High-toughness Al-Si-Mg-Cu-Ca alloy and preparation method thereof

Abstract

The invention provides a high-toughness Al-Si-Mg-Cu-Ca alloy and a preparation method thereof. The high-toughness Al-Si-Mg-Cu-Ca alloy is prepared from the following components in percentage by weight: 6.5 to 7.5 percent of Si, 0.3 to 0.5 percent of Mg, 3.0 percent of Cu, 0.5 to 1.0 percent of Ca, 0.20 + / -0.05 percent of Sc and the balance of Al. The microelements are adjusted on the basis of the Al-Si-Mg alloy, and high strength and plasticity can be achieved. The aluminum alloy product with excellent performance can be obtained through traditional gravity casting under the condition that no extra machining technology is needed, and the production efficiency can be greatly improved. The magnesium alloy with the components after ultrasonic melt treatment can be used for casting large-size specification samples, has few internal defects and can be used for preparing main force-bearing structural member products.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and particularly to a high-strength and tough Al-Si-Mg-Cu-Ca alloy and a preparation method thereof. Background Art

[0002] Aluminum-silicon-magnesium casting alloys have good strength, ductility and corrosion resistance, and can produce excellent castings, which are widely used in the automotive industry. However, with the increasing demand for lightweight parts, it is necessary to improve the strength and ductility of aluminum-silicon-magnesium casting alloys for further industrial applications. After adding copper, nano-scale Al2Cu precipitates will form in the Al-Si-Mg alloy during aging treatment, thus significantly improving the strength. However, the improvement of the strength of the aluminum-silicon-magnesium alloy after adding copper is usually achieved by sacrificing its ductility. In addition, adding copper will also significantly reduce the melting point and eutectic temperature of the aluminum-silicon-magnesium alloy, resulting in an increase in the solidification range of the alloy and the formation conditions of porosity.

[0003] The grain refinement of Al-Si-Mg alloys is usually achieved by adding Al-5Ti-B, ultrasonic treatment, semi-solid formation, iron microalloying and strontium addition. The latest research shows that Sc can refine the grains and secondary dendrite arm spacing, modify the eutectic Si and β-Al5FeSi, and precipitate fine Al3Sc dispersoids, thus synergistically enhancing the strength and ductility. It has also been found that adding a small amount of Sc can reduce the hot tearing and shrinkage porosity of aluminum alloys, especially Al-Si-Mg alloys. Therefore, Sc has significant potential to reduce the disadvantages of Al-Si-Mg alloys, including more porosity and ductility loss.

[0004] The high strength of Al-Re-based alloys is the result of the combined action of fine grains of different types of nano-precipitates and effective hardening. The composite addition of Cu element with rare earth elements such as Sc, Sr, Zr, etc. forms primary phases such as Al2Cu and Al3Zr to provide nucleation sites to refine the grains, and can adjust the coarse flaky eutectic silicon into a fibrous structure to improve the comprehensive properties of the alloy. Therefore, adding a small amount of rare earth elements can effectively improve the strength of casting alloys, and this alloy addition will not significantly increase the alloy cost and alloy density.

[0005] In summary, although Al-Si-based alloys are widely used and have obvious advantages, due to their large grain size and lack of effective precipitation strengthening, their strength and plasticity are poor, and they have not been widely used in high-strength structural parts. The purpose of the present invention is to improve the strength and plasticity of Al-Si-based alloys so that they can be more widely used as main load-bearing structural parts. Summary of the Invention

[0006] The object of the present invention is to provide a high-strength and tough Al-Si-Mg-Cu-Ca alloy and a preparation method thereof. By adjusting trace elements on the basis of Al-Si-Mg alloy, higher strength and plasticity can be achieved.

[0007] According to one object of the present invention, the present invention provides a high-strength and tough Al-Si-Mg-Cu-Ca alloy, comprising the following components:

[0008] Si 6.5 - 7.5 wt.%, Mg 0.3 - 0.5 wt.%, Cu 3.0 wt.%, Ca 0.5 - 1.0 wt.%, Sc 0.20 ± 0.05 wt.%, and the balance is Al.

[0009] Further, the Cu content in the alloy is 3 wt.%, the Mg content is 0.5 wt.%, the Si content is 7 wt.%, the Ca content is 1 wt.%, and Al is the matrix component.

