Low-cost high-toughness aluminum-silicon die-casting alloy and preparation method thereof

Abstract

The invention discloses a low-cost high-toughness aluminum-silicon die-casting alloy and a preparation method thereof, and belongs to the technical field of light alloy materials. The alloy comprises the following components in percentage by mass: 7.0%-10.0% of Si, 0.8%-1.5% of Zn, 0.0%-0.5% of Mg, 0.0%-0.6% of Mn, 0.0%-0.2% of Ti, less than 0.2% of Fe and the balance of Al and inevitable impurities. The core of the invention is that Zn is used as a modificator to replace traditional Sr, eutectic silicon is effectively converted into a fibrous form, and the problems of deterioration decline, porosity increase and poisoning reaction caused by Sr deterioration are avoided. On the basis, Mg element is added to further refine the eutectic silicon structure, and the Mg element is combined with Zn to form a nano precipitated phase reinforced matrix. The alloy has excellent mechanical properties without heat treatment in a die-casting state, the yield strength is 130-160 MPa, the tensile strength is 260-300 MPa, the ductility is 10-16%, meanwhile, the alloy has excellent casting fluidity and heat crack resistance, the cost is low, and the alloy is particularly suitable for integrated die-casting forming of large structural parts of automobiles.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of light alloy, in particular to a low-cost high-strength and high-toughness aluminum-silicon die casting alloy and a preparation method thereof. BACKGROUND

[0002] Lightweight is an important way to save energy and reduce emissions. As the most widely used light alloy, aluminum alloy has been widely used in the fields of automobiles, aerospace, high-speed rail, etc. Especially the wide application of large aluminum alloy die castings in the automobile industry has greatly promoted the development process of automobile lightweight technology.

[0003] Among them, Al-Si series cast aluminum alloy has become the research focus of cast aluminum alloy due to its excellent casting performance, good fluidity and comprehensive mechanical properties. In the microstructure of aluminum-silicon alloy, eutectic silicon is one of the main reasons affecting the thermal conductivity and mechanical properties of cast aluminum-silicon alloy. The eutectic silicon in the alloy exists in the form of coarse flake, which will reduce the mechanical properties of the alloy, especially the plasticity. Therefore, it is usually necessary to modify the eutectic silicon from coarse flake to fine fibrous shape, so as to improve the strength and toughness of the aluminum-silicon alloy.

[0004] At present, commercial die casting aluminum-silicon alloy generally uses strontium (Sr) as a modifier. For example, the representative Aural-2 alloy (composition: Al-10Si-0.5Mn-0.3Mg) is modified by adding Sr, but the elongation of the die casting state is usually less than 7%, often relying on subsequent heat treatment to further optimize the morphology of eutectic silicon and improve plasticity. However, heat treatment will cause deformation of the casting and increase the cost.

[0005] In order to avoid the problems caused by heat treatment, the industry also tries to reduce the silicon content in the alloy to improve the plasticity. For example, the Al-7Si-0.5Mn-0.3Mg-0.1Sr die casting alloy developed by Alcoa is based on this idea. However, this scheme introduces new challenges: the reduction of silicon content will cause the liquidus temperature of the alloy to rise, the flowability of the melt to deteriorate, and the liquid-solid phase interval to increase, thereby significantly increasing the tendency of thermal cracking of the casting and being extremely unfavorable for the forming of complex components.

[0006] In addition, the Sr modifier itself has a series of inherent drawbacks: first, it is prone to "modification decay", that is, the modification effect decreases with the extension of the melt standing time, the production process window is narrow, and the stability is poor; second, the addition of Sr will significantly increase the tendency of the alloy melt to absorb gas, leading to an increase in the porosity of the casting and damaging its mechanical properties and sealing performance; third, Sr element is easy to react with boron (B), fluorine (F) and other elements in the melt to lose effectiveness, which requires high purity of raw materials and strict control of production process.

[0007] Therefore, it is of great significance to explore new modifiers, develop new aluminum-silicon die casting alloys with low cost, good casting performance and high strength and toughness. SUMMARY

[0008] In view of the above problems existing in the prior art, the purpose of the present application is to provide a low-cost high-strength aluminum-silicon die casting alloy and a preparation method thereof, which solves the problems of the prior art, such as dependence on strontium (Sr) modification, resulting in alloy modification recession, high porosity, easy poisoning, and subsequent heat treatment to meet the plasticity standard, which causes casting deformation and cost increase.

