Pouring method of aluminum-silicon alloy casting and aluminum liquid refining method of aluminum-silicon alloy casting

Abstract

The invention relates to the technical field of aluminum alloy casting, and particularly provides a pouring method of an aluminum-silicon alloy casting and a molten aluminum refining method of the aluminum-silicon alloy casting, the method comprises the following steps: adding a strontium-containing TCB refiner accounting for 0.2 wt%-0.8 wt% of the total weight of molten aluminum into the molten aluminum for refining, the strontium content in the TCB refiner being 1 wt%-5 wt%; degassing is conducted through a degassing machine in the refining process, and standing is conducted after degassing is completed; and after standing is finished, the density equivalent of the molten aluminum is detected, and pouring is conducted under the condition that the density equivalent reaches a preset range. Therefore, the feeding capacity of the molten aluminum is improved, and the problems that according to an aluminum-silicon alloy heat exchanger in the related technology, due to the fact that the thickness difference of the wall thickness of the water containing inner cavity in different areas is large, and the structure is complex, a feeding path is long, shrinkage cavities are prone to occurring in devices, the water containing inner cavity leaks and leaks, and products are poor are solved.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy casting, and in particular to a pouring method for aluminum-silicon alloy castings and a method for refining aluminum liquid. Background Art

[0002] Heat exchangers are usually made of aluminum-silicon alloy and are manufactured using low-pressure or gravity sand casting processes. The product has thicker and thinner walls. The thicker wall areas have slower cooling rates and longer solidification times, requiring the internal liquid metal to travel a longer path for shrinkage compensation. The thinner wall areas have faster cooling rates, which may cause the shrinkage compensation channels to close prematurely, leading to shrinkage defects in the castings. Adjusting the casting process can easily lead to other problems, increase costs, and still result in a higher rate of casting leakage defects.

[0003] Regarding the aluminum-silicon alloy heat exchanger in the related technology, the wall thickness varies greatly in different areas, and the complex structure leads to a long shrinkage feeding path, which makes the device prone to shrinkage holes and low yield. No effective solution has been proposed so far. Summary of the Invention

[0004] The present invention provides a method for casting an aluminum-silicon alloy casting and a method for refining aluminum liquid, which at least solves the problem of aluminum-silicon alloy heat exchangers, where the thickness of the wall varies greatly in different areas, and the complex structure leads to a long shrinkage feeding path, which makes the device prone to shrinkage cavities and low yield.

[0005] According to one aspect of the present invention, a method for casting an aluminum-silicon alloy casting is provided, comprising: adding a strontium-containing TCB refiner, whose total weight accounts for 0.2 wt % to 0.8 wt % of the total weight of the aluminum liquid, to the aluminum liquid for refining, wherein the strontium content of the TCB refiner is 1 wt % to 5 wt %; degassing the aluminum liquid during the refining process using a degasser, and allowing the aluminum liquid to stand after the degassing is completed; and detecting the density equivalent of the aluminum liquid after the standing period, and casting the aluminum liquid when the density equivalent reaches a preset range.

[0006] Optionally, the total weight of the TCB refiner accounts for 0.4 wt % to 0.6 wt % of the total amount of the aluminum liquid.

[0007] Optionally, the total weight of the TCB refiner accounts for 0.5 wt % of the total weight of the aluminum liquid.

[0008] Optionally, the TCB refiner has a strontium content of 2 wt %-3 wt %.

[0009] Optionally, degassing is performed by a degasser during the refining process, and the liquid is allowed to stand after the degassing is completed, including: adding a slag agent to the aluminum liquid; degassing by the degasser for 10 minutes to 20 minutes, a degassing flow rate of 14 L / min to 16 L / min, and a degassing pressure of 3 bar to 5 bar; and standing for 2 minutes to 10 minutes after the degassing is completed.

[0010] Optionally, before adding a strontium-containing TCB refiner having a total weight accounting for 0.2 wt %-0.8 wt % of the total weight of the molten aluminum to the molten aluminum for refining, the method further includes: melting the intermediate alloy aluminum ingot and the recycled material in a melting furnace, wherein the proportion of the recycled material to the total amount of the melted material does not exceed 50 wt %; and adding the melted aluminum liquid to a holding furnace for insulation so that the temperature of the aluminum liquid reaches 700°C-740°C.

[0011] Optionally, a strontium-containing TCB refiner having a total weight proportion of 0.2 wt %-0.8 wt % of the total weight of the aluminum liquid is added to the aluminum liquid for refining, including: calculating a first addition amount of the aluminum-strontium alloy based on a strontium element proportion of 0.008 wt %-0.025 wt % of the total weight of the aluminum liquid and the strontium content of the aluminum-strontium alloy; calculating a second addition amount of the strontium-containing TCB refiner based on the strontium content of the TCB refiner, the total weight of the aluminum liquid, and the total weight proportion of 0.2 wt %-0.8 wt %; and adding the aluminum-strontium alloy and the strontium-containing TCB refiner to the aluminum liquid for modification according to the first addition amount and the second addition amount.

