High-elongation al-si alloy integrated die casting, and microstructure control method and use thereof

Abstract

The application provides a high-elongation Al-Si alloy integrated die casting, and a structure control method and application thereof. The structure control method of the high-elongation Al-Si alloy integrated die casting comprises the following steps: firstly, Al-Ti-B intermediate alloy containing a specific titanium-boron ratio is added to the die-casting Al-Si alloy, and the Al-Ti-B intermediate alloy is completely melted in a short time through an auxiliary process, so that a melt I is obtained; secondly, Al-Sr intermediate alloy is rapidly added to the melt I, and smelting modification treatment is performed to obtain a melt II; finally, the melt II is die-cast to obtain the high-elongation Al-Si alloy integrated die casting. The application has the advantages of simple process and low cost, and the prepared high-elongation Al-Si alloy integrated die casting can ensure that the long-distance filling part of the integrated die casting has high elongation while maintaining good tensile strength.

Description

Technical Field

[0001] This invention relates to Al-Si alloy technology, and more particularly to a high-elongation Al-Si alloy integral die casting, its microstructure control method, and its applications. Background Technology

[0002] With the advent of lightweighting in automobiles, automotive structural components are developing towards integrated, lightweight, and high-efficiency design and manufacturing, such as unibody die-cast car bodies and unibody die-cast subframes. Currently, research on heat-treatable die-cast aluminum alloys for automotive structural components focuses on Al-Si alloys, which are widely used in the production of automotive parts and unibody die-cast car bodies due to their excellent casting properties.

[0003] However, Al-Si alloys also have certain problems in use. Their overall performance is affected by the morphology, distribution, and size of the coarse α-Al dendrites and brittle Si phases in the alloy. The Al / Si interface in the eutectic structure is not well matched, and the coarse plate-like or needle-like eutectic Si will severely cut the alloy matrix, causing stress concentration at the tips and corners of the eutectic Si, resulting in a decrease in the mechanical properties of the alloy, especially its plasticity.

[0004] To improve the plasticity of die-cast Al-Si alloys, modification treatment is a commonly used method. Adding Sr to the Al-Si alloy alters the morphology of the eutectic Si. While this can achieve better mechanical properties in small die-cast parts, it also exacerbates the alloy's gas absorption tendency, reduces melt fluidity, and significantly decreases mechanical properties over long distances. Besides modification treatment, grain refinement is another effective way to improve the plasticity of die-cast Al-Si alloys. However, when using Sr as a modifier, it is difficult to achieve good refinement and modification effects simultaneously in die-cast parts. This is because Sr-containing modifiers and boron-containing refiners easily interact, leading to poisoning and a decrease in both refinement and modification efficiency. Therefore, how to avoid poisoning and control the solidification structure of die-cast Al-Si alloys to improve their plasticity has become an urgent engineering problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to address the problem that the addition of Sr and B to die-cast Al-Si alloys leads to poisoning during the refining process, resulting in a decrease in refining and modification efficiency. This invention proposes a method for controlling the microstructure of integrated die-cast parts with high elongation of Al-Si alloys. The method is simple, low-cost, and produces integrated die-cast parts with high elongation of Al-Si alloys that maintain good tensile strength while also possessing high elongation.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a method for controlling the microstructure of a high-elongation Al-Si alloy integrated die-casting part, comprising the following steps:

[0007] Step (1) Raw material preparation: Al-Ti-B master alloy, die-cast Al-Si alloy and Al-Sr master alloy;

[0008] (2) Melting and refining: The Al-Ti-B master alloy is added to the die-cast Al-Si alloy melt, and the auxiliary process is used to promote its complete melting in a short time to obtain melt I;

[0009] (3) Modification treatment: Al-Sr master alloy is added to melt I in one go, and the mixture is stirred thoroughly to make it homogeneous. The modification treatment yields melt II.

