Heat-treatment-free Al-Si alloy suitable for large-scale integrated gravity / low-pressure casting forming and preparation method of heat-treatment-free Al-Si alloy

Abstract

The invention relates to a heat treatment-free Al-Si alloy suitable for large-scale integrated gravity / low-pressure casting molding and a preparation method thereof, and the Al-Si alloy comprises the following components in percentage by mass: 8.0%-8.5% of Si, 0.5%-0.7% of Mg, 0.15%-0.25% of Zn, 0.2%-0.25% of Zr, 0.15%-0.25% of Y and the balance of Al and inevitable impurity elements. In the Al-Si alloy, Mg and Zn are added, so that the strength of the alloy is effectively improved on the premise of not influencing the flowability of the alloy; by adding Zr, primary alpha-Al can be refined, and formed Al3Zr can stably exist as a nucleation core; al3Y is generated by adding Y, grains can be further refined, gas dissolved in the alloy is reduced, in addition, Y can be adsorbed on the growth surface of eutectic Si, the original growth mode is changed, and the eutectic Si is converted into a fiber shape from a plate shape.

Description

Technical Field

[0001] The invention belongs to the technical field of cast aluminum alloys, and in particular relates to a heat-treatment-free Al-Si alloy suitable for large-scale integrated gravity / low-pressure casting and a preparation method thereof. Background Art

[0002] Al-Si alloy is a kind of metal material mainly composed of aluminum and silicon. Hypoeutectic Al-Si alloy refers to Al-Si alloy with silicon content <12.6wt%, generally 5wt% to 12wt%. Aluminum-silicon alloy has good casting performance, can fill complex mold cavities and is not prone to thermal cracking, and is suitable for making castings with complex structures. In addition, since Al-Si alloy also has the characteristics of low density, high specific strength and corrosion resistance, it is widely used in aerospace, automobile and digital fields.

[0003] In recent years, aluminum alloy castings have developed in the direction of integration, complexity, and thin-walling. Under this condition, the performance requirements for aluminum alloy castings have become increasingly high, especially for casting performance and mechanical properties, requiring the ability to fill complex cavities and have strong mechanical properties in the cast state. Although traditional Al-Si alloys have good casting properties, they are not strong enough in the cast state and cannot meet the performance requirements of Al-Si alloys at this stage. Although heat treatment strengthening can greatly improve the mechanical properties of Al-Si alloys, it increases costs and increases carbon emissions. In addition, there is a risk of deformation of castings during the heat treatment process, which affects subsequent use. Therefore, it is of great practical significance to develop a high-strength and tough Al-Si alloy that does not require heat treatment. Summary of the invention

[0004] In view of this, the present invention provides a heat-treatment-free Al-Si alloy suitable for large-scale integrated gravity / low-pressure casting and a preparation method thereof to solve the technical problems of high cost, high carbon emission and easy deformation of castings in the prior art methods of heat treatment to strengthen the mechanical properties of Al-Si alloys.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows.

[0006] In the first aspect, the present invention provides a heat-treatment-free Al-Si alloy suitable for large-scale integrated gravity / low-pressure casting, including Si: 8.0wt%~8.5wt%, Mg: 0.5wt%~0.7wt%, Zn: 0.15wt%~0.25wt%, Zr: 0.2wt%~0.25wt%, Y: 0.15wt%~0.25wt%, and the remainder is Al and unavoidable impurity elements.

[0007] Preferably, it includes Si: 8.0wt%, Mg: 0.6wt%, Zn: 0.2wt%, Zr: 0.2wt%, Y: 0.15wt% to 0.25wt%, and the balance is Al and inevitable impurity elements.

[0008] In a second aspect, the present invention further provides a method for preparing a heat-treatment-free Al-Si alloy suitable for large-scale integrated gravity / low-pressure casting, comprising the following steps:

[0009] Step 1: Weigh pure Al, Al-Si alloy, pure Mg, pure Zn, Al-Y master alloy and Al-Zr master alloy in proportion;

[0010] Step 2: Melt pure Al and Al-Si alloy at 800±2.5℃, stir evenly, cool to 760±2.5℃ and keep warm, skim off impurities to obtain a melt;

[0011] Step 3: first add pure Mg wrapped with aluminum foil to the melt, wait until it is completely melted, stir evenly, and keep warm; then add pure Zn wrapped with aluminum foil to the melt, wait until it is completely melted, stir evenly, and keep warm;

[0012] Step 4: then add the Al-Zr master alloy wrapped with aluminum foil to the melt, wait until it is completely melted, stir evenly, and keep warm; then add the Al-Y master alloy wrapped with aluminum foil to the melt, wait until it is completely melted, stir evenly, and keep warm;

[0013] Step 5: Finally, add a slag remover to the melt, stir evenly, skim off impurities, pass argon gas into the melt for refining, and skim off impurities again;

[0014] Step 6: Measure the temperature of the melt after refining. When the melt is cooled to 720±2.5°C, pour the melt into a steel mold preheated to 200±2.5°C to obtain a casting.

