Casting forming method for 7-series aluminum alloy cast rod

Abstract

The invention belongs to the technical field of metal material casting forming, and particularly relates to a 7-series aluminum alloy casting rod casting forming method which sequentially comprises the following steps: a centrifugal casting stage: casting mold preparation, smelting and refining, pouring and centrifugal solidification; and a gravity casting stage: mold preparation, secondary pouring and solidification, demolding and post-treatment. According to the casting forming method, the centrifugal casting and gravity casting combined composite casting technology is adopted, and the quality of a casting rod is improved from the outer layer to the inner layer; by means of multi-parameter collaborative optimization and fine regulation and control of the microstructure, fine regulation and control of the microstructure are achieved, the casting rod forms a uniform and fine grain structure from the outer layer to the interior, the strength and toughness of the casting rod are effectively improved, and the existing technical problems are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material casting and forming, and in particular relates to a casting and forming method for a 7 series aluminum alloy cast bar. Background Art

[0002] 7-series aluminum alloys are widely used in many high-end fields such as aerospace and automotive manufacturing due to their high strength, good corrosion resistance, and excellent overall performance. The main alloying elements of 7-series aluminum alloys are zinc (Zn) and magnesium (Mg), and elements such as copper (Cu) are added for strengthening. Typical alloys such as 7075 have a zinc content of 5.1% to 6.1%, a magnesium content of 2.1% to 2.9%, and a copper content of 1.2% to 2.0%. Zinc and magnesium form the strengthening phase MgZn2, which gives the alloy high strength; the addition of copper further improves strength and heat resistance. However, this series of alloys has a wide solidification range and is prone to defects such as segregation and shrinkage cavities, which places high demands on the casting process.

[0003] In order to obtain high-quality 7 series aluminum alloy casting rods, the casting process needs to focus on solving the following problems: first, controlling the solidification process, reducing component segregation, and ensuring structural uniformity; second, effectively removing gas and inclusions to improve the density of the casting rods; third, optimizing process parameters to ensure the dimensional accuracy and surface quality of the casting rods.

[0004] 7-series aluminum alloys contain high levels of alloying elements such as zinc, magnesium, and copper, and have a wide solidification temperature range, making compositional segregation highly likely to occur during the casting process. For example, during solidification, the composition of the solid phase that crystallizes first and last differs, leading to uneven element distribution between and within dendrites. In particular, the low-melting-point eutectic phase tends to accumulate at grain boundaries, severely impacting the mechanical properties and corrosion resistance of the cast rods and resulting in unstable product performance.

[0005] During the melting and pouring process, aluminum alloy liquids are prone to absorbing gases, especially hydrogen. The solubility of hydrogen decreases dramatically during solidification. If this gas cannot be effectively expelled, it will form pores within the cast rod. Furthermore, aluminum alloys are easily oxidized during melting to form alumina inclusions. These inclusions can split the matrix, reducing the strength and toughness of the cast rod and becoming a source of cracks.

[0006] The solidification structure of 7-series aluminum alloy cast bars significantly influences their performance. A fine, uniform grain structure effectively enhances the strength and toughness of the cast bars. However, due to the high alloying element content and complex solidification process, conventional grain refinement methods are limited in effectiveness. Adding only traditional modifiers is difficult to achieve the desired grain refinement effect. Furthermore, different casting processes have significant variations in the effect of grain refinement, making precise control difficult and making it difficult to achieve optimal microstructure and properties of the cast bars. Summary of the Invention

[0007] The present invention addresses the problems in the prior art and proposes a method for casting 7 series aluminum alloy rods based on the 7 series aluminum alloy casting process. The technical solution of the present invention is as follows:

[0008] A 7 series aluminum alloy casting rod casting method comprises the following steps in sequence:

[0009] Step 1: Centrifugal casting stage

[0010] Step 1.1 Mold preparation: Clean the mold of the centrifugal casting machine, preheat it to 200-300℃, and spray a layer of 0.2-0.5mm thick paint on the inner wall of the mold to increase the mold life and improve the surface quality of the cast rod;

[0011] Step 1.2 Melting and Refining: Select 7 series aluminum alloy raw materials, heat them to 750-800℃ in a melting furnace to melt them, add refining agents and refine them for 15-20 minutes to fully remove the gas and inclusions in the alloy liquid. After refining, let it stand for 5-10 minutes to allow the slag to float fully.