[0010] According to another object of the present invention, the present invention provides a preparation method of the above high-strength and tough Al-Si-Mg-Cu-Ca alloy, comprising the following steps:

[0011] Ingredient preparation: Weigh aluminum ingots, silicon, magnesium, copper, calcium, and scandium raw materials according to the above alloy component ratio and perform surface treatment;

[0012] Melting: Melting is carried out in a pit resistance furnace. Set the furnace temperature to 730 °C. Put the preheated aluminum ingots into the crucible of the melting furnace, let it stand until melted, and then add other alloy elements and perform temperature control;

[0013] Refining treatment: Add a refining agent to the melt, stir and then heat up to 750 °C and let it stand for 10 minutes;

[0014] Degassing and slag removal: Degas the melt through argon treatment and remove the floating slag;

[0015] Casting: Pour the standing aluminum alloy into a preheated mold and perform air cooling to room temperature.

[0016] Further, the temperature control range during the melting process is 720 - 750 °C, and after adding alloy elements such as calcium, copper, and scandium to the melt, it is continuously heated to 750 °C and subjected to a standing treatment.

[0017] Further, the ultrasonic melt treatment step is that when the melt temperature drops to 710 °C, insert a titanium alloy rod preheated to 400 °C into the melt and perform ultrasonic treatment for 5 minutes to refine the grains of the alloy.

[0018] Further, before casting, remove impurities and ensure the excellent quality of the casting by performing gas treatment and slag treatment on the alloy melt.

[0019] Beneficial effects

[0020] The technical solution of the present invention adjusts trace elements on the basis of an Al-Si-Mg alloy, which can achieve relatively high strength and plasticity. Without the need for additional processing techniques, aluminum alloy products with excellent properties can be obtained through traditional gravity casting, which can significantly improve production efficiency. The magnesium alloy with this composition after ultrasonic melt treatment can cast large-size samples with fewer internal defects and can be used for the preparation of main load-bearing structural parts products. Description of the drawings

[0021] Figure 1 It is a process flow chart of an embodiment of the present invention. Specific embodiments

[0022] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention.

[0024] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined. In addition, the terms "mounted", "connected" and "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] Example 1

[0026] A high-strength and tough Al-Si-Mg-Cu-Ca alloy, comprising the following components:

[0027] Si 6.5 - 7.5 wt.%, Mg 0.3 - 0.5 wt.%, Cu 3.0 wt.%, Ca 0.5 - 1.0 wt.%, Sc 0.20 ± 0.05 wt.%, and the balance is Al and inevitable impurity elements (if the impurity elements can be avoided, then there are no impurity elements).

[0028] In the present invention, the strength of the Al-Si-Mg alloy system is improved by adding a variety of alloy elements. Cu and Ca are selected as the main alloy elements to enhance the strength, and Sc is selected as the microalloying element. Al-Si-Mg-Cu-Ca-Sc alloys with different Cu or Ca contents are designed. By adding Cu, the strength of the Al-Si-Mg alloy can be significantly improved. At the same time, the addition of Ca is the key to achieving such high strength. The Ca element segregates at the small-angle grain boundaries and dislocation cores, reducing the dislocation mobility, and realizing the synergistic strengthening of thermodynamics and kinetics, which can improve the strength and the properties at room temperature and medium temperature simultaneously.

[0029] In the present invention, the strength of the Al-Si-Mg alloy system is improved by adding a variety of alloy elements. Among them, Cu and Ca are selected as the main alloy elements to enhance the strength, and Sc is selected as the microalloying element. Al-Si-Mg-Cu-Ca-Sc alloys with different Cu or Ca contents are designed. Adding Cu can significantly improve the strength of the Al-Si-Mg alloy. At the same time, the addition of Ca is the key to achieving such high strength. Ca segregates along the small-angle grain boundaries to the dislocation cores, reducing the dislocation energy through thermodynamics or applying the solute drag effect kinetically, reducing the dislocation mobility and stabilizing the small-angle grain boundaries for strengthening, which can improve the strength and the properties at room temperature and medium temperature simultaneously.

[0030] As Figure 1 shown, the main steps of the present invention include two parts: alloy design and alloy melting. (1) Alloy design

[0031] The present invention selects the Al-Si-Mg-based alloy as the basis because the Al-Si-Mg-based alloy is currently widely used, its casting performance is stable, and it has high room temperature strength and good corrosion resistance. Due to its excellent forming performance, in the present invention, the main load-bearing structural parts are improved based on the Al-Si-Mg alloy, enabling it to have the ability to produce complex structural parts.