[0012] Optionally, after standing, the density equivalent of the aluminum liquid is detected, including: pouring a normal pressure sample and a vacuum sample through the aluminum liquid after standing, wherein the vacuum degree of the vacuum sample is 80±5mbar, and the vacuum time is maintained for 4min-6min during the pouring process; detecting the difference between the density of the normal pressure sample and the density of the vacuum sample to determine the density equivalent, wherein the density equivalent is used to characterize the gas content in the aluminum liquid.

[0013] Optionally, the method further includes: if the density equivalent does not reach a preset range, re-degassing and allowing the aluminum liquid to stand until the density equivalent of the aluminum liquid after standing reaches a preset range.

[0014] Optionally, when the density equivalent reaches a preset range, pouring includes: measuring the temperature of the aluminum liquid when the density equivalent reaches the preset range; and pouring when the temperature of the aluminum liquid reaches 723° C.-733° C.

[0015] According to another aspect of the present invention, a method for refining molten aluminum of an aluminum-silicon alloy is provided, comprising: calculating a first addition amount of the aluminum-strontium alloy based on a strontium element ratio of 0.008 wt % to 0.025 wt % in the total weight of the aluminum liquid and the strontium content of the aluminum-strontium alloy; calculating a second addition amount of the strontium-containing TCB refiner based on the strontium content of the TCB refiner, the total weight of the aluminum liquid, and a total weight ratio of strontium in the TCB refiner of 0.2 wt % to 0.8 wt %; adding the aluminum-strontium alloy and the strontium-containing TCB refiner to the aluminum liquid for modification according to the first addition amount and the second addition amount; and performing degassing in a degasser during the refining process, and allowing the aluminum liquid to stand after the degassing is completed.

[0016] The casting method of aluminum-silicon alloy castings provided by the embodiment of the present invention can improve the shrinkage feeding ability of molten aluminum and the mechanical properties and thermal cracking resistance of the casting by adding a strontium-containing TCB refiner and coordinating degassing and standing. This solves the problem of aluminum-silicon alloy heat exchangers, which have large differences in wall thickness in different areas and a complex structure resulting in a long shrinkage feeding path, which makes the device prone to shrinkage cavities and low yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without inventive effort.

[0018] Figure 1 The present invention is a flow chart of a method for casting an aluminum-silicon alloy casting according to an embodiment of the present invention.

[0019] Figure 2 This is a flow chart of TCB refiner and aluminum-strontium alloy addition in aluminum liquid refining according to an embodiment of the present invention.

[0020] Figure 3 It is a schematic diagram of an aluminum-silicon alloy heat exchanger according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The following describes embodiments of the present invention in more detail with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0022] The heat exchanger is a key component in a burner-mounted heating boiler. It consists primarily of a combustion chamber and an outer shell, with the cavity between the two forming a water jacket. Gas in the combustion chamber heats the heating and domestic water within the water jacket, requiring high sealing performance for both the combustion chamber and the water jacket to prevent water leakage into the outer shell or combustion chamber. However, the complex structure and large thickness variations lead to a high probability of shrinkage defects and low yield rates.

[0023] There is also a method in the related art to adjust the casting process to ensure the shrinkage compensation effect of the casting and reduce leakage defects, so as to achieve the purpose of water flow through the water jacket of the heat exchanger without leakage. During the adjustment process, optimization can be achieved by changing the pouring method, changing the runner position, and adding or adjusting the riser position. However, changing the pouring method, changing the runner position, and adjusting the riser position takes a long time and has a high investment cost. It is difficult to ensure the molding quality of the casting and it is easy to cause other defects. By adding risers for shrinkage compensation, the process yield of the casting itself is reduced, the later processing cost is increased, and the heat exchanger structure is complex, which increases the workload of product design.

[0024] In addition, related technologies also use refiners and modifiers to improve the microstructure and mechanical properties of alloys to ensure the shrinkage feeding effect of castings and reduce leakage defects. However, since the defects caused by insufficient shrinkage feeding are not obvious, the direct addition of any refiner cannot effectively improve the shrinkage feeding capacity and improve the yield rate. In order to solve the above technical problems, the embodiments of the present invention are as follows: Figure 1 This is a flow chart of a method for casting an aluminum-silicon alloy casting according to an embodiment of the present invention. As shown in the figure, an embodiment of the present invention provides a method for casting an aluminum-silicon alloy casting, and the specific steps of the method are as follows.

[0025] In step S101, a strontium-containing TCB refiner accounting for 0.2 wt% to 0.8 wt% of the total amount of the molten aluminum is added to the molten aluminum for refining, wherein the strontium content in the TCB refiner is 1 wt% to 5 wt%.

[0026] Step S102: Degassing is performed by a degasser during the refining process, and the product is allowed to stand still after the degassing is completed.