[0012] Step 1.3 Pouring and centrifugal solidification: Transfer the refined alloy liquid to the ladle of the centrifugal casting machine, adjust the temperature to 720-740℃, start the centrifugal casting machine, rotate the mold at a speed of 1200-1500r / min, and then pour the alloy liquid into the rotating mold at a pouring rate of 5-8kg / s; under the action of centrifugal force, the alloy liquid fills the mold and begins to solidify. At the same time, start the cooling device, using a combination of air cooling and water cooling to control the cooling rate of the outer layer of the cast rod, so that the outer layer solidifies quickly to form a dense structure. When the temperature of the outer layer of the cast rod drops to 500-550℃, stop water cooling and continue air cooling;

[0013] Step 2: Gravity casting stage

[0014] Step 2.1 Mold preparation: Clean the gravity casting mold, remove surface impurities and oil stains, preheat to 150-200℃, and spray the release agent with a thickness of 0.1-0.3mm;

[0015] Step 2.2 Secondary pouring and solidification: The centrifugally cast ingot and the mold are transferred to a gravity casting machine. The remelted alloy liquid in the smelting furnace is adjusted to 720-730°C and slowly poured into the mold through a ladle to supplement the interior of the ingot. The pouring speed is controlled at 3-5 kg / s to ensure that the molten metal fills the interior of the ingot evenly. After pouring, the ingot is allowed to solidify naturally in the mold. Water mist can be sprayed on the mold surface for cooling as needed. The cooling rate is controlled at 1-3°C / s to promote uniform solidification inside the ingot and eliminate internal defects such as shrinkage cavities and porosity.

[0016] Step 2.3 Demolding and post-processing: After the cast rod is completely solidified, open the mold and take out the cast rod, clean and polish it to remove surface sand and burrs.

[0017] As an improvement of the above technical solution, the pouring temperature of the centrifugal casting is higher than the pouring temperature of the gravity casting, and the temperature difference is controlled within the range of 10°C to 20°C.

[0018] As an improvement of the above technical solution, the cooling rate of the outer layer of the cast rod reaches 5°C / s to 10°C / s during centrifugal casting, and the cooling rate of the inner layer of the cast rod is maintained at 1°C / s to 3°C / s during gravity casting.

[0019] As an improvement of the above technical solution, after the centrifugal casting, when the temperature of the outer layer of the cast rod drops to 500° C. to 550° C., it is transferred and gravity casting is performed.

[0020] The 7 series aluminum alloy casting method of the present invention effectively solves the casting problems of 7 series aluminum alloy and improves the product quality and performance. Its beneficial effects are:

[0021] 1. Utilize a composite casting process to improve ingot quality from the outside in. This process combines centrifugal casting with gravity casting. Centrifugal casting utilizes centrifugal force to tightly fill the mold with molten metal, promoting shrinkage compensation and discharging gases and inclusions. This increases the density of the ingot's outer layer, refines the grain size, and improves element distribution. Gravity casting, with its simple equipment and flexible operation, supplements solidification and compaction within the ingot, eliminating defects such as shrinkage cavities and porosity. The two processes work in tandem to improve ingot quality from the outside in.

[0022] 2. Collaborative optimization of multiple parameters. During the casting process, key parameters such as temperature, cooling rate and time nodes are collaboratively optimized. The pouring temperatures of centrifugal casting and gravity casting are coordinated with each other, and the temperature difference is controlled at about 10 to 20 ° C, and fine-tuned according to actual conditions, which not only ensures the fluidity and filling effect of the alloy liquid, but also prevents adverse effects on the solidified structure, controls the solidification process and tissue quality, and reduces casting defects; in terms of cooling rate, the centrifugal casting stage quickly cools and refines the outer grains, and the gravity casting stage cools relatively slowly to ensure uniform internal structure; in terms of time nodes, the time of transfer from centrifugal casting to gravity casting is accurately grasped to ensure that the outer layer of the cast rod has been basically solidified and the interior is convenient for additional pouring and solidification.