[0032] On the basis of the Al-Si-Mg alloy, elements such as Cu and Ca are added for modification. The design principles for the addition of relevant elements are as follows:

[0033] The Si content ranges from 4% to 13%, with excellent casting performance, less shrinkage, good corrosion resistance and airtightness, and also good mechanical properties and welding performance.

[0034] Mg is dissolved in the Al-Cu alloy to form a solid solution, which improves the mechanical properties of the alloy through solid solution strengthening. Mg can refine the grain size, form a stable phase structure during the heat treatment process, and at the same time, Mg has the effect of improving the corrosion resistance of the alloy.

[0035] In the aluminum alloy, Cu can improve the mechanical properties of the aluminum alloy through solid solution strengthening and precipitation strengthening mechanisms, and improve the corrosion resistance and electrical conductivity of the alloy.

[0036] Ca can be used as a modifier to change the morphology of eutectic silicon, making it transform from thick plate-like or needle-like to fine fibrous or granular. This refinement effect can significantly improve the plasticity (such as elongation) and fatigue resistance of the alloy. The modification effect of Ca is more stable, especially under long-term melting or high-temperature conditions, with less decline phenomenon, which is suitable for industrial production. Therefore, the content of Ca in the alloy of the present invention is 0.5 - 1.0 wt.%.

[0037] Sc can refine the grain and secondary dendrite arm spacing, modify eutectic Si and β-Al5FeSi, and precipitate fine Al3Sc dispersoids, thereby synergistically enhancing strength and ductility. At the same time, the addition of a small amount of Sc can reduce the hot tearing and shrinkage porosity of aluminum alloys, especially Al-Si-Mg alloys.

[0038] Therefore, in summary, the present invention adds Cu, Ca, and Sc elements to the Al-Si-Mg alloy to design a new type of low-cost Al-Si-Mg-Cu-Ca-Sc alloy, and melts and prepares the main load-bearing structural parts of the aluminum alloy.

[0039] (II) Alloy Melting

[0040] Prepare materials according to the designed composition of the alloy, and conduct melting and casting experiments using the traditional metal gravity casting method. The specific steps are as follows:

[0041] a. Conduct melting in a pit resistance melting furnace. Preheat the stainless steel mold for casting in the resistance furnace at 200 - 300 °C in advance, and adjust the temperature of the pit furnace to 720 - 750 °C.

[0042] b. Weigh the raw materials according to the designed composition of the alloy. Mechanically polish the surface of the weighed aluminum ingots and the remaining intermediate alloys until the surface shows metallic luster to remove the surface oxide layer. After mechanical polishing, put them into the resistance furnace for preheating, and the preheating temperature is 200 - 300 °C, aiming to evaporate the surface moisture.

[0043] c. When the temperature of the resistance furnace reaches the set temperature of 720 - 750 °C, place the preheated aluminum ingots into the melting crucible of the pit furnace and let them stand for 15 - 20 min. After standing, the aluminum ingots are completely melted, and then quickly add the remaining preheated master alloys and let them stand and heat-insulate for 10 - 15 min.

[0044] d. After standing and heat-insulating, carry out refining. Add the refining agent into the molten liquid, continuously stir the molten liquid during the adding process, and after adding, let it stand and heat-insulate for 10 - 15 min; after standing, introduce argon for 10 - 15 min for degassing treatment; after degassing, start slag removal, and use a stainless steel spoon to remove the overburned products and impurities on the surface. Then let it stand for 10 - 15 min.

[0045] e. When the temperature of the melt drops to 710 °C, insert the titanium alloy rod preheated to 400 °C into the melt (depth about 30 mm), after ultrasonic treatment for 5 min, withdraw the ultrasonic device, and at this time the temperature of the melt is about 695 °C.

[0046] f. After the standing in the previous step, start casting. Before casting, start to lower the temperature of the resistance furnace. When the temperature drops to 680 - 720 °C, start casting. Pour the standing aluminum alloy into a square mold preheated to 250 °C for air cooling. Note that the casting speed should not be too fast to prevent the formation of a deeper riser.

[0047] Performance Test

[0048] Cut the prepared alloy samples for tensile property testing. The specifications of the tensile specimens conform to the GB / T 6397 - 1986 standard, and the tensile test method conforms to the GB / T228.1 - 2010 standard.

