sandpaper, degreased with acetone, weighed, and the surface area was measured; then it was placed in a 0.1mol / L hydrochloric acid solution at 25℃ for 20 hours; the corrosion rate was calculated.

[0033] (3) The die-cast aluminum alloy is made into a plate-shaped tensile specimen with a gauge length of 25 mm. The specimen is tested at room temperature using a universal testing machine at a speed of 1 mm / min, and the maximum tensile strength is recorded.

[0034] The obtained data is shown in the table below:

[0035] Results show that, compared with Comparative Example 1, Examples 1-3 exhibit significantly better crack resistance, corrosion resistance, and mechanical properties than Comparative Example 1. This indicates that the present invention effectively suppresses the hot cracking tendency of high-zinc aluminum alloys through the synergistic effect of grain refinement, electromagnetic levitation, and pulsed electric field. Furthermore, through microstructure control and heat treatment processes, the continuous network of zinc-rich phases was successfully transformed into dispersed, isolated particles, thereby significantly improving the material's resistance to intergranular corrosion. Moreover, while solving the problems of hot cracking and corrosion, strength was not sacrificed; instead, mechanical properties were improved through grain refinement and precipitation strengthening.

[0036] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a hot-cracking resistant die-cast aluminum alloy, characterized in that: Includes the following steps: Step 1: Melt the high-zinc base aluminum alloy, add a slag remover, and refine and remove the slag. Aluminum melt is obtained; Step 2: Electromagnetically levitate the aluminum melt, add refining agent and modifier, and continue smelting to obtain modified aluminum melt; Step 3: The modified aluminum melt is die-cast under the assistance of a pulsed electric field, and then heat-treated to obtain a die-cast aluminum alloy; The refining agent is Al-Ti-C; the modifying agent includes lanthanum and ytterbium.

2. The method for preparing a hot-cracking resistant die-cast aluminum alloy according to claim 1, characterized in that: The refining agent is an Al-5Ti-0.2C master alloy; the amount of the refining agent added accounts for 2~3 wt% of the base aluminum alloy.

3. The method for preparing a hot-cracking resistant die-cast aluminum alloy according to claim 1, characterized in that: The modifier is composed of Al-20La master alloy and Al-20Yb master alloy in a mass ratio of 1:1; the amount of modifier added accounts for 2 to 3 wt% of the base aluminum alloy.

4. The method for preparing a hot-cracking resistant die-cast aluminum alloy according to claim 1, characterized in that: In step 2, the process parameters for electromagnetic levitation melting are: current of 50~90A and temperature of 730~760℃.

5. The method for preparing a hot-cracking resistant die-cast aluminum alloy according to claim 1, characterized in that: In step 3, the process parameters of the die casting process are: die casting specific pressure of 70~100MPa; and the parameters of the pulse electric field are: current density of 10~18A / mm², pulse width of 18~22μs, and pulse frequency of 45~55Hz.

6. The method for preparing a hot-cracking resistant die-cast aluminum alloy according to claim 1, characterized in that: In step 3, the heat treatment includes solution treatment, primary aging treatment, and secondary aging treatment; The process parameters for the solution treatment are: heat treatment at 500~550℃ for 4~5 hours, followed by water cooling to room temperature; The process parameters for the first-stage aging treatment are: holding at 140~150℃ for 4~5 hours, then air-cooling to room temperature after removal from the furnace; The process parameters for the secondary aging treatment are: holding at 170~180℃ for 5~6 hours, and then cooling to room temperature with the furnace.

7. The method for preparing a hot-cracking resistant die-cast aluminum alloy according to claim 6, characterized in that: The water cooling to room temperature is performed using a 0.1-0.5 g / L sodium dodecyl sarcosinate aqueous solution at 25-30°C.

8. The method for preparing a hot-cracking resistant die-cast aluminum alloy according to claim 1, characterized in that: The elemental composition of the high-zinc base aluminum alloy is as follows (by mass fraction): 9.0-12.0% silicon, 0.70-0.95% iron, 1.5-3.0% copper, 1.5-2.0% zinc, ≤0.30% magnesium, ≤0.50% nickel, ≤0.50% manganese, ≤0.10% tin, ≤0.005% calcium, ≤0.10% lead, with the balance being aluminum and unavoidable impurities.

9. The method for preparing a hot-cracking resistant die-cast aluminum alloy according to claim 1, characterized in that: The slag remover is composed of sodium chloride, potassium chloride, cryolite, and sodium fluorosilicate in a mass ratio of 3~4:3~4:1~1.5:0.5~1.

10. A die-cast aluminum alloy resistant to thermal cracking, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 9.

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