[0023] 3. Fine-tuning the microstructure. Addressing the significant impact of the solidification structure of 7-series aluminum alloys on their performance and the limited effectiveness of conventional grain refinement methods, we achieved fine-tuning of the microstructure through composite casting processes and parameter optimization. This resulted in a uniform, fine grain structure from the outer layer to the inner core of the cast rod, effectively improving its strength and toughness and resolving existing technical challenges. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart of the casting method for the 7 series aluminum alloy cast rods described in the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0026] like Figure 1 The 7 series aluminum alloy casting rod casting method of the present invention comprises the following steps in sequence:

[0027] Step 1, centrifugal casting stage

[0028] Step 1.1 Mold preparation: Clean the mold of the centrifugal casting machine, preheat it to 200-300℃, and spray a 0.2-0.5mm thick coating on the inner wall of the mold, such as zircon-based coating, silica sol coating, forsterite-based coating, boron nitride coating, etc., to increase the mold life and improve the surface quality of the cast rod;

[0029] Step 1.2 Melting and Refining: Select 7 series aluminum alloy raw materials, heat them to 750-800℃ in a melting furnace to melt them, add refining agents (such as C2Cl6, etc.) and refine them for 15-20 minutes to fully remove the gas and inclusions in the alloy liquid. After refining, let it stand for 5-10 minutes to allow the slag to float fully.

[0030] Step 1.3 Pouring and centrifugal solidification: Transfer the refined alloy liquid to the ladle of the centrifugal casting machine, adjust the temperature to 720-740℃, start the centrifugal casting machine, rotate the mold at a speed of 1200-1500r / min, and then pour the alloy liquid into the rotating mold at a pouring rate of 5-8kg / s; under the action of centrifugal force, the alloy liquid fills the mold and begins to solidify. At the same time, start the cooling device, using a combination of air cooling and water cooling to control the cooling rate of the outer layer of the cast rod, so that the outer layer solidifies quickly to form a dense structure. When the temperature of the outer layer of the cast rod drops to 500-550℃, stop water cooling and continue air cooling;

[0031] Step 2: Gravity casting stage

[0032] Step 2.1 Mold preparation: Clean the gravity casting mold, remove surface impurities and oil stains, preheat to 150-200℃, and spray release agent with a thickness of 0.1-0.3mm;

[0033] Step 2.2 Secondary pouring and solidification: The centrifugally cast ingot and the mold are transferred to a gravity casting machine. The remelted alloy liquid in the smelting furnace is adjusted to 720-730°C and slowly poured into the mold through a ladle to supplement the interior of the ingot. The pouring speed is controlled at 3-5 kg / s to ensure that the molten metal fills the interior of the ingot evenly. After pouring, the ingot is allowed to solidify naturally in the mold. Water mist can be sprayed on the mold surface for cooling as needed. The cooling rate is controlled at 1-3°C / s to promote uniform solidification inside the ingot and eliminate internal defects such as shrinkage cavities and porosity.

[0034] Step 2.3 Demolding and Post-Processing: After the cast bars have completely solidified, the mold is opened and the bars are removed. They are then cleaned and polished to remove surface sand and flash. The bars are then dimensional measured and visually inspected. Internal flaw detection is performed using equipment such as ultrasonic flaw detectors to ensure quality. Qualified bars undergo heat treatment, such as T6 treatment (solution treatment + artificial aging), to further improve their microstructure and properties.

[0035] The 7-series aluminum alloy ingot casting method described herein utilizes coordinated centrifugal and gravity casting temperatures. The pouring temperature for centrifugal casting is slightly higher than that for gravity casting to ensure good alloy fluidity and smooth mold filling during centrifugal casting. The pouring temperature for gravity casting is slightly lower to avoid significantly affecting the solidified outer layer structure during centrifugal casting. The temperature difference between the two is controlled to be approximately 10°C to 20°C, and in actual production, fine-tuned based on factors such as alloy composition and ingot specifications.

[0036] The 7-series aluminum alloy ingot casting method described herein utilizes coordinated cooling rates. Rapid cooling during the centrifugal casting phase refines the outer grains, while relatively slow cooling during the gravity casting phase ensures uniform internal microstructure. By controlling the air cooling intensity and water cooling flow rate, the outer cooling rate during centrifugal casting reaches 5°C / s to 10°C / s, while the internal cooling rate during gravity casting is maintained at 1°C / s to 3°C / s, optimizing both internal and external microstructures.

[0037] The 7-series aluminum alloy casting rod casting method described in the present invention has reasonable control over the timing nodes. The time of transfer from centrifugal casting to gravity casting is accurately grasped. If the transfer is too early, the outer layer of the cast rod will not be fully solidified and will be easily deformed; if the transfer is too late, the overall temperature of the cast rod will be too low, which is not conducive to internal shrinkage compensation and solidification during gravity casting. Generally, after centrifugal casting, the transfer is carried out when the temperature of the outer layer of the cast rod drops to 500℃~550℃. At this time, the outer layer of the cast rod has basically solidified and has a certain strength. At the same time, the interior is still in liquid or semi-solid state, which is convenient for supplementary pouring and solidification during gravity casting.