[0049] Process sheet samples with a gauge length of 15 mm from the cast plates for uniaxial tensile testing. The samples for the tensile test are sheets with a total length of 55 mm and a thickness of 2 mm. The tensile test is carried out on an Instron4505 machine at room temperature, and the crosshead speed is 1.0 mm / min. The strain in the tensile test is measured by an extensometer. Three samples are tested for tensile in each case. See Examples 2 - 4 for details.

[0050] Example 2:

[0051] This example adopts a new alloy element design and uses traditional gravity casting to prepare a new type of high-strength and high-ductility aluminum alloy material with excellent properties, including the following steps

[0052] Step S1: Batching:

[0053] Al-7Si-0.5Mg-3Cu-0.2Sc is weighed and mixed, and the raw materials are surface treated (to remove dirt and oxide skin). After mixing, the raw materials are preheated in a resistance furnace at 200°C for 1h.

[0054] Step S2: Smelting:

[0055] The melting furnace temperature is set to 730°C. When the melting furnace temperature rises to the predetermined temperature, the preheated pure aluminum ingot is placed in the crucible of the melting furnace. After it is left to stand and melt, the preheated pure Al, pure Cu, Al-20Si master alloy, and Al-2Sc master alloy are added to the crucible of the melting furnace respectively. Then, the melting temperature is raised to 750°C and kept at this temperature for 10 minutes.

[0056] Step S3:

[0057] Next, the refining process begins. The refining agent is added to the melt. The melt is stirred continuously during the addition process. After the addition is completed, the temperature is raised to 750°C and then kept at this temperature for 10 minutes.

[0058] Step S4:

[0059] After standing, argon gas was introduced for 10 minutes for degassing. After degassing, the surface was scraped and the surface scum was removed with a stainless steel spoon. Finally, the furnace temperature was lowered to 720°C.

[0060] Step S5:

[0061] Casting: pouring the aluminum alloy that has been left to stand still into a square mold preheated at 250°C to obtain a block of cast aluminum alloy, and air-cooling the ingot to room temperature;

[0062] Step S6:

[0063] The composition of the new high-strength cast aluminum alloy obtained in Example 1 of the present invention was detected by using a spectrometer, and the detection result was: the new high-strength cast aluminum alloy obtained in Example 1 of the present invention includes: 7.05wt% Si, 0.47wt% Mg, 2.91wt% Cu, the total amount of impurity elements Fe and Ni is less than 0.05wt%, and the balance is aluminum.

[0064] Step S7: Performance testing: the aluminum alloy ingot obtained by smelting is machined, and the aluminum alloy ingot is processed into a tensile performance test specimen for tensile performance testing. The tensile test method complies with the GB / T228.1-2010 standard. The experiment is repeated three times to ensure the accuracy of the data.

[0065] Example 3

[0066] Compared with Example 2, in Step S1 of Example 3, the alloy composition is changed to Al-7Si-0.5Mg-3Cu-1Ca-0.2Sc, and in Step S2, an Al-10Ca master alloy is added. The remaining steps are the same as those in Example 2.

[0067] The composition of the comparative cast magnesium alloy obtained in Example 3 was detected using a spectral analyzer. The detection results showed that the comparative cast magnesium alloy obtained in Example 3 included: 7.01 wt% Si, 0.48 wt% Mg, 2.96 wt% Cu, 1.05 wt% Ca, 0.17 wt% Sc. The total amount of impurity elements Fe and Ni was less than 0.05 wt%, and the balance was aluminum.

[0068] Next, performance testing was carried out. The aluminum alloy ingot obtained by melting was machined into a tensile property test specimen for tensile property testing. The tensile test method conformed to the GB / T 228.1-2010 standard, and the experiment was repeated three times to ensure the accuracy of the data.

[0069] Example 3 illustrates that the alloy composition design in the present invention is necessary. When adding 1.0 wt% Ca, an aluminum alloy product with better plasticity can be obtained, and the strength improvement is relatively small.

[0070] Example 4

[0071] Compared with Example 5, in Example 4, after Step S4, when the melt temperature drops to 710 °C, a titanium alloy rod preheated to 400 °C is inserted into the melt (depth 30 mm). With a power of 1200 W, after ultrasonic treatment for 5 minutes, the ultrasonic device is withdrawn. At this time, the temperature of the melt is approximately 695 °C. The remaining steps are the same as those in Example 3.