[0009] To solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0010] A low-cost high-strength aluminum-silicon die casting alloy, comprising the following components in percentage by mass: Si: 6.7%-10.0%, Zn: 0.8%-1.5%, Mg: 0.0%-0.5%, Mn: 0.0%-0.6%, Ti: 0.0%-0.2%, Fe: less than 0.2%, and the balance being Al and unavoidable impurities; wherein the Zn serves as a modifier to make the eutectic silicon in the alloy present a fibrous morphology.

[0011] In the aluminum-silicon alloy of the present application, zinc (Zn) as a modifier is used to improve the morphology of eutectic silicon in high-pressure cast aluminum-silicon alloy, so that it is transformed into a fibrous form, thereby improving its mechanical properties; magnesium (Mg) mainly functions to further refine the eutectic silicon structure on the basis of Zn modification and produce fine precipitates, thereby strengthening the mechanical properties of the alloy; iron (Fe) mainly functions to inhibit the occurrence of "mold sticking phenomenon" and prevent the adhesion of the casting to the mold, facilitating demolding, but the addition of Fe will form needle-shaped or sheet-shaped intermetallic compounds, thereby reducing the mechanical properties of the alloy, so the content of Fe should not be too high; manganese (Mn) is used to improve the negative effects of Fe and assist in improving the strength of the alloy; titanium (Ti) is used to refine the casting grains and improve the comprehensive performance of the alloy; aluminum (Al) is the base element and constitutes the main component of the alloy, which is the basic structural phase of the alloy and ensures the basic properties of the alloy.

[0012] Further, the mass percentage of Zn is 1%-1.5%, and the mass percentage of Mg is 0.2%-0.5%.

[0013] Further, the mass percentage of Mn is 0.1%-0.6%, and the mass percentage of Ti is 0.01%-0.2%.

[0014] Further, in the die casting state, the yield strength is ≥130 MPa, the tensile strength is ≥240 MPa, and the elongation is ≥12%.

[0015] Further, the unavoidable impurities are ≤0.4%.

[0016] The preparation method of the low-cost high-toughness die-casting aluminum-silicon alloy comprises the following steps:

[0017] (1) Melting and refining: pure Al, pure Si, pure Fe, Al-Mn intermediate alloy, Al-Mg intermediate alloy, Al-Ti intermediate alloy, and Al-Zn intermediate alloy are weighed according to the metering ratio, dried after preheating, and melted into an alloy melt, and the melt is subjected to refining and degassing treatment;

[0018] (2) Die-casting forming: the melt treated in step (1) is injected into a mold preheated to 200-230 DEG C at a pouring temperature of 680-700 DEG C to form a die-casting, and the injection process adopts two-stage injection speed control: low-speed injection is used to make the melt flow smoothly to the inlet of the mold, and then high-speed injection is used to make it quickly fill the entire mold cavity.

[0019] Further, in step (1), the refining is specifically: 0.3% to 0.6% of the refining agent by mass of the melt is added to the melt, and the melt is fully stirred to remove inclusions in the melt.

[0020] Further, the refining agent is magnesium chloride or calcium chloride.

[0021] Further, in step (1), the degassing treatment is to remove impurity gas by introducing nitrogen into the refined melt.

[0022] Further, in step (2), the speed of the low-speed injection is 0.1-0.25 m / s, and the speed of the high-speed injection is 1.5-3 m / s.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] 1. The present application provides a low-cost high-toughness aluminum-silicon die-casting alloy, which successfully converts eutectic silicon into fibrous form by using Zn as a modifier, thereby obtaining high elongation (10%-16%) in the die-casting state; at the same time, the high Si content ensures high strength, and in combination with the Mg element, the strength of the alloy is further improved by the nano precipitates formed by the cooperation of Mg and Zn, so that the yield strength reaches 130-160 MPa, the tensile strength reaches 260-300 MPa, and the perfect balance of high strength and toughness is achieved. The alloy composition discards the process-sensitive Sr and other high-valence metal elements, avoids the problems of modification decay, increased porosity, and easy poisoning by elements such as B and F caused by Sr modification, and has low cost. In addition, in terms of casting performance, the high Si content also ensures excellent fluidity and hot cracking resistance, and is particularly suitable for the production of large automobile parts.