[0027] Step S103: After the standing period is completed, the density equivalent of the aluminum liquid is detected, and when the density equivalent reaches a preset range, pouring is performed.

[0028] The casting method of the aluminum-silicon alloy casting provided in this embodiment can improve the shrinkage feeding ability of the molten aluminum and the mechanical properties and thermal cracking resistance of the casting by adding a strontium-containing TCB refiner, in combination with degassing and static standing. This solves the problem of aluminum-silicon alloy heat exchangers, which are prone to shrinkage cavities and low yield due to large thickness differences in different areas of the wall and a complex structure resulting in a long shrinkage feeding path.

[0029] The aforementioned TCB refiner, also known as an aluminum-silicon alloy grain refiner, TCB (TiC-B), primarily composed of TiC (titanium carbide) and Boron (boron), refines alloy grains through heterogeneous nucleation, improving mechanical properties and casting quality. However, in aluminum-silicon alloy castings with complex structures and significant variations in wall thickness, such as in the casting of heat exchangers, the shrinkage feeding capability provided by conventional TCB refiners is insufficient, resulting in significant shrinkage defects and a high rate of defective parts.

[0030] To this end, this embodiment incorporates strontium (Sr) into the TCB refiner. Sr has been shown to effectively improve casting properties in aluminum alloys. This embodiment utilizes a strontium-containing TCB refiner at a total weight percentage of 0.2 wt% to 0.8 wt% of the total molten aluminum. This improves the shrinkage feeding capability of the molten aluminum during the refining of aluminum-silicon alloy castings, further enhancing the moldability of complex structures during the casting process and improving the yield rate of precious aluminum alloy castings. Sr can be added in the form of pure Sr or an Al-Sr aluminum-strontium alloy.

[0031] Specifically, the addition of strontium (Sr) to the TCB refiner can inhibit the formation of coarse plate-like Si phases in Al-Si aluminum-silicon alloys and promote the fiberization of eutectic Si, making the eutectic phase more uniformly distributed, reducing solidification shrinkage stress, and reducing shrinkage tendency.

[0032] During the solidification process, strontium (Sr) can change the solidification sequence. In Al-Si aluminum-silicon alloys, Sr preferentially forms high-melting-point compounds (such as strontium disilicide (Al2Si2Sr)) with aluminum (Al) and silicon (Si). This slightly increases the eutectic temperature and slows down the overall solidification process. This prolongs the existence of the mushy zone (solid-liquid two-phase region), allowing the melt more time to flow and feed.

[0033] Furthermore, strontium (Sr) adsorbs at the solid-liquid interface, reducing the surface tension between the melt and the solid phase and improving the wettability of the melt between dendrites. This allows the melt to more easily penetrate the interdendritic spaces, enhancing the capillary feeding effect. Sr can also partially reduce aluminum oxide (Al2O3), reducing the obstruction of the oxide film (Al2O3) to melt flow.

[0034] The addition of strontium (Sr) combines with hydrogen (H) to form strontium dihydride (SrH2), reducing the solubility of hydrogen in the melt and lowering the porosity of the aluminum-silicon alloy. Reducing porosity reduces melt flow resistance and improves the feeding path. Strontium (Sr) also absorbs hydrogen (H) from the air. After degassing, unreacted and unexpelled hydrogen (H) remains in the molten aluminum, increasing its gas content. The purpose of allowing the molten aluminum to rest after degassing is to allow time for bubbles in the molten aluminum to float and exhaust, further reducing its gas content.

[0035] Too low a strontium (Sr) content can lead to insufficient feeding capacity, incomplete eutectic silicon (Si) degradation, and the formation of hard Si phases between dendrites, which hinder melt flow. This poisoning of the Si in the Al-Si alloy leads to failure of the titanium diboride (TiB2), coarsening the grains, and increasing the feeding distance. Excessive Sr content, on the other hand, can form coarse Sr compounds. Furthermore, excess Sr reacts with aluminum (Al) and silicon (Si) to form massive strontium tetraaluminide (Al4Sr) or strontium disilicide (SrSi2), which become new inclusion sources and block the feeding path.

[0036] To this end, this embodiment provides a method of using a strontium-containing TCB refiner with a total weight accounting for 0.2 wt %-0.8 wt % of the total amount of molten aluminum, and the strontium content in the TCB refiner is 1 wt %-5 wt % to refine the molten aluminum before pouring.

[0037] As mentioned above, the addition of strontium (Sr) combines with hydrogen (H) to form strontium dihydride (SrH2), which reduces the solubility of hydrogen in the melt and lowers the porosity of the aluminum-silicon alloy. However, SrH2 decomposes at high melting temperatures (>700°C), releasing hydrogen (H2). This increases gas production during the aluminum refining process, necessitating the use of a degasser to remove the released H2. This prevents further dissolution of the released H2, which can lead to insignificant porosity reduction.

[0038] The purpose of standing still after degassing is to allow strontium Sr and TCB refiner to further play a role in the aluminum liquid, making the aluminum liquid performance uniform and stable, and facilitating subsequent pouring.