[0015] Preferably, in step 1, the purity of pure Al is ≥99.8%, the purity of pure Mg is ≥99.8%, and the purity of pure Zn is ≥99.8%.

[0016] Preferably, in step 1, the Al-Si alloy is an Al-20wt% Si alloy, the Al-Y master alloy is an Al-10wt% Y master alloy, and the Al-Zr master alloy is Al-5wt% Zr.

[0017] Preferably, the pure Al, pure Mg and pure Zn have their surface oxide films removed and are preheated to 200±2.5° C. before use.

[0018] Preferably, in step 2, the stirring time is 3 minutes and the insulation time is 20 minutes.

[0019] Preferably, in step 3, the stirring time is 2 minutes and the insulation time is 5 minutes.

[0020] Preferably, in step 4, the stirring time is 2 minutes and the insulation time is 10 minutes.

[0021] Preferably, in step 5, the amount of the slag remover added is 1 wt% of the mass of the melt.

[0022] Preferably, in step 5, the purity of the nitrogen is 99.99%, and the ventilation time of the nitrogen is 2 minutes.

[0023] Preferably, in step 5, the stirring time is 2 min.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The heat-treatment-free Al-Si alloy suitable for large-scale integrated gravity / low-pressure casting of the present invention is obtained by adding trace amounts of Mg, Zn, Zr and Y to the Al-Si alloy. The addition of Mg and Zn effectively improves the strength of the alloy without affecting the fluidity of the alloy. The addition of Zr plays a role in refining the primary α-Al, and the formed Al3Zr can stably exist as a nucleation core. The addition of Y, on the one hand, generates Al3Y, which can further refine the grains. On the other hand, Y, as a rare earth element, can purify the melt and reduce the gas dissolved in the alloy. In addition, Y will be adsorbed on the growth surface of eutectic Si, changing the original growth mode and changing the morphology of eutectic Si from plate-like to fibrous.

[0026] The heat-treatment-free Al-Si alloy suitable for large-scale integrated gravity / low-pressure casting molding of the present invention has low cost and simple operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments and comparative examples of the present invention, the drawings required for use in the embodiments and comparative examples will be briefly introduced below. Obviously, the drawings described below are only some embodiments and comparative examples of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 In the figure, (a) and (b) are the microstructure pictures of the alloy of Example 1 of the present invention at 50 times and 1000 times respectively;

[0029] Figure 2 In the figure, (a) and (b) are the microstructure pictures of the alloy of Example 2 of the present invention at 50 times and 1000 times respectively;

[0030] Figure 3 In the figure, (a) and (b) are the microstructure pictures of the alloy of comparative example 1 of the present invention at 50 times and 1000 times respectively;

[0031] Figure 4 Among them, (a) and (b) are the microstructure pictures of the alloy of comparative example 2 of the present invention at 50 times and 1000 times respectively;

[0032] Figure 5 In the figure, (a) and (b) are the structural pictures of the alloy of comparative example 3 of the present invention at 50 times and 1000 times respectively. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with embodiments and comparative examples.

[0034] Example 1

[0035] An Al-Si alloy prepared in this embodiment has a chemical composition of Si: 8.3%, Mg: 0.66%, Zn: 0.23%, Zr: 0.23%, Y: 0.16%, and the rest is Al and unavoidable impurity elements.

[0036] The preparation method of the Al-Si alloy of this embodiment comprises the following steps:

[0037] Step 1: pure Al, Al-20wt% Si alloy, pure Mg, pure Zn, Al-10wt% Y master alloy and Al-5wt% Zr master alloy are weighed according to the above components.

[0038] Step 2: Place pure Al and Al-20wt% Si alloy in a graphite clay crucible and melt them at 800°C in a resistance furnace. After all the pure Al and Al-20wt% Si alloy are melted, stir for 3 minutes, lower the temperature of the resistance furnace to 760°C and keep it warm for 20 minutes to remove refractory impurities on the surface of the melt.

