Heat-treatment-free aluminum alloy material for low-pressure casting and preparation method thereof

Abstract

The invention discloses a heat treatment-free aluminum alloy material for low-pressure casting and a preparation method of the heat treatment-free aluminum alloy material. The heat treatment-free aluminum alloy material is prepared from the following elements in percentage by mass: 9.0%-12.0% of Si, 0.1%-0.6% of Mg, 0.1%-0.5% of Cu, 0.05%-0.2% of Mn, 0.05%-0.2% of Ti, 0.01%-0.04% of Sr, 0.05%-0.2% of Fe, 0.04%-0.2% of Nb, inevitable impurity elements and the balance of Al. By optimizing the element ratio of the aluminum alloy material, a low-pressure casting product has good strength and hardness under the condition that heat treatment is not needed after casting, and the strength and hardness are obviously higher than those of an A356.2 material commonly used in low-pressure casting at present.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum alloy materials, and particularly relates to a heat-treatment-free aluminum alloy material for low-pressure casting and a preparation method thereof. Background Art

[0002] Due to its characteristics of low density, high strength, excellent thermal conductivity, strong corrosion resistance, easy processing and forming, and recyclability, aluminum alloy has been widely used in many fields such as the automotive industry, aerospace, communication electronics, mechanical equipment, and construction. Especially in the automotive field, with the increasing demand for lightweight development of new energy vehicles, automotive structural parts are developing towards integrated, ultra-thin-walled lightweight, and high-efficiency design and manufacturing. Since the 1970s, aluminum alloy has been widely used in the automotive field and has become a key material for automotive lightweighting.

[0003] Integrated thin-walled low-pressure castings need to undergo high-temperature solution and aging heat treatment to meet the strength required for vehicle body performance. However, heat treatment is prone to cause component deformation and surface defects, and additional shaping means are required to improve the dimensional accuracy and defects of the components, ultimately resulting in a very high scrap rate of the products. At the same time, the heat treatment process requires a large amount of energy and time costs, generally accounting for more than 20% of the manufacturing cost of automotive components. The heat treatment and shaping processes increase the production cost of automotive products.

[0004] In order to reduce production processes, lower component production costs, and achieve green manufacturing, the development of heat-treatment-free aluminum alloy materials for integrated large-scale low-pressure thin-walled castings is extremely urgent. In addition, heat-treatment-free aluminum alloy components do not require long-term high-temperature heat treatment, effectively avoiding deformation during high-temperature heat treatment, and can manufacture medium and large-sized thin-walled metal components, with great application prospects.

[0005] Currently, heat-treatment-free high-pressure die-cast aluminum alloys are mainly Al-Si-Mg series and Al-Mg-Si series aluminum alloys. Under the condition of a high cooling rate of 500 - 1000 K / s in high-pressure die casting, the grains and phase structures are fine, and the solution strengthening effect is strong. For example, the A356.2 aluminum alloy material commonly used in current low-pressure casting.

[0006] Patent document CN119320898A discloses a high-performance heat-treatment-free recyclable gravity or low-pressure casting aluminum alloy and its manufacturing method. The mass percentages of each element in the aluminum alloy satisfy: Zn: 3 - 10wt%; Mg: 0.25 - 3wt%; Ca: 0.5 - 3wt%; Si: 0.05 - 2wt%; Fe: 0.05 - 2wt%; unavoidable inclusions not greater than 0.15wt%; and the balance Al. The as-cast yield strength of the alloy of the present invention in gravity / low-pressure casting is ≥210MPa, the tensile strength is ≥280MPa, and the elongation is ≥5%, reaching the mechanical properties of industrial A356 casting aluminum alloy in the T6 heat-treatment state, and high-performance components can be manufactured without heat treatment. However, the Si content in this component is relatively low, which will inevitably reduce the flow filling ability of the material itself.