[0039] In this embodiment, as an optional solution, the total weight of the TCB refiner relative to the total amount of molten aluminum is 0.4 wt % to 0.6 wt %. As mentioned above, the strontium (Sr) content further affects the shrinkage feeding ability of the casting. Within the aforementioned range of 0.2 wt % to 0.8 wt %, a TCB refiner content of 0.4 wt % to 0.6 wt % is further preferred to more precisely control the Sr content and ensure the shrinkage feeding ability of the molten aluminum.

[0040] Furthermore, as an optional solution, the total weight of the TCB refiner accounts for 0.5 wt% of the total amount of the aluminum liquid.

[0041] For similar reasons, a TCB refiner with a strontium content of 2 wt%-3 wt% is an alternative. This can effectively improve the shrinkage feeding capacity of the aluminum liquid, thereby reducing the defective rate of aluminum-silicon alloy castings.

[0042] As an optional solution, degassing is performed by a degasser during the refining process, and the aluminum is allowed to stand for 2 minutes to 10 minutes after the degassing is completed. The solution includes: adding a slag remover to the aluminum liquid; degassing by the degasser for 10 minutes to 20 minutes, a degassing flow rate of 14 L / min to 16 L / min, and a degassing pressure of 3 bar to 5 bar; and standing for 2 minutes to 10 minutes after the degassing is completed.

[0043] Degassing during aluminum refining is to remove hydrogen and inclusions (such as aluminum oxide Al2O3) from the molten aluminum, preventing defects such as porosity and looseness in the castings. The temperature range is 700°C to 740°C. Excessively high temperatures (>750°C) intensify hydrogen dissolution and oxidation burns. Excessively low temperatures (<700°C) impair fluidity, hindering the deterioration of the aluminum-strontium alloy, resulting in a weakened deterioration effect and poor degassing.

[0044] The degassing medium can be argon (Ar). Argon is an inert gas that does not react with the aluminum liquid. It removes hydrogen and inclusions through bubble flotation. The hydrogen partial pressure within the argon bubbles is zero, so hydrogen in the aluminum liquid diffuses into the bubbles and floats to the surface. Argon is typically blown through rotary jets or through permeable bricks.

[0045] If the degassing time is too short, the hydrogen H2 will not be removed in time and will redissolve in the aluminum liquid. If the degassing time is too long, the argon Ar will be wasted, and the refining time will be extended, resulting in energy waste. The preferred degassing time is 10-20 minutes.

[0046] A degassing flow rate that is too low will result in incomplete contact with the molten aluminum, making it difficult for the H2 to diffuse and hindering its extraction. A degassing flow rate that is too high will cause the molten aluminum to tumble and cause temperature loss. Preferably, the degassing flow rate is 14 L / min to 16 L / min.

[0047] The degassing pressure is similar to the degassing flow rate. Too high or too low will lead to the deterioration of the aluminum liquid refining effect. Preferably, the degassing pressure is 3 bar ~ 5 bar.

[0048] In this embodiment, the preferred degassing time is 15 min, the degassing flow rate is 15 L / min, and the degassing pressure is 4 bar.

[0049] As an optional solution, a strontium-containing TCB refiner with a total weight accounting for 0.2 wt%-0.8 wt% of the total amount of the aluminum liquid is added to the aluminum liquid before refining. The method also includes: melting the intermediate alloy aluminum ingot and the return material through a melting furnace, and the proportion of the return material to the total amount of the melting material does not exceed 50 wt%; adding the melting aluminum liquid to a holding furnace for insulation so that the aluminum liquid temperature reaches 700℃-740℃.

[0050] In actual production, the sources of molten aluminum can include master alloy aluminum ingots and recycled materials. The recycled materials contain a lot of impurities. Therefore, the ratio of recycled materials to the total amount of chemical materials is controlled to no more than 50wt%. The molten aluminum from the chemical materials is added to the holding furnace for insulation to keep the molten aluminum temperature at 700℃-740℃. This is to ensure that the molten aluminum temperature reaches the degassing and refining temperature requirements for effective degassing.

[0051] Figure 2 This is a flow chart of TCB refiner and aluminum strontium alloy addition in aluminum liquid refining according to an embodiment of the present invention. Figure 2 As shown, as an optional solution, step S101, adding a strontium-containing TCB refiner with a total weight accounting for 0.2 wt%-0.8 wt% of the total weight of the aluminum liquid to the aluminum liquid for refining, including: step S1011, calculating a first addition amount of the aluminum-strontium alloy according to the strontium element accounting for 0.008 wt%-0.025 wt% of the total weight of the aluminum liquid and the strontium content of the aluminum-strontium alloy; step S1012, calculating a second addition amount of the strontium-containing TCB refiner according to the strontium content of the TCB refiner, the total weight of the aluminum liquid, and the total weight proportion of strontium in the TCB refiner of 0.2 wt%-0.8 wt%; step S1013, adding the aluminum-strontium alloy and the strontium-containing TCB refiner to the aluminum liquid for modification treatment according to the first addition amount and the second addition amount.

