A heat treatable high strength low carbon cast aluminum alloy and method of making same

Abstract

The present application relates to a kind of heat-treatable high-toughness low-carbon casting aluminum alloy and its preparation method, the alloy includes Si:6.5-8.5wt%; Fe:0.01-0.55wt%; Mg:0.40-0.65wt%; Cu:0.005-0.50wt%; Zn:0.30-2.0wt%; Mn:0.005-0.40wt%; Cr:0.005-0.20wt%; Mo:0.005-0.05wt%; Ce:0.005-0.10wt%; Ti:0.05-0.20wt%; Sr:0.005-0.03wt%; The sum of the weight percentage of the rest impurities is controlled below 0.5wt%, and the balance is Al.The aluminum alloy piece of the present application has excellent yield strength and excellent elongation after heat treatment.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, specifically to a heat-treatable high-strength, high-toughness, low-carbon cast aluminum alloy and its preparation method. Background Technology

[0002] Aluminum alloys, due to their excellent properties such as lightweight, high strength, good corrosion resistance, and formability, have been widely used in the automotive manufacturing industry. Cast aluminum alloys, in particular, offer significant advantages in the manufacture of automotive chassis components and subframes. A356.2 alloy, as a typical cast aluminum alloy grade, is widely used due to its excellent casting and mechanical properties. A356.2 alloy belongs to the hypoeutectic aluminum-silicon alloy family and possesses good overall performance.

[0003] However, with the continuous development of the automotive industry, automakers have increasingly higher requirements for vehicle lightweighting and cost control. Vehicle lightweighting not only improves fuel efficiency and reduces emissions, but also enhances vehicle power and handling performance. Therefore, reducing product thickness has become an important means of achieving lightweighting. However, existing A356.2 aluminum alloys have certain limitations in terms of mechanical properties, with relatively low strength (tensile strength 280-310 MPa, yield strength 200-230 MPa, elongation after fracture 6-10%). Especially when reducing product thickness, they cannot meet the requirements for high strength and high toughness. To meet the demands of automotive lightweighting and material cost reduction, there is an urgent need to develop a cast aluminum alloy material with higher strength and better toughness. This material should provide sufficient strength and durability even with reduced thickness, thus meeting the demands of modern automotive manufacturing for lightweighting and high performance. Therefore, developing a cast aluminum alloy material with both high strength and good toughness has become a key research focus and challenge.

[0004] However, the repeated recycling process inevitably introduces and enriches the impurity element Fe, resulting in low-carbon aluminum generally exhibiting a high Fe content. In the field of traditional high-strength aluminum alloys (especially in the T6 heat-treated state), Fe is considered a harmful impurity. This is because Fe readily forms coarse, needle-like iron-rich phases, severely disrupting the matrix and causing a sharp decline in alloy elongation. To ensure product toughness, current technologies impose extremely stringent restrictions on Fe content (typically requiring <0.15%), which directly renders low-carbon aluminum with high Fe content (Fe > 0.20%) unsuitable for manufacturing high-end structural components, forcing it to be used in downgraded applications. On the other hand, while die-casting processes objectively require a certain Fe content to prevent mold sticking, the brittle fracture problem caused by high Fe in existing die-cast aluminum alloys remains prominent after T6 heat treatment, making it difficult to achieve a balance between high strength and good plasticity.

[0005] Currently, conventional methods for addressing the hazards of high Fe (such as physical iron removal) have shortcomings such as high cost, limited effectiveness, or narrow process window, and cannot fundamentally resolve the technical contradiction between high Fe content and high performance requirements in low-carbon aluminum.

[0006] Therefore, how to utilize the characteristics of die casting process to develop an aluminum alloy material that can tolerate high Fe content and still maintain excellent elongation after T6 heat treatment has become a key technical issue for breaking through the bottleneck of low-carbon aluminum application and realizing the green transformation of the aluminum industry.

[0007] Patent CN117821813B discloses an aluminum alloy material for automotive subframes and its preparation method. The material composition in this patent is: Si: 7.5-9.5%, Cu: 0.8-1.7%, Zn≤0.6%, Mn≤0.2%, Mg: 0.35-0.65%, Fe≤0.25%, Mo: 0.03%-0.25%, Sr: 0.01-0.45%, where 8.7≤Cu+19.8 Mg ≤ 11.5%; Zn / Mg mass fraction ratio is 0.5-1.5%; Fe+Mn+Mo mass fraction sum is 0.2-0.65%; Fe / Mo mass fraction ratio is 2.0-6.5%. The patent, by controlling the ranges of Zn / Mg and Fe / Mo, and simultaneously regulating the design range of the sum of Fe+Mn+Mo mass fractions, eliminates the root cause of "poisoning," achieving dual effects of fine-grain strengthening and interface coherent strengthening. Furthermore, the dispersion strengthening effect brought about by the precipitation of Cu, Mg, Zn, and Mo during artificial aging improves the mechanical properties of the material. Generally, below the solidus line, a high solution heat treatment temperature can accelerate the release of residual stress and atomic diffusion in the material, reduce element segregation, and the higher the solution temperature, the greater the amount of dissolved elements, resulting in a better age hardening effect. However, the high Si and Cu content in the patented design significantly reduces the solidus temperature of the material, making it impossible to perform heat treatment at higher solution temperatures. The solution temperature is limited to the range of 500±10℃, resulting in an unsatisfactory solution effect. As a result, although the yield strength of the alloy in this patented system is significantly improved, its elongation is still not better than that of A356.2. Summary of the Invention

[0008] In view of the above problems, the purpose of this invention is to overcome the defects of the prior art by providing a heat-treatable high-strength and high-toughness low-carbon cast aluminum alloy material, and to provide a method for preparing a heat-treatable high-strength and high-toughness low-carbon cast aluminum alloy.