[0025] 2. The application also provides a preparation method of the aluminum-silicon die casting alloy. The method optimizes key parameters such as pouring temperature, mold temperature and injection speed, and ensures good forming and organization densification of the alloy. Finally, the prepared alloy can meet the requirements in the die casting state, completely eliminates the subsequent heat treatment process which is energy-consuming and easy to cause deformation and bubbling, greatly improves the production efficiency and yield, and perfectly meets the technical requirements of integrated die casting. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Figure 1 is a micrograph of eutectic silicon in the comparative example and the examples of the application; wherein, Figure 1 (a) is the comparative example alloy, Figure 1 (b) is the example 1 alloy, Figure 1 (c) is example 2, Figure 1 (d) is the example 3 alloy, Figure 1 (e) is the example 4 alloy Figure 1 (f) is the example 5 alloy, Figure 1 (g) is the example 6 alloy,

[0027] Figure 2 Figure 2 is a micrograph of precipitated phase in the example 2 alloy of the application. DETAILED DESCRIPTION

[0028] The application will be further described in detail below with reference to the drawings and examples. It should be noted that the following examples are only used to explain the application, but not to limit the application. Any modification or equivalent replacement of the application without departing from the spirit and essence of the application falls within the protection scope of the application. The experimental methods used in the application are conventional methods unless otherwise specified. The materials and reagents used in the application can be purchased or synthesized by known methods unless otherwise specified.

[0029] The application provides a low-cost high-strength and high-toughness aluminum-silicon die casting alloy and a preparation method thereof. The core idea is that zinc (Zn) is used as a core modifier to replace traditional strontium (Sr), thereby fundamentally avoiding the process defects inherent in Sr modification. By introducing magnesium (Mg) and Zn to work together, eutectic silicon fibers are formed while nano precipitates are formed to strengthen the mechanical properties of the alloy. Finally, a simple and low-cost aluminum-silicon alloy is obtained, which has high strength and high toughness without the need for heat treatment in the die casting state, to meet the stringent requirements of integrated die casting for material performance and process stability.

[0030] I. Examples and comparative examples

[0031] To verify the technical effects of the present application, six embodiments (Embodiments 1-6) are provided, and one prior art is provided as a comparative example (Al-10Si-0.5Mn-0.3Mg-0.1Fe-0.01Sr alloy). The specific chemical composition (wt%) of each alloy is shown in Table 1.

[0032] Table 1. Chemical composition of the alloy of the embodiments and the comparative example (wt%)

[0033] Alloy Si Zn Mg Mn Ti Fe Sr Al and unavoidable impurities Example 1 7.2％ 1.5％ — 0.5％ 0.1％ 0.1％ — Balance Example 2 6.7％ 1.5％ 0.2％ 0.5％ 0.1％ 0.1％ — Balance Example 3 6.7％ 1.5％ — — — — — Balance Example 4 6.7％ 1.5％ 0.5％ — — — — Balance Example 5 9.8％ 1.5％ — 0.5％ 0.1％ 0.1％ — Balance Example 6 9.5％ 1.5％ 0.2％ 0.5％ 0.12％ 0.1％ — Balance Comparative Example 9.8％ — 0.3％ 0.5％ 0.12％ 0.1％ 0.01％ Balance

[0034] II. Alloy preparation method

[0035] The die-casting aluminum-silicon alloy involved in the embodiments and the comparative example is prepared by the following general process:

[0036] (1) batching and melting:

[0037] According to the composition requirements shown in Table 1, industrial pure aluminum, industrial pure silicon, pure iron, Al-Mn intermediate alloy, Al-Mg intermediate alloy, Al-Ti intermediate alloy, and Al-Zn intermediate alloy are used as raw materials. After preheating and drying at 200°C, the raw materials are placed in a crucible resistance furnace and heated to 750±10°C to completely melt them.