[0052] When adding a strontium-containing TCB refiner, aluminum-strontium alloy can be added simultaneously or slightly later for modification. This modification alters the morphology of the eutectic silicon from coarse, needle-like flakes to fine fibers or spheres, significantly improving the plasticity and strength of the aluminum-silicon alloy. Strontium modification is an environmentally friendly alternative to traditional sodium or antimony processes, offering more stable and long-lasting results.

[0053] If the amount of strontium (Sr) added is too low, the modification effect will be insufficient, and the silicon phase will remain needle-shaped. If the amount is too high, a brittle Sr-Al-Si phase may form, increasing the melt viscosity and the tendency to get gas. When adding Sr, it is necessary to add it when the aluminum liquid temperature is 720-740℃ and stir it evenly.

[0054] Strontium (Sr) is easily burned and needs to be added during the refining process, and long-term high-temperature retention is avoided. This is also the reason why the above-mentioned degassing process cannot be carried out for a long time.

[0055] During the aluminum liquid refining process, the modifier strontium Sr is added at the same time as the TCB refiner to prevent the titanium diboride TiB2 in the TCB refiner from reacting with strontium Sr to form SrB6 strontium hexaboride, which reduces the modification efficiency.

[0056] As an optional solution, the density equivalent of the aluminum liquid is tested after the static state, including: pouring a normal pressure sample and a vacuum sample through the static aluminum liquid, wherein the vacuum degree of the vacuum sample is 80±5mbar and the vacuum time is maintained for 4 minutes to 6 minutes during the pouring process; and detecting the difference between the density of the normal pressure sample and the density of the vacuum sample to determine the density equivalent.

[0057] Density Equivalent is a standardized representation of the difference between the density measured in a vacuum and at atmospheric pressure. It is usually calculated by taking the difference between the atmospheric density of a sample at atmospheric pressure and the vacuum density of a sample at vacuum.

[0058] Density equivalents can include absolute density equivalents, directly using the density difference Δρ = ρa − ρv, where ρa is the vacuum density and ρv is the atmospheric density. Alternatively, relative density equivalents can be used, normalizing the density difference to atmospheric density or vacuum density: density equivalent = Δρ / ρv or Δρ / ρa. In this example, absolute density equivalents are used to assess the purity and gas content of the molten aluminum.

[0059] When the density equivalent meets the requirements, confirm that the purity is high enough, the gas content is low enough, and the shrinkage feeding capacity of the aluminum liquid has been effectively improved before pouring.

[0060] As an optional solution, the method further includes: if the density equivalent does not reach a preset range, re-degassing and allowing the aluminum liquid to stand until the density equivalent of the aluminum liquid after standing reaches a preset range.

[0061] If the density equivalent does not reach the preset range, it means that the degassing is not complete and it is necessary to re-degas and let it stand. For specific parameters, refer to the above degassing process and standing parameters. Continue until the density equivalent of the aluminum liquid after standing reaches the preset range.

[0062] As an optional solution, when the density equivalent reaches a preset range, pouring includes: measuring the temperature of the aluminum liquid when the density equivalent reaches the preset range; and pouring when the temperature of the aluminum liquid reaches 723°C-733°C.

[0063] If the temperature of the molten aluminum is too low, its fluidity is poor and it is easy to cause surface defects. If the temperature is too high, it is easy to corrode the mold and increase the solidification yield, which requires higher shrinkage feeding capacity. Therefore, the temperature of the molten aluminum should be measured again before pouring. The pouring temperature is controlled by adjusting the insulation temperature of the insulation resistance furnace to ensure that the molten aluminum temperature meets the pouring temperature of 723℃~733℃.

[0064] The embodiment of the invention also provides a method for refining aluminum liquid of aluminum-silicon alloy, which is applied to the casting of aluminum-silicon alloy castings. Figure 2 As shown, optionally, the aluminum liquid refining method of the aluminum-silicon alloy provided in the embodiment of the present invention can be used in the casting method of the aluminum-silicon alloy casting provided in the above embodiment. The method includes the following steps.

[0065] Step S1011: Calculate a first addition amount of the aluminum-strontium alloy based on the strontium element accounting for 0.008 wt %-0.025 wt % of the total weight of the aluminum liquid and the strontium content of the aluminum-strontium alloy.

[0066] Step S1012 , calculating a second addition amount of the strontium-containing TCB refiner based on the strontium content of the TCB refiner, the total amount of molten aluminum, and the total weight proportion of strontium in the TCB refiner of 0.2 wt % to 0.8 wt %.

[0067] Step S1013 : adding the aluminum-strontium alloy and the strontium-containing TCB refiner to the aluminum liquid for modification treatment according to the first addition amount and the second addition amount.