[0039] Step 3: Add pure Mg wrapped in aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 5 minutes; add pure Zn wrapped in aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 5 minutes.

[0040] Step 4: Add Al-5wt% Zr master alloy wrapped with aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 10 minutes; add Al-10wt% Y master alloy wrapped with aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 10 minutes.

[0041] Step 5: Add 1 wt% of the melt mass of a slag remover, stir for 2 minutes, skim off impurities, and then pass high-purity argon (99.99%) into the melt for refining, ventilate for 2 minutes, and skim off impurities again.

[0042] Step 6: Measure the temperature of the melt after refining. When the melt is cooled to 720°C, pour it into a steel mold preheated to 200°C to obtain a casting.

[0043] The chemical composition of the casting was tested, the alloy's low-power and high-power structures were observed with a microscope, and the tensile mechanical properties of the alloy were tested with a universal mechanical testing machine. Figure 1 As shown in Tables 1 and 2.

[0044] Example 2

[0045] An Al-Si alloy prepared in this embodiment has a chemical composition of Si: 8.21%, Mg: 0.67%, Zn: 0.22%, Zr: 0.25%, Y: 0.25%, and the rest are Al and unavoidable impurity elements.

[0046] The preparation method of the Al-Si alloy of this embodiment comprises the following steps:

[0047] Step 1: pure Al, Al-20wt% Si alloy, pure Mg, pure Zn, Al-10wt% Y master alloy and Al-5wt% Zr master alloy are weighed according to the above components.

[0048] Step 2: Place pure Al and Al-20wt% Si alloy in a graphite clay crucible and melt them at 800°C in a resistance furnace. After all the pure Al and Al-20wt% Si alloy are melted, stir for 3 minutes, lower the temperature of the resistance furnace to 760°C and keep it warm for 20 minutes to remove refractory impurities on the surface of the melt.

[0049] Step 3: Add pure Mg wrapped in aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 5 minutes; add pure Zn wrapped in aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 5 minutes.

[0050] Step 4: Add Al-5wt% Zr master alloy wrapped with aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 10 minutes; add Al-10wt% Y master alloy wrapped with aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 10 minutes.

[0051] Step 5: Add 1 wt% of the melt mass of a slag remover, stir for 2 minutes, skim off impurities, and then pass high-purity argon (99.99%) into the melt for refining, ventilate for 2 minutes, and skim off impurities again.

[0052] Step 6: Measure the temperature of the melt after refining. When the melt is cooled to 720°C, pour it into a steel mold preheated to 200°C to obtain a casting.

[0053] The chemical composition of the casting was tested, the alloy's low-power and high-power structures were observed with a microscope, and the tensile mechanical properties of the alloy were tested with a universal mechanical testing machine. Figure 2 As shown in Tables 1 and 2.

[0054] Comparative Example 1

[0055] An Al-Si alloy prepared in this comparative example has a chemical composition of Si: 8.43%, Mg: 0.68%, Zn: 0.25%, Zr: 0.21%, and the rest being Al and unavoidable impurity elements, calculated by mass fraction.

[0056] The preparation method of the Al-Si alloy of this comparative example comprises the following steps:

[0057] Step 1: Weigh pure Al, Al-20wt% Si alloy, pure Mg, pure Zn, and Al-5wt% Zr master alloy according to the above components.

[0058] Step 2: Place pure Al and Al-20wt% Si alloy in a graphite clay crucible and melt them at 800°C in a resistance furnace. Stir for 3 minutes after all the raw materials are melted. Lower the temperature of the resistance furnace to 760°C and keep it warm for 20 minutes to remove refractory impurities on the surface of the melt.

[0059] Step 3: Add pure Mg wrapped in aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 5 minutes; add pure Zn wrapped in aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 5 minutes.

[0060] Step 4: Add Al-5wt% Zr master alloy wrapped with aluminum foil and press it into the melt. After it is completely melted, stir for 2 minutes and keep warm for 10 minutes.

[0061] Step 5: Add 1 wt% of the melt mass of a slag remover, stir for 2 minutes, skim off impurities, and then pass high-purity argon (99.99%) into the melt for refining, ventilate for 2 minutes, and skim off impurities again.