[0009] The objective of this invention can be achieved through the following technical solution: a heat-treatable high-strength, high-toughness, low-carbon cast aluminum alloy, comprising: Si: 6.5-8.5 wt%; Fe: 0.01-0.55 wt%; Mg: 0.40-0.65 wt%; Cu: 0.005-0.50 wt%; Zn: 0.30-2.0 wt%; Mn: 0.005-0.40 wt%; Cr: 0.005-0.20 wt%; Mo: 0.005-0.05 wt%; Ce: 0.005-0.10 wt%; Ti: 0.05-0.20 wt%; Sr: 0.005-0.03 wt%; the sum of the weight percentages of other impurities is controlled below 0.5 wt%, with the balance being Al; wherein: The mass ratio of Fe / (Mn+Cr) elements is 0.5-4:1; The sum of the weight percentages of Fe, Mn, and Cr elements is ≤1.2wt%.

[0010] Furthermore, the microstructure of the cast aluminum alloy comprises α-Al, Al-Si eutectic structure and precipitated phases; The precipitated phases include AlFe(Mn,Cr)Si phase, π-Al8Mg3FeSi6 phase, and Al 12 Mo, Mg2Si phase and Q-Al5Si5Cu2Mg8 phase; The tissue contains AlFe(Mn,Cr)Si phase and π-Al8Mg3FeSi6 phase distributed in a diffuse particle pattern, with morphologies including short rod-shaped and blocky.

[0011] This invention also provides a method for preparing a heat-treatable high-strength, high-toughness, low-carbon cast aluminum alloy, the method comprising the following steps: Step S1: First, weigh out the pure Al raw materials, Cu raw materials, Mg raw materials, Zn raw materials, Al-Fe, Al-Mn, Al-Cr, Al-Mo, Al-Si, Al-Ti, Al-Sr and Al-Ce alloys according to the mass ratio; Step S2: First, put pure aluminum into the heating furnace and heat it to 680°C to obtain molten aluminum. After the molten aluminum is completely melted, let it stand and keep it at the temperature for 20-30 minutes. Step S3: Heat to 780℃, add Al-Si alloy, Cu raw material, Al-Fe, Al-Mn, Al-Mo and Al-Cr to the aluminum liquid in proportion, and wait for it to completely dissolve; Step S4: Cool down to 740℃, add Al-Ce, and keep warm for 20~30 minutes; Step S5: Cool down to 720℃, add Mg raw materials, Zn raw materials, Al-Ti and Al-Sr alloy, hold for 15-20 minutes and then degas and refine; Step S6: Cast a small sample for composition analysis. If it passes the analysis, send the melt into the casting equipment to form an aluminum alloy component.

[0012] Further: In step S5, degassing and refining involves introducing a dry gas, either nitrogen or argon, into the aluminum alloy melt. The amount of solid refining gas added is 0.2-0.4% of the melt mass, and the refining time is 10-20 minutes.

[0013] Further: The aluminum alloy components are subjected to T6 heat treatment, specifically: the aluminum alloy components are subjected to solution heat treatment at 510-540℃ for 3-6 hours. After solution treatment, they are rapidly cooled with cooling water for 2-4 minutes until the temperature drops below 65℃, and then artificially aged at 165-180℃ for 4-8 hours.

[0014] Furthermore, the aluminum alloy product obtained after T6 heat treatment has the following mechanical properties: tensile strength ≥340 MPa, yield strength ≥290 MPa, and elongation ≥9%.

[0015] Furthermore: In step S6, the mold cooling of the casting equipment adopts a contour spray intelligent system for spray cooling, which includes a multi-functional atomizing nozzle and a contour spray nozzle layout structure.

[0016] Furthermore, the contour-following spray intelligent system includes: The spray head valve body of the sprayer is equipped with a low-concentration spray ratio solenoid valve and a high-concentration spray ratio solenoid valve. The valve body is connected to the low-concentration release agent pipeline and the high-concentration release agent pipeline respectively. The two sets of ratio solenoid valves independently control the on / off and flow rate of the corresponding release agent. The three-fluid atomizing nozzle is equipped with a high-concentration spray port, a compressed gas port, and a low-concentration spray port. The spray volume is adjusted by controlling the opening and closing of the internal needle valve through the proportional solenoid valve. The contour-following nozzles are positioned to match the contour of the molded product and consist of long nozzles, short nozzles, and irregularly shaped contour-following nozzles. A high-pressure energy storage tank is connected to the compressed gas supply circuit of the contour spray intelligent system and is equipped with a high-pressure spray head. The solenoid valve bus valve island is electrically connected to the industrial computer and receives analog control signals output by the industrial computer to drive the proportional solenoid valves to operate.

[0017] Furthermore, in the three-fluid atomizing nozzle, the high-concentration spray proportional solenoid valve is connected to the corresponding high-concentration spray port, and the low-concentration spray proportional solenoid valve is connected to the corresponding low-concentration spray port. The two sets of proportional solenoid valves independently control the flow rate of their respective release agents. The industrial computer outputs analog signals to each proportional solenoid valve via the solenoid valve bus island, achieving precise control of the spray volume. During the casting process, the water:release agent ratio is 40~120:1.

[0018] This invention's three-fluid atomizing nozzle can simultaneously supply both low-concentration and high-concentration release agents. Two independent proportional solenoid valves control their respective flow rates. An industrial computer outputs precise analog signals via a bus valve island to achieve differentiated spraying control by region and proportion. In areas with poor heat dissipation, such as deep mold cavities, the flow rate and concentration can be appropriately increased, while in easily cooled areas like protrusions, the amount is precisely controlled. This ensures effective release while preventing excessive release agent accumulation that could affect casting quality, achieving an optimal balance between cooling efficiency and release performance.

[0019] Furthermore, the layout of the contour-following nozzle is matched with the contour-following structure of the mold cavity, wherein: Long nozzles are used to spray coatings deep into the cavity of the mold. Short nozzles are used for spraying and cooling the raised areas of the mold; The irregularly shaped spray nozzle is designed for complex or narrow areas of the mold, and achieves close-fitting spraying with its irregular structure; The three types of nozzles are used together to achieve comprehensive spraying and cooling of the mold without any blind spots.