[0007] Patent document CN119020645A discloses a heat-treatment-free low-pressure casting aluminum alloy, which includes by weight percentage: Si: 4.0 - 10.5%, Fe: 0 - 1.0%, Mn: 0.1 - 0.8%, Mg: 0 - 0.6%, La: 0.022 - 0.22%, V: 0.033 - 0.33%, B: 0.033 - 0.33%, and the balance is Al; the mass ratio of La, V and B is 2:3:3. However, the alloy in the document will add La / V elements and requires complex pretreatment, increasing the cost.

[0008] Patent document CN117737523A discloses a low-pressure casting aluminum alloy and its preparation method for thin-walled parts. The chemical composition of the aluminum alloy is: Si: 6.5 - 9wt%, Mg: 0.2 - 0.7wt%, Fe: 0.1 - 0.25wt%, Ti: 0.01 - 0.18wt%, Mn: 0.05 - 0.3wt%, Cr: 0.05 - 0.2wt%, Cu: 0.01 - 0.5wt%, and the balance is Al and unavoidable impurity elements. This preparation method combines the composition optimization of the aluminum alloy, and large-sized integrated aluminum alloy thin-walled parts with excellent mechanical properties can be prepared by using the low-pressure casting process without solution heat treatment. However, the alloy in the document mainly improves the yield strength through the solid solution effect of Mn / Cr / Cu, and this document can only avoid the solution step and still needs to be aged. While the present invention improves the alloy strength through the modification effect and grain refinement effect of Sr, and the castings do not need heat treatment. Summary of the Invention

[0009] The object of the present invention is to provide a heat-treatment-free aluminum alloy material for low-pressure casting and its preparation method, which is applied to large thin-walled low-pressure casting aluminum alloy automotive structural parts to solve the problems of casting heat-treatment deformation and poor mechanical properties in the prior art. After low-pressure casting, the as-cast average tensile strength of this material is ≥240 MPa, the yield strength is ≥130 MPa, and the elongation after fracture is ≥6%, which is significantly higher than the mechanical properties of the current A356.2 material in the same state. It not only improves the strength of the parts but also reduces the heat-treatment and shaping processes after casting of the parts, thereby reducing the production cost of the parts.

[0010] In order to achieve the above object, the technical solution of the present invention is as follows:

[0011] A heat-treatment-free aluminum alloy material for low-pressure casting of the present invention is composed of the following elements by mass fraction: 9.0% - 12.0% of Si, 0.1% - 0.6% of Mg, 0.1% - 0.5% of Cu, 0.05% - 0.2% of Mn, 0.05% - 0.2% of Ti, 0.01% - 0.04% of Sr, 0.05% - 0.2% of Fe, 0.04% - 0.2% of Nb and inevitable impurity elements, and the balance is Al.

[0012] The functions of each element in the heat-treatment-free aluminum alloy material for low-pressure casting of the present invention are as follows:

[0013] Silicon (Si) has the functions of improving fluidity, increasing the tensile strength and hardness of the alloy, and enhancing airtightness, wear resistance, corrosion resistance and thermal conductivity, but it will reduce the elongation after fracture. The best fluidity can be obtained from eutectic to hypereutectic. However, the crystallized silicon (Si) is easy to form hard spots, making the machinability poor, so generally it does not exceed the eutectic point.

[0014] The addition of magnesium (Mg) is used to increase the strength and impact resistance of the aluminum alloy and improve the machining performance; when the Mg content is too high, it will cause large shrinkage during cooling, and it is easy to produce hot cracks and porosity; when the addition amounts of Si and Mg elements are too high, the elongation after fracture will decrease; however, when the addition amounts of Si and Mg elements are too low, the strength will be reduced.

[0015] Iron (Fe) often exists in the form of coarse needle-shaped Fe-rich phases in aluminum alloys. Although it can improve the mechanical properties of the alloy, it also seriously cuts the Al matrix, resulting in a sharp drop in elongation, making the casting brittle and the machining performance poor.