[0068] Step S1014: degassing is performed by a degasser during the refining process, and the molten aluminum is allowed to stand after the degassing is completed. The molten aluminum after standing can be used for casting aluminum-silicon alloy castings.

[0069] The steps of adding TCB refiner and strontium aluminum alloy may be performed according to the above steps S1011 to S1013.

[0070] The aluminum liquid refining method of the above-mentioned aluminum-silicon alloy provided in the embodiment of the present invention modifies the aluminum liquid by using an aluminum-strontium alloy to change the metallographic structure and improve the plastic strength. By adding a strontium-containing TCB refiner and coordinating degassing and standing, the shrinkage feeding ability of the aluminum liquid can be improved, and the mechanical properties and thermal cracking resistance of the casting can be improved. This solves the problem of aluminum-silicon alloy heat exchangers, where the wall thickness varies greatly in different areas and the complex structure leads to a long shrinkage feeding path, which makes the device prone to shrinkage cavities and low yield.

[0071] As mentioned above, the TCB refiner and the aluminum strontium alloy can be added simultaneously, or the TCB refiner can be added first and then the aluminum strontium alloy can be added within a preset time, for example, 10 seconds, 15 seconds.

[0072] It should be noted that this embodiment also provides an optional implementation, which is described in detail below.

[0073] Figure 3 Schematic diagram of the aluminum-silicon alloy heat exchanger according to the embodiment of the present invention, as shown in FIG. Figure 3As shown, in the related art, an AlSi alloy heat exchanger is cast by sand gravity casting. The main structure is composed of an outer shell and a combustion chamber. The cavity between the outer shell and the combustion chamber is a water jacket. The heat exchanger mainly uses gas in the combustion chamber to heat the heating water and domestic water in the water jacket. There is a certain proportion of leakage defects in the water jacket and the combustion chamber, which makes it difficult to meet the finished product inspection requirements.

[0074] Even adjusting the casting process, changing the pouring temperature, pouring method, or gating system structure, it's still difficult to ensure shrinkage compensation across the heat exchanger's varying wall thicknesses without causing leakage. Furthermore, these castings are sensitive to changes in the casting process, making it difficult to change the casting process without introducing other defects. However, the heat exchanger's relatively complex structure makes it difficult to add risers or chillers to compensate for shrinkage, and this increases the workload for subsequent cleaning and sawing.

[0075] This embodiment relates to a method for improving leakage defects in AlSi alloy heat exchangers by adding a strontium-containing TCB refiner. By adding the TCB refiner during the pre-furnace aluminum treatment process, the heterogeneous nucleation substrate in the molten aluminum is increased. The Ti in the TCB refiner significantly inhibits α-Al grain growth, promotes equiaxed grain formation, reduces the thickness of the mushy zone, and enhances the shrinkage feeding capacity of the molten aluminum. This reduces casting void defects, improves heat exchanger leakage, and reduces the defect rate.

[0076] Before the aluminum liquid is refined and degassed, a strontium-containing TCB refiner is added in an amount of 0.5% of the total weight of the aluminum liquid to be refined. The main components of the TCB refiner include (strontium Sr: 2.0~3.0%, carbon C: 0.03~0.10%, boron B: 1.5~2.5%, silicon Si≤0.3%, iron Fe≤0.3%, and the matrix is ​​aluminum Al). Combined with the existing aluminum liquid composition control, casting process, and casting parameters of the product casting, the leakage defect rate is reduced.

[0077] In this embodiment, TCB refiner is added before the aluminum liquid is refined and degassed, the degassing time is 15 minutes, the degassing flow rate is 14-16 L / min, the degassing pressure is 3-5 bar, the aluminum liquid refining temperature is 700-740°C, and the aluminum liquid density equivalent is detected after standing for 5 minutes after degassing.

[0078] The specific process is introduced as follows.

[0079] 1. Heat exchanger material composition requirements are as follows: Silicon (Si) (10-11)%, Iron (Fe) ≤ 0.55%, Copper (Cu) ≤ 0.05%, Zinc (Zn) ≤ 0.10%, Magnesium (Mg) (0.20-0.45)%, Manganese (Mn) ≤ 0.45%, Nickel (Ni) ≤ 0.05%, Lead (Pb) ≤ 0.05%, Tin (Sn) ≤ 0.05%, Titanium (Ti) ≤ 0.15%, and other impurity elements ≤ 0.15%. The remaining element is aluminum (Al). The product is pre-furnace smelting using an aluminum-silicon alloy + master alloy batching process.

[0080] Casting materials: Use centralized melting furnace for centralized material processing. The materials are composed of master alloy aluminum ingots that meet the composition requirements and recycled materials. The proportion of recycled materials shall not exceed 50% of the total weight of the charging materials.

[0081] The insulation temperature of the centralized melting furnace is 700~760℃, and the molten aluminum is discharged from the centralized melting furnace to the insulation furnace of the casting unit.