[0020] Traditional die-casting spraying uses a robotic arm linked with a machine tool, with the spray nozzle reciprocatingly scanning the mold. This process involves long strokes and is time-consuming, resulting in insufficient cooling of deep cavities, bosses, and complex contours, leading to significant temperature differences between different areas of the mold. This invention employs long, short, and irregularly shaped spray nozzles arranged to conform to the mold's contour. The sprayer descends to its designated position in a single stroke, simultaneously spraying the entire mold cavity without any blind spots. This significantly reduces the spraying time per mold, eliminates localized hot spots caused by incomplete spraying, ensures a more uniform cooling rate across all areas of the mold, and significantly improves the overall rapid cooling effect.

[0021] Furthermore, the high-pressure energy storage tank serves as a supplementary source of compressed air for the casting equipment, while simultaneously providing high-pressure spraying to the mold, achieving stable and rapid overall cooling of the mold. The high-pressure energy storage tank, designed with a pressure of 0.5-2.5 MPa, has two functions: 1) During normal spraying, when all spray heads are spraying simultaneously, a large flow of compressed gas needs to be released at the same time. The high-pressure accumulator acts as a supplementary source of compressed air, preventing instability in the spraying system due to insufficient air pressure, ensuring that the atomization effect and spray volume of each spray head accurately respond to control commands, and guaranteeing uniformity and consistency in spraying; 2) During die casting, molten aluminum easily adheres locally to the mold surface, forming residual aluminum skin. If not removed in time, this will lead to surface defects in subsequent castings and the accumulation of local hot spots in the mold. The high-pressure spray head of this invention, relying on the high-pressure, high-flow-rate gas provided by the high-pressure energy storage tank, performs directional and powerful blowing on the areas of the mold where aluminum adheres, effectively removing residues from the mold surface, maintaining mold surface cleanliness, and simultaneously using the high-pressure airflow to provide additional cooling compensation to this area, further ensuring uniform cooling of the entire mold.

[0022] Compared with existing technologies, the working mechanism and advantages of this heat-treatable high-strength and high-toughness low-carbon cast aluminum alloy are as follows: 1) In the cast aluminum alloy of this invention, silicon (Si) is the key element for improving fluidity, mainly because the latent heat of crystallization of silicon is much higher than that of aluminum, thus significantly improving casting performance. Too low a Si content will reduce the eutectic structure, leading to poor fluidity and low casting performance. A high Si content easily generates primary Si crystals and also easily leads to localized Si segregation, which is detrimental to the material's ductility. Furthermore, increasing the Si content will lower the solid-liquid phase temperature of the material, thereby reducing the range of solution treatment temperature and affecting the heat treatment effect. Verification has shown that a Si content range of 6.5-8.5 wt% is more suitable, ensuring both material fluidity and a relatively high solution treatment temperature, thus guaranteeing the heat treatment effect. Adding 0.005-0.03 wt% strontium to modify Si can obtain a more ideal Al-Si eutectic structure.

[0023] 2) Iron (Fe) readily forms needle-like β-Al5FeSi phase. β-Al5FeSi exhibits kinetic advantages during solidification and is extremely easy to form under conditions of high Fe content (>0.2wt%) and slow cooling, making it difficult to avoid. This phase easily tears the matrix and degrades material properties. This invention, through the combined addition of manganese (Mn) and chromium (Cr) and a contour spraying system, enables rapid cooling of the mold, providing extremely high supercooling for material cooling. This allows the iron-rich phase to completely transform into a multi-element AlFe(Mn,Cr)Si phase. This multi-element phase has better effects than Al(Fe,Mn)Si or Al(Fe,Cr)Si phases, with finer precipitates and more rounded morphologies, further eliminating the adverse effects of Fe and ensuring material elongation. Verification showed that the Fe / (Mn+Cr) element mass ratio of 0.5-4:1 had the best effect, with a total addition amount of <1.2wt%. Excessive addition of Mn and Cr can easily lead to an increase in the size of Fe-containing precipitates, while insufficient addition will result in incomplete deterioration.

[0024] 3) In this application, Cu, Mg, and Zn are used as the main strengthening elements. Through elemental complexation, they form precipitated phases Q-Al3Cu2Mg9Si7 and β″-Mg5Si6, which significantly improve material properties. Their combined strengthening effect is superior to that of a single β-Mg2Si or Q-Al5Cu2Mg8Si6 phase. Simultaneously, because the bonding force between Cu and Mg and Si atoms is stronger than that of Zn, the MgZn2 phase is more difficult to form. Most of the Zn remains dissolved in the aluminum matrix, causing lattice distortion and promoting the formation of more small-sized clusters, further enhancing the material's properties. The alloy's mechanical properties are improved. Zn promotes the formation of Mg, Si, and Cu solute clusters during aging, driving the transformation of solute clusters from the GP region to the pre-precipitated phase, reducing the aging time to reach peak strength, shortening processing time and reducing production costs. It also improves the density of solute clusters during aging, promoting the formation of high-density and uniformly distributed solute clusters, which serve as the core for the pre-precipitated β″-Mg5Si6 phase and Q-Al3Cu2Mg9Si7, improving the precipitation density and distribution uniformity of the precipitated phases, thereby further enhancing the material's peak strength. Adding a small amount of Mo forms Al... 12 The Mo phase acts as a supplementary strengthening agent, while the addition of Ce can further purify the molten aluminum and reduce oxide inclusions.

[0025] 4) Traditional die casting spraying uses a spraying robot linked with a machine tool to complete the spraying and blowing actions on the mold. The reciprocating spraying and blowing motion of the nozzle on the mold is time-consuming, the mold insulation effect is poor, and the production efficiency is affected. The contour spraying system of this invention does not require the sprayer to move up and down to spray. Instead, the sprayer descends to the position in one go and sprays all parts of the mold in one go, which greatly improves the spraying efficiency, shortens the production cycle, saves energy and is highly efficient. At the same time, it can make the mold cool down quickly as a whole, providing the necessary supercooling for the subsequent Fe phase transformation. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the die-casting island of the present invention.

[0027] Figure 2 This is a schematic diagram of the contour spray intelligent system of the present invention.

[0028] Figure 3 This is a schematic diagram of the intelligent spraying mechanism of the present invention.

[0029] Figure 4 This is a schematic diagram of the spray head structure of the present invention.