[0062] Step 6: Measure the temperature of the melt after refining. When the melt is cooled to 720°C, pour it into a steel mold preheated to 200°C to obtain a casting.

[0063] The chemical composition of the casting was tested, the alloy's low-power and high-power structures were observed with a microscope, and the tensile mechanical properties of the alloy were tested with a universal mechanical testing machine. Figure 3 As shown in Tables 1 and 2.

[0064] Comparative Example 2

[0065] An Al-Si alloy prepared in this comparative example has a chemical composition of Si: 8.33%, Mg: 0.62%, Zn: 0.22%, Y: 0.23%, and the rest being Al and unavoidable impurity elements, calculated by mass fraction.

[0066] The preparation method of the Al-Si alloy of this comparative example comprises the following steps:

[0067] Step 1: Weigh pure Al, Al-20wt% Si alloy, pure Mg, pure Zn, and Al-10wt% Y master alloy according to the above components.

[0068] Step 2: Place pure Al and Al-20wt% Si alloy in a graphite clay crucible and melt them at 800°C in a resistance furnace. After all the raw materials are melted, stir for 3 minutes, lower the temperature of the resistance furnace to 760°C and keep it warm for 20 minutes to remove refractory impurities on the surface of the melt.

[0069] Step 3: Add pure Mg wrapped in aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 5 minutes; add pure Zn wrapped in aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 5 minutes.

[0070] Step 4: Add Al-10wt%Y master alloy wrapped with aluminum foil and press it into the melt. After it is completely melted, stir for 2 minutes and keep warm for 10 minutes.

[0071] Step 5: Add 1 wt% of the melt mass of a slag remover, stir for 2 minutes, skim off impurities, and then pass high-purity argon (99.99%) into the melt for refining, ventilate for 2 minutes, and skim off impurities again.

[0072] Step 6: Measure the temperature of the melt after refining. When the melt is cooled to 720°C, pour it into a steel mold preheated to 200°C to obtain a casting.

[0073] The chemical composition of the casting was tested, the alloy's low-power and high-power structures were observed with a microscope, and the tensile mechanical properties of the alloy were tested with a universal mechanical testing machine. Figure 4 As shown in Tables 1 and 2.

[0074] Comparative Example 3

[0075] An Al-Si alloy prepared in this comparative example has a chemical composition of Si: 8.46%, Mg: 0.65%, Zn: 0.24%, and the rest being Al and unavoidable impurity elements, calculated by mass fraction.

[0076] The preparation method of the Al-Si alloy of this comparative example comprises the following steps:

[0077] Step 1: Weigh pure Al, Al-20wt% Si alloy, pure Mg, and pure Zn according to the above components.

[0078] Step 2: Place pure Al and Al-20wt% Si alloy in a graphite clay crucible and melt them at 800°C in a resistance furnace. Stir for 3 minutes after all the raw materials are melted. Lower the temperature of the resistance furnace to 760°C and keep it warm for 20 minutes to remove refractory impurities on the surface of the melt.

[0079] Step 3: Add pure Mg wrapped in aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 5 minutes. Add pure Zn wrapped in aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 minutes and keep warm for 5 minutes.

[0080] Step 4: Add 1 wt% of the melt mass of a slag remover, stir for 2 minutes, skim off impurities, and then pass high-purity argon gas into the melt for refining. Pass gas for 2 minutes and skim off impurities again.

[0081] Step 5: Measure the temperature of the melt after refining. When the melt is cooled to 720°C, pour it into a steel mold preheated to 200°C to obtain a casting.

[0082] The chemical composition of the casting was tested, the alloy's low-power and high-power structures were observed with a microscope, and the tensile mechanical properties of the alloy were tested with a universal mechanical testing machine. Figure 5 As shown in Tables 1 and 2.

[0083] Table 1 Chemical composition of Examples 1, 2 and Comparative Examples 1 to 3 (unit: wt%)

[0084] Group Si Mg Zn Zr Y other Al Example 1 8.30 0.66 0.23 0.23 0.16 ≤0.15 margin Example 2 8.21 0.67 0.22 0.25 0.25 ≤0.15 margin Comparative Example 1 8.43 0.68 0.25 0.21 0 ≤0.15 margin Comparative Example 2 8.33 0.62 0.22 0 0.23 ≤0.15 margin Comparative Example 3 8.46 0.65 0.24 0 0 ≤0.15 margin

[0085] Table 2 Tensile mechanical properties of Examples 1, 2 and Comparative Examples 1 to 3