[0082] 2. After discharging, the aluminum liquid is temperature-measured. Refining and degassing are performed when the aluminum liquid temperature is between 700°C and 740°C. This process combines degassing with aluminum-strontium alloy modification and TCB refinement. The aluminum liquid is degassed using argon at a refining temperature of 700°C to 740°C. The aluminum liquid is added with an Sr content of 0.008-0.025%. The TCB refiner is added at a level of 0.5% of the total aluminum liquid. Degassing is performed using a dedicated degasser. The degassing parameters are: degassing time of 15 minutes, degassing flow rate of 14-16 L / min, and degassing pressure of 3-5 bar. After degassing, the aluminum liquid is allowed to rest for 5 minutes before its density is measured.

[0083] The refining degassing treatment is carried out by a degasser. The degasser rotates at a low speed to enter the molten aluminum. After the degasser automatically adds the slag agent, the degasser rotates at a high speed to create a vortex, which promotes the uniform fusion reaction of the molten aluminum and the slag agent in the insulation furnace. After 1 minute and 30 seconds of the degassing process, the degassing speed is restored to medium speed for degassing.

[0084] 3. After degassing, let the aluminum liquid stand for 5 minutes. After standing, perform density equivalent test on the aluminum liquid. Pour density equivalent test samples under normal pressure and negative pressure respectively. The vacuum degree of the vacuum sample is required to be (80±5) mbar. The vacuum time is maintained for 4 minutes. The density difference between the normal pressure and vacuum samples is calculated by the testing equipment to obtain the density equivalent. The heat exchanger requires a density equivalent range of 0~2.

[0085] When the density equivalent exceeds the required range, the aluminum liquid needs to be degassed twice on site to reduce the gas content in the aluminum liquid. After degassing, it should be left to stand for 5 minutes to test the density equivalent. Casting can only be carried out after the density equivalent meets the requirements.

[0086] 4. Before pouring, the aluminum liquid should be temperature-measured again. The pouring temperature is controlled by adjusting the insulation temperature of the insulation resistance furnace to ensure that the aluminum liquid temperature meets the pouring temperature (723~733℃). After the aluminum liquid meets the temperature, the heat exchanger is cast using the sand casting process.

[0087] The sand mold gravity casting process has a filling time of 7 to 10 seconds. The pouring is completed automatically by a robot. After the pouring is completed, the height of the aluminum liquid in the riser of the sand bag can be used to determine whether the mold is filled properly.

[0088] 5. After the casting is completed and the gating system is sawn and cleaned, the cover is welded and the water jacket airtightness test is performed. The heat exchanger is produced using a sand casting process and the product material is AlSi10 (ISO 3522). The overall structure includes the outer shell and the combustion chamber. The cavity between the outer shell and the combustion chamber is the water jacket. The product inspection requirements are as follows.

[0089] The air tightness test adopts quantitative leakage detection, with a leakage rate of ≤0.8ml / min and a test pressure of 3.0±0.1bar. Quantitatively unqualified parts are re-inspected by water inspection to determine the leakage location. The test pressure is 4.50+0.5bar, and the pressurized medium is compressed air. The leak detection is carried out underwater, and the pressure is maintained for 2 minutes without leakage or obvious deformation.

[0090] The customer requires that all castings delivered must be tested for water jacket air tightness.

[0091] 6. Summarizing multiple rounds of data, the addition of TCB refiner reduced the quantitative defective (NG) rate by 4.47%, the body leakage rate by 3.39%, and the body leakage scrap rate by 0.97%. See Table 1 below, which shows the heat exchanger quality data.

[0092] Table 1 Heat exchanger quality data

[0093] Quantitative inspection number Quantitative NG number Quantitative NG rate Body leakage NG number Body leakage rate Number of scrapped bodies due to leakage Body leakage scrap rate Add TCB refiner 2000 82 4.10% 38 1.90% 5 0.25% No TCB refiner added 2000 169 8.45% 106 5.30% 24 1.20%

[0094] The standard for NG products can be slight leakage in quantitative leakage testing, for example, a leakage rate > 0.8 ml / min and ≤ 4 ml / min (five times the leakage rate of good products). This can be repaired by soldering.

[0095] The standard for scrapping is severe leakage, for example, a leakage rate of >4 ml / min, which cannot be repaired by welding and can only be scrapped.

[0096] As can be seen from Table 1 above, after adding the TCB refiner containing strontium, the defective product rate NG, leakage rate and scrap rate were significantly reduced.

[0097] It should be noted that the term "including" and its variations used in the embodiments of the present invention are open inclusions, that is, "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments". The modifications of "one" and "multiple" mentioned in the embodiments of the present invention are illustrative and not restrictive. Those skilled in the art should understand that unless the context clearly indicates otherwise, they should be understood as "one or more".

[0098] The various steps described in the method implementation methods provided by the embodiments of the present invention may be performed in different orders and / or in parallel. In addition, the method implementation methods may include additional steps and / or omit the steps shown. The scope of protection of the present invention is not limited in this respect.