[0038] (2) refining and degassing:

[0039] After the alloy is completely melted, 0.5% of the total mass of the melt is added as a refining agent (magnesium chloride), and the mixture is stirred for 1 hour to remove inclusions in the melt. Subsequently, high-purity nitrogen gas (N2, purity ≥ 99.99%) is introduced into the bottom of the melt for degassing treatment, with a gas flow rate of 100 L / min for 10-30 min.

[0040] (3) standing and die casting:

[0041] After refining and degassing, the melt is allowed to stand at 740°C for 20 min. Then, the temperature is lowered to the pouring temperature (680-690°C), and the cold chamber die casting machine is used for die casting. The die casting mold temperature is 230°C, and during die casting, the melt is first pushed smoothly to the entrance of the mold at a low injection speed of 0.25 m / s, and then continuously injected into the mold at a high injection speed of 2.0 m / s until the melt fills the entire mold cavity. Immediately start the pressurization program, apply a final pressure of 100 MPa to the metal in the injection chamber through the injection punch to compact the casting and compensate for solidification shrinkage, and maintain the pressure for 5 seconds to obtain the die-casting sample; the die-casting sample is a standard tensile test bar.

[0042] III. Microstructure and mechanical property analysis

[0043] 1. Microstructure observation of all the alloys in as-cast state was performed by scanning electron microscope (SEM), and the results are shown in Figs. 1-6. Figure 1

[0044] From Figs. 1-6, it can be seen that: Figure 1 (a) The eutectic silicon morphology of the comparative example alloy with Sr as the modifier has been changed from coarse flake to fiber with more branches, indicating that the Sr modifier has played a role.

[0045] Figure 1 (b) to (g) show the microstructure of the alloys of the embodiments of the present application. All the embodiments with Zn as the modifier, the eutectic silicon has been successfully modified from flake to typical fiber morphology with well-developed branches. This indicates that Zn can effectively replace Sr to achieve modification of eutectic silicon. Figure 1 In particular, by comparing (b) (Example 1, without Mg) with (c) (Example 2, containing 0.2% Mg), or (d) (Example 3, without Mg) with (e) (Example 4, containing 0.5% Mg), or (f) (Example 5, without Mg) with (g) (Example 6, containing 0.2% Mg), it can be found that after introducing Mg element on the basis of Zn modification, the fiber morphology of eutectic silicon is more fine and dense. This proves that the addition of Mg has a synergistic promoting effect on the modification effect of Zn, which can further refine the eutectic silicon structure.

[0046] Figure 1 Figure 1 Figure 1 Figure 1 Figure 1 Figure 1

[0047] Figure 2 The micro-morphology of the precipitated phase in Example 2 alloy is shown in Fig. 7. It can be observed that due to the addition of Mg element, nanoscale second phase precipitates are formed at the grain boundaries and the like of the alloy. These precipitated phases are one of the key factors to improve the strength of the alloy.

[0048] 2. Room temperature tensile property test of all the alloys in as-cast state was performed by a universal testing machine, and the results are summarized in Table 2.

[0049] Table 2. Comparison of mechanical properties of examples and comparative examples (as-cast state)

[0050]

[0051]

[0052] From the test results in Table 2, the following conclusions can be drawn:

[0053] (1) The core advantage of Zn modification: plasticity improvement​​​​​​​​

[0054] Comparing Examples 5 and 6 of the present invention with a high silicon content and a comparative example with the same high silicon content, it can be found that although the strength levels are comparable, the elongation of the alloy of the present invention (14.5%, 12.2%) is significantly higher than that of the comparative example (6.7%). This fully demonstrates that using Zn instead of Sr as a modifier can significantly improve the plasticity of the alloy while maintaining high strength, achieving a good combination of strength and toughness.