[0030] The diagram shows: 1. Sprayer nozzle valve body; 2. Low-concentration spray ratio solenoid valve; 3. High-concentration spray ratio solenoid valve; 4. High-concentration spray port; 5. Compressed gas port; 6. Low-concentration spray port; 7. High-pressure energy storage tank; 8. Solenoid valve bus valve island; 9. Low-concentration release agent pipeline; 10. High-concentration release agent pipeline; 11. Irregularly shaped conformal nozzle; 12. High-pressure spray head. Figure 5 Microstructure of aluminum alloy in Example 15 (2000x magnification).

[0031] Figure 6 Comparative Example 1: Microstructure of aluminum alloy (2000x magnification).

[0032] Figure 7 Comparative Example 2: Microstructure of aluminum alloy (2000x magnification).

[0033] Figure 8 Comparative Example 3: Microstructure of aluminum alloy (2000x magnification). Detailed Implementation

[0034] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0035] The objective of this invention can be achieved through the following technical solution: a heat-treatable high-strength, high-toughness, low-carbon cast aluminum alloy, comprising: Si: 6.5-8.5 wt%; Fe: 0.01-0.55 wt%; Mg: 0.40-0.65 wt%; Cu: 0.005-0.50 wt%; Zn: 0.30-2.0 wt%; Mn: 0.005-0.40 wt%; Cr: 0.005-0.20 wt%; Mo: 0.005-0.05 wt%; Ce: 0.005-0.10 wt%; Ti: 0.05-0.20 wt%; Sr: 0.005-0.03 wt%; the sum of the weight percentages of other impurities is controlled below 0.5 wt%, with the balance being Al. Specifically, the mass ratio of Fe / (Mn+Cr) is 0.5-4:1; the sum of the weight percentages of Fe+Mn+Cr is ≤1.2 wt%. The above-mentioned cast aluminum alloy is obtained by the following method: Step S1: Weigh out the pure Al raw materials, Cu raw materials, Mg raw materials, Zn raw materials, Al-Fe, Al-Mn, Al-Cr, Al-Mo, Al-Si, Al-Ti, Al-Sr and Al-Ce alloys according to the mass ratio.

[0036] Step S2: First, put pure aluminum into the heating furnace and heat it to 680°C to obtain molten aluminum. After the molten aluminum is completely melted, let it stand and keep it at the temperature for 20-30 minutes. Step S3: Heat to 780℃, add Al-Si alloy, Cu raw material, Al-Fe, Al-Mn, Al-Mo and Al-Cr to the aluminum liquid in proportion, and wait for it to completely dissolve; Step S4: Cool down to 740℃, add Al-Ce, and keep warm for 20~30 minutes; Step S5: Cool down to 720℃, add Mg raw materials, Zn raw materials, Al-Ti and Al-Sr alloy, hold for 15-20 minutes, then introduce dry gas into the aluminum alloy melt. The gas is either nitrogen or argon. Add solid refining agent at a rate of 0.2-0.4% of the melt mass, and refine for 10-20 minutes.

[0037] Step S6: Cast a small sample for composition analysis. If it passes the analysis, send the melt into the casting equipment to form an aluminum alloy component.

[0038] During the casting process, a self-designed intelligent spray system with multi-functional atomizing nozzles and contour-following spray nozzle layout is used for mold cooling. Its structure is as follows: Figure 1-4 As shown: The casting of heat-treatable high-strength, high-toughness, low-carbon cast aluminum alloys in the following embodiments is achieved using integrated die-casting islands (see...). Figure 1The die-casting island comprises the die-casting main unit, a part-retrieving robot, a contour spray intelligent system, and peripheral auxiliary devices. These units work together to form a complete automated casting production unit. The overall layout of the die-casting island balances operator safety with equipment efficiency. The contour spray intelligent system is installed in the mold opening and closing area of ​​the die-casting main unit. It automatically descends and positions itself as the mold opens, completes the mold spraying and cooling process, and then quickly exits to match the die-casting cycle.

[0039] like Figure 2-4 As shown, the contour spraying intelligent system consists of a sprayer body, a contour nozzle assembly, a fluid supply module, and a control system. The fluid supply module includes a low-concentration release agent pipeline 9, a high-concentration release agent pipeline 10, and a compressed gas supply pipeline. The control system uses an industrial computer to uniformly schedule the actions of each proportional solenoid valve via a solenoid valve bus valve island 8. During spraying operations, the contour spraying intelligent system eliminates the need for the sprayer to move up and down repeatedly inside the mold. Instead, the sprayer descends to its final position and simultaneously sprays all areas of the mold, significantly shortening the spraying time, improving production efficiency, and ensuring rapid and uniform cooling of the mold as a whole, thus creating the necessary supercooling conditions for complete transformation of the iron-rich phase.

[0040] Among them, the structure of the intelligent spraying mechanism is as follows: Figure 3 As shown, the intelligent spraying mechanism has a contour-following support frame. Various spray nozzles, including long nozzles, short nozzles, and irregularly shaped spray nozzles 11, are arranged on the frame according to the contour of the mold cavity. The long nozzles are specifically designed for the deep cavity structure of the mold, with sufficient extension length to reach deep into the mold cavity for spraying, ensuring uniform cooling in the deep cavity area. The short nozzles are arranged for protruding and shallow flat areas of the mold, achieving precise close-range spraying. The irregularly shaped spray nozzles 11 are customized for complex contours and narrow areas of the mold, employing an irregular structure adapted to the local features of the cavity to eliminate spraying dead angles. The arrangement of the three types of nozzles is consistent with the spatial position of the corresponding mold area, ensuring complete spraying coverage.

[0041] The high-pressure spray head 12 is independently arranged in the mechanism to correspond to the aluminum-adhesive area of ​​the mold. It relies on the high-pressure, high-flow-rate compressed gas provided by the high-pressure energy storage tank 7 to powerfully blow and clean the aluminum skin adhering to the mold surface.

[0042] like Figure 4 As shown, the core structure of the spray head is a three-fluid atomizing nozzle, which consists of the spray head valve body 1 of the sprayer and its integrated functional components. The components indicated by the reference numerals in the attached drawings and their functions are as follows: Sprayer nozzle valve body 1: This is the main structural component of the spray nozzle. It has independent low-concentration release agent flow channels and high-concentration release agent flow channels inside, which are connected to the low-concentration release agent pipe 9 and the high-concentration release agent pipe 10, respectively. It also has a compressed gas channel connected to the compressed gas port 5.