[0010] (4) Die casting: Die casting melt II yields an integrated die casting of Al-Si alloy with high elongation.

[0011] Furthermore, in the Al-Ti-B master alloy, 1.8 ≤ Ti / B ≤ 2.5, and the Ti and B elements mainly form the mesophase TiB2. TiB2 exists in the form of particles with a particle size of 0.01-1.5 μm and a mass fraction of 1%-10%, preferably 2%-6%. Unless otherwise specified, all percentages in this invention refer to mass percentages.

[0012] Furthermore, the Si mass content in the Al-Si alloy is ≥5%;

[0013] Furthermore, the Sr mass content in the Al-Sr master alloy is 5%-15%, or 85%-95%.

[0014] Furthermore, in step (2), the amount of Al-Ti-B master alloy added should meet the following requirements: the content of Al-Ti-B master alloy in melt I is 0.1% to 3.0%, preferably 1% to 2%, where B is in excess and belongs to in-furnace borosilicate.

[0015] Furthermore, the auxiliary process described in step (2) enables the Al-Ti-B master alloy to completely dissolve within 1 minute and allows TiB2 particles to be dispersed throughout the melt. The short time mentioned in step (2) is less than or equal to 1 minute, and the auxiliary process includes, but is not limited to, ultrasonic melt vibration, electromagnetic stirring, or rapid induction heating.

[0016] Furthermore, unlike traditional smelting, this invention utilizes a large-capacity ladle technology for integrated die casting, adding the raw materials (Al-Ti-B master alloy and Al-Sr master alloy) used for refining and modification in the ladle. In step (3) of this invention, Sr is introduced into melt I by rapidly adding Al-Sr master alloy after smelting and before die casting and mixing it quickly. This effectively shortens the contact time between Sr and B, avoids the poisoning effect of Sr and B, and enables the die-cast Al-Si alloy to maintain high tensile strength while also having high elongation.

[0017] Furthermore, in steps (2) and (3), an Al-Ti-B master alloy and an Al-Sr master alloy are added to the melt using a robotic arm.

[0018] Furthermore, the amount of Al-Sr added in step (3) should meet the following requirement: the mass fraction of Sr in melt II is 0.01-0.05%.

[0019] Furthermore, in step (4), the first-stage injection speed is 0.1-0.7 m / s, the second-stage injection speed is 0.5-3.5 m / s, the mold temperature is 50-300℃, the die-casting machine unit clamping force is >3000t, and the vacuum degree is <200mbar.

[0020] Another objective of this invention is to disclose a high-elongation Al-Si alloy integral die-casting part, which is prepared by the above method.

[0021] Furthermore, the elongation of the high-elongation Al-Si alloy integral die casting is 12%-17%.

[0022] Furthermore, the high-elongation Al-Si alloy integrated die-casting part can still maintain an elongation of more than 70% near the gate position when the filling distance reaches 500-800 mm.

[0023] Another object of the present invention is to disclose the use of a high-elongation Al-Si alloy integral die casting in the field of automotive structural parts.

[0024] This invention discloses a high-elongation Al-Si alloy integral die-casting part, its microstructure control method, and its applications, which have the following advantages compared with the prior art:

[0025] 1) In traditional Al-Si casting alloys, the eutectic Si phase morphology is generally coarse, needle-like, and randomly distributed on the α-Al matrix. These sharply pointed eutectic Si phases are prone to stress concentration under load, thus becoming crack initiation points and severely affecting the alloy's mechanical properties. In this invention, the alloy contains Sr and B elements, which play a synergistic role in producing high-elongation Al-Si alloys. B refines the alloy's microstructure and improves its fluidity, while Sr transforms the coarse, needle-like eutectic Si into fine, fibrous structures. Together, they ensure that the die-cast structure of the Al-Si alloy is fine, uniform, and dense after long-distance filling, thereby improving the overall elongation of the integrated die-cast part.