[0055] (2) The strengthening effect of Mg

[0056] Building upon Zn modification, the introduction of Mg further refined the eutectic silicon structure and precipitated finer precipitates, thereby improving the alloy's performance. For example, under similar Si content conditions (compare Example 1 with Example 2, or Example 3 with Example 4, or Example 5 with Example 6), the addition of Mg resulted in a clear increase in both the yield strength and tensile strength of the alloy. This strengthening effect is attributed to the finer, denser eutectic silicon structure observed in the microstructure. Figure 1 (e) and nano-precipitated phases ( Figure 2 This aligns with the findings, confirming that Mg achieves precipitation strengthening through the formation of a second phase. Furthermore, the elongation decreases with increasing strength, consistent with the material science principle that precipitation strengthening is typically accompanied by a slight sacrifice in plasticity.

[0057] Furthermore, the alloy of this invention exhibits good melt flowability and filling ability under optimized die casting process, and the resulting castings are well formed and have no tendency to hot crack, which proves its excellent casting process performance and fully meets the requirements of integrated die casting of large structural parts.

[0058] In summary, this invention, by using Zn as a modifier and optimizing the proportions of elements such as Si and Mg, has successfully developed an aluminum-silicon alloy that simultaneously possesses high strength and excellent plasticity in the die-cast state without heat treatment. This alloy effectively avoids many of the drawbacks of Sr modification and is inexpensive, making it particularly suitable for large, integrated die-cast structural parts requiring high strength, toughness, and production efficiency.

[0059] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-cost, high-strength, high-toughness die-cast aluminum-silicon alloy, characterized in that, By weight percentage, it includes the following components: Si: 6.7%-10.0%, Zn: 0.8%-1.5%, Mg: 0.0%-0.5%, Mn: 0.0%-0.6%, Ti: 0.0%-0.2%, Fe: less than 0.2%, with the balance being Al and unavoidable impurities; wherein, Zn acts as a modifier to give the eutectic silicon in the alloy a fibrous morphology.

2. The low-cost, high-strength, high-toughness die-cast aluminum-silicon alloy according to claim 1, characterized in that, The Zn content is 1%-1.5% by mass, and the Mg content is 0.2%-0.5% by mass.

3. The low-cost, high-strength, high-toughness die-cast aluminum-silicon alloy according to claim 1, characterized in that, The mass percentage of Mn is 0.1%-0.6%, and the mass percentage of Ti is 0.01%-0.2%.

4. The low-cost, high-strength, high-toughness die-cast aluminum-silicon alloy according to claim 2 or 3, characterized in that, In the die-cast state, its yield strength is ≥130MPa, tensile strength is ≥240MPa, and elongation is ≥12%.

5. The low-cost, high-strength, high-toughness die-cast aluminum-silicon alloy according to claim 1, characterized in that, The unavoidable impurities are ≤0.4%.

6. A method for preparing a low-cost, high-strength, and high-toughness die-cast aluminum-silicon alloy according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Melting and refining: Weigh pure Al, pure Si, pure Fe, Al-Mn master alloy, Al-Mg master alloy, Al-Ti master alloy, and Al-Zn master alloy according to the metric ratio, preheat and dry them, melt them into alloy melt, and then refine and degas the melt. (2) Die casting: The melt processed in step (1) is injected into a mold preheated to 200-230°C at a casting temperature of 680-700°C and die cast. The injection process adopts two-stage injection speed control: first, low-speed injection allows the melt to flow smoothly to the entrance of the mold, and then high-speed injection is switched to quickly fill the entire mold cavity.

7. The method for preparing low-cost, high-strength, and high-toughness die-cast aluminum-silicon alloy according to claim 6, characterized in that, In step (1), the refining specifically involves adding 0.3% to 0.6% of the refining agent by mass of the melt to the melt and stirring thoroughly to remove inclusions in the melt.

8. The method for preparing low-cost, high-strength, and high-toughness die-cast aluminum-silicon alloy according to claim 7, characterized in that, The refining agent is magnesium chloride or calcium chloride.

9. The method for preparing low-cost, high-strength, and high-toughness die-cast aluminum-silicon alloy according to claim 6, characterized in that, In step (1), the degassing process involves introducing nitrogen gas into the refined melt to remove impurity gases.

10. The method for preparing low-cost, high-strength, and high-toughness die-cast aluminum-silicon alloy according to claim 6, characterized in that, In step (2), the speed of the low-speed injection is 0.1-0.25 m / s, and the speed of the high-speed injection is 1.5-3 m / s.

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