[0043] Low-concentration spray ratio solenoid valve 2: Installed above the spray head valve body 1 of the sprayer, it precisely adjusts the flow rate of low-concentration release agent by controlling the opening of the needle valve in the low-concentration release agent flow channel. It is suitable for conventional cooling spraying of general areas of the mold.

[0044] High-concentration spray ratio solenoid valve 3: It is installed independently and in parallel with the low-concentration spray ratio solenoid valve 2 above the spray head valve body 1 of the sprayer. It controls the opening of the needle valve in the high-concentration release agent flow channel and precisely adjusts the flow rate of the high-concentration release agent. It is suitable for special areas of the mold or parts that need to enhance the release effect.

[0045] High-concentration spray nozzle 4: Located at the outlet end of the three-fluid atomizing nozzle, corresponding to the outlet of the high-concentration release agent flow channel, through which the high-concentration release agent is atomized and sprayed out.

[0046] Compressed gas port 5: Located in the middle of the three-fluid atomizing nozzle, compressed gas is introduced through this port and mixed with the liquid release agent in the nozzle. The liquid release agent is broken and atomized by the kinetic energy of the gas, and the droplets are driven to be sprayed out at high speed to the surface of the mold.

[0047] Low-concentration spray nozzle 6: Located at the outlet end of the three-fluid atomizing nozzle, corresponding to the outlet of the low-concentration release agent flow channel, through which the low-concentration release agent is atomized and sprayed out.

[0048] The high-concentration spray nozzle 4, compressed gas nozzle 5, and low-concentration spray nozzle 6 together constitute a three-fluid atomization structure. Two sets of proportional solenoid valves independently control the on / off state and flow rate of the two concentrations of release agent, realizing on-demand switching and precise control of different spray modes.

[0049] High-pressure energy storage tank 7: Connected to the compressed gas supply pipeline, it has dual functions of compressed air energy storage and buffering, and high-pressure spraying. When all spray heads are turned on at the same time, the instantaneous demand for compressed gas is large. The high-pressure energy storage tank 7 releases pre-stored high-pressure gas to supplement the gas source and prevent spraying instability caused by sudden pressure drop. When performing high-pressure purging cleaning, the high-pressure energy storage tank 7 provides high-pressure, high-flow-rate gas to the high-pressure spray head 12 to powerfully purge specific areas of the mold, remove adhering aluminum skin and residues, keep the mold surface clean, and accelerate local cooling of the mold.

[0050] Solenoid valve bus island 8: Integrated into the control loop of the intelligent spray system, it receives digital instructions from the industrial computer and converts them into analog signals to output to each proportional solenoid valve, realizing precise coordinated control of the low-concentration spray proportional solenoid valve 2 and the high-concentration spray proportional solenoid valve 3, ensuring that each spray head operates accurately according to the preset program, timing, and flow rate.

[0051] Low-concentration mold release agent pipeline 9: connects the low-concentration mold release agent supply source with the low-concentration mold release agent flow channel inside valve body 1, providing a continuous and stable liquid supply for the low-concentration spray channel.

[0052] High-concentration mold release agent pipeline 10: connects the high-concentration mold release agent supply source with the high-concentration mold release agent flow channel inside the valve body 1, providing a continuous and stable liquid supply for the high-concentration spray path.

[0053] Irregularly shaped spray nozzle 11: Adopting an irregular shape design that adapts to the specific complex contours or narrow areas of the mold, it can reach deep into positions that conventional spray nozzles cannot reach, ensuring full cavity coverage without dead angles.

[0054] High-pressure spray head 12: Connected to the high-pressure gas outlet of high-pressure energy storage tank 7, it generates high-pressure, high-flow airflow, which is specially used to perform high-pressure purging on areas of the mold that are prone to aluminum adhesion, effectively removing casting residues and maintaining stable surface quality of the mold.

[0055] The extremely high mold cooling rate provided by the above-mentioned contour spray intelligent system of the present invention forms a synergistic mechanism with the alloy composition system, which is interdependent and indispensable: (1) High supercooling is a key prerequisite for the complete metamorphism of iron-rich phases. Iron (Fe) is the most difficult harmful impurity to avoid in aluminum alloy casting. Its needle-like β-Al5FeSi phase easily tears the aluminum matrix, significantly worsening the material's elongation. This invention introduces manganese (Mn) and chromium (Cr) into the alloy for combined modification, transforming the harmful needle-like β-Al5FeSi phase into a more rounded, multi-element AlFe(Mn,Cr)Si phase. However, the complete completion of this phase transformation requires strict control over solidification undercooling—if the cooling rate is insufficient, the modification effect of Mn and Cr will be greatly reduced, and the iron-rich phase may still precipitate in a coarse form. The contour spray intelligent system provides a sufficiently high and uniform undercooling for the solidification of the molten aluminum by rapidly and uniformly cooling the entire mold. This allows the iron-rich phase in the alloy to precipitate quickly at more nucleation sites, ultimately distributing as fine, dispersed short rod-shaped and blocky AlFe(Mn,Cr)Si phases uniformly in the matrix, fundamentally eliminating the adverse effects of Fe and ensuring the material's elongation.

[0056] In other words, relying solely on the compositional regulation of Mn and Cr cannot achieve complete metamorphism on its own. It must be combined with the high cooling rate provided by the contour spray system. Only through the combined effect of the two can the optimal morphological control of the iron-rich phase be achieved.