[0026] 2) This invention improves the method of adding B by using an online addition method combined with assisted melting and dispersion technology to control the microstructure of Al-Si alloy, refine the grains, and improve elongation.

[0027] 3) This invention improves the method of adding Sr by using short-contact addition in the spoon before die casting, which can effectively avoid poisoning between Sr and B, thereby efficiently improving the morphology of Si and increasing the elongation. Compared with the matrix, the elongation can be increased by 25%-100%, reaching 12%-17%.

[0028] 4) The microstructure control method for high elongation Al-Si alloy integrated die casting of the present invention is easy to implement, has low production cost, and is applicable to industrial mass production. Attached Figure Description

[0029] Figure 1 A schematic diagram of the microstructure control method for integrated die-cast parts with high elongation Al-Si alloy;

[0030] Figure 2 This is a schematic diagram comparing the mechanical properties of the high-elongation Al-Si alloy integral die casting and the Al-Si alloy matrix in Example 1.

[0031] Figure 3 This is a schematic diagram comparing the stress-strain curves of the high-elongation Al-Si alloy integral die casting and the Al-Si alloy without modification treatment in Example 2. Detailed Implementation

[0032] The present invention will be further described below with reference to the embodiments:

[0033] Example 1

[0034] This embodiment discloses a method for controlling the microstructure of a high-elongation Al-Si alloy integral die-casting part, such as... Figure 1 As shown, it includes the following steps:

[0035] (1) Raw material preparation: 1) Al-Ti-B master alloy (where Ti and B elements mainly exist in the form of the meso phase TiB2, TiB2 exists in the form of particles with a particle size of 1μm and a TiB2 mass content of 2%); 2) Die-cast Al-Si alloy (Si mass content of 7%); 3) Al-Sr master alloy (Sr mass content of 10%).

[0036] (2) Melting and refining: The Al-Ti-B master alloy is added to the die-cast Al-Si melt and is completely melted within 5 minutes by electromagnetic stirring to obtain melt I, in which the content of Al-Ti-B master alloy is 1.0%;

[0037] (3) Modification treatment: Al-Sr alloy is added to melt I in one go, so that the mass content of Sr in the melt is 0.02% of the total mass of the melt. The mixture is stirred thoroughly to make it uniform, and the modification treatment yields melt II.

[0038] (4) Die casting: Die casting melt II yields Al-Si alloy integrated die castings with high elongation. The die casting conditions are as follows: first-stage injection speed is 0.3 m / s, second-stage injection speed is 1.4 m / s, mold temperature is 240℃, die casting machine unit clamping force is >3000t, and vacuum degree is <200mbar.

[0039] The Al-Si alloy integral die-cast part obtained in this embodiment has an elongation of 12.5%, which is 30% higher than that of the matrix.

[0040] Figure 2 This is a schematic diagram comparing the mechanical properties of the Al-Si integrated die casting of this embodiment (Example 1) with the Al-Si alloy matrix. It can be seen that the elongation of the alloy die casting after refinement and modification treatment is significantly increased, indicating that the present invention is effective.

[0041] Example 2

[0042] This embodiment discloses a method for controlling the microstructure of a high-elongation Al-Si alloy integral die-casting part, including the following steps:

[0043] (1) Raw material preparation: 1) Al-Ti-B master alloy (where Ti and B elements mainly exist in the form of the meso phase TiB2, TiB2 exists in the form of particles with a particle size of 1μm and a TiB2 mass content of 2%); 2) Die-cast Al-Si alloy (Si mass content of 6.5%); 3) Al-Sr master alloy (Sr mass content of 10%).

[0044] (2) Melting and refining: The Al-Ti-B master alloy is added to the die-cast Al-Si melt and is completely melted within 5 minutes by electromagnetic stirring to obtain melt I, in which the content of Al-Ti-B master alloy is 1.5%;

[0045] (3) Modification treatment: Al-Sr alloy is rapidly added to melt I so that the mass content of Sr in the melt is 0.02% of the total mass of the melt. The mixture is stirred thoroughly to make it homogeneous. The modification treatment yields melt II.