[0086] Group Tensile strength(Mpa) Yield strength(MPa) Elongation(%) Example 1 240.9 136.5 6.7 Example 2 249.6 139.3 9.7 Comparative Example 1 232.9 127.8 5.4 Comparative Example 2 232.5 131.3 6.5 Comparative Example 3 227.1 123.6 4.4

[0087] According to Table 2 and Figure 1 to Figure 5It can be seen that Zr added to Al-Si alloy refines the grains to a certain extent, but cannot modify eutectic Si. Y addition alone can modify eutectic Si well, but the degree of grain refinement is limited. When Zr and Y are added in combination, the grains can be further refined, and the grains are transformed from coarse columnar crystals to fine equiaxed crystals. Eutectic Si grows into fibers, which improves the comprehensive mechanical properties of the alloy. The tensile strength of the alloy proposed by the present invention reaches 249.6Mpa, the yield strength reaches 139.3Mpa, and the elongation reaches 9.7%.

[0088] Obviously, the above embodiments are merely examples for clear explanation, and are not intended to limit the embodiments. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. Al-Si alloy, characterized in that It includes Si: 8.0wt%~8.5wt%, Mg: 0.5wt%~0.7wt%, Zn: 0.15wt%~0.25wt%, Zr: 0.2wt%~0.25wt%, Y: 0.15wt%~0.25wt%, and the balance is Al and unavoidable impurity elements.

2. The Al-Si alloy according to claim 1, characterized in that It includes Si: 8.2wt%, Mg: 0.6wt%, Zn: 0.2wt%, Zr: 0.2wt%, Y: 0.15wt% to 0.25wt%, and the balance is Al and inevitable impurity elements.

3. The method for preparing the Al-Si alloy according to claim 1 or 2, comprising the following steps: Step 1: Weigh pure Al, Al-Si alloy, pure Mg, pure Zn, Al-Y master alloy and Al-Zr master alloy in proportion; Step 2: Melt pure Al and Al-Si alloy at 800±2.5℃, stir evenly, cool to 760±2.5℃ and keep warm, skim off impurities to obtain a melt; Step 3: first add pure Mg wrapped with aluminum foil to the melt, wait until it is completely melted, stir evenly, and keep warm; then add pure Zn wrapped with aluminum foil to the melt, wait until it is completely melted, stir evenly, and keep warm; Step 4: then add the Al-Zr master alloy wrapped with aluminum foil to the melt, wait until it is completely melted, stir evenly, and keep warm; then add the Al-Y master alloy wrapped with aluminum foil to the melt, wait until it is completely melted, stir evenly, and keep warm; Step 5: Finally, add a slag remover to the melt, stir evenly, skim off impurities, pass argon gas into the melt for refining, and skim off impurities again; Step 6: Measure the temperature of the melt after refining. When the melt is cooled to 720±2.5°C, pour the melt into a steel mold preheated to 200±2.5°C to obtain a casting.

4. The method for preparing an Al-Si alloy according to claim 3, characterized in that: In step 1, the purity of pure Al is ≥99.8%, the purity of pure Mg is ≥99.8%, and the purity of pure Zn is ≥99.8%.

5. The method for preparing the Al-Si alloy according to claim 3, characterized in that: In step 1, the Al-Si alloy is an Al-20wt% Si alloy, the Al-Y master alloy is an Al-10wt% Y master alloy, and the Al-Zr master alloy is an Al-5wt% Zr.

6. The method for preparing an Al-Si alloy according to claim 3, characterized in that: Before use, the pure Al, pure Mg and pure Zn have their surface oxide films removed and are preheated to 200±2.5°C.

7. The method for preparing an Al-Si alloy according to claim 3, characterized in that: In step 2, the stirring time is 3 minutes and the insulation time is 20 minutes.

8. The method for preparing an Al-Si alloy according to claim 3, characterized in that: In step 3, the stirring time is 2 minutes and the insulation time is 5 minutes.

9. The method for preparing an Al-Si alloy according to claim 3, characterized in that: In step 4, the stirring time is 2 minutes and the insulation time is 10 minutes.

10. The method for preparing an Al-Si alloy according to claim 3, characterized in that: In step 5, the purity of the nitrogen is 99.99%, the ventilation time of the nitrogen is 2 minutes, the stirring time is 2 minutes, and the amount of the slag remover added is 1 wt% of the mass of the melt.

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