[0099] The term "embodiment" in this specification refers to specific features, structures or characteristics described in conjunction with the embodiment that can be included in at least one embodiment of the present invention. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor does it mean that it is mutually exclusive with other embodiments and is independent or optional. The various embodiments in this specification are described in a related manner, and the same or similar parts between the various embodiments are referenced to each other. In particular, for the device, equipment, and system embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts refer to the partial description of the method embodiment.

[0100] The above-described embodiments merely represent several implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of protection. It should be noted that a person of ordinary skill in the art would be able to make various modifications and improvements without departing from the scope of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for casting an aluminum-silicon alloy casting, characterized in that: include: A strontium-containing TCB refiner, whose total weight accounts for 0.2 wt % to 0.8 wt % of the total weight of the aluminum liquid, is added to the aluminum liquid for refining, wherein the strontium content in the TCB refiner is 1 wt % to 5 wt %; During the refining process, degassing is carried out through a degasser and the degassing is allowed to stand after completion; After the standing period is completed, the density equivalent of the aluminum liquid is detected, and pouring is performed when the density equivalent reaches a preset range.

2. The method according to claim 1, characterized in that The total weight of the TCB refiner accounts for 0.4 wt % to 0.6 wt % of the total amount of the aluminum liquid.

3. The method according to claim 2, characterized in that The total weight of the TCB refiner accounts for 0.5 wt % of the total amount of the aluminum liquid.

4. The method according to claim 1, wherein The TCB refiner has a strontium content of 2 wt % to 3 wt %.

5. The method according to claim 1, wherein During the refining process, degassing is carried out by a degasser and the steel is left to stand after degassing, including: adding a slagging agent to the aluminum liquid; The degassing time of the degassing machine is 10min-20min, the degassing flow rate is 14L / min~16L / min, and the degassing pressure is 3bar~5bar; After degassing, let it stand for 2-10 minutes.

6. The method according to claim 1, characterized in that Before adding 0.2 wt % to 0.8 wt % of a strontium-containing TCB refiner to the molten aluminum for refining, the method further comprises: The master alloy aluminum ingot and the recycled materials are melted in a melting furnace, wherein the recycled materials and the total amount of the melted materials do not exceed 50 wt %; The aluminum liquid of the smelting material is added to the insulation furnace for insulation so that the temperature of the aluminum liquid reaches 700°C-740°C.

7. The method according to claim 1, characterized in that A strontium-containing TCB refiner, whose total weight accounts for 0.2 wt % to 0.8 wt % of the total weight of the molten aluminum, is added to the molten aluminum for refining, including: Calculating a first addition amount of the aluminum-strontium alloy based on a strontium element ratio of 0.008 wt % to 0.025 wt % of the total weight of the aluminum liquid and a strontium content of the aluminum-strontium alloy; Calculate the second addition amount of the strontium-containing TCB refiner based on the strontium content of the TCB refiner, the total amount of aluminum liquid, and the total weight ratio of 0.2 wt % to 0.8 wt %; According to the first addition amount and the second addition amount, the aluminum-strontium alloy and the strontium-containing TCB refiner are added to the aluminum liquid for modification treatment.

8. The method according to claim 1, characterized in that After the standing period, the density equivalent of the aluminum liquid is detected, including: The aluminum liquid after standing is used to cast the atmospheric pressure sample and the vacuum sample, wherein the vacuum degree of the vacuum sample is 80±5mbar, and the vacuum time is maintained for 4min-6min during the casting process; Detecting a difference between the density of the atmospheric pressure sample and the density of the vacuum sample to determine a density equivalent, wherein the density equivalent is used to characterize the gas content in the aluminum liquid; After the standing period is completed and the density equivalent of the aluminum liquid is detected, the method further includes: If the density equivalent does not reach the preset range, degassing and resting are repeated; Until the density equivalent of the aluminum liquid after standing reaches a preset range.

9. The method according to any one of claims 1 to 8, characterized in that When the density equivalent reaches the preset range, pouring includes: When the density equivalent reaches a preset range, measuring the temperature of the aluminum liquid; When the temperature of the aluminum liquid reaches 723° C.-733° C., pouring is performed.

10. A method for refining molten aluminum of aluminum-silicon alloy, characterized in that: include: Calculate the first addition amount of the aluminum-strontium alloy based on the strontium element accounting for 0.008 wt %-0.025 wt % of the total weight of the aluminum liquid and the strontium content of the aluminum-strontium alloy; The second addition amount of the strontium-containing TCB refiner is calculated based on the strontium content of the TCB refiner, the total amount of aluminum liquid, and the total weight proportion of strontium in the TCB refiner of 0.2 wt % to 0.8 wt %. adding an aluminum-strontium alloy and a strontium-containing TCB refiner to the aluminum liquid for modification according to a first addition amount and a second addition amount; During the refining process, degassing is carried out by a degasser and the steel is allowed to stand after degassing is completed.

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