[0046] (4) Die casting: Die casting melt II yields Al-Si alloy integrated die castings with high elongation. The die casting conditions are as follows: first-stage injection speed is 0.3 m / s, second-stage injection speed is 1.4 m / s, mold temperature is 240℃, die casting machine unit clamping force is >3000t, and vacuum degree is <200mbar.

[0047] The high-elongation Al-Si alloy integral die-cast part obtained in this embodiment has an elongation of 14.2%, which is about 50% higher than that of the matrix.

[0048] Figure 3 This is a schematic diagram comparing the stress-strain curve of the Al-Si integrated die-cast part (Example 2) of this embodiment with the stress-strain curve of the Al-Si alloy without modification treatment. It can be seen that the combined addition of Sr and B has a significant impact on the elongation of the die-cast part, increasing the elongation by about 50% compared to the alloy without modification treatment by adding Sr and B before die casting.

[0049] Example 3

[0050] This embodiment discloses a method for controlling the microstructure of a high-elongation Al-Si alloy integral die-casting part, including the following steps:

[0051] Raw material preparation: 1) Al-Ti-B master alloy (where Ti and B elements mainly exist in the form of the meso phase TiB2, TiB2 exists in the form of particles with a particle size of 1μm and a TiB2 mass content of 2%); 2) Die-cast Al-Si alloy (Si mass content of 7%); 3) Al-Sr master alloy (Sr mass content of 10%).

[0052] (2) Melting and refining: The Al-Ti-B master alloy is added to the die-cast Al-Si melt and is completely melted within 5 minutes by electromagnetic stirring to obtain melt I, in which the content of Al-Ti-B master alloy is 1.0%;

[0053] (3) Modification treatment: Al-Sr alloy is rapidly added to melt I so that the mass content of Sr in the melt is 0.02% of the total mass of the melt. The mixture is stirred thoroughly to make it homogeneous. The modification treatment yields melt II.

[0054] (4) Die casting: Die casting melt II yields Al-Si alloy integrated die castings with high elongation. The die casting conditions are as follows: first-stage injection speed is 0.3 m / s, second-stage injection speed is 1.4 m / s, mold temperature is 240℃, die casting machine unit clamping force is >3000t, and vacuum degree is <200mbar.

[0055] The Al-Si alloy integral die-cast part obtained in this embodiment has an elongation of up to 12.4%.

[0056] As can be seen from Table 1, the elongation of the die castings produced by the embodiments of the present invention is significantly improved compared with the matrix, indicating that the microstructure control method in the present invention is effective and can obtain Al-Si alloy integrated die castings with high elongation.

[0057] Compare with Example 1

[0058] This comparative example discloses an Al-Si alloy die casting, which uses in-furnace addition of Sr and B to achieve an elongation of only 7.9% in the Al-Si alloy die casting. The steps are as follows:

[0059] Raw material preparation: 1) Al-Ti-B master alloy (where Ti and B elements mainly exist in the form of meso phase TiB2, TiB2 exists in the form of particles with a particle size of 1.0μm and a TiB2 mass content of 2%); 2) Die-cast Al-Si alloy (Si mass content of 7%); 3) Al-Sr master alloy (Sr mass content of 10%).

[0060] (2) Melting, refining and modification treatment: Al-Ti-B master alloy and Al-Sr master alloy are added together to the die-cast Al-Si melt, and electromagnetic stirring is used to make it completely melted within 5 minutes to obtain melt I.

[0061] (3) Die casting: Al-Si alloy die castings are obtained by conventional smelting of the die casting melt I. The die casting conditions are as follows: the first injection speed is 0.3 m / s, the second injection speed is 1.4 m / s, the mold temperature is 240℃, the clamping force of the die casting machine unit is >3000t, and the vacuum degree is <200mbar.