[0057] (2) Uniform cooling ensures the uniformity of the as-cast microstructure and lays the foundation for heat treatment. Cu, Mg, and Zn are the main strengthening elements in this invention. The Q-Al5Cu2Mg8Si6 and β″-Mg5Si6 phases precipitated during T6 heat treatment are the core of the material strength enhancement. The density and uniformity of the precipitated phases are highly dependent on the uniformity of the solute element distribution in the as-cast microstructure. If the casting cooling is uneven, the solute elements will segregate at the solidification front, making it difficult for them to be fully dissolved into the matrix during subsequent solution treatment. The uniformity of the precipitated phase distribution during the artificial aging stage will also decrease, resulting in batch-to-batch fluctuations in material properties. The contour spray intelligent system ensures the consistency of the cooling rate in each area of ​​the mold, minimizing the segregation of solute elements such as Cu, Mg, and Zn in the as-cast microstructure. This provides a uniform initial microstructure for subsequent T6 heat treatment (solution treatment at 510–540℃ for 3–6 h, aging at 165–180℃ for 4–8 h), ensuring that the precipitated phases are distributed in the matrix with high density and uniform dispersion, ultimately achieving a tensile strength ≥340 MPa and a yield strength ≥290 MPa. The comprehensive mechanical performance indicators are MPa and elongation ≥9%.

[0058] (3) Synergistic optimization of Al-Si eutectic morphology by cooling rate and Sr modification effect This invention adds 0.005–0.03 wt% Sr to modify the Al-Si eutectic structure. The effectiveness of Sr modification is closely related to the cooling rate. At higher cooling rates, the Sr modification efficiency is significantly improved, and the eutectic Si morphology changes from coarse needle-like flakes to fine, rounded fibers, further reducing the cutting effect of Si relative to the matrix. This, combined with the high cooling rate provided by the contour spraying system, results in sufficient refinement and spheroidization of the eutectic structure, synergistically ensuring the material elongation.

[0059] (3) Rapid cooling shortens the production cycle and, in conjunction with Zn, promotes rapid aging and reduces costs. This invention adds an appropriate amount of Zn, which can promote the rapid formation of Mg, Si, and Cu solute clusters during the aging process, drive the transformation of the GP zone to the pre-precipitated β″ phase, and shorten the time required to reach peak aging. The contour spray intelligent system significantly shortens the spraying time per mold, improving the die-casting production cycle. Combined with the Zn accelerated aging process, it simultaneously reduces the time required for both casting and heat treatment, effectively reducing energy consumption and production costs while ensuring material performance, and has significant engineering application value.

[0060] This invention forms a multi-layered synergistic system: the contour spray intelligent system provides a high and uniform cooling rate, which is the physical prerequisite for the full transformation of the Fe phase; the combination of Fe / (Mn+Cr) ratio control and cooling rate is the composition-process synergy for eliminating acicular iron phase and ensuring elongation; the matching of uniform as-cast microstructure and T6 heat treatment parameters is the microstructure basis for maximizing the effectiveness of the Cu-Mg-Zn strengthening system; the organic combination of these three elements jointly supports the comprehensive performance target of the high-strength, high-toughness, low-carbon cast aluminum alloy of this invention.

[0061] The present invention will now be described in detail through specific embodiments.

[0062] Examples 1-15 and Comparative Examples 1-2 For details of the specific components in the embodiments, please refer to Table 1. For ease of comparison, the F value in Table 1 refers to the mass ratio of Fe / (Mn+Cr) elements, and the S value refers to the sum of the weight percentages of Fe+Mn+Cr elements.

[0063] Table 1 shows the elemental content of aluminum alloys in the examples and comparative examples.

[0064] The heat-treatable high-strength, high-toughness, low-carbon cast aluminum alloys of the above embodiments and comparative examples were obtained by the following methods: Step S1: First, weigh out the pure Al raw materials, Cu raw materials, Mg raw materials, Zn raw materials, Al-20Fe, Al-15Mn, Al-10Cr, Al-10Mo, Al-20Si, Al-75Ti, Al-10Sr and Al-20Ce alloys according to the mass ratio.

[0065] Step S2: First, put pure aluminum into the heating furnace and heat it to 680°C to obtain molten aluminum. After the molten aluminum is completely melted, let it stand and keep it at the temperature for 20-30 minutes. Step S3: Heat to 780℃, add Al-20Si alloy, Cu raw material, Al-20Fe, Al-15Mn, Al-10Mo and Al-10Cr to the aluminum liquid in proportion, and wait for it to completely dissolve; Step S4: Cool down to 740℃, add Al-20Ce, and keep warm for 20~30 minutes; Step S5: Cool down to 720℃, add Mg raw material, Zn raw material, Al-75Ti and Al-10Sr alloy, hold for 15-20 minutes, then introduce dry gas, namely nitrogen, into the aluminum alloy melt, add solid refining dosage of 0.3% of the melt mass, and refine for 15 minutes to carry out degassing refining; Step S6: Cast a small sample for composition analysis. If it passes the analysis, send the melt into the casting equipment to form an aluminum alloy component. The mold of the casting equipment is cooled by the above-mentioned contour spray intelligent system. During the spraying process, the specific ratio of the high-concentration spray solution is water:release agent 50:1, and the specific ratio of the low-concentration spray solution is water:release agent 100:1.

[0066] High-pressure energy storage tank, pressure set at 1.5 MPa.

[0067] Step S7: Perform T6 heat treatment on the aluminum alloy component. Specifically, the aluminum alloy component is subjected to solution heat treatment at 520℃ for 6 hours. After solution treatment, it is rapidly cooled with cooling water for 3 minutes to below 65℃, and then artificially aged at 175℃ for 6 hours.

[0068] In the examples in Table 2, "material state" refers to the product after casting without heat treatment; "T6 state" refers to the product after casting with heat treatment. In this invention, the testing of tensile strength, tensile strength, yield strength and elongation is carried out in accordance with the national standard GB / T 228.1-2010.

[0069] Table 2 Performance comparison table of each embodiment and comparative example:

[0070] As can be seen from the specific results in Table 2 above: Compared with Example 15, Comparative Example 1 has a lower amount of Mn and Cr added, resulting in an F value as high as 6.25. The high F value means that the total amount of (Mn+Cr) is severely deficient relative to 0.50% Fe, and it is impossible to fully transform the harmful needle-like β-Fe phase into short rod-like and blocky AlFe(Mn,Cr)Si phase during solidification. The results show that there are untransformed needle-like β-Fe phases in the microstructure, and the mechanical properties show a significant reduction in elongation.