[0016] Manganese (Mn) in aluminum alloy can reduce the harmful effects of iron, transform the acicular β-Al5FeSi phase into the Chinese character-shaped or massive α-Al5(Fe,Mn)3Si2 phase, and improve the elongation and strength of the alloy after fracture. In addition, the atomic radius of Mn is quite different from that of Al, so the addition of Mn will increase the degree of lattice distortion of the alloy, significantly refine the grains, increase the grain boundaries of the alloy, and significantly improve the mechanical properties of the alloy.

[0017] The addition of copper (Cu) can improve the fluidity, tensile strength and hardness of the alloy, but reduces the corrosion resistance and plasticity, and increases the hot cracking tendency.

[0018] Strontium (Sr) is a surface-active element that plays a modification role and can improve the mechanical properties, plastic workability and final product quality of the alloy (such as improving the surface roughness, etc.).

[0019] Titanium (Ti) is often added in the form of Al-Ti or Al-Ti-B master alloys. Ti forms the TiAl3 phase with Al, which becomes a non-spontaneous nucleus during crystallization, can significantly refine the grain structure of aluminum alloy, improve the mechanical properties of the alloy, and reduce the hot cracking tendency of the alloy.

[0020] Niobium (Nb) forms the Ti2NbAl metal compound in aluminum alloy, which has a certain strengthening effect on the alloy, improves the toughness of the alloy and increases the elastic modulus of the alloy.

[0021] The preparation method of a heat-treatment-free aluminum alloy material for low-pressure casting described in the present invention includes the following steps:

[0022] (1) Melting: First, heat and melt the A00 pure aluminum ingot and the Al-98% Si alloy block, and keep it warm at 730 - 760 °C for 30 - 60 min; then add the Al-50% Mg, Al-50% Cu and Al-10% Mn alloy blocks for melting, and control the melting temperature at 725 - 735 °C to obtain molten aluminum liquid;

[0023] (2) Refining and degassing: Lower the temperature of the molten aluminum liquid to 715 - 730 °C, add a solid refining agent to the melt and introduce Ar gas for refining and degassing for 15 - 25 min, so that the gas content of the molten aluminum liquid ≤ 0.15 ml / 100 g;

[0024] (3) Add the Al-5% Ti-B, Al-3% Nb-B and Al-10% Sr alloy blocks to the molten aluminum liquid at 735 - 750 °C for alloy refinement and modification treatment, and then keep the melt static and warm for 20 - 30 min to obtain refined aluminum liquid;

[0025] (4) Casting: Carry out low-pressure casting on the refined aluminum liquid to obtain the heat-treatment-free aluminum alloy material described.

[0026] Preferably, the A00 pure aluminum ingot and alloy blocks of Al-98% Si, Al-50% Mg, Al-50% Cu, Al-10% Mn, Al-5% Ti-B, Al-3% Nb-B and Al-10% Sr should be preheated and dried in a drying furnace heated to 100-300 °C before melting.

[0027] Preferably, the total of the heat preservation time in step (3) and the casting time in step (4) should not exceed 2 h.

[0028] Preferably, for the low-pressure casting in step (4), the temperature is 700-710 °C and the pressure is 250-500 mbar.

[0029] Compared with the prior art, the positive effects of the present invention are as follows:

[0030] By optimizing the element ratio of the aluminum alloy material, the low-pressure casting products of the present invention have good strength and hardness without heat treatment after casting, which are significantly higher than those of the A356.2 material commonly used in current low-pressure casting. For large thin-walled parts of low-pressure casting, the present invention not only improves the strength and hardness on the basis of A356.2, but also saves the heat treatment and shaping processes, reducing the production cost of the products. Description of the Drawings

[0031] Figure 1 It is the metallographic structure of the as-cast state after low-pressure casting of the heat-treatment-free aluminum alloy material of the present invention.

[0032] Figure 2 It is the metallographic structure of the as-cast state after low-pressure casting of the A356.2 material. Detailed Embodiments

[0033] Those of ordinary skill in the art in this technical field should recognize that this embodiment is only used to illustrate the present invention and is not used as a limitation to the present invention. As long as changes and modifications are made to the embodiment within the scope of the present invention, they can be within the scope of the claims of the present invention.