[0038] The 7 series aluminum alloy cast rods described in the present invention are cast and formed using a horizontal centrifugal casting machine equipped with a high-precision variable frequency speed regulating motor with a speed adjustment range of 500 to 2000 r / min, which can accurately control the centrifugal force; equipped with an automated pouring system, which can accurately control the pouring temperature and speed; and provided with a cooling device, which can cool the mold and cast rods by a combination of air cooling and water cooling.

[0039] The 7 series aluminum alloy ingots described in the present invention are cast using a conventional gravity casting machine equipped with a melting furnace, a ladle and other equipment. The melting furnace has a precise temperature control system that can control the melting temperature within a range of ±5°C. The mold is made of high-strength heat-resistant mold steel, and a rationally designed pouring system, riser and exhaust system ensure smooth filling of the molten metal and solidification and shrinkage feeding.

[0040] The temperature coordination in the 7 series aluminum alloy casting method of the present invention is mainly based on considerations such as alloy properties, casting process requirements, and ensuring product quality:

[0041] 1. Ensure alloy fluidity and mold filling: During centrifugal casting, the alloy liquid must quickly and fully fill the mold under the action of centrifugal force. Therefore, a higher pouring temperature (720-740°C) is required to ensure good alloy fluidity and avoid defects such as under-pouring and cold shuts. Gravity casting, on the other hand, relies on the alloy liquid's own gravity to fill the mold, placing relatively low demands on fluidity. A lower pouring temperature (720-730°C) can both meet mold filling requirements and reduce air absorption and oxidation of the alloy liquid. Through temperature coordination, both casting processes can achieve excellent mold filling at their respective stages.

[0042] 2. Preventing adverse effects on the solidified structure: After centrifugal casting, the outer layer of the cast rod has partially solidified to form a structure of a certain strength. If the pouring temperature of gravity casting is too high, the high-temperature alloy liquid may remelt the outer layer when it contacts the solidified outer layer, destroying the dense structure and grain structure formed by centrifugal casting. If the temperature is too low, the alloy liquid will lack fluidity when filling the interior of the cast rod, and shrinkage cannot be effectively compensated, which can easily cause defects such as shrinkage cavities and shrinkage. Maintaining a reasonable temperature difference between the two (about 10-20°C) can ensure smooth gravity casting while minimizing adverse effects on the solidified outer layer of the centrifugal casting.

[0043] 3. Controlling the Solidification Process and Microstructure Quality: Appropriate temperature coordination helps control the solidification sequence and speed throughout the casting process. Centrifugal casting rapidly cools the steel to form a dense outer structure, while gravity casting's relatively low temperatures and slow cooling rates facilitate uniform solidification and shrinkage feeding within the structure, refine internal grains, and reduce compositional segregation. Temperature coordination allows for a uniform, fine grain structure from the outer layer to the inner portion of the cast rod, improving overall microstructure quality and performance consistency.

[0044] 4. Reduce Casting Defects: Improper temperature coordination can lead to a range of casting defects. For example, excessively high temperatures in gravity casting can increase air absorption in the molten alloy, leading to the formation of porosity. Excessively low temperatures can lead to inadequate shrinkage compensation, increasing the risk of shrinkage cavities and porosity. Improper temperatures in centrifugal casting can also affect mold filling and solidification quality. Proper temperature coordination can effectively reduce the occurrence of defects such as porosity, inclusions, shrinkage cavities, and porosity, thereby improving product qualification rates.

[0045] The 7-series aluminum alloy ingot casting method described in this invention first uses centrifugal casting to establish a foundation, followed by gravity casting to refine the internal structure. During centrifugal casting, the powerful centrifugal force tightly packs the molten metal in the mold, effectively facilitating shrinkage compensation and allowing gases and inclusions to converge and drain toward the center. This significantly increases the density of the ingot's outer layer, refines the outer grain size, and improves the distribution of alloying elements. Initial centrifugal casting creates a high-quality outer layer foundation for the ingot, reducing the likelihood of defects in the outer layer during subsequent gravity casting.