[0062] The elongation of the Al-Si alloy die casting obtained in this comparative example is shown in Table 1, which is only 7.9%. This is due to the poisoning phenomenon of SrB6 formed by the reaction between Sr and B, which leads to a certain degree of decrease in the elongation of the alloy die casting compared with the matrix.

[0063] Table 1 shows the performance results of each embodiment and the substrate.

[0064] Elongation (%) matrix 9.6 Example 1 12.5 Example 2 14.2 Example 3 12.4 Compare with Example 1 7.9

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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 method for controlling the microstructure of a high-elongation Al-Si alloy integrated die-casting part, characterized in that, Includes the following steps: Step (1) Raw material preparation: Al-Ti-B master alloy, die-cast Al-Si alloy and Al-Sr master alloy; (2) Melting and refining: The Al-Ti-B master alloy is added to the die-cast Al-Si alloy melt, and the auxiliary process is used to promote its complete melting in a short time to obtain melt I; (3) Modification treatment: Al-Sr master alloy is added to melt I in one go, and the mixture is stirred thoroughly to make it homogeneous. The modification treatment yields melt II. (4) Die casting: Die casting melt II yields an integrated die casting of Al-Si alloy with high elongation.

2. The method for controlling the microstructure of high elongation Al-Si alloy integrated die-cast parts according to claim 1, characterized in that, In step (1), the composition of the Al-Ti-B master alloy is 1.8≤Ti / B≤2.

5. The Ti and B elements mainly form the intermediate phase TiB2. TiB2 exists in the form of particles with a particle size of 0.01-1.5μm and a mass fraction of 1%-10%. And / or, the Si mass content in the Al-Si alloy is ≥5%; And / or, the Sr mass content in the Al-Sr master alloy is 5%-15%, or 85%-95%.

3. The method for controlling the microstructure of high elongation Al-Si alloy integrated die-cast parts according to claim 1, characterized in that, In step (2), the amount of Al-TiB2 master alloy added should meet the following requirements: the content of Al-Ti-B master alloy in melt I is 0.1% to 3.0%.

4. The method for controlling the microstructure of high elongation Al-Si alloy integrated die-cast parts according to claim 1, characterized in that, The auxiliary process described in step (2) is ultrasonic melt vibration, electromagnetic stirring or rapid induction heating.

5. The method for controlling the microstructure of high elongation Al-Si alloy integrated die-cast parts according to claim 1, characterized in that, Step (3) involves adding Sr to melt I after smelting and before die casting, which can effectively shorten the contact time between Sr and B and avoid the poisoning effect of Sr and B.

6. The method for controlling the microstructure of high elongation Al-Si alloy integrated die-cast parts according to claim 1 or 4, characterized in that, In step (3), the amount of Al-Sr master alloy added should meet the following requirement: the mass fraction of Sr in melt II is 0.01%-0.05%.

7. The method for controlling the microstructure of high elongation Al-Si alloy integrated die-cast parts according to claim 1, characterized in that, In step (4), the first-stage injection speed is 0.1-0.7 m / s, the second-stage injection speed is 0.5-3.5 m / s, the mold temperature is 50-300℃, the die-casting unit clamping force is >3000t, and the vacuum degree is less than 200mbar.

8. A high-elongation Al-Si alloy integral die-casting part, characterized in that, The high-elongation Al-Si alloy integral die casting is prepared by the method described in any one of claims 1-6, and the elongation is 12%-17%.

9. The high elongation Al-Si alloy integral die-casting part according to claim 8, characterized in that, The high-elongation Al-Si alloy integrated die-casting part can still maintain an elongation of more than 70% near the gate position when the filling distance reaches 500-800 mm.

10. Use of the high elongation Al-Si alloy integral die casting as described in claim 8 or 9 in the field of automotive structural components.

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