[0071] Compared with Example 15, Comparative Example 2 differs in that it contains more Mn and Cr elements, reducing the F value to 0.63, but the S value is 1.30. The excessively high S value directly leads to a significant increase in the absolute volume fraction of precipitates in the later stages of solidification. These excessive precipitates aggregate and coarsen at grain boundaries, forming numerous brittle particles without needle-like morphology, which become preferential crack initiation sites under load. The results show that although no needle-like Fe phase is present in the microstructure, the precipitate size is significantly coarsened. The presence of such coarse precipitates is detrimental to the improvement of mechanical properties, manifested as a significant decrease in elongation.

[0072] As can be seen from the above data, each embodiment simultaneously satisfies the following conditions: the Fe / (Mn+Cr) element mass ratio is 0.5-4:1; the sum of the weight percentages of Fe+Mn+Cr elements is ≤1.2wt%; in the raw material state, the tensile strength of each embodiment is 189~220MPa, the yield strength is 89~107MPa, and the elongation is 9.3%~13.5%; in the T6 heat-treated state, the tensile strength of each embodiment is 350~374MPa, the yield strength is 292~310MPa, and the elongation is 9.2%~13.0%.

[0073] In particular, Examples 6 and 7 exhibited superior comprehensive mechanical properties (Tension strength ≥370MPa, Yield strength ≥305MPa, Elongation ≥9.2%) in the T6 state, confirming the positive effects of synergistic modification of Mn and Cr and appropriate addition on the refinement of precipitates and the regulation of Fe phase morphology.

[0074] The cast aluminum alloy provided by this invention, after T6 heat treatment, maintains high tensile strength (≥350MPa) and yield strength (≥292MPa) while its elongation is stably maintained above 9.0%. It can meet the comprehensive requirements of high strength and toughness for load-bearing structural components such as automotive chassis parts, steering knuckles, and suspension brackets, and has good industrial application prospects and economic benefits.

[0075] Figure 5 The image shows the microstructure (2000x magnification) of the cast aluminum alloy in Example 15 of this invention. As can be seen from the figure, under high Fe content, the Fe-containing precipitates are completely modified through Mn / Cr modification combined with contour spraying process. The precipitates are rounded, uniformly and finely distributed, which can effectively improve the reduction in elongation caused by high Fe content.

[0076] Figure 6 The microstructure of the cast aluminum alloy in Comparative Example 1 of this invention (2000x magnification) shows that: under high Fe (>0.2wt%) content, the Fe-containing precipitates are modified by Mn / Cr combined with contour spraying process. However, Fe / (Mn+Cr) is not suitable. The Mn and Cr contents are small. Although the precipitates have a modification effect, the presence of β-Al5FeSi needle-like phases can still be found. The presence of these needle-like phases deteriorates the elongation of the material.

[0077] Figure 7 The microstructure of the cast aluminum alloy in Comparative Example 2 of this invention (2000x magnification) shows that: under high Fe (>0.2wt%) content, Fe-containing precipitates are modified by Mn / Cr combined with contour spraying process. However, if the total amount of Fe+Mn+Cr is too high, the precipitates will be significantly coarsened. The presence of these coarse phases will also deteriorate the elongation of the material.

[0078] Figure 8The microstructure of the cast aluminum alloy in Comparative Example 3 of this invention (2000x magnification) shows that under high Fe (>0.2wt%) content, the Fe-containing precipitates do not show significant deterioration and refinement effects when sprayed by a conventional robotic arm, which is not conducive to improving the material properties.

[0079] Comparative Example 3 Without using a contour spray system, and otherwise the same as in Example 15, i.e., using conventional methods for mold cooling, the results are as follows: This comparative example uses the exact same alloy composition and T6 heat treatment parameters as Example 15. The only difference is the mold cooling method during the die casting stage—a traditional robotic arm reciprocating scanning spraying system is used instead of the contour spraying intelligent system. The preparation steps are as follows: Steps S1 to S5 are exactly the same as in Example 15. Step S6: Cast a small sample for composition analysis. If it passes the analysis, send the melt into the die-casting equipment for molding. Instead of using a contour spray intelligent system, a traditional robotic arm reciprocating scanning spraying method is used for mold cooling: the spraying robotic arm is linked with the die-casting machine, and the nozzle starts from the top of the mold, spraying the inner cavity of the mold at a uniform speed in a reciprocating scanning stroke; the spraying medium ratio is water:release agent = 50:1, resulting in an aluminum alloy component.

[0080] Step S7: The T6 heat treatment parameters are exactly the same as those in Example 15, namely: solution treatment at 520°C for 6 hours, rapid cooling with cooling water for 3 minutes to below 65°C, and aging at 175°C for 6 hours.

[0081] Take a cross section of the cast component, prepare a metallographic sample, observe the morphology of the iron-rich precipitate phase under a 2000x optical microscope, and take metallographic photographs.

[0082] Figure 8 The microstructure of the cast aluminum alloy in Comparative Example 3 is shown at 2000x magnification. As can be seen from the figure, although the Mn / Cr content in the alloy meets the modification ratio requirement of Fe / (Mn+Cr) under high Fe (>0.2wt%) content, the mold cooling efficiency is low due to the traditional reciprocating scanning spray cooling method, resulting in insufficient solidification undercooling and inadequate modification of the iron-rich phase. Coarse, blocky AlFe(Mn,Cr)Si phases can still be observed in the microstructure. Compared to the fine, dispersed distribution in Example 15 (using a contour spray intelligent system), the iron-rich phases are coarser, exhibiting a stronger cutting effect on the matrix, which corresponds to the decrease in elongation and other mechanical properties.

[0083] The alloy composition and T6 heat treatment process of Comparative Example 3 and Example 15 were exactly the same, the only difference being the mold cooling method. Comparative Example 3 used a traditional robotic arm reciprocating scanning spray cooling method, while Example 15 used a contour spray intelligent system. The results showed that the T6 elongation of Comparative Example 3 decreased from 9.2% in Example 15 to 8.8%, and the tensile strength decreased from 351 MPa to 342 MPa. Microscopic metallographic analysis showed that some of the Fe-containing phases in Comparative Example 3 were coarse, indicating that without the high uniform cooling rate provided by the contour spray intelligent system, even if the Fe / (Mn+Cr) ratio requirement was met, the iron-rich phase could not be fully modified. This proves that the contour spray intelligent system is a necessary process guarantee for the optimal performance of the composition system of this invention.