[0034] Examples 1-14

[0035] For the heat-treatment-free aluminum alloy materials for low-pressure casting in Examples 1-14, the mass fractions of the element compositions are shown in Table 1, and the preparation method includes the following steps:

[0036] S1 Preheating: According to the mass percentages of each component designed, the raw materials are weighed respectively: A00 pure aluminum ingot and alloy blocks of Al-98% Si, Al-50% Mg, Al-50% Cu, Al-10% Mn, Al-5% Ti-B, Al-3% Nb-B and Al-10% Sr, and they are preheated and dried in a drying furnace heated to 200 °C.

[0037] S2 Melting: First, add pure aluminum ingot A00 and Al-98% Si alloy into the crucible and heat to melt. Keep it at 750 °C for 30 min, then add Al-50% Mg, Al-50% Cu, and Al-10% Mn alloys, and control the melting temperature at 725 - 735 °C to obtain molten aluminum liquid;

[0038] S3 Refining and degassing: Wait until the temperature of the molten aluminum liquid drops to 725 °C. Press the sodium-free refining agent for aluminum alloy into the molten aluminum liquid through a degassing machine, and introduce Ar gas for degassing treatment. The degassing time is 20 min, and the degassing temperature is 715 - 725 °C;

[0039] Use a hydrogen detector to detect the gas content. When the gas content > 0.15 ml / 100 g, repeat S3 until the gas content of the molten aluminum liquid ≤ 0.15 ml / 100 g;

[0040] S4 Alloy refinement: Add Al-5% Ti-B, Al-3% Nb-B, and Al-10% Sr to the molten aluminum liquid at 740 °C for alloy refinement and modification treatment, and then keep the melt static for heat preservation for 25 min;

[0041] Conduct a composition test on the molten aluminum liquid. In the case of unqualified composition test, add the corresponding raw materials for correction; repeat S4 until the composition test is qualified to obtain refined aluminum liquid.

[0042] S5 Casting: Pass through the national standard casting test bar mold, and conduct low-pressure casting on the refined aluminum liquid to obtain the heat-treatable aluminum alloy material. The total heat preservation and casting time do not exceed 2 h.

[0043] Table 1 Mass fractions of element compositions of Examples 1 - 15 and Comparative Examples 1 - 6

[0044]

[0045] Except for Example 15 compared with other examples, only quenching treatment is carried out immediately after casting, and others remain the same.

[0046] Comparative Example 6: Use commercially available A356.2 aluminum alloy, and the mass percentages of the components are: 7.3% silicon; 0.35% magnesium; 0.1% titanium; 0.020% strontium; 0.11% iron; the maximum of each single impurity element is 0.05%, and the rest is Al.

[0047] Test experimental examples

[0048] 1. Conduct low-pressure casting on the heat-treatable aluminum alloy materials of Examples 1 - 15 and the aluminum alloy materials of Comparative Examples 1 - 6 under the same conditions after melting and casting. The comparison of mechanical properties in the as-cast state is shown in Table 2.

[0049] Table 2 Comparison of as-cast mechanical properties of the as-cast heat-treatable aluminum alloy materials in Examples 1-15 and Comparative Examples 1-6 after low-pressure casting

[0050]

[0051]

[0052] As can be seen from Table 2, under the same conditions, the tensile strength, yield strength and elongation after fracture of the heat-treatable aluminum alloy materials in Examples 1-15 of the present invention in the as-cast state are significantly higher than those of the A356.2 material. There has been a great breakthrough on the basis of the A356.2 material commonly used in current low-pressure casting. Therefore, the products have high mechanical properties without heat treatment.

[0053] Figure 1 is the metallographic structure of the heat-treatable aluminum alloy material of Example 1 in the as-cast state after low-pressure casting, Figure 2 is the metallographic structure of the A356.2 material of Comparative Example 6 in the as-cast state after low-pressure casting. It can be seen that the grains of the heat-treatable aluminum alloy material of Example 1 are finer, and the eutectic silicon is more evenly and dispersedly distributed, making the heat-treatable aluminum alloy material of Example 1 have higher strength and better plasticity.