[0072] The composition of the comparative cast magnesium alloy obtained in Example 4 was detected using a spectral analyzer. The detection results showed that the comparative cast magnesium alloy obtained in Example 4 included: 6.99 wt% Si, 0.49 wt% Mg, 2.95 wt% Cu, 1.07 wt% Ca, 0.18 wt% Sc. The total amount of impurity elements Fe and Ni was less than 0.05 wt%, and the balance was aluminum.

[0073] Next, performance testing was carried out. The aluminum alloy ingot obtained by melting was machined into a tensile property test specimen for tensile property testing. The tensile test method conformed to the GB / T 228.1-2010 standard, and the experiment was repeated three times to ensure the accuracy of the data.

[0074] Example 4 demonstrates that ultrasonic melt treatment is necessary. When ultrasonic melt treatment is increased, the enhancement of the alloy's strength and plasticity is more significant. The strength of the new high-strength cast aluminum alloy in comparison is much higher than that of the new high-strength cast aluminum alloy in Example 2.

[0075] The performance test results of the above examples are shown in the following table:

[0076]

[0077]

[0078] Under the premise of slightly increasing the cost, the present invention can achieve relatively high strength and plasticity by adjusting trace elements based on the Al-Si-Mg alloy. Without the need for additional processing techniques, aluminum alloy products with excellent performance can be obtained through traditional gravity casting, which can significantly improve production efficiency. The magnesium alloy with this composition after ultrasonic melt treatment can be used to cast large-sized samples with fewer internal defects and can be used for the preparation of main load-bearing structural parts.

[0079] Compared with the prior art, in terms of performance, the aluminum alloy products of the alloy of the present invention have excellent strength; in terms of preparation cost, since the alloying elements are all added in trace amounts and do not involve complex process methods and procedures, the preparation cost is relatively low; therefore, this new magnesium alloy has the potential for commercial production.

[0080] The manufacturing process of the present invention conforms to the concept of safety and environmental protection and will not cause any pollution to the environment. When the alloy composition deviation and impurity elements meet the regulations, products that have exceeded the service life can be recycled and remelted to save costs.

[0081] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-strength and tough Al-Si-Mg-Cu-Ca alloy, characterized in that: Includes the following ingredients: Si 6.5~7.5wt.%, Mg 0.3~0.5wt.%, Cu 3.0wt.%, Ca 0.5~1.0wt.%, Sc0.20±0.05wt.%, and the balance is Al.

2. The high-strength and tough Al-Si-Mg-Cu-Ca alloy according to claim 1, characterized in that: The alloy contains 3 wt.% Cu, 0.5 wt.% Mg, 7 wt.% Si, 1 wt.% Ca, and Al as a matrix component.

3. The method for preparing a high-strength and tough Al-Si-Mg-Cu-Ca alloy according to claim 1 or 2, characterized in that: The following steps are involved: Ingredients: weigh aluminum ingots, silicon, magnesium, copper, calcium and scandium raw materials according to the above alloy composition ratio and perform surface treatment; Melting: Melting is carried out in a pit-type resistance furnace, the furnace temperature is set to 730°C, the preheated aluminum ingot is placed in the crucible of the melting furnace, and it is left to stand until it melts, and then other alloy elements are added and the temperature is controlled; Refining treatment: add refining agent to the melt, stir, heat to 750℃ and let stand for 10 minutes; Degassing and slag removal: The melt is degassed and slag is removed by treating it with argon gas; Casting: Pour the aluminum alloy after standing into the preheated mold and air-cool it to room temperature.

4. The method for preparing the high-strength and tough Al-Si-Mg-Cu-Ca alloy according to claim 3, characterized in that: The temperature control range during the smelting process is 720-750° C., and the melt is further heated to 750° C. after adding alloy elements such as calcium, copper, and scandium, and is then left to stand.

5. The method for preparing the high-strength and tough Al-Si-Mg-Cu-Ca alloy according to claim 3 or 4, characterized in that: The ultrasonic melt treatment step is to insert a titanium alloy rod preheated to 400°C into the melt when the melt temperature drops to 710°C and perform ultrasonic treatment for 5 minutes to refine the grains of the alloy.

6. The method for preparing the high-strength and tough Al-Si-Mg-Cu-Ca alloy according to claim 3, characterized in that: Before casting, the alloy melt is subjected to gas treatment and slag treatment to remove impurities and ensure the excellent quality of the casting.

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