[0084] The above description represents a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of the present invention's concept are within the scope of protection of the present invention.

Claims

1. A heat-treatable, high-strength, high-toughness, low-carbon cast aluminum alloy, characterized in that, The alloy comprises Si: 6.5-8.5 wt%; Fe: 0.01-0.55 wt%; Mg: 0.40-0.65wt%; Cu: 0.005-0.50wt%; Zn: 0.30-2.0wt%; Mn: 0.005-0.40wt%; Cr: 0.005-0.20wt%; Mo: 0.005-0.05wt%; Ce: 0.005-0.10 wt%; Ti: 0.05-0.20 wt%; Sr: 0.005-0.03 wt%; the sum of the weight percentages of other impurities is controlled below 0.5 wt%, with the balance being Al; wherein: The mass ratio of Fe / (Mn+Cr) elements is 0.5-4:1; The sum of the weight percentages of Fe, Mn, and Cr elements is ≤1.2wt%.

2. The heat-treatable high-strength, high-toughness, low-carbon cast aluminum alloy according to claim 1, characterized in that, The microstructure of the cast aluminum alloy comprises α-Al, Al-Si eutectic structure and precipitated phases; The precipitated phases include AlFe(Mn,Cr)Si phase, π-Al8Mg3FeSi6 phase, and Al 12 Mo, Mg2Si phase and Q-Al5Si5Cu2Mg8 phase; The tissue contains AlFe(Mn,Cr)Si phase and π-Al8Mg3FeSi6 phase, which are distributed in a diffuse granular manner, and their morphologies include short rod-shaped and blocky.

3. A method for preparing a heat-treatable high-strength, high-toughness, low-carbon cast aluminum alloy as described in claim 1 or 2, characterized in that, The method includes the following steps: Step S1: First, weigh out the pure Al raw materials, Cu raw materials, Mg raw materials, Zn raw materials, Al-Fe, Al-Mn, Al-Cr, Al-Mo, Al-Si, Al-Ti, Al-Sr and Al-Ce alloys according to the mass ratio; Step S2: First, put pure aluminum into the heating furnace and heat it to 680°C to obtain molten aluminum. After the molten aluminum is completely melted, let it stand and keep it at the temperature for 20-30 minutes. Step S3: Heat to 780℃, add Al-Si alloy, Cu raw material, Al-Fe, Al-Mn, Al-Mo and Al-Cr to the aluminum liquid in proportion, and wait for it to completely dissolve; Step S4: Cool down to 740℃, add Al-Ce, and keep warm for 20~30 minutes; Step S5: Cool down to 720℃, add Mg raw materials, Zn raw materials, Al-Ti and Al-Sr alloy, hold for 15-20 minutes and then degas and refine; Step S6: Cast a small sample for composition analysis. If it passes the analysis, send the melt into the casting equipment to form an aluminum alloy component.

4. The preparation method according to claim 3, characterized in that, In step S5, degassing and refining involves introducing a dry gas, either nitrogen or argon, into the aluminum alloy melt. The amount of solid refining gas added is 0.2-0.4% of the melt mass, and the refining time is 10-20 minutes.

5. The preparation method according to claim 3, characterized in that, The aluminum alloy components are subjected to T6 heat treatment, specifically: the aluminum alloy components are subjected to solution heat treatment at 510-540℃ for 3-6 hours. After solution treatment, they are rapidly cooled with cooling water for 2-4 minutes until the temperature drops below 65℃. Then, they are subjected to artificial aging at 165-180℃ for 4-8 hours.

6. The preparation method according to claim 5, characterized in that: The aluminum alloy product obtained after T6 heat treatment has the following mechanical properties: tensile strength ≥340 MPa, yield strength ≥290 MPa, and elongation ≥9%.

7. The preparation method according to claim 3, characterized in that: In step S6, the mold cooling of the casting equipment is achieved by using a contour spray intelligent system for spray cooling. The contour spray intelligent system includes a multi-functional atomizing nozzle and a contour spray nozzle layout structure.

8. The preparation method according to claim 7, characterized in that: The contour-following spray intelligent system includes: The spray head valve body (1) of the sprayer is equipped with a low-concentration spray ratio solenoid valve (2) and a high-concentration spray ratio solenoid valve (3). The valve body is connected to the low-concentration release agent pipeline (9) and the high-concentration release agent pipeline (10) respectively. The two sets of ratio solenoid valves independently control the on / off and flow rate of the corresponding release agent. The three-fluid atomizing nozzle is equipped with a high-concentration spray port (4), a compressed gas port (5) and a low-concentration spray port (6). The spray volume is adjusted by controlling the opening and closing of the internal needle valve through the proportional solenoid valve. The contour nozzles are distributed to match the contour of the molded product and consist of long nozzles, short nozzles and irregular contour nozzles (11); A high-pressure energy storage tank (7) is connected to the compressed gas supply circuit of the contour spray intelligent system and is equipped with a high-pressure spray head (12). The solenoid valve bus island (8) is electrically connected to the industrial computer and receives the analog control signals output by the industrial computer to drive the proportional solenoid valves to operate.

9. The preparation method according to claim 8, characterized in that: In the three-fluid atomizing nozzle, the high-concentration spray proportional solenoid valve (3) is connected to the high-concentration spray port (4), and the low-concentration spray proportional solenoid valve (2) is connected to the low-concentration spray port (6). The two sets of proportional solenoid valves independently control the flow rate of their respective release agents. The industrial computer outputs analog signals to each proportional solenoid valve through the solenoid valve bus island (8) to achieve precise control of the spray volume.

10. The preparation method according to claim 8, characterized in that: The layout of the contour-following nozzle is matched with the contour-following structure of the mold cavity, wherein: Long nozzles are used to spray coatings deep into the cavity of the mold. Short nozzles are used for spraying and cooling the raised areas of the mold; The irregularly shaped spray nozzle (11) is designed for complex or narrow locations of molds, and achieves close-fitting spraying with an irregular structure; The three types of nozzles are used together to achieve comprehensive spraying and cooling of the mold without any blind spots.

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