[0054] As can be seen from Table 2, the present invention has higher Mg and Cu contents and has a better solid solution strengthening effect. By adding a small amount of Sr and Nb, fine grain strengthening is achieved, while the yield strength is increased and the plasticity is improved.

[0055] 2. Generally speaking, the current heat-treatable aluminum alloy materials are all for body parts. These parts will all undergo body assembly and corresponding paint baking hardening treatment (about 200 °C, 45 minutes - 1 hour). Therefore, the heat-treatable aluminum alloy materials in Examples 1-15 and the aluminum alloy materials in Comparative Examples 1-6 were subjected to a baking treatment at 180 °C for 3 h, and the mechanical properties were tested by a tensile machine. The mechanical properties are shown in Table 3 below.

[0056] Table 3 Corresponding mechanical properties of Examples 1-15 and Comparative Examples 1-6 after paint baking

[0057]

[0058]

[0059] As can be seen from Table 3, the material strength of the proportioning examples with higher Mg and Cu contents is higher after baking treatment. The quenched state will inhibit the precipitation of alloying elements and enhance the solution strengthening effect, and also has higher strength compared with the as-cast state. Compared with Comparative Example 6, the strength of both the examples and Comparative Example 6 has increased after baking treatment, but the strength of the examples is higher. The elongation after fracture of Comparative Example 6 is as low as 3.8% after baking treatment. Thanks to the fine grain strengthening effect, the elongation after fracture of the examples still remains above 6%.

Claims

1. A heat - treatable - free aluminum alloy material for low - pressure casting, characterized in that, It consists of elements with the following mass fractions: 9.0% - 12.0% of Si, 0.1% - 0.6% of Mg, 0.1% - 0.5% of Cu, 0.05% - 0.2% of Mn, 0.05% - 0.2% of Ti, 0.01% - 0.04% of Sr, 0.05% - 0.2% of Fe, 0.04% - 0.2% of Nb and inevitable impurity elements, with the balance being Al.

2. The preparation method of the heat-treatable aluminum alloy material for low-pressure casting according to claim 1, wherein, It includes the following steps: (1) Melting: First, heat and melt the A00 pure aluminum ingot and the Al-98% Si alloy block, and hold the temperature at 730 - 760 °C for 30 - 60 min; then add the Al-50% Mg, Al-50% Cu and Al-10% Mn alloy blocks for melting, and control the melting temperature at 725 - 735 °C to obtain molten aluminum liquid. (2) Refining and degassing: Lower the temperature of the molten aluminum liquid to 715 - 730 °C, add a solid refining agent to the melt and introduce Ar gas for refining and degassing for 15 - 25 min, so that the gas content of the molten aluminum liquid ≤ 0.15 ml / 100 g. (3) Add the Al-5% Ti-B, Al-3% Nb-B and Al-10% Sr alloy blocks to the molten aluminum liquid at 735 - 750 °C for alloy refinement and modification treatment, and then keep the melt static and hold for 20 - 30 min to obtain refined aluminum liquid. (4) Casting: Carry out low-pressure casting on the refined aluminum liquid to obtain the heat-treatable aluminum alloy material described above.

3. The preparation method of the heat-treatable aluminum alloy material for low-pressure casting according to claim 2, characterized in that, The A00 pure aluminum ingot and the Al-98% Si, Al-50% Mg, Al-50% Cu, Al-10% Mn, Al-5% Ti-B, Al-3% Nb-B and Al-10% Sr alloy blocks should be preheated and dried in a drying furnace heated to 100 - 300 °C before melting.

4. The preparation method of the heat-treatable aluminum alloy material for low-pressure casting according to claim 2, characterized in that, The total of the holding time in step (3) and the casting time in step (4) should not exceed 2 h.

5. The preparation method of the heat-treatable aluminum alloy material for low-pressure casting according to claim 2, wherein, The temperature of the low-pressure casting in step (4) is 700 - 710 °C and the pressure is 250 - 500 mbar.

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