[0046] After centrifugal casting forms an outer layer of a certain quality, gravity casting is then performed. Gravity casting, leveraging the simplicity and flexibility of gravity casting equipment, can be used to further solidify and compact the interior of the cast rod. By properly controlling pouring and solidification conditions during gravity casting, defects such as shrinkage cavities and porosity that may exist within the cast rod after centrifugal casting can be further eliminated, resulting in a more uniform internal structure and improved overall rod quality and performance. If the order is reversed, gravity casting will make it difficult to form a dense outer layer. The solidified portion will be easily deformed by centrifugal force during subsequent centrifugal casting, hindering the use of centrifugal force to expel gases and inclusions, making it difficult to achieve the goal of combining casting to improve cast rod quality.

[0047] The 7 series aluminum alloy casting rod casting method of the present invention has the following comparative table of product technical indicators:

[0048] Technical indicators Conventional casting This case density 95％～97％ 98％～99％ Grain size 50~100μm 20~50μm Component segregation degree 5％～8％ 3％～5％ tensile strength 400~500MPa 500~600MPa Yield strength 300~400MPa 400~500MPa Elongation 10％～15％ 15％～20％ Porosity 0.5％～1％ 0.1％～0.3％ Inclusion defect area ratio 0.2％～0.5％ 0.05％～0.1％

[0049] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. 7 series aluminum alloy casting rod casting method, characterized in that: The following steps are included in sequence: Step 1: Centrifugal casting stage Step 1.1 Mold preparation: Clean the mold of the centrifugal casting machine, preheat it to 200-300℃, and spray a layer of 0.2-0.5mm thick paint on the inner wall of the mold to increase the mold life and improve the surface quality of the cast rod; Step 1.2 Melting and Refining: Select 7 series aluminum alloy raw materials, heat them to 750-800℃ in a melting furnace to melt them, add refining agents and refine them for 15-20 minutes to fully remove the gas and inclusions in the alloy liquid. After refining, let it stand for 5-10 minutes to allow the slag to float fully. Step 1.3 Pouring and centrifugal solidification: Transfer the refined alloy liquid to the ladle of the centrifugal casting machine, adjust the temperature to 720-740℃, start the centrifugal casting machine, rotate the mold at a speed of 1200-1500r / min, and then pour the alloy liquid into the rotating mold at a pouring rate of 5-8kg / s; under the action of centrifugal force, the alloy liquid fills the mold and begins to solidify. At the same time, start the cooling device, using a combination of air cooling and water cooling to control the cooling rate of the outer layer of the cast rod, so that the outer layer solidifies quickly to form a dense structure. When the temperature of the outer layer of the cast rod drops to 500-550℃, stop water cooling and continue air cooling; Step 2: Gravity casting stage Step 2.1 Mold preparation: Clean the gravity casting mold, remove surface impurities and oil stains, preheat to 150-200℃, and spray release agent with a thickness of 0.1-0.3mm; Step 2.2 Secondary pouring and solidification: The centrifugally cast ingot and the mold are transferred to a gravity casting machine. The remelted alloy liquid in the smelting furnace is adjusted to 720-730°C and slowly poured into the mold through a ladle to supplement the interior of the ingot. The pouring speed is controlled at 3-5 kg / s to ensure that the molten metal fills the interior of the ingot evenly. After pouring, the ingot is allowed to solidify naturally in the mold. Water mist can be sprayed on the mold surface for cooling as needed. The cooling rate is controlled at 1-3°C / s to promote uniform solidification inside the ingot and eliminate internal defects such as shrinkage cavities and porosity. Step 2.3 Demolding and post-processing: After the cast rod is completely solidified, open the mold and take out the cast rod, clean and polish it to remove surface sand and burrs.

2. The casting method of 7 series aluminum alloy rod according to claim 1, characterized in that: The pouring temperature of the centrifugal casting is higher than that of the gravity casting, and the temperature difference is controlled within the range of 10°C to 20°C.

3. The casting method of 7 series aluminum alloy cast rod according to claim 1, characterized in that: During the centrifugal casting, the cooling speed of the outer layer of the cast rod reaches 5°C / s to 10°C / s, and during the gravity casting, the cooling speed of the inner layer of the cast rod is maintained at 1°C / s to 3°C / s.

4. The casting method of 7 series aluminum alloy rod according to claim 1, characterized in that: After the centrifugal casting, when the temperature of the outer layer of the cast rod drops to 500° C. to 550° C., the rod is transferred and